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March 30, 2011

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.





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