Saturday, March 10, 2012

Meteorological March Madness and Sunday Storms


When you can come up with a title using alliteration, USE IT!  Remember that cut off low that I talked about a week ago?  I said these are never easy to forecast as the models do not handle them correctly.  Well, this one is a classic example of that.  This low is FINALLY going to move north and east of the state Sunday into Monday morning dragging a boundary into the state.  If you look back at previous blog posts, I also mentioned you always have to keep the door open for the possibility of severe weather.

The Storm Prediction Center has placed much of Arkansas in a slight risk for severe weather.  Remember ,this is "slight".  At this time, I do not expect an outbreak due to limiting factors.  I would be much more concerned if we had ample amounts of instability in place and the models are not on board with that.  I think rain showers and clouds will keep that to a minimum.  However, if we develop some very warm and humid air Sunday morning and afternoon, then the concern is enhanced.  So while I don't expect that to happen, you always watch it.  This is Arkansas and it's March!  We get thunderstorms and some of those can always be severe.  The main concern will be high winds, but an isolated tornado can't be ruled out.  The SPC correctly mentions the strengthening low level jet which should be strong.  This is a concern and can promote storms to become severe and rotate.  But, the limiting factor in all this are the instability levels. 

I also expect rainfall to be heavy, especially across western Arkansas.  This is where the highest chance for rain will develop and it may take awhile for this to advance eastward into central and eastern Arkansas, but it should as the day continues Sunday.

Now onto next week.  We will develop a pattern which almost resembles summer.  Warm and somewhat humid air will advance to the north as a ridge of high pressure develops.  There will be small disturbances which move through the flow aloft and that can spark off a few showers and storms.  The most likely time for that to happen is during the heating of the day as well.  The chance is small though.  With the possibility of rain and some clouds as well, this will keep temperatures from soaring.  However, they will be quite warm for this time of year and could easily challenge daily record highs.  I have a list of those at the bottom of this post.

Here are a few maps explaining Sunday and the weather beyond.

The NAM shows instability levels moving northward into the state ahead of a cold front.  This is valid Sunday at 7 PM.  While these levels are elevated, they are not very high.  It will be enough though to develop thunderstorms and a few could become severe.  Measured in joules per Kilogram, CAPE here is less than 1000.  So there is some instability, but if it gets higher, I'll have more concern.
This is the forecast Energy Helicity Index.  A combination of instability and shear.  These are on the low end of the scale due to the limited instability.  Again, if this gets higher, there will be more of a concern for tornadoes.

Simulated radar from the NAM late Sunday afternoon shows ongoing showers and storms with cloud cover across the state, especially western Arkansas.  This will help keep the atmosphere "worked over".  Meaning lower instability.
The SPC has placed most of Arkansas under a slight risk for severe weather.
As I mentioned, we'll go into a pattern which almost resembles summer.  Here's a list of record highs next week for Little Rock.  I think we will easily be within 5-10 degrees of these and could challenge them.

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