Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200516

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1216 AM CDT Mon Mar 20 2017

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 340 PM CDT Sun Mar 19 2017

Scattered convection continues to shift eastward from central to
eastern MO this afternoon.  This activity is in an areas of 850 mb
warm air advection, theta-e advection, and moisture convergence on
the nose of a modest southwesterly low level jet.  This activity
should weaken with most of it dissipating by early evening.  More
elevated convection is expected to develop later this evening and
overnight as a stronger low level jet ramps up across northern MO.
There is still uncertainty as to the location of this convection
with most of the models, particularly the high resolution CAMs
keeping most of the convection north-northeast of our forecast area
tonight.  The operational GFS model looks too far south with its QPF
tonight.  For now will just go with scattered convection mainly
across northeast MO and west central IL late tonight.  Could not
rule out isolated hail in the stronger cores due to favorable lapse
rates and vertical wind shear.  With low level warm air advection
along with southerly surface winds and gradually rising surface dew
points temperatures will fall this evening, but then become nearly
steady or rise slightly overnight.  Most of the convection on Monday
should be east of the Mississippi River as the low level jet weakens
and veers.  A cold front will be dropping southward through our area
on Monday, but there will be some capping/CIN over MO and the
moisture profile will be more favorable for convection in IL ahead
of a weak shortwave.  Highs on Monday will be unseasonably warm, 10
to 20 degrees above normal, with the warmest readings across central
and southeast MO where the least cloud cover is expected along with
the highest 850 mb temperatures.


.LONG TERM...  (Monday Night through Next Sunday)
Issued at 340 PM CDT Sun Mar 19 2017

(Monday Night-Saturday)
   The cold front over or just south of the St. Louis metro will
push southward to the Missouri Bootheel by Tuesday morning. This
will usher in slightly cooler and drier air to the area. A shortwave
pushes through the area Tuesday providing chances for showers with a
few thunderstorms south of St Louis.  High pressure will provide a
small break on Wednesday. There is a bit of uncertainty with the
system that will impact the area late this week into the weekend.
The GFS/ECMWF has displayed some timing and placement issues. That
being said decided to go with a GFS/CMC solution for this forecast.
A warm front will move up from the south ahead of the cold front in
the central plains on Thursday. This will provide chances for
showers and thunderstorms during the morning hours before the warm
front pushes north of the area. A cold front will slowly push
through the area Friday with chances of showers and thunderstorms on
tap through Saturday.



.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1210 AM CDT Mon Mar 20 2017

A southwesterly low-level jet atop southeasterly surface winds will
produce LLWS conditions through approximately 12z at the
terminals. Isolated to scattered SHRA/TSRA are possible during the
first 0-6 hours at all terminals except KCOU. The best opportunity
for SHRA/TSRA appears to be at KUIN between 08-12z. Initially
southeast winds will gradually veer and become southwesterly ahead
of an approaching cold front, then become westerly to
northwesterly after fropa. MVFR cigs are possible during 15-21z
ahead of the cold front, but confidence was too low to include in
the 06z TAFs.





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