Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 192041
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
341 PM CDT Sun Mar 19 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.

GKS

.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.

Kelly

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1123 AM CDT Sun Mar 19 2017

Scattered convection will likely impact COU early this afternoon,
but should remain west or southwest of the St Louis area taf
sites. Could not rule out sprinkles in the St Louis metro area
this afternoon from low-mid level clouds. These low-mid level
clouds will dissipate or shift east of the taf sites late this
afternoon and early this evening. Elevated convection is expected
to develop late tonight in the UIN area on the nose of a west-
southwesterly low level jet. This convection should weaken and
shift toward the St Louis metro area early Monday morning. Due to
uncertainty in coverage and timing may just include VCTS in the
UIN taf late tonight, and VCSH in the St Louis metro area tafs
early Monday morning. There will be some LLWS late tonight, but
will leave it out of the tafs for now as the magnitude does not
look quite strong enough for inclusion in the tafs. The prevailing
cloud ceilings will likely drop into the MVFR catagory at the
tafs sites, and possibly down to IFR in UIN late tonight and early
Monday morning with increasing low level moisture ahead of an
approaching cold front. Sely surface winds will veer around to a
southwesterly direction Monday morning.

SPECIFICS FOR KSTL: Scattered convection will impact central and
southeast MO this afternoon, but should remain west or southwest
of the STL area. Could not rule out sprinkles in STL this
afternoon from low-mid level clouds. These low-mid level clouds
will dissipate or shift east of the STL area this evening.
Elevated convection is expected to develop late tonight in
northeast MO and west central IL on the nose of a west-
southwesterly low level jet. This convection should weaken and
shift toward STL early Monday morning. Due to uncertainty in
coverage and timing may just include VCSH in the STL taf early
Monday morning. There will be some LLWS late tonight, but will
leave it out of the STL taf for now as the magnitude does not
look quite strong enough for inclusion in the taf. The prevailing
cloud ceiling will likely drop into the MVFR catagory early
Monday morning with increasing low level moisture ahead of an
approaching cold front. Sely surface winds will veer around to a
southwesterly direction by late Monday morning.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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