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58 posts from November 2017
11/21/2017
11/20/2017
FROST FLOWERS: Rare Weather Phenomenon Spotted In Kentuckiana...
Frost flowers were spotted Monday morning in Kentuckiana! It's a pretty rare phenomenon that only happens in sub-freezing temperatures when a plant's stem hasn't frozen previously and the soil is wet, but not frozen.
What is a frost flower and where do you look?
The National Weather Service put together a very cool article about Frost Flowers. This rare phenomena is explained in an article by Glen Conner, a state Climatologist Emeritus for Kentucky:
Frost flowers are thin layers (perhaps credit card thickness) of ice that are extruded through slits from the stems of white or yellow wingstem plants, among others. Their formation requires freezing air temperature, soil that is moist or wet but not frozen, and a plant's stem that has not been previously frozen. (Practically speaking, a once per year event, although not all individuals produce frost flowers on the first day of good conditions).
The water in the plant's stem is drawn upward by capillary action from the ground. It expands as it freezes and splits the stem vertically and freezes on contact with the air. As more water is drawn from ground through the split, it extrudes a paper thin ice layer further from the stem. The length of the split determines if the frost flower is a narrow or wide ribbon of ice. It curls unpredictably as it is extruded, perhaps from unequal friction along the sides of the split, to form "petals". These flowers, no two of which are alike, are fragile and last only until they sublimate or melt.
To find them, look for tall weeds, especially in locations that are seldom mowed. They seem to like the same habitat purple ironweed, blackberrries and wingstems with the actual frost flowers forming on the wingstems.
-Rick DeLuca
https://www.facebook.com/RickDeLucaWeather
11/19/2017
NWS Confirms Tornado in Meade County
The following information comes directly from the National Weather Service office in Louisville.
...NWS Damage Survey for 11/18/2017 Tornado Event...
.Meade County, Kentucky Tornado...
EF Scale Rating: EF-1
Estimated Peak Wind: 100-105 mph
Path Length/Statue/: 1.8 miles
Path Width/Maximum/: 50 yards
Fatalities: 0
Injuries: 1
Start Date: 11/18/2017
Start Time: 4:32 PM EST
Start Location: 3 miles NNW of Irvington, KY
Start Lat/Lon: 37.9222 / -86.3086
End Date: 11/18/2017
End Time: 4:34 PM EST
End Location: 3 miles N of Irvington, KY
End Lat/Lon: 37.9287 / -86.2763
Survey Summary:
The tornado touched down just inside the Breckinridge-Meade County
line a mile north of Irvington. It pushed a large tobacco barn 15
feet eastward, tore off its roof, and collapsed several walls.
Debris from the barn was scattered over a half mile downwind. The
tornado moved east-northeast, skipping along a wooded area where
several trees were snapped or uprooted, then hit a mobile home on
Fackler Road, rolling the anchored unit several times, destroying
the home. The owner sustained only minor injuries as he rolled over
with his house, crawling out of a hole after it settled. A garage
on the property was also destroyed. The tornado continued skipping
along the northwest side of Sandy Hill Rd, damaging outbuildings on
another farm, before crossing KY highway 261 at Guston Rd. A split
level home on Guston Rd had part of its roof removed, with
insulation spattered on the lee side of the home. An occupant of
the home reported he was descending the stairs as the roof was torn
off, and was briefly drawn up the stairs as it occurred. Debris from
the split level home was dropped across the road, where a few more
trees were snapped and uprooted. The tornado then flattened a fence
and peeled a section of sheet metal on an outbuilding before
lifting. The NWS thanks Meade County EMA and Remote Aerial for their
assistance in this damage survey.
-Hannah Strong
Cold Air Invades for Thanksgiving Week
There are two different cold fronts coming through Kentuckiana this week bringing bitterly cold air. The first one will come through Tuesday night, which means Wednesday morning will be very cold. That's a travel day for many people being the day before a holiday, so let's break down what you will see.
Temperatures Wednesday morning will be in the upper 20s, but notice the direction the wind is coming from. It's coming out of the north/northwest in the image below. That means the wind chill values will be much lower than temperatures.
Wind chills, according to the North American Model, will be in the teens across Kentuckiana. The good news here: even with wind chills that cold, it will still take more than 30 minutes for frostbite to set in if you're exposed to this bitterly cold air. Even as cold as it will be, this is not considered dangerous unless you are outside without a coat/gloves/hat, etc. for an extended period of time.
Temperatures on Thanksgiving morning will be similar, but wind chills won't be quite as low. Notice the wind pattern in the image below. It's hard to pick one out near Louisville because there will be a High Pressure very near us Thursday and Friday. Thanksgiving and Black Friday will start cold, but not with wind chills in the teens.
If you're not spending the holiday in Louisvile, here's how you can figure out the wind chill for where you are traveling. This chart is from NOAA.
-Hannah Strong
VIDEO: 2017 Hurricanes Simulation
How can you see the atmosphere?
The answer is blowing in the wind! Tiny particles, known as aerosols, are carried by winds around the globe. This visualization uses data from NASA satellites combined with our knowledge of physics and meteorology to track three aerosols: dust, smoke, and sea salt.
Video Credit: NASA Goddard
Sea salt, shown here in blue, is picked up by winds passing over the ocean. As tropical storms and hurricanes form, the salt particles are concentrated into the spiraling shape we all recognize. With their movements, we can follow the formation of Hurricane Irma and see the dust from the Sahara, shown in tan, get washed out of the storm center by the rain. Advances in computing speed allow scientists to include more details of these physical processes in their simulations of how the aerosols interact with the storm systems. The increased resolution of the computer simulation is apparent in fine details like the hurricane bands spiraling counter-clockwise. Computer simulations let us see how different processes fit together and evolve as a system.
By using mathematical models to represent nature we can separate the system into component parts and better understand the underlying physics of each. Today's research improves next year's weather forecasting ability. Hurricane Ophelia was very unusual. It headed northeast, pulling in Saharan dust and smoke from wildfires in Portugal, carrying both to Ireland and the UK. This aerosol interaction was very different from other storms of the season. As computing speed continues to increase, scientists will be able to bring more scientific details into the simulations, giving us a deeper understanding of our home planet.
Pretty cool, right?! Let me know your thoughts in the links below!
-Katie McGraw
11/18/2017
Saturday Post-Storm Analysis
Saturday's cold front packed quite the punch! Our WDRB counties saw 12 Severe Thunderstorm Warnings and 1 Tornado Warning through the afternoon. That cold front is now dropping our temperatures. This temperature fall actually happened in about 3 hours.
Just as forecast, wind was the main threat today. That's why there were so many thunderstorm warnings. As the night continues and the sun rises tomorrow, it is likely more damage reports will come in. Measured wind gusts exceeded 50 mph in several places around Kentuckiana.
On Sunday the National Weather Service office in Louisville will do a damage survey for the one tornado warning they issued.
It was near Mount Washington in Bullitt County. Above you can see the reflectivity. This is the exact moment the tornado warning was issued. Below is the velocity showing the rotation. Because winds were so universally strong today, we did not see the normal reds and greens next to each other in these rotation couplets. Instead you see dark red next to pink/orange.
There was a small debris signature near this area of rotation for only a couple radar scans. However that debris signature wasn't as tight/organized as we normally see in a storm like this. The strong winds, especially higher up in the atmosphere, could have scattered any debris making it look less organized. I'm not convinced there was a tornado touch down in this area, but it is VERY possible. The National Weather Service will let us know tomorrow, so watch for updates. Katie and I will keep you posted through the day.
-Hannah Strong
NOWCAST: Latest about Today's Storm Threat
Severe Risk:
The Storm Prediction Center has increased our severe weather risk from a marginal to a slight risk for severe weather for the entire viewing area. A slight risk is defined by SPC as an area of organized severe storms, which is not widespread in coverage with varying levels of intensity.
The main threats will be damaging gusty winds, localized heavy rain and frequent lightning. The secondary threats are isolated tornadoes and hail. A few isolated strong to severe storms are possible this afternoon as a defined squall line moves through the area.
Set Up:
Temps have increased significantly in the past day. That's because there is a warm front moving through the area. But the warm up is brief. There will be a strong trailing cold front that will sweep through the area later today. Widespread precipitation will be likely ahead of the front with gusty showers and storms.
Ingredients: Summary: There is a narrow window of limited instability as storms move through the area, but there will be a ton of wind energy, that could allow for a few damaging wind gusts and storms.
WIND SHEAR:
We will have tons of wind energy today. It is already so breezy (40-50 mph) even ahead of the cold front. When it comes to severe storms, as a rule, we look for at least 35 kt winds aloft as a severe criteria.
Check out these 850 mb winds at 3 pm! Around 65-70 mph at 850 mb. This is a 50-60 kt low level jet and means there is enough mid level wind energy to mix down and cause some damaging winds even with a narrow window of instability. There is also a bit of directional wind shear that could allow a brief tornado or two.
As I mentioned, it is going to be windy, even when it is not storming today. There is a wind advisory in effect today until 10 pm. Winds will be increasing during the day and will be the fastest when the showers and storms move through. The winds will also change direction from a southerly wind to a NW wind following the front.
Instability: Heat and moisture (or dew points) both are fuel for storms. The increase of each, will in turn, increase our instability. Instability is key to severe weather development.
Temps are unseasonably warm and increased substantially in the last day. Roughly 25-30 degrees. Our temps will increase to the mid and upper 60s before the front, which is about 10 degrees above average.
Notice the dew point is also on the rise. Not overwhelming, but should get to the low 60s, which signifies moisture is being transported into the area and increasing instability.
Meteorologists often refer to "weak instability" (CAPE less than 1000 Jkg-1), "moderate instability" (CAPE from 1000-2500 Jkg-1), "strong instability" (CAPE from 2500-4000 Jkg-1), and "extreme instability" (CAPE greater than 4000 Jkg-1). Models suggest there is a narrow corridor of roughly 300-600 J/kg CAPE before the front. This is considered weak instability. This will limit the severe potential, but as mentioned above, the wind energy could overcome the lack of instability and we could still see a few rogue severe storms.
TIMING:
We are currently seeing a few light showers. Which could actually help limit instability a tad.
It looks as though the main line will arrive to our NW counties around 2-4 pm
Showers and storms will continue to push from the NW to SE through our area QUICKLY during the afternoon and early evening. There will be bursts of heavy rain embedded within the main line. Expect around .5''-1'' of rain with locally higher amounts.
Majority of the showers and storms will end by the early evening. Roughly 7-9 pm.
But there could be a few isolated showers lingering into tonight, leading to a few flurries as temps drop significantly and quickly.
Hour By Hour:
Headed the U of L Game? Prepare for a change of seasons during the game! It will be warm to start. Then stormy. Then much colder. Temps will drop from the upper 60s to the 40s and then the 30s late tonight.
My thoughts:
A few rogue strong to severe storms are certainly possible with the ingredients we have available, but this will not be an event. Here is a summary of everything we discussed. Which is a lot.
To find out the details about the rest of the weekend, and of course Thanksgiving, be sure to join Hannah this evening on WDRB News. If and when storms become severe, we will be keeping you informed in a variety of ways. One of those is on social media. The links to my pages are below!
Severe Thunderstorm Watch Issued
A Severe Thunderstorm Watch has been issued for all of our viewing area until 6:00 pm EST and DOES includes Louisville.
Below is an image of the counties included in both watches as well as detailed information from the National Weather Service.
SEVERE THUNDERSTORM WATCH INFORMATION:
THE NATIONAL WEATHER SERVICE HAS EXTENDED SEVERE THUNDERSTORM
WATCH 516 TO INCLUDE THE FOLLOWING AREAS UNTIL 6 PM EST /5 PM
CST/ THIS EVENING
IN KENTUCKY THIS WATCH INCLUDES 45 COUNTIES
IN EAST CENTRAL KENTUCKY
ANDERSON BOURBON BOYLE
CLARK FAYETTE FRANKLIN
GARRARD HARRISON JESSAMINE
MADISON MERCER NICHOLAS
SCOTT WOODFORD
IN NORTH CENTRAL KENTUCKY
BULLITT HARDIN HENRY
JEFFERSON LARUE NELSON
OLDHAM SHELBY SPENCER
TRIMBLE WASHINGTON
IN SOUTH CENTRAL KENTUCKY
CASEY GRAYSON GREEN
HART LINCOLN LOGAN
MARION TAYLOR
IN SOUTH CENTRAL KENTUCKY
ADAIR ALLEN BARREN
BUTLER CLINTON CUMBERLAND
EDMONSON METCALFE MONROE
RUSSELL SIMPSON WARREN
THIS INCLUDES THE CITIES OF ALBANY, BARDSTOWN, BEDFORD,
BOWLING GREEN, BROWNSVILLE, BURKESVILLE, CAMPBELLSVILLE,
CARLISLE, COLUMBIA, CYNTHIANA, DANVILLE, EDMONTON, ELIZABETHTOWN,
FRANKFORT, FRANKLIN, GEORGETOWN, GLASGOW, GREENSBURG,
HARRODSBURG, HODGENVILLE, JAMESTOWN, LA GRANGE, LANCASTER,
LAWRENCEBURG, LEBANON, LEITCHFIELD, LEXINGTON, LIBERTY,
LOUISVILLE, MORGANTOWN, MUNFORDVILLE, NEW CASTLE, NICHOLASVILLE,
PARIS, PROVIDENCE, RICHMOND, RUSSELLVILLE, SCOTTSVILLE,
SHELBYVILLE, SHEPHERDSVILLE, SPRINGFIELD, STANFORD, TAYLORSVILLE,
TOMPKINSVILLE, VERSAILLES, AND WINCHESTER.
SEVERE THUNDERSTORM WATCH 516 REMAINS VALID UNTIL 6 PM EST /5 PM
CST/ THIS EVENING FOR THE FOLLOWING AREAS
IN INDIANA THIS WATCH INCLUDES 10 COUNTIES
IN SOUTH CENTRAL INDIANA
CLARK CRAWFORD DUBOIS
FLOYD HARRISON JEFFERSON
ORANGE PERRY SCOTT
WASHINGTON
IN KENTUCKY THIS WATCH INCLUDES 4 COUNTIES
IN NORTH CENTRAL KENTUCKY
BRECKINRIDGE MEADE
IN NORTHWEST KENTUCKY
HANCOCK OHIO
THIS INCLUDES THE CITIES OF BRANDENBURG, CORYDON, ENGLISH,
HARDINSBURG, HARTFORD, HAWESVILLE, JASPER, JEFFERSONVILLE,
LEWISPORT, MADISON, NEW ALBANY, PAOLI, SALEM, SCOTTSBURG,
AND TELL CITY.
Stay tuned for the latest information. A few showers have started to develop and the line of storms is just out to our west. Hannah and I will be here and keeping you informed for the rest of today. Be sure to watch the news this evening with Hannah on WDRB for the latest information. If and when storms go severe, we will be updating all of our social media pages, and cut into programming if necessary. The links to my social media pages are below.
-Katie McGraw
WATCH LIKELY TO BE ISSUED
The National Weather Service in Louisville is likely to issue a Severe Thunderstorm Watch soon.... Details below
Probability of Watch Issuance...80 percent
SUMMARY...Severe threat will increase into the early afternoon hours
ahead of progressive cold front. Severe thunderstorm watch will be
issued by 18z to account for this potential.
DISCUSSION...Strong 12hr mid-level height falls will overspread the
OH Valley and mid-south region this afternoon ahead of a progressive
cold front. Large-scale forcing for ascent will be focused across
this region but environmental capping is expected to restrict
appreciable pre-frontal convection, except for the warm advection
corridor across the OH Valley. Latest visible satellite imagery
suggests strongest boundary-layer heating is noted just ahead of the
front from central AR into southwest IL. This is supported in OA
fields where surface-3km lapse rates are now on the order of 6.5
C/km where partial sunshine is observed. Given the strong capping
observed, thunderstorms are expected to initiate along the surging
cold front. Latest radar data supports this scenario with convection
gradually increasing along the wind shift from east-central IL into
southeast MO where lightning is currently observed. Damaging wind
threat will increase with frontal convection as it matures,
potentially encouraging strong environmental winds to mix to the
surface with stronger downdrafts.
-Katie McGraw
11/17/2017
Update to Saturday's Showers and Storms
Severe Risk:
The Storm Prediction Center has issued an "Marginal Risk" for severe weather for our entire area. A Marginal risk is an area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity.
The main threats will be damaging gusty winds, localized heavy rain that could potentially lead to flooding in spots and lightning.
Temps are increasing as we speak. That's because there is a warm front out to the west. But there will be a strong trailing cold front that will sweep through the area on Saturday. Therefore, our warm up is brief. Precipitation will be likely ahead of the front with gusty showers and storms.
Ingredients: Summary: There is only a narrow window of limited instability as storms move through the area, but there will be a ton of wind energy, that could allow for a few damaging wind gusts and storms.
WIND SHEAR:
We will have tons of wind energy tomorrow. Winds will start to pick up tonight and it will get windy by tomorrow, even before storms arrive. When it comes to severe storms, as a rule, we look for at least 35 kt winds aloft as a severe criteria.
Check out these 850 mb winds at 1 pm! Around 65 mph! Certainly enough for strong to severe storms to develop even with the lack of instability.
As I mentioned, it is going to be windy even when it is not storming. There is a wind advisory in effect starting tomorrow morning at 7 am through 10 pm.
There will be two waves of peak winds. Expect gusts of 40 mph in the morning. Then they will increase and become even faster as the showers and storms move through. The winds will also change direction from a southerly wind to a NW wind.
Instability: Meteorologists often refer to "weak instability" (CAPE less than 1000 Jkg-1), "moderate instability" (CAPE from 1000-2500 Jkg-1), "strong instability" (CAPE from 2500-4000 Jkg-1), and "extreme instability" (CAPE greater than 4000 Jkg-1). Models suggest our there will be a narrow window of CAPE values around 100-400 J/kg or "weak instability" on Saturday. This will limit the severe potential, but we could still see a few rogue severe storms because the wind energy will overcome the weak instability.
Rain Totals:
There will be bursts of heavy rain embedded within the main line. Expect around .5''-1'' of rain with locally higher amounts.
TIMING:
Although model timing differences exist, trends continue to point to a line of showers/storms arriving Saturday afternoon through the early evening. A rough estimate would be around 12-7 pm. The squall line will race across Kentuckiana.
There could be a few on and off showers tonight and tomorrow morning.
A rough ETA for our NW counties is 1-4 pm.
Showers and storms will push NW to SE through our area during the afternoon and early evening.
These showers and storms will impact the U of L game. Keep in mind, the weather is not going to be great for a game tomorrow. Prepare to see many seasons in one day as temps will drop from the upper 60s to the 40s and then the 30s.
Majority of the showers and storms will end by the early evening.
But there could be a few isolated showers lingering into Saturday night, leading to a few flurries as temps drop significantly and quickly.
My thoughts?
A few rogue strong to severe storms are certainly possible with the ingredients we have available, but this will not be an "event". Winds will be gusting close to 40-50 mph, so it is not of the question a few could make it to severe criteria. If and when storm become severe, we will be keeping you informed in a variety of ways. One of those is on social media. The links to my pages are below!
To find out the details about the rest of the weekend, and of course Thanksgiving, be sure to join Marc and Rick this evening on WDRB News. Again, we will be making tweaks to the forecast over the next few days, so be sure to keep up to date with the forecast!
