Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 221142

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

.SHORT TERM...  (Through Late Tonight)
Issued at 340 AM CDT Wed Mar 22 2017

Showers this morning are confined to southern Missouri including the
far southern few counties of the CWA at the moment.  The northern
reaches of the rain is occurring in a band of mid level
frontogenesis while the showers and thunderstorms along the
Missouri/Arkansas border is being forced by low-mid level moisture
convergence.  The rain over the southern CWA should push south of
the area this morning as the upper flow turns slightly northwest as
an upper ridge builds into the area.  With high clouds streaming
over the area today and a continued persistent cool northeast-
easterly flow, went below MOS guidance for highs.

Should be dry this evening, but there will be an increasing chance
for showers overnight across central and northeast Missouri as the
low level flow turns out of the southwest.  This will allow broad
moisture convergence to set up on the nose of a 35kt low level jet.
MOS temperatures in the 30s look good for lows tonight.


.LONG TERM...  (Thursday through Tuesday)
Issued at 340 AM CDT Wed Mar 22 2017

It still looks like an active weather pattern for Thursday through
next Tuesday.  A trof of low pressure will be developing in the
Great Plains at the start of the period.  Models are continuing to
produce QPF on Thursday in the strong moisture return ahead of the
trof on Thursday.  Still concerned that PoPs might be too high since
models tend to be too wet in strong moisture return situations.
Should see warmer temperatures on Thursday regardless of PoPs
especially over central Missouri where highs will likely approach 70
degrees in southerly flow.

The strengthening system over the Plains will continue to push warm
and moist air into the region on Friday.  Temperatures will rise
into the mid 70s and lower 80s across the area ahead of the system
Friday afternoon.  Still looks like Friday will be dry...except for
possibly a few thunderstorm possibly over the eastern Ozarks. Storms
will move into the area Friday night as the system drifts into
western Missouri.  GFS keeps the highest MUCAPE values well south of
the area over Arkansas Friday night so severe threat looks minimal.
As the system slowly spins east on Saturday there could be a greater
threat of severe storms if there`s some dry time from late morning
into the afternoon to allow the atmosphere to heat up.  GFS pushes
CAPE values up to 1000+ J/Kg by 18Z with 35-45kts of 0-6km shear.
This would be enough for at least a marginal threat...and any breaks
in the overcast could significantly increase those values with a
little additional heating.

The system weakens and moves northeast Sunday with a some lingering
showers possible primarily over west central Illinois.  Another
weaker wave is forecast to move from the Great Plains into Missouri
on Monday bringing us another chance of rain.  Medium range guidance
diverges at the end of the period with the GFS being quite a bit
slower than the ECMWF bringing another wave into the Great Plains.
Leaned toward the slower and drier solution for Tuesday.



.AVIATION...  (For the 12z TAFs through 12z Thursday Morning)
Issued at 632 AM CDT Wed Mar 22 2017

Mainly dry and VFR conditions are expected through the period.
Exceptions are MVFR ceilings around 1500FT AGL around KUIN
through 15Z. There will also be scattered showers with some MVFR
ceilings across central and northeast Missouri including KCOU
after 06Z tonight. East-northeasterly winds will continue
through the end of the period.

SPECIFICS FOR KSTL: Mainly dry and VFR conditions are expected
through the period. MVFR ceilings are expected to stay north of
the terminal early in the period. Scattered showers are expected
to stay mainly west and north of the area after 12Z on Thursday
morning. East-northeasterly winds will continue through the end of
the period.





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