Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 230446

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1146 PM CDT Wed Mar 22 2017

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 326 PM CDT Wed Mar 22 2017

As surface ridge shifts off to the east tonight, winds to veer to
the southeast across the region. So southeast winds along with mid
and high clouds, lows will be a bit milder with near normal lows in
the low 30s to low 40s.

In the meantime, next weather system to begin lifting northeastward
out of the desert southwest towards region. Will see increasing low
level moisture, weak instability and developing warm front lift
northeastward through region late tonight. Scattered showers and/or
drizzle to develop along and north of boundary and move across
central/northeast MO and west central IL. Then as system exits area,
precipitation to taper off from south to north, coming to an end
late Thursday afternoon. As for high temperatures tomorrow, it will
depend on cloud cover and precipitation. For now have highs in the
mid 50s to low 70s, with the warmest temps over central MO.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 326 PM CDT Wed Mar 22 2017

A very active pattern seems in store thru the middle of next week.
Main focus will be potential for severe threat on Sat, otherwise,
PoPs in general.

Mdls are in fairly good agreement thru the weekend in a general
sense. An upper trof will begin traversing the Rockies tonight with
strong lee cyclogenesis thru Fri. While mdls agree with the general
soln, the small differences among solns will have a big impact on
the severe threat for the CWA. Mdls are suggesting a classic cold
core system, tho the GFS is more stacked than the other guidance.
Location and timing of sfc features will determine locations of any
severe threat.

Expect a dry slot to push into the area ahead of the approaching sfc
low. Have trended temps warmer, but are probably still not warm enuf
even with a short period of warming. Low topped TSRA will be
possible, potentially supercells where hodographs are optimized,
with all severe threats possible near the sfc low. Further south,
appears there will be enuf CAPE with steep enuf lapse rates to
support at least a hail threat. Will need to continue to monitor
this event as it approaches.

Otherwise, trended warm thru Sat. Generally trended twd a compromise
beyond with mdl solns continuing to diverge. Generally capped PoPs
in low chance or slight chance range beyond Mon. The GEM is faster
with moving the sfc ridge out of the area and the next approaching
system. Have kept low PoPs to account for this soln, but have low
confidence in this soln.



.AVIATION...  (For the 06z TAFs through 06z Thursday Night)
Issued at 1145 PM CDT Wed Mar 22 2017

VFR conditions are expected to prevail at the TAF sites for much
of the valid period. A warm front will approach our region later
tonight and will result in scattered showers maybe a thunderstorm
developing out ahead of it. Have placed in VCSH when the highest
probs are expected at most of the TAF sites mainly during Thursday
morning, with the addition of a TEMPO group at UIN. A period of
MVFR conditions is now expected at UIN with it possible elsewhere
but less likely. Clearing is then anticipated for later on Thursday
afternoon into evening as the warm front pushes thru. Surface
winds will gradually veer from easterly to southeast tonight and
southerly on Thursday. LLWS has been added for much of Thursday
night with a 45-50kt low level jet expected.





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