Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262108

Area Forecast Discussion
National Weather Service Saint Louis MO
408 PM CDT TUE APR 26 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 332 PM CDT Tue Apr 26 2016

Current bowing convective system over SW IL has a well established
cold pool and will continue to move east into the western OH
Valley into a large region of unstable air in advance of it. The
deep convective line with any severe threat should clear the area by
500 pm with trailing stratiform rain clearing the CWA by early
evening. A prominent outflow boundary with the convective system,
which should have completely moved through the CWA by 00z, has
largely stabilized the air mass to boundary layer based storms in
its wake. I will retain some low chance pops this evening on the
fringes of our CWA however I think the vast majority of the
evening in the wake of the present system will be dry. Current
thinking is that overnight we will see a MCS that has evolved
across the Plains early this evening, move west to east into central
and finally eastern MO in the predawn hours. Additional showers
and thunderstorms could develop late this evening and overnight
ahead of the aforementioned progressive Plains MCS in response to
the LLJ and WAA along north of the retreating outflow boundary/warm
front composite. There will be a severe threat with this overnight
activity given MUCAPE of 1000+ j/kg and increasing southwesterly
deep layer shear, but not nearly as great as the system that moved
through today.


.LONG TERM...  (Wednesday through Next Tuesday)
Issued at 332 PM CDT Tue Apr 26 2016

A little unclear how everything will pan out on Wednesday. There
will likely be ongoing convection from a decaying MCS over parts
of eastern MO in the morning that will move into IL. However it
does appear that there will be sufficient air mass recovery in the
wake of the morning convection. How much and the most favored
corridors are hard to say. Mid level lapse rates will remain steep
and heating should lead to SBCAPE of at least 1500 j/kg over parts
of central MO by early afternoon. The combination of the east-northeast
rotating short wave trof and large scale ascent, and the attendant
advancing cold front should result in thunderstorm development
along/ahead of the cold front by mid afternoon. Coverage should
then increase through the remainder of the afternoon, with storms
persisting into the evening as the front and trof progress east.
We will probably see a mixed convective mode with all severe
weather threats. Most of the activity should have moved out of the
CWA by 06z Thursday.

The trof will be lifting to the northeast on Thursday with the
cold front advancing into the OH/TN Valley region. Present
indications are that increasingly deep westerly flow in the wake
of the front will lead to good drying and little if any

Next round of showers and thunderstorms looks to unfold Friday
night into the weekend. First with the LLJ, WAA, and a lead
impulse Friday night/Saturday and then with another formidable
upper trof and attendant cold front Saturday night into Sunday.



.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 645 AM CDT Tue Apr 26 2016

Outside of some patchy MVFR CIGs in the north around UIN, VFR
conditions (outside of TSRA) are expected to prevail for the TAF
sites thru this evening. A cluster of TSRA is expected to roll
down from the KS-MO-NE junction this morning and affect COU and
the STL metro sites later this morning and early afternoon. A
brief period of gusty winds at the onset is also expected. A
frontal boundary is then anticipated to stall just north of I-70
for tonight and should promote low CIG formation for areas to the
north, including UIN, with MVFR CIGs returning there and perhaps
dropping into IFR category. Widespread rain and TSRA is then
expected to overspread the region later this evening and





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