Friday, April 01, 2011

Severe Possible Monday

1:30 PM Saturday Update.... WOW, it's a great day with temperatures already in the lower 70s, plenty of sun, and low humidity.  BIG changes are coming with details still not clear.

First of all, Sunday, hold onto your hats.  Winds will be sustained out of the south 20-25 mph with gusts from 30-40 mph.  The fire danger will once again be elevated.  I expect storms to fire north and west of the state Sunday night and travel to the northeast.  Rain and storms will develop along and just ahead of an advancing cold front which will move through central Arkansas around 9 am to noon Monday.  Severe weather will be possible with this line as it slides through the state.  By the early afternoon, I think conditions will destabilize across eastern Arkansas enough to increase the severe potential as the front moves into that area of the state.  Most of the activity will be over by mid to late afternoon. 

I also want to give everyone notice about cold temperatures Tuesday morning.  I think most of the state could be in the 30s for lows and if the winds diminish enough, we could have some frost.

Everyone needs to stay up to date with the latest weather information for Sunday night into Monday.  I'll keep you updated here and on Channel 7 News this weekend.

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Sorry, I didn't get this posted earlier today.  It has been one of those days.

When I dove into the details of the data Thursday for the situation coming up on Monday, I got very concerned due to the high amounts of instability and spin in the atmosphere.  The models spun up a surface low across southeast Oklahoma and tracked it along the front into northern Arkansas.  This would help promote the "backing" of the surface winds.  Basically it would bring in a south to southeast component to the wind and it would change direction with height.  This would lead to the development of tornadic supercells.   The development of the low on the front would also slow it's eastward progression allowing for more instability to develop ahead of it during the heating of the day.

Fast forward to today's model run.  It still looks like plenty of instability, but from what I saw, the surface low may spin up further north and east.  This would bring the front through faster.  The threat for severe weather is definitely there, but could be limited due to the early morning frontal passage.  It's possible to still get morning tornadoes and severe weather, but it's usually not as widespread as the afternoon hours when heating gets involved.  Nevertheless, the situation must be watched carefully throughout the weekend and everyone needs to be "weather aware" Monday.  Climatologically, this is a very favored time of the year for severe storms.  I'll keep you updated.

Check out the maps below from the afternoon run of the GFS.

This is the GFS valid 7 AM.  Notice the plume of high surface moisture values shooting northeastward.  You can see the front has entered NW Arkansas at this time as drier air is moving into the state.  Dewpoints of 55 degrees and higher are needed for significant severe weather.  This indicates values around 60 to 65 degrees.  Plenty of juice (fuel) for storms.
This is Convective Available Potential Energy (CAPE).  It's a measure of the buoyancy or instability in the air.  Levels here are exceeding 1000 j/kg which is adequate for severe weather.  Notice how those levels drop off across NW Arkansas as stable air behind the front enters that corner of the state.
This surface map shows the front and winds at the surface out of the southwest.  I will have more concern if a surface low develops around here and changes those surface winds out of the southeast.  We must watch that carefully as that would lead to the development of rotation with storms.

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