Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 270528

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1228 AM CDT WED APR 27 2016

Issued at 948 PM CDT Tue Apr 26 2016

Convection over eastern Kansas and northwest Missouri is
proceeding slowly eastward...about as expected. Looks like the
leading edges will be moving into the western fringes of our CWFA
by 06-07Z. Have made minor tweaks to the PoPs to slow the precip
accordingly. RAP is forecasting 1000-1500 J/Kg of MUCAPE along
with increasing deep layer shear...and this continues to point
toward the possibility of elevated severe storms with severe hail
being the primary threat.



.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 06z TAFs through 06z Wednesday Night)
Issued at 1230 AM CDT Wed Apr 27 2016

Pockets of IFR are showing up here and there in observations
around the STL Metro area. Earlier guidance hinted at this and
subsequent runs continue to develop and expand IFR ceilings across
much of the area before daybreak. More confidence in this now
since it`s actually developing. Otherwise, expect waves of showers
and thunderstorms across the area over the next 24 hours...likely
ending early to mid Wednesday evening. Any thunderstorm will be
capable of lowering flight conditions to IFR. Hail and gusty winds will also be a continuing

Specifics for KSTL:

Looks like Lambert will be in and out of IFR ceilings for a few
hours and likely prevailing IFR by 09-11Z. The first wave of
showers and thunderstorms should be moving into the vicinity of
the terminal by 10Z. And then another wave of storms is likely
after 18Z Wednesday.  Strength of the storms is uncertain at this
time, but any storm could produce brief periods of IFR conditions
in heavy rain. Hail and gusty winds will also be a continuing





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