05/02/2016

Is El Nino Connected To The Polar Vortex?

"’Polar vortex’ set to strike the U.S. as snowstorm death toll rises” (Slate). “Polar vortex transforms Mid-Atlantic to Mid-Antarctic” (Washington Post). “Economic impact of ‘polar vortex’ could reach $5B” (CBS News).  These are all real headlines from 2014 and 2015, when the phrase “polar vortex” first appeared in public lexicon. 

These words might evoke images of a giant spinning tornado of cold air wiping out everything in its path.  However, the “polar vortex” historically describes the strong westerly winds that zoom around the northern pole in the stratosphere every winter (Waugh et al 2016) (footnote 1).

The stratosphere is the layer of the atmosphere between about 6 and 30 miles above the Earth’s surface. El Niño operates in the troposphere, the layer of the atmosphere closest to Earth’s surface. So how can El Niño be connected to the polar vortex, and why should we care?

7

Image Credit: NASA

Cold air outbreaks and the stratospheric polar vortex

The stratospheric polar vortex weakens when large-scale atmospheric waves (e.g., 800 miles across) from the lower atmosphere travel up into the winter stratosphere. When these waves break—yes, even atmospheric waves break—the polar vortex can rapidly decelerate and even reverse direction completely.

When the vortex breaks down, there is an event called a major “sudden stratospheric warming” (SSW). The “warming” refers to the dramatic increase in temperature (~50-70 degrees F in a few days!) over the polar stratosphere during these events (see the figure below).  These events occur roughly every other year in the Northern Hemisphere.

1

The evolution of a polar vortex collapse in January 2009.  (left) Prior to the event, stratospheric winds (gray arrows) circle counterclockwise, from west to east, around the pole.  The vortex (solid black line) is nearly circular, and the temperatures at 10 hPa (roughly 31 km in altitude) are cooler than usual. (middle) As the waves from below break in the stratosphere, the vortex elongates and wobbles (like a spinning top that you nudge). Temperatures warm rapidly. (right) The vortex splits into two pieces, and the winds near the pole reverse direction. Note: For simplicity, only winds north of 30° are shown. NOAA Climate.gov image adapted from Butler et al. (2015).

These rapid decelerations of the stratospheric polar vortex can sometimes affect the circulation all the way to the surface and lead to changes in surface temperatures for days to weeks afterwards (Baldwin and Dunkerton 2001; see figure below). In particular, there is an increased likelihood of cold, Arctic air spilling into the mid-latitudes (where most people live) (footnote 2). Thus, these intrusions of cold air actually occur when the stratospheric polar vortex weakens or completely dissipates, not when the vortex strengthens.

2

Average surface temperature anomalies for 60 days following 35 vortex breakdown events (using JRA-55 reanalysis).  Gray shading indicates anomalies greater than 2 standard deviations, indicating a statistically robust deviation from average. The breakdown of the polar vortex produces long-lasting temperature anomalies. Greenland and northeastern Canada become unusually warm, while Europe and Asia become unusually cold. Adapted from Butler et al (2014).

It is important to note that many intrusions of cold Arctic air, including the ones described in the headlines above, are largely unrelated to the stratospheric polar vortex, and are instead due to normal meanders of the tropospheric jet stream (footnote 3).

But understanding and predicting break downs of the stratospheric polar vortex is a potentially important opportunity for improving seasonal forecasting skill, because of the intra-seasonal to seasonal persistence of its effects on surface weather. In other words, if we had more advance warning that the polar vortex were going to weaken, it’s possible we could forecast winter temperatures more accurately farther in advance.

Because the periodic breakdowns of the polar vortex are driven by the same waves that drive tropospheric weather patterns, they generally cannot be predicted by weather models more than 10-15 days in advance.  So in terms of forecasting, they may provide additional skill if your model forecast is created while an event is happening (Sigmond et al 2013); but what if you’re making a seasonal forecast (i.e., predicting 3 months in advance)? Here’s where El Niño comes in.

Perfectly placed wave trains

ENSO influences climate all over the world by generating planetary-scale “wave trains” (footnote 4) that shift the jet stream and associated weather patterns.  During El Niño winters (footnote 5), these wave trains may occur more often in an ideal location (footnote 6) to strengthen into the stratosphere, causing a weaker stratospheric polar vortex in late winter and more frequent major disruptions of the polar vortex (e.g., García-Herrera et al 2006; Garfinkel and Hartmann 2007; Cagnazzo and Manzini 2009; Fletcher and Kushner 2011; Butler and Polvani 2011).

While ENSO’s influence on North American wintertime climate is directly tied to these wave trains, the wintertime climate over Europe and Asia is dominated instead by the occurrence of the polar vortex breakdown (or lack thereof) no matter the phase of ENSO (Ineson and Scaife 2009; Butler et al 2014; Richter et al 2015; see figure below).  So, if a forecast model were able to simulate the enhanced probability of polar vortex breakdowns during El Niño and the subsequent impacts on surface climate (which can be a big “if”! (7)), we might see enhanced seasonal predictive skill for wintertime climate over the North Atlantic/Eurasian regions (8) (Domeisen et al 2015; Scaife et al 2016).

3

How sudden stratospheric warming (SSW) events modify El Niño’s impacts on winter climate. (left). Difference in winter (November-March) temperature anomalies between (left) all El Niño winters and all La Niña winters. (middle) between El Niño and La Niña winters with at least one SSW, and (right) between El Niño and La Niña winters with no SSWs.  The warm temperature anomalies over North America remain similar regardless of SSW events, but the temperature anomalies over Europe, Asia, and Greenland are either negative or positive depending on the occurrence of an SSW.  Solid black contour indicates statistically significant anomalies. From Butler et al. (2014).

How did the polar vortex behave during the big El Niño winter of 2015-2016?

The average response of the stratospheric polar vortex to past El Niños is weakening of the vortex in late winter and an increased chance of polar vortex breakdowns (i.e., SSWs) (9). This is generally what we saw this past winter, except that during early winter from November to mid-January the vortex was extraordinarily strong (see figure below). The strong vortex may have contributed to the hemispheric-wide warmth we saw in early winter (fewer cold air outbreaks!).

However, in February, planetary-scale waves propagated upward and began to pummel the vortex, leading to a breakdown of the polar vortex on March 5, 2016.  This breakdown of the vortex was so strong that it is the earliest final breakup on record (the vortex will not return until next winter).

4

Daily zonal (west-to-east) winds [meters/second] in the polar stratosphere at 10 hPa (about 31 kilometers altitude) and 60°N. The grey shading shows the range of natural variability from 1979-2016.  The black dashed line shows the daily average. The red line shows the daily zonal winds for 2015-2016.  Data is from NCEP-NCAR reanalysis.

The circulation in the stratosphere has influenced the surface occasionally since the event (see the figure below), and may have contributed to recent record warmth over Greenland as well as a persistence of winter-like weather into spring for some mid-latitude regions.

Nevertheless, the seasonal climate impacts of final warmings are still somewhat uncertain. Overall the impacts of this event may be less than if the same event occurred two months ago during the height of winter, because its impacts are felt more prominently against a colder starting condition.

5

65-90°N geopotential height anomalies (standardized by the JFM mean/standard deviation) for Nov 1 2015 - April 12 2016.  Geopotential height is the height above the surface at which you find a given level of air pressure. A positive anomaly means the pressure is unusually high for a given altitude, which is generally linked to warmer than usual conditions. Negative anomalies mean lower pressure and colder air. In early winter, the vortex was anomalously strong (blue shading); in Jan/Feb, the stratosphere was largely decoupled from the troposphere; and in late winter, the vortex was anomalously weak (red shading) following a final major SSW on March 5.

The bottom line is that El Niño, with its modified planetary waves, tends to promote the breakdown of the polar vortex, especially in late winter, which in turn modifies the atmospheric circulation pattern associated with the El Niño. This additional stratospheric influence on wintertime climate is major for Asia, Europe and Greenland, but is more subtle for North America. Nonetheless, it represents yet another phenomenon that could improve sub-seasonal and seasonal climate forecasts if models could capture its effects effectively.

This is a guest post by Dr. Amy Butler (@DrAHButler) who is a research scientist at the University of Colorado Cooperative Institute for Research in Environmental Sciences (CIRES) and sits within the NOAA Chemical Sciences Division (CSD).  Her research focuses on large-scale climate patterns and phenomenon, such as the Arctic and Antarctic Oscillations and sudden stratospheric warmings. Lead reviewer: Anthony Barnston

Footnotes

(1) There is also a stratospheric polar vortex in the Southern Hemisphere, where the winds circle clockwise around the southern pole during austral winter and spring.  The strength and timing of the breakup of the Southern Hemisphere polar vortex in spring plays a major role in the annual ozone hole.

(2) This shift brings cold Arctic air into mid-latitude regions  like the eastern United States, northern Europe and Asia. We also see warmer temperatures over Greenland and southern Eurasia. We see roughly opposite-signed temperature anomalies when the polar vortex is very strong.  The changes are strongest over the North Atlantic-Eurasian region, and the pattern looks like the negative phase of the North Atlantic Oscillation or Arctic Oscillation.

(3) The stratospheric polar vortex is often linked (or coupled) to the tropospheric polar jet stream in wintertime, but not always—sometimes they do their own thing and there is little to no relationship between them.  But when they are coupled, and the polar vortex weakens or breaks down, it causes the tropospheric polar jet stream to meander southward.

(4) In many ways, the atmosphere behaves like a fluid. It flows. It eddies. It also spawns massive waves. Planetary waves, which may show up as broad ups and downs in the flow of a jet stream, are very long waves, with 1,000 or more miles between a crest and an adjacent trough. We call them “wave trains” because the structure may consist of several peaks and troughs, making it looks like the cars of a train.   Planetary wave trains may not move forward or backward, but remain approximately stationary, and when that is the case the waves in the train are known as stationary waves. During El Niño, a stationary wave train may stretch all the way from the subtropical Pacific into Canada, forming a broad right-curving arc.

(5) La Niña winters show a less robust relationship with SSWs. Most models indicate fewer SSWs during La Nina, while observations show more SSWs occurring during La Nina winters (Butler and Polvani 2011).  However, that result appears to be quite sensitive to the dataset used and the threshold chosen to define La Nina events.

(6) In particular, the geopotential heights are anomalously low over the North Pacific.  This encourages constructive linear interference with the climatological wave pattern (Fletcher and Kushner 2011). This means that the negative departure from the average geopotential height in the North Pacific during an El Niño adds to the already normally relatively lower heights in that location.

(7) Many models still do not simulate stratospheric processes or their linkages to the surface well.

(8) Of course, this relationship and its potential implications for improved subseasonal to seasonal forecast skill is complicated by the fact that ENSO is merely one factor that can affect the stratosphere.  For example, Eurasian snow cover, Arctic sea ice, the 11-year solar cycle, the Quasi-Biennial Oscillation, and the Madden-Julian Oscillation have all been shown to potentially influence the stratospheric polar vortex.

(9) Note that this is not a perfect relationship.  For example, there were no major SSWs during the last big El Niño winter 1997-98.

References

Baldwin MP, Dunkerton TJ (2001) Stratospheric Harbingers of Anomalous Weather Regimes. Science (80- ) 294:581–584. doi: 10.1126/science.1063315

Butler AH, Polvani LM (2011) El Niño, La Niña, and stratospheric sudden warmings: A reevaluation in light of the observational record. Geophys Res Lett. doi: 10.1029/2011GL048084

Butler AH, Polvani LM, Deser C (2014) Separating the stratospheric and tropospheric pathways of El Niño–Southern Oscillation teleconnections. Environ Res Lett 9:024014.

Cagnazzo C, Manzini E (2009) Impact of the Stratosphere on the Winter Tropospheric Teleconnections between ENSO and the North Atlantic and European Region. J Clim 22:1223–1238. doi: 10.1175/2008JCLI2549.1

Domeisen DI V., Butler AH, Fröhlich K, et al (2015) Seasonal Predictability over Europe Arising from El Niño and Stratospheric Variability in the MPI-ESM Seasonal Prediction System. J Clim 28:256–271. doi: 10.1175/JCLI-D-14-00207.1

Fletcher CG, Kushner PJ (2011) The Role of Linear Interference in the Annular Mode Response to Tropical SST Forcing. J Clim 24:778–794. doi: 10.1175/2010JCLI3735.1

García-Herrera R, Calvo N, Garcia RR, Giorgetta M a. (2006) Propagation of ENSO temperature signals into the middle atmosphere: A comparison of two general circulation models and ERA-40 reanalysis data. J Geophys Res 111:D06101. doi: 10.1029/2005JD006061

Garfinkel CI, Hartmann DL (2007) Effects of the El Niño–Southern Oscillation and the Quasi-Biennial Oscillation on polar temperatures in the stratosphere. J Geophys Res 112:D19112. doi: 10.1029/2007JD008481

Ineson S, Scaife AA (2009) The role of the stratosphere in the European climate response to El Niño. Nat Geosci 2:32–36. doi: 10.1038/ngeo381

Richter J, Deser C, Sun L (2015) Effects of stratospheric variability on El Niño teleconnections. Environ Res Lett 10:124021.

Scaife AA, Karpechko AY, Baldwin MP, et al (2016) Seasonal winter forecasts and the stratosphere. Atmos Sci Lett. doi: 10.1002/asl.598

Sigmond M, Scinocca JF, Kharin V V., Shepherd TG (2013) Enhanced seasonal forecast skill following stratospheric sudden warmings. Nat Geosci 6:98–102. doi: 10.1038/ngeo1698

Waugh DW, Sobel AH, Polvani LM (2016) What is the polar vortex, and how does it influence weather? Bull Am Meteorol Soc. doi: 10.1175/BAMS-D-15-00212.1

 

 

 

Unsettled Pattern Continues for Great Steamboat Race...

A series of storm systems diving out of Canada look to keep our weather on the unsettled side as we head into the middle of the week.  

The first low looks to arrive tomorrow with isolated showers expected during the afternoon.  

Satrad

Unfortunately, the second low looks to impact our weather on Wednesday and will bring scattered showers that could impact the Great Steamboat Race.

Let's time it out on AdvanceTrak starting Wednesday morning...

While it will be cool, we should be off to a dry start Wednesday morning as rain approaches from the northwest.

At1

The arrival of a potent cold front brings a batch of showers into our central viewing area by late morning.

At2

We see a break in the activity during the midday as the front pushes to the southeast.

At3

However, scattered instability showers look to redevelop during the afternoon with heating.  In addition, winds will become quite gusty with a northwest wind over 20 mph at times with cool temps.

At4

Fortunately, it looks like these showers should diminish by the time the steamboat race gets started.  However, the wind will continue to gust.

At5

All the rain should be finished by mid evening as temps fall into the 50's.

At6

Although the forecast for the boat race doesn't look as good as the one for the horse race later in the week, it's also not that bad. 

Enjoy :)

WDRB Meteorologist Jeremy Kappell

Jeremy 6sx

Jeremy's Bio

Find me on Facebook!

Follow me on Twitter!

Email me at jkappell@wdrb.com

 

05/01/2016

SPC Updates Severe Risk

The Storm Prediction Center updates us on the potential for strong storms later this evening/overnight.

Mcd0527

 AREAS AFFECTED...PORTIONS OF CENTRAL/SOUTHERN INDIANA...FAR   SOUTHEASTERN ILLINOIS...SOUTHWESTERN OHIO    CONCERNING...SEVERE THUNDERSTORM WATCH 136...    VALID 020121Z - 020315Z  

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 136   CONTINUES.   

SUMMARY...THE THREAT FOR DAMAGING WINDS AND LARGE HAIL WILL PERSIST   FOR AT LEAST A COUPLE MORE HOURS. THEREAFTER...CELLS SHOULD   GRADUALLY WEAKEN...BUT CONVECTIVE TRENDS WILL BE MONITORED FOR   POTENTIAL DOWNSTREAM WATCH ISSUANCE.   

DISCUSSION...SEVERAL ROBUST SUPERCELLS ARE PUSHING EAST ACROSS   CENTRAL INDIANA AND FAR SOUTHEASTERN ILLINOIS THIS EVENING. RECENT   KIND VWP DATA DEPICT A KINEMATIC ENVIRONMENT SUPPORTIVE OF CYCLONIC   ROTATION...AS SOUTHERLY LOW-LEVEL WINDS VEER TO VIGOROUS WESTERLY   FLOW AT/ABOVE 6 KM AGL. FURTHERMORE...SEVERAL ZDR ARC SIGNATURES   HAVE BEEN OBSERVED...DEPICTING RAIN DROP SIZE SORTING WITHIN A   VEERING STORM-RELATIVE WIND PROFILE. THESE CELLS WILL CONTINUE TO BE   CAPABLE OF LARGE HAIL...STRONG WINDS...AND PERIODIC LOW-LEVEL   MESOCYCLONES.   

FARTHER EAST...A NORTHWARD-PROGRESSING OUTFLOW BOUNDARY IS   INITIATING NEW CONVECTION ACROSS PORTIONS OF OHIO. MOST   LIKELY...THIS ACTIVITY SHOULD ALTER THE DOWNSTREAM ENVIRONMENT   ENOUGH SUCH THAT THE INDIANA CELLS MOVING EAST WILL WEAKEN OVER   TIME. ADDITIONALLY...RELATIVELY LOW SFC DEW POINTS WILL ALLOW TEMPS   TO FALL FAIRLY QUICKLY THIS EVENING...STABILIZING THE BOUNDARY   LAYER. AS SUCH...DOWNSTREAM WATCH ISSUANCE IS NOT ANTICIPATED...BUT   CONVECTIVE TRENDS WILL BE MONITORED FOR SUSTAINED UPDRAFT   ORGANIZATION WITH EASTWARD EXTENT.

I'll have a full update on what to expect tonight on WDRB News at 10. 

WDRB Meteorologist Jeremy Kappell

Jeremy 6sx

Jeremy's Bio

Find me on Facebook!

Follow me on Twitter!

Email me at jkappell@wdrb.com

Severe Thunderstorm Watch Issued!

The Storm Prediction Center has issued a Severe Thunderstorm Watch for much of Kentuckiana including the city of Louisville until 8 pm EDT.

Watch

URGENT - IMMEDIATE BROADCAST REQUESTED

   SEVERE THUNDERSTORM WATCH NUMBER 133

   NWS STORM PREDICTION CENTER NORMAN OK

   135 PM CDT SUN MAY 1 2016

 

   THE NWS STORM PREDICTION CENTER HAS ISSUED A

   * SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

     SOUTHERN INDIANA

     MUCH OF WESTERN AND CENTRAL KENTUCKY

     EXTREME SOUTHWEST OHIO

     PARTS OF WESTERN AND MIDDLE TENNESSEE

   * EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 135 PM UNTIL

     800 PM CDT.

 

   * PRIMARY THREATS INCLUDE...

     SCATTERED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE

     ISOLATED DAMAGING WIND GUSTS TO 60 MPH POSSIBLE

 

   SUMMARY...THUNDERSTORMS ARE DEVELOPING FROM WESTERN TENNESSEE TO

   WESTERN KENTUCKY AND SOUTHERN INDIANA...AND THESE STORMS SHOULD

   INCREASE SOME IN COVERAGE AND INTENSITY THROUGH THE AFTERNOON WHILE

   SPREADING EASTWARD.  THE STRONGEST STORMS WILL BE CAPABLE OF

   PRODUCING LARGE HAIL AND ISOLATED DAMAGING GUSTS.

 

   THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90

   STATUTE MILES EAST AND WEST OF A LINE FROM 55 MILES NORTH

   NORTHWEST OF LEXINGTON KENTUCKY TO 35 MILES SOUTHEAST OF JACKSON

   TENNESSEE.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

   ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).

 

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

   REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

   FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

   AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

   THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

   AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

   DO PRODUCE TORNADOES.

 

Be sure to Find me on Facebook and Follow me on Twitter for continuous updates this afternoon and evening.

WDRB Meteorologist Jeremy Kappell

Jeremy 6sx

Jeremy's Bio

Find me on Facebook!

Follow me on Twitter!

Email me at jkappell@wdrb.com

UPDATED: Another and Better Chance for Severe Weather

Happy May!

After a rather soggy Saturday, we got through without any severe weather and that is always good news! We rounded out April with some showers and ended up only being .83'' deficient for the month. Normally, we would have seen 4.01'' and we had 3.18'' for April 2016. 

Background Info: 

Our set up is similar to yesterday, except now the warm front has lifted north and crossed our region. There is a surface low as well as a stationary cold front and an upper level disturbance. That cold front will linger until tomorrow morning, when it finally sweeps through the area. Therefore, for the rest of today we are in the area in between the warm and cold fronts, known as the warm sector. 

5-1 srf radar

The warm sector is so named, because it is filled with warm moist air following the passage of a warm front. In the past 24 hours, we have increased temps about 10-15 degrees. Our winds have shifted to the south, so we are getting some nice warm air from the gulf. 

5-1 temp change

I noticed the increase in moisture, the moment I stepped out the door this morning. It is noticeably humid. That is because dew points have increased to the low and mid 60s. A 60° dew point is when you go from comfortable to sticky. This is all conducive for the production of severe weather. 

5-1 dw pt temps

Not to mention, models are predicting some high levels of instability. We are currently in the midst of some recovery time and even seeing breaks in the clouds, allowing us to heat up. This is key for destabilization of the atmosphere and to help produce severe weather. Below are both the GFS and NAM, showing CAPE values at 1500 to even >2000 J/KG from the afternoon until this evening.

In layman's terms? High CAPE values like this = high potential for severe storms. 

5-1 cape

5-1 nam cape

**UPDATE**

SPC originally had our region under the "marginal" risk for severe weather. At 12:20 this afternoon they increased it to the slight risk for most of our region, which is a step up from before and means they also feel there is a better chance for severe weather. CAPE levels are high, there is also enough deep- layer wind shear to enable supercells and the mid-level atmosphere is drier.

The take home note: It is a day to be weather aware. 

Slight risk

The main threats with the severe storms will be large hail and gusty damaging winds. Cannot rule out a tornado, but severe hail and damaging winds (those that are greater than 60 mph) are more likely. The greatest threat area looks to be southern IN and Northern KY, north of I-64. But that doesn't mean supercell growth won't happen elsewhere. 

5-1 severe weather three

Timing it out

Scroll through these various Advancetrak images to get an idea of when these storms are expected to develop. 

  • After several hours of clearing and warming temps into the upper 70s, by 1-2 we should start to see some storm development. Even these early storms could pack a punch. 

 5-1 adv 130 hrrr

  • After 3 pm, there is an even greater potential for severe storms. These will continue through the early evening hours as they progress east. 

5-1 adv 3 pm

5-1 adv 530 pm

  • Let's say around 8 pm, showers and storms will begin to taper off and the threat for severe diminishes. 

5-1 adv 730

The stationary cold front will begin to move tomorrow morning. It will bring with it more clouds than anything else. A chance for a stray shower is possible though, but shouldn't impact your day all that much. Temperatures will be cooler for Monday following the cold front as well- back to the lower 70s. 

5-1 mon 8 am

As suspected, SPC bumped us up to the "slight risk" for severe weather, which I agree with.  I believe we have a better chance to see severe storms today than we did yesterday.  The ingredients needed for severe storms are lining up so much better today than Saturday. We have heat, moisture, forcing, instability and wind shear too. 

I am keeping a close eye on the forecast, models and changes. Jeremy is back today (after winning an AP award for best weather anchor and running the marathon Saturday (!!!)) and he will be updating you as well. During the news tonight on WDRB, following the severe storms, he will be talking about that Derby forecast and you don't want to miss it! 

If and when storms become severe, a lot of updates will be found on Facebook and twitter. Find me on social media!

Katie McGraw's Facebook Page

Katie McGraw's Twitter Page

My headshot

-Meteorologist Katie McGraw

04/30/2016

Odd Markings Found At The Bottom Of The Caspian Sea...

The Operational Land Imager (OLI) on NASA's Landsat 8 satellite acquired this large natural-color image showing a view of the Caspian Sea around the Tyuleniy Archipelago on April 16, 2016. Ocean scientist Norman Kuring of NASA’s Goddard Space Flight Center found a puzzling feature in the image -- lines crisscrossing the North Caspian Sea. On its own, the image was strikingly beautiful. Shallow waters surrounding the Tyuleniy Archipelago allow you to see the dark green vegetation on the sea bottom. But the question remained: what caused those lines?

Reiner_gamma

Image Credit: NASA image by Norman Kuring, NASA’s Ocean Color web

The dark green areas—possibly sea grass or benthic algae—and the lines are features of the sea bottom. “You can tell this by the fact that marks laid down in January have not moved by April,” Kuring said. “If those were water features, they would not persist through one tidal cycle.”

It’s possible that some of the marks have a human origin. Similar lines show up in the world’s oceans because of trawling. But the scientific literature and a January satellite image suggest that a majority of the marks in the images were gouged by ice. In January, blocks of ice stand at the leading end of many lines, most notably in the northeast corner of the image. By April, ice has melted and only the scour marks persist.

Stanislav Ogorodov, a scientist at Lomonosov Moscow State University who has published research on the phenomenon, agrees: “Undoubtedly, most of these tracks are the result of ice gouging.” Ogorodov notes that this part of the Caspian is very shallow—about 3 meters deep. Ice that forms here in wintertime is usually about 0.5 meters thick, so most of it never touches the seafloor. But the ice tends to be “warm” and thin, which gives rise to relatively weak ice cover that is easily deformed by wind and currents. When pieces of ice are pushed together, some ice is forced upward and downward into so-called “hummocks.” The keels of hummocks, frozen into the ice fields, can reach the seafloor and scour the bed as the ice moves.

 

Severe Storms Possible All Weekend

Happy Saturday! 

And a soggy one it is! After some light rain last night/overnight, showers spilled over the region from 7-10 am and will continue into the early afternoon. 

Our set up for today includes two low pressure systems and a warm front. Our first dose of rain is thanks to the warm front, as it starts to lift north toward the area. We will get a brief break this afternoon, before a second round of showers and storms arrives this evening/tonight. 

4-30 srf radar

The Storm Prediction Center has almost our entire region under the risk for severe weather this evening. As the warm front lifts, it will increase our dew point temps and the moisture content of the atmosphere.  There is also decent wind sheer as winds increase aloft. Therefore, there could be some strong to severe storms. The main threat is going to be hail and gusty winds. However, it really all depends on what happens during the dry time today. 

4-30 spc today

Some of us will continue to see some rain this afternoon, mainly in the NE portion of the area. The rest of us will be briefly dry before act two this evening. It looks as though it will remain cloudy, and therefore, limit instability. It is going to be a touch and go situation for tonight in terms of severity, until we see what happens this afternoon. 

4-30 sat 3 pm

The good news: One of the many events going on tonight is the opening night at Churchill Downs!

The bad news: Prepare for showers and storms. They will be scattered at first, but the likelihood of them increases throughout the evening. 

4-30 church downs opening night

By this evening, more showers and storms begin to fire off and this is our best chance for some severe weather. Again, threats are mainly small hail and gusty winds. It all comes down to the afternoon hours and if destabilization is able to occur, which will encourage severe weather.

4-30 8 pm

A positive of the wet weather is that pollen counts are a lot lower today. But they spike right back up tomorrow and into next week. That's because Sunday/Monday will not be nearly as soggy. 

Note there are three new main allergens: oak, mulberry and grasses. 

4-30 allergies

Showers and storms will clear out overnight and we will start off Sunday with mostly cloudy skies. 

4-30 sun 6 am

4-30 sun 10 am

BUT we are not done with the rain quite yet!

More showers and storms are possible for tomorrow afternoon but they will be more scattered. Notice on AT, the showers and storms are fewer and farther between compared to today, but some will have the potential to become severe. For now, SPC has us under a "marginal" threat level for tomorrow, which is the lowest level. The ingredients for tomorrow are almost the opposite from today. Models are showing more instability, but the winds are veering and there is no convergence. With CAPE levels as high as they are though, severe weather is possible. 

4-30 sun 3 pm

We could see some heavy rain at times with these showers and storms. Models are not in complete agreement with this. I will say about half an inch to an inch. Below are the GFS, NAM, Euro models and they go from the lowest rain totals possible to the highest. 

4-30 gfs lowest

4-30 nam preci

4-30 euro highest

The cold front will finally trace through on Monday, keeping clouds thick. There could also be a rogue shower around, but for the most part, we will be dry. 

4-30 mon am

Remember, you can always have your forecast on the go by downloading our smartphone app! Just check it out before you leave the house in order to plan ahead! 

App

Rick will be in this evening for Jeremy and he will have the latest on the severe weather threat on WDRB. Be sure to tune in to see the latest data! Also, the derby is now on the seven day forecast! 

I'll see you tomorrow morning from 6-9 am with another update in the forecast! Before then, let's connect!

Find me on social media!

Katie McGraw's Facebook Page

Katie McGraw's Twitter Page

My headshot

-Meteorologist Katie McGraw

04/29/2016

Rain Chances this Weekend. . . Timing and Strength

So many events; so little time; so many eyes on the forecast! 

This is a high pressure time of the year for meteorologists in Kentuckiana! With this being my first Thunder, KDF and soon to be Derby- I am learning this first hand!

Unfortunately, Mother Nature AND computer models don't care about our outdoor plans. This is a tricky forecast for the weekend, due to a complex pattern. On top of that, the models just do not want to agree. They can't even stay in agreement with themselves from run to run. So the confidence in the forecast is bit lower than normal, which is something I, nor any meteorologist, enjoys. 

Friday Night:

We are tracking showers and storms to our southwest, spread along a warm front. They are pretty close to our region, but they are approaching a dry air mass around our neck of the woods. That's thanks to a cold front that swept through the area yesterday, it cooled us down a bit and cleared out the humidity and moisture content and is now providing a barrier from the rain. 

4-29 current radar

Therefore, as these showers and storms approach, some are burning off and becoming virga. Virga is rain that doesn't reach the surface, because the atmosphere is too dry. However, eventually, the rain will win out and we will see some this evening and tonight. 

4-29 satradwfronts

Notice on AT of the HRRR model, there is a decent chance for some rain tonight, but shouldn't be a complete washout as this shows, because of the low dew point temperatures.

4-29 hrr 1130

Saturday:

Heading into tomorrow, there will be rain for Mini/Marathon and it appears they should spill out across the region by mid morning and at times the rain could be rather heavy.  There is also not only the potential for rain, but for thunderstorms as well.

4-29 adv sat 10 am

4-29 adv 1130 am

We will get a break mid-day, where spotty showers and storms are possible. If this clears out completely and we are able to recover from the morning rain, it will improve the chances for severe weather in the later part of the day.  

Sat 6 pm

The Storm Prediction Center has the western portion of Kentucky and SW of Indiana under the "slight" risk for severe weather for tomorrow evening. This is where a low will be positioned. Meantime, the previously mentioned warm front will lift to the north. Dew point temps will increase, providing some nice moisture content and westerly flow aloft could be strong enough to produce some strong to severe storms. The main threat is going to be hail and gusty winds. 

4-29 spc sat

The better potential for severe extends from SW IL to Eastern Texas, but it cannot be ruled out for us! 

4-29 severe risk over weekend

The second wave moves through late Saturday, following the warm front, spiking our chances for showers and storms. Again, these could pack a punch and could be strong to severe. 

4-29 sat 10 pm

After those clear out overnight, we will be dry to start off Sunday. But then a lazy cold front will drop from the north during the afternoon on Sunday. 

4-29 sun 8 am

It will fire off another round of some showers and storms. As of now, we are under the lowest risk from SPC for severe weather. There is some decent CAPE, but there is no convergence and there is no real forcing to produce severe weather. However, there is a chance for severe weather on Sunday afternoon as well as Saturday. 

4-29 adv sun 3 pm

My, oh my. What a tricky forecast. So many elements to consider and it doesn't stop on Sunday. There is more tricky forecasting for next week. 

Marc has the latest information and data for you tonight on WDRB. Be sure to tune in! Also, be sure to download our weather app, so you can check the radar before you head out the door this weekend! 

App

I'll see you tomorrow morning from 6-9 am! Before then, let's connect! Find me on social media!

Katie McGraw's Facebook Page

Katie McGraw's Twitter Page

My headshot

-Meteorologist Katie McGraw

04/28/2016

Remembering One Of The Largest Tornado Outbreaks In U.S. History...

It was around this date five years ago that the largest sequence of tornadoes in recorded history began over the Southeastern United States. During the four day period between April 25th and April 28th 2011, an astonishing 358 tornadoes occurred from Texas through Georgia, and as far north as Southern Canada! 205 tornadoes touched down on April 27th alone, making it the most prolific tornado outbreak every recorded even surpassing the raw number of tornadoes produced during the Super Outbreak of April 3, 1974. In total, 348 people perished during the four day series of outbreaks with 238 fatalities occurring in the hardest hit state of Alabama.

1

In an unprecedented fashion, SPC issued Moderate and High Risks for severe weather on three consecutive days covering April 25th, 26th and the 27th.  

2

Image Credit: NOAA

The long duration event was driven by a very strong and slow moving upper level trough of low pressure that had dug deep into the Southern Plains. By the 27th, the powerful upper storm system began to eject eastward into the Southeastern US with jet stream winds in excess of 140 mph. 

3

Image Credit: NOAA

These high speed, upper level winds combined with a super warm and moist air mass at the surface to produce an absolute explosion of thunderstorms on the 27th.

 

Video Courtesy: thewxmann

Similar to what occurred on April 3, 1974, every storm that developed that day began to rapidly rotate producing a swarm of tornadoes.  

 

Video Courtesy: Charles Kuster

Not only were there an extreme number of tornadoes, many of them grew to monsterous proportions with 44 tornadoes being assessed as strong, EF-3 or greater in intensity and four of them were classified as EF-5! To put this in perspective, the US only averages around one EF-5 per year. This rivals only the 1974 Super Outbreak that produced 63 strong tornadoes and a staggering six EF-5's. 

 

Video Courtesy: TVNweather

The 2011 severe weather season went on to produce the catastrophic Joplin Missouri EF-5 and will go down as the deadliest year for tornadoes in the last 60 years. 

In total, 540 people perished due to tornadic storms in 2011.  This compares to only 564 that were killed by tornadoes during the 10 year period from 2001 through 2010. Hopefully, we don't see a season like EVER again!

 

 

 

 

 

 

04/27/2016

Tornado Watch Issued for Parts of Kentuckiana!

A Tornado Watch has been issued for portions of Southwest Indiana and West-Central Kentucky.  This watch remains in effect until midnight EDT/11 pm CDT and includes several of our western counties.

Warnings

URGENT - IMMEDIATE BROADCAST REQUESTED

   TORNADO WATCH NUMBER 117

   NWS STORM PREDICTION CENTER NORMAN OK

   510 PM CDT WED APR 27 2016

   THE NWS STORM PREDICTION CENTER HAS ISSUED A

   * TORNADO WATCH FOR PORTIONS OF

     SOUTHWEST INDIANA

     WESTERN KENTUCKY

   * EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 510 PM

     UNTIL 1100 PM CDT.

   * PRIMARY THREATS INCLUDE...

     A COUPLE TORNADOES POSSIBLE

     ISOLATED DAMAGING WIND GUSTS TO 70 MPH POSSIBLE

     ISOLATED LARGE HAIL EVENTS TO 1.5 INCHES IN DIAMETER POSSIBLE

 

   SUMMARY...ISOLATED THUNDERSTORMS OVER WESTERN KY ARE INTERACTING

   WITH A WEAK BOUNDARY...AND BECOMING OCCASIONALLY SEVERE.  ISOLATED

   TORNADOES AND LOCALLY DAMAGING WIND GUSTS WILL BE POSSIBLE FOR A FEW

   HOURS THIS EVENING.

 

   THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 45 STATUTE

   MILES EAST AND WEST OF A LINE FROM 40 MILES NORTHEAST OF

   EVANSVILLE INDIANA TO 45 MILES WEST SOUTHWEST OF BOWLING GREEN

   KENTUCKY.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

   ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).

   PRECAUTIONARY/PREPAREDNESS ACTIONS...

 

   REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

   TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

   AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

   THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

   AND POSSIBLE WARNINGS.

 

Marc and Rick will have a full update on our severe threat this evening on WDRB News.

 

WDRB Meteorologist Jeremy Kappell

Jeremy 6sx

Jeremy's Bio

Find me on Facebook!

Follow me on Twitter!

Email me at jkappell@wdrb.com