Monday, February 17, 2014

Severe Weather Chances Thursday


Yep.  You read that right.  Severe weather is possible later this week.  I know you're probably shaking your head right now thinking "This shouldn't surprise me.  After all, this is Arkansas."  I remember something similar happened a few years ago and I'm not sure if it was 2010 or 2011.  We had several inches of snow early in the month, then just a couple weeks later severe weather hit.  Because of the severely cold winter, many may not be in severe weather mode, but we need to start now since our primary severe weather season is getting ready to kick off.

A few weeks ago I talked about sea surface temperatures in the Gulf of Mexico.  All of the arctic air that has blasted through the state has also cooled those waters significantly.  Similar to last winter and spring, this could delay any significant "outbreaks" of severe weather until those Gulf waters warm.  That doesn't mean we can't have some severe weather.  Look at last year.  Outside of the Botkinburg tornado in April, we didn't have an "outbreak" until May 30th!  That's very, very late for Arkansas severe weather standards.  At this time, there isn't a standard definition of "outbreak".  

With all that said, I do think few strong to severe thunderstorms WILL be possible Thursday afternoon and early evening.  The data over the past couple of days really gets this cranked up across eastern Arkansas and points east.  There will be some instability and dewpoint temperatures will be high enough to support that threat as a pacific cold front scoots through the state. I'll have a couple maps below to look at.

One more thing.  I still think we will go back into a cold weather pattern next week.  This zonal west to east flow will begin to amplify once again with a western Canada/Alaskan ridge.  This will send a downstream trough over the central and eastern United States sending arctic air south again.  As far as moisture is concerned, it's wayyyyyyy too early to speculate about that.  So enjoy the "February Thaw" while it lasts.  All signs are pointing towards below average temperatures next week.

This is the overnight run of the GFS and it's valid Thursday at 6PM.  This indicates a surge of surface dewpoint temperatures into the low 60s across much of the SW half of the state.  That's high enough to support severe weather.  The surface low is over the Great Lakes (black circle).  The front extends south of that.  See the "kink" in the black lines south of that low from Indiana into Arkansas?  That's the cold front.  Behind it, you can clearly see the drier surface air.
This is the 6Z NAM and it only goes out 84 hours which makes this valid at noon Thursday.  This is a map indicating CAPE (Convective Available Potential Energy).  The higher the value, the more unstable the air is.  This is all surface based.  Notice the corridor of highest instability will be across Louisiana into eastern Arkansas at this time.   The surface low is at the top of the map near Kansas City with the front entering NW Arkansas and extending into central Texas.
The Storm Prediction Center has highlighted much of Arkansas Thursday for the potential for some severe weather.  The purple area east is for Friday as the front moves away.  Right now, it's not clear what will be the primary severe weather threats and I'll keep you posted.

3 comments:

Bruce Wayne said...

This will NOT be a major severe weather event for Arkansas. CAPE is low. EHI is not good. Overall worst threat looks to be from a line from Jonesboro to Pine Bluff to El Dorado and points to the east for severe weather. Little Rock NWS is passing the worst of the weather to Memphis in which their NWS also doesn't believe in a major outbreak, more of a linear line of thunderstorms. Hail and wind is the highest threat with the freezing line at about 12,000 feet at that time. At the VERY worst, Hail to 1.75 inches in diameter. Winds to 70 mph and one or two EF-0s or maybe even an EF-1 tornado at MAX. Straight line winds will be the bigger problem the further east of Arkansas you go. Overall, NO big severe weather maker with this one for Arkansas. As you said, we've got a way to go before the Gulf warms back up again for a significant severe weather outbreak in Arkansas.

Anonymous said...

I can't wait for the arctic air to come back! This weather is way too warm, it needs to cool back down to the 20's again!

Anonymous said...

I think this weather is just wonderful, a little less wind would be nice but just to see my grass and driveway is a joy.