Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 311120
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
620 AM 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 12z TAFs through 12z Wednesday Morning)
Issued at 620 AM CDT Tue May 31 2016

VFR conditions, outside of any TSRA, will prevail at the TAF
sites thru the valid period. A period of SHRA/TSRA this morning
is likely at COU and STL metro sites but should remain south of
UIN. This activity expected to dissipate or weaken late this
morning with sparse activity this afternoon and early evening with
probs too low for inclusion into the TAF at this time. Activity
associated with the cold front to our west look to approach in
two waves: the first should be weakening late this evening or
overnight as it moves in and pushes ahead of the front and will
probably be at least in vicinity of UIN and COU, but probs
decrease heading towards STL metro...and the second wave
developing during late Wednesday morning and continuing into the
afternoon as the cold front actually moves thru our region, but
this is also beyond the valid period.

Specifics for KSTL: VFR outside of any TSRA. One wave of SHRA/TSRA
expected thru about 14z this morning with probs decreasing
thereafter as activity should either exit or dissipate. Very hit
and miss for this afternoon and early evening and is something
that will need to be monitored for updates but probs too low at
this time for mention. Two waves of TSRA from front to the west
expected, but the first wave looks to fall apart before reaching
late tonight, with a better chance on Wednesday late morning as
the cold front begins to move thru.

TES

&&

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

$$

WFO LSX



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