Friday, March 28, 2014

Friday Severe Weather

The round of storms Thursday night into this morning fizzled out as it moved south for a couple reasons.   The dynamics with this system pulled to the north of Arkansas and as the line moved south, it encountered less instability.  We expected it to play out like that.

Now the next round will gather over northeast Texas later this morning and pull into southern Arkansas.   It will then overspread the state this afternoon with heavy rain and thunderstorms.  We really need to pay attention to where this boundary that moved in last night sets up.  It will be somewhere near or just south of the metro.  North of the boundary, the main threat today will be heavy rain and maybe some hail.  South of the boundary, the instability will really increase.  This means the threat over southern Arkansas will be very heavy rain, large hail, high winds, and an isolated tornado can't be ruled out.  The threat will decrease early tonight. 

Here's some good news.  After some morning cloud cover Saturday, the weekend looks great.  I'm still very concerned about the middle of next week.  I think strong thunderstorms and heavy rain will threaten us once again

I'm going to use maps from the HRRR courtesy of below.  For the most part, this model has done a great job.  Yesterday, it did indicate storms firing on the dry line out in Oklahoma and moving into western Arkansas, but that never happened.  I mentioned this possibility in a video and referred to it as "low confidence".  However, it did a great job with the line across northwest Arkansas and had it fizzling out as it pushed south.

The top panel is simulated radar, the bottom left panel is instability (CAPE), and the bottom right panel shows you surface dewpoints.  Notice in these maps the highest instability and the highest moisture levels stay across the southern half of the state.  Further north, cool surface temperatures will promote more of a heavy rain threat and maybe some hail.  Please remember, no model is perfect, but this should have a good handle on the situation.

By 3PM, the storms are over western Arkansas and some could be severe.  Look at the high levels of instability and moisture there.
BY 5PM, very heavy rain and storms are overspreading the state with the highest instability levels over the south central and southeast sections of the state.
BY 7 PM, the worst of the severe threat will be confined to far southern and southeastern Arkansas with heavy rain elsewhere.
The SPC has placed the area in yellow in a slight risk for severe weather
There's a small, 5% chance for a tornado within 25 mils of any given point over southwest Arkansas. (brown)
There's a 30% chance for severe winds within 25 miles of a given point over southern Arkansas. (red)
The hail threat is elevated too.  There's a 30% chance for severe hail within 25 miles of a given point (red)

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