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41 posts from March 2011

March 31, 2011

My Concern Is Increasing For A Potential Severe Weather Event

In the short term, cold will dominate our weather but with a significant push of warm air late this weekend our attention will rapidly change toward severe weather. I am becoming more concerned that the setup could allow for a severe weather event and this will be the main point of discussion over the next few days.


Short Term Forecast Discussion


I don't want to forget about the next couple of days, so I do briefly want to touch on that. Our normal high this time of the year is in the lower 60s, so it has been quite a cold stretch here as of late. We will be dominated by clouds today and tomorrow, so unfortunately we won't get a ton of relief. Notice the extensive cloud cover again in our region as of 6 am this morning, which should lock us in the clouds for this day.




A weak clipper type system will slip through the Ohio Valley and generate a few showers tomorrow. Notice the widespread light showers developing after around midday tomorrow. That will keep things chilly again with the possibility of a few showers tomorrow. :(




If you have out door plans, then Saturday is your day because scattered storms will begin Sunday in advance of our next event which leads us into that severe weather discussion.



Severe Weather Forecast Discussion


I have been talking about the severe weather potential for Monday on the blog since early this week and each day I have become more concerned. To be honest, I am really starting to get concerned that in the mid south there will be a severe weather outbreak and it could very easily include the Ohio Valley. We are on the northern edge of the system, so it is a bit more complicated to definitively say how bad it will be, but the ingredients look like they are coming together for a significant event. The Storm Prediction Center appears they agree with my assessent as well as they have now placed us in the risk for severe weather for Monday.


Let's get into some of the details. Just a quick reminder of the Severe Weather Ingredients needed for severe storms in the Ohio Valley.


Severe Ingredients 


We know forcing will not be a problem with a very strong low pressure moving across the Ohio Valley. The front this storm has with it will be very powerful.


The wind shear is remarkably strong on this storm system. I normally show winds about 1 mile off the ground, but let me show you winds even closer to the ground this morning. Let's look at winds about 2000 feet off the ground.



GFS Winds At About 2000 Feet Off The Ground For Monday

Note the winds at 2000 feet are a bearish 60 - 70 mph over the Ohio River. That is very, very strong.



GFS Winds At About 1 Mile Off The Ground For Monday

Note the winds 1 mile off the ground increase to near 70 mph. Again, these are tremendously strong winds.

I speak regularly that wind energy without instability is like having a Corvette running poor gas. If you don't use high octane fuel in that very powerful Corvette engine, then it will never run right and never reach its potential. The atmosphere can have very strong winds, but if there is not good fuel then it will never produce much if any severe weather in the Ohio Valley. Fuel for storms comes in the form of instability, and with this huge wind energy I would like to see at least 1000 units of instability to produce severe weather in this situation.



GFS Instability For Monday

Note the GFS is now indicating a large area of moderate instability. Notice the  1500 - 2000 units of instability over the Ohio Valley which would be a would be a major problem.


Gfs CAPE 1 



Looking at the data, we are starting to see a real threat developing for Monday. If the timing for the storms is late then that would increase that threat more. I want to show you the last two runs of the GFS noting when it is indicating the greatest threat of storms.


GFS Precipitation for Late Monday (Yesterday's Run)

Note the GFS dialing in an outbreak of storms late Monday right over our area. From the GFS, this is a strong signal of severe weather outbreak for at least the region.




GFS Precipitation for Late Monday (1AM Run From Today)

Note the incredibly consistent GFS showing almost the same exact solution two runs in a row and very consistent with the past few days. I will say it again, the GFS is showing significant severe weather outbreak for the region in a time that is very favorable for severe weather.





Yesterday, the Storm Prediction Center mentioned this severe weather threat in their wording, but today they have actually included our area in the severe weather threat. Our concern is Monday, and that labeled as day 5 on their severe weather threat.


SPC 4-8 


In addition, the Storm Prediction Center is using strong wording as well.

"Widespread severe storms are becoming increasingly probably Day 5. Gulf Moisture will advect northward through the Lower-Mid Mississippi Valley... Southeastern States and Ohio Valley in association with very strong eastward migrating low level jet. More widespread thunderstorm development will become probable as forcing for deep ascent attending the upper trough shifts east of strong elevated mixed layer. Threat will exist for supercells and line segments with tornadoes... large hail and damaging wind."




My Severe Weather Forecast Discussion


It appears more and more likely with each passing day that severe weather will affect the Ohio Valley on Monday, and could potentially be a significant severe weather event. All signals point toward winds that will be remarkably strong on Monday. The GFS continues to indicate moderate instability which is more than sufficient to support severe weather in this scenario. The low pressure is a very powerful system with a rock solid cold front. We will be located in the warm sector of the storm in a location that is normally a climotological location that is favored for severe weather.

To be honest, I am concerned. I think Monday at the bare minimum will have severe weather in our area. At the worst case, we could see a severe weather outbreak. The wind shear and moderate instability support large hail, damaging winds, and tornadoes. At this point, everything remains on the table and I will be monitoring this storm system very, very closely.



Full Forecast Discussion


In contrast to what we just discussed, today will be quiet and chilly. Skies will be mainly cloudy with a cool high near 48.




Tonight skies will remain mostly cloudy and temperatures will dip again into the mid 30s. Brrrrr!




Showers are possible tomorrow although nothing looks heavy. I think Saturday looks like a great start to the weekend with a high near 58 under partly cloudy skies. Sunday we will see the warm front move through allowing warmer air to push into the area with scattered t-storms. I do not think it will rain all day on Sunday at all. After a potential bout with severe weather on Monday, temperatures will cool significantly again on Tuesday and Wednesday.







I cannot emphacize enough how important it is to stay up to date on the storm approaching Monday. We will be discussing this heavily on Fox41 on TV in the days leading up to the storm and the blog will be active with an in depth discussion to keep you prepared for the storm.


March 30, 2011

Midday update... Sleet falling again in Louisville

With some sleet falling in downtown Louisville, I just wanted to quickly update you on what we are seeing around the area. There is no question that the severe weather will be the bigger story in the next 7 days, but we still have to get through an ugly Wednesday first.


For a full look at the severe weather threat over the next 7 days, please view my previous blog entry...




Snow/Sleet Discussion


Well we probably have another 2-3 hours where we could continue to see some snow or sleet across parts of the area. Tempertures in Louisville have dipped into the upper 30s with many areas north of the river cold enough to support all snow now.




Notice some of the lower 30s just north of the river. On a day like today, about 37 is is cold enough to support all snow and that is what we are seeing now in many areas north of the river.




Radar indicates snow showers and light snow from the Ohio River north. Remember a few slick spots on elevated surfaces is possible.




Louisville is showing a sleet/snow mix right now and that should continue here for a few more hours.


StormViewHD 2 


The bottom line is we have about 2 to 3 hours more of precipitation chances. Louisville will continue to see a sleet/snow mix. Not road concerns are anticipated. North of the Ohio river more snow than anything will continue for a few hours more. A small accumulation on the grassy surfaces could occur in areas like North Vernon, IN to Seymour, IN to Bedford, IN and maybe a county south. By late in the afternoon the system will be departing and drying conditions will settle in.

Sleet/Snow chances today and Severe Weather Risk Looms...

Today is not going to be the most spring-like day unfortunately. We are seeing light rain and sleet showers across part of the area this morning and we will discuss whether you could see an accumulation. In the longer range a severe risk is looming and the Storm Prediction Center has picked up on the risk I mentioned earlier this week.


Forecast Discussion


This morning we are seeing rain and sleet showers across the area. Nothing is really of any significance, but none-the-less you may run into these on the way to work today.






South of around E-town, KY, most of this is going to be rain, near the river this will be a rain/sleet shower mix, but north of the river a mix of sleet and snow will occur... in particular near Bedford, IN to Seymour, IN to North Vernon, IN. It is not out of the question that the northern areas could see a light accumulation of snow on the grassy surfaces. Regardless this is nothing to be overly concerned about at all.


Severe Weather Discussion


I started talking about severe potential for Monday earlier this week and spent the day yesterday discussing that potential in detail. This is clearly going to be the focus of the blog for the next 5 days or so. The GFS computer model continues to paint a picture that will produce a significant severe weather event from Sunday through Monday over areas east of the Rockies. I think the Mississippi River Valley through the Tennessee Valley will see a significant event, but the Ohio Valley still is not a guarantee. Let's look at the setup from the GFS as it is showing nice run to run agreement with subtle differences. I want to show you the GFS runs from 7 pm yesterday and 1 am today.


GFS Surface Setup For Monday at 1 pm (7PM Run)

Note storms are trying to fire around midday on Monday from this run of the GFS.




GFS Surface Setup For Monday at 7 pm (1AM Run)

Note storms are trying to fire late afternoon on Monday from this run of the GFS. If the storms were to fire later in the day, then a severe episode could occur in the Ohio Valley.





Regardless which solution verifies, what we see from the GFS consistently is moderate instability at minimum. Remember, I like to see a minimum of 1000 units of instability to support severe weather when powerful mid level winds are present. First, let's look at the strength of those winds 1 mile off the ground.


GFS Winds 1 mile off the ground for Monday

Note the massive area of 65 - 80 mph winds 1 mile off the ground over the Ohio Valley per the GFS. That is a serious concern if that is coupled with instability.




If we can couple that wind energy with good fuel, good instability, then we will have a problem. Here is a look at the instability values.


GFS Instability For Monday

Note the widespread 1000+ units of instability in our region just like the GFS indicated yesterday.


Gfs CAPE 1 



It appears now that I am not the only one concerned about this storm. The Storm Prediction Center is now starting to pick up on this threat as well. Note their words from this morning for the Sunday/Monday timeframe.


"Monday/ Day6 ... Potential will exist for a more substantial severe threat as moisture advects northeastward through the Mississippi and Tennessee Valley regions... east of amplifying... but progressive upper trough. Storms may develop along and east of southeastward advancing front along eastern periphery of warmer EML plume. Strength of low-level jet and deep shear along with adequate instability could support the potential for a significant severe event.

If model solutions continue to converge... a risk area will likely need to be introduced in the next 4-8 update... especially from the Mississippi Valley through the southeastern states and possibly into southern parts of the Ohio Valley."



My Severe Weather Forecast Thoughts


Basically the GFS continues to point toward a significant severe weather event anywhere from Louisiana to Arkansas to Tennessee toKentucky and points east. The storm system has remarkable wind energy, sufficient instability, and powerful forcing from a major front. I will say that I do believe we will have, at bare minimum, a slight risk of severe weather for our area, but as the details evolve this could be a real problem for our area. It would not surprise me to see a moderate risk of severe weather introduced at some point for our region, but that still could be slightly south of our area. Hail, damaging winds, and tornadoes can occur from setups like this one. I am concerned about Monday, but there are features of this storm that have to evolve. I can tell you that I will be watching this very closely in the coming days.

One side note of this storm, since this has such a strong front, we should see another strong push of colder air in the middle of next week.



My Extended Forecast


Louisville will see rain/sleet showers today, E-town south will see mainly rain showers, and north of the river will see sleet/snow showers through early afternoon. It is indeed possible that a light snow accumulation from our south central Indiana counties could occur. Late in the afternoon, the storm will be departing amd we will shut down the precipitation. Highs top in the mid 40s.




Tonight will be chilly with a low near the freezing mark under mostly cloudy skies.




Tomorrow should be a quiet day with showers returning by Friday. Saturday looks like the better weekend day with highs in the mid 50s under partly cloudy skies. On Sunday, the warm front will move through firing scattered t-storms and allow temps to warm significantly. You already know, Monday is the day to watch and will remain a big focus in the coming days.