Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 211110
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
610 AM CDT Tue Apr 21 2015

.SHORT TERM: (Through Tuesday night)
Issued at 345 AM CDT Tue Apr 21 2015

Closed H500 low over the UP of MI this mrng will continue to spin
across shtrn Ontario thru mid week keeping the Midwest in NW flow.
Two embedded short waves in the NW flow will affect the region...one
today and the other tonight. The first is expected to pass over the
sthrn CWA this aftn sparking a few showers. Thunder probs look
better today than 24 hrs ago. Precip chances should increase across
sthrn MO from west to east from late mrng thru the aftn...continuing
into the evng. Temps should warm to near avg today with a WSW
wind. Winds will once again pick up later this mrng and become
gusty...esp north of I70 where there will be a heightened fire
danger due to the breezy conditions, RH values below 30% and dry
fuels. Meanwhile...the second short wave is fcst to pass north of
the area tonight pushing a cold front thru the region. There will
be separate precip chance along the bndy as it sinks south
overnight...though the best chances should be across IL...closer
to the better upper lvl support. The front sinks south of the FA
Wed ending any lingering precip threat.

2%

.LONG TERM: (Wednesday through Monday)
Issued at 345 AM CDT Tue Apr 21 2015

A cold Canadian high pressure is fcst to be in control Wed/Thu
producing cool conditions with highs in the mid 50s to low
60s...some 5 to 10 degrees below avg. 850 temps are expected to
approach zero as far south as STL on Wed. Thu mrng appears to be the
coldest mrng with widespread lows in the 30s. Frost will be possible
late Wed night into Thu mrng due to the sfc ridge axis being aligned
over the CWA keeping winds light overnight. The wildcard will be the
potential for a mid cloud deck to edge into the wrn and sthrn
portion of the CWA towards Thu mrng. Seems a bit too early to put
anything in the grids let alone issue a headline but definitely
something to keep an eye on.

Upper heights begin to rise Fri as a weak ridge approaches the area
in advance of the next system. Though the upper lvl features are
similar...the track of the sfc low is substantially different. The
GFS has a much farther south...less thundery...solution than the
ECMWF taking the low from OK into the Deep South while the ECMWF
takes it from KS into the OH Vly. Either way...precip is fcst to
overspread the CWA Fri PM with the best chances Fri night into Sat
mrng. Sat looks like a cloudy cool rainy day...potentially cooler
than the fcst indicates if the GFS solution verifies. High pressure
builds in for Sat night and Sun. NW flow looks like it will redvlp
early next week as another significant trough dvlps. The next chance
for precip arrives early next week as a short wave drops SE.
Significant differences exist at this time so kept PoPs in the
15%-35% range to give guidance to come into better agreement. Temps
are expected to remain aob normal into early next week as NW flow
keeps warmer temps at bay for the foreseeable future.

2%

&&

.AVIATION:  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 544 AM CDT Tue Apr 21 2015

Mid level clouds will spread east-southeastward through the
region today. It appears that any showers will remain south of the
taf sites today, but may briefly impact the taf sites tonight as a
cold front drops southward through our area. Will have some low
level cloudiness tonight, but the cloud ceiling should remain in
the VFR catagory. The southwesterly surface wind will become
relatively strong and gusty later this morning, then veer around
to a wly direction this afternoon. The surface wind will weaken
this evening and veer around to a nwly direction tonight after
fropa.

Specifics for KSTL: Mid level clouds will spread east-southeastward
into STL today. There may be showers this afternoon just south of
STL. The better chance of rain should occur tonight as a cold
front moves southward through STL around 06Z Wednesday. The cloud
ceiling should lower down to around 4000-5000 feet later tonight.
The clouds wil clear out Wednesday morning. Swly surface wind will
become relatively strong ad gusty later this morning, veering
around to a wly direction. The surface wind will weaken early this
evening, then veer around to a nwly direction late tonight after
fropa.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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