Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 311737
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1237 PM CDT TUE MAY 31 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 342 AM CDT Tue May 31 2016

An old MCV was located over central MO early this morning in a
region of otherwise weak westerly flow aloft.  This feature has only
recently blossomed in its ability to generate precipitation, with an
axis of rather solid, yet very light rain, having developed from
northeast MO thru central MO and into the eastern Ozarks.
Temperatures at most locations were in the 60s under cloudy skies.
The surface map shows a largely warm sector setup in place, with any
syntopic fronts well to the north and west.

A vigorous storm system over the northern high Plains is expected to
drop southeastward today and, in effect, steer and accelerate the
MCV east-northeastward, but during the morning hours it will be slow
going in its trek thru our region.  The effect should be that the
area of light showers should slowly work its way thru much of our
region this morning as a result, and have significantly boosted
PoPs.

Between the sun getting higher in the sky and beginning to exercise
diurnal influences on the MCV and it exiting our eastern forecast
area anyway by midday, should see rain chances drop for the afternoon
hours with some sunshine as instability struggles to reset and there
will be a lack of any focus.  Any convection associated with the
approaching cold front from the west should be delayed on its
arrival into our forecast area until tonight.

Temperatures today will be tricky considering the rain and clouds,
and generally leaned on the cool side of MOS for most sites, with
forecast maxes in the upper 70s and lower 80s.

TES

.LONG TERM...  (Tonight through Monday)
Issued at 342 AM CDT Tue May 31 2016

Tonight - Wednesday night

Any remaining diurnal convection will gradually diminish after
sunset. Not expecting much activity tonight but can`t rule out an
isld SHRA/TSTM. Strong shortwave is fcst to track from ND to cntrl
Ontario. It will drag an assoc cold front thru the region on Wed.
Precip coverage should begin increasing across NE MO prior to 12Z
as the cold front approaches. Bndry will make steady progress thru
the CWA on Wed and should clear the sthrn zones by Wed evng. A
broken line of SHRAs/TSTMs is expected to accompany FROPA. SPC has
locations north of I-70 in a Marginal Risk for SVR TSTMs. The main
limiting factor is less than 30 kts of shear.

Thursday - Friday Night

The upper pattern will become zonal across the nthrn CONUS with a
closed low across TX. The front is expected to be aligned from
the Red Rvr Vly...NE to TN and OH Vlys. The front will stall in
response to an area of low pressure assoc with the upper low
across TX. Models are now indicating an overrunning event that
should take place SW of the CWA for the end of the week and may
extend as far N as sthrn MO and sthrn IL Thu/Fri. Given this new
scenario...not confident how far N the precip will extend...though
the ECMWF indicates precip as far N as the sthrn STL metro area by
Fri. Not ready to jump on that solution yet...but this possibility
is something to keep in mind over the next couple model runs. As a
result...have expanded the slight/chance PoPs from Thu-Fri night
across the sthrn CWA to account for this potential scenario.

Saturday - Monday

A short wave embedded in the nthrn stream will carve out a
significant trough across the ern CONUS over the wknd. The short
wave will drag an accompanying cold front thru the region Sat. There
should be at least some convection that dvlps along this bndry as
00Z guidance indicates the front will pass thru most of the CWA
drng the PM hrs. In the wake of the short wave...the CWA will be
in NW flow thru at least the middle of next week. This should
provide a much needed break from the recent wet weather pattern.

2%

&&

.AVIATION...  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1230 PM CDT Tue May 31 2016

Main concern over the next 24 hours will be on convective trends
across the area and its possible impacts at the terminals. Outside
of thunderstorms...conditions are expected to be VFR. Believe best
chance of showers/storms will begin this evening and last into the
overnight period across portions of central and northeastern
Missouri. As a result...have a prevailing group for shra vcts and
added a tempo for low MVFR visbys in TSRA at both KCOU and KUIN
tonight. IFR visbys will also be possible in any heavier
thundershower. For the metro terminals...not quite as high of a
chance for activity as expect area of showers/storms to weaken
overnight as it progresses eastward toward the area due to better
forcing further to the north combined with loss of most of the
instability diurnally. Kept a VCSH group in for now but moved up
timing with best chance of seeing showers/weak storms very late
tonight through late Wednesday morning.

Initially SE winds this afternoon will become either calm or
light/variable as frontal boundary approaches. Behind the
front...winds will be light out of the west/northwest.


Specifics for KSTL:

Main concern over the next 30 hours will be on convective trends
and its possible impacts at Lambert Field. Outside of
thunderstorms...conditions are expected to be VFR. Believe best
chance of showers/storms will be very late tonight through mid
morning on Wednesday...though higher chances will remain west. Kept
a VCSH group in for now but moved up timing.

Initially SE winds this afternoon will become either calm or
light/variable as frontal boundary approaches. Behind the
front...winds will be light out of the west/northwest.

Gosselin

&&

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

$$

WFO LSX



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