Area Forecast Discussion
Issued by NWS St. Louis, MO

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322
FXUS63 KLSX 030425
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1125 PM CDT MON MAY 2 2016

.SHORT TERM...  (Through Late Tonight)
Issued at 257 PM CDT Mon May 2 2016

Weak shortwave trough currently over western Missouri will move
across the CWA this evening. This may be enough for a few light
showers or sprinkles over the area this evening. Otherwise, expect
the rest of the night to be dry as some weak subsidence works into
the area. MOS guidance is in good agreement and looks reasonable
for lows.

Britt

.LONG TERM...  (Tuesday through Next Monday)
Issued at 257 PM CDT Mon May 2 2016

(Tuesday through Thursday)

GFS/ECMWF/NAM are still in agreement that upper pattern will be
highly amplified over North America at midweek with north-
northwesterly flow setting up over Missouri and Illinois.  Still
looks like another upper trough will pass through the area on
Tuesday with only limited low level moisture and forcing, so will go
with a mainly dry forecast at this point.  Models are in good
agreement that an upper low will drop through the Great Lakes into
the Ohio Valley on Wednesday.  The attendant cold front will pass
through the area late Tuesday night into early Wednesday night, and
the GFS/NAM shows the best low level moisture and forcing will still
limit rain chances to just the eastern part of the CWA. Still expect
Thursday to be dry as the upper low moves off to the southeast as
subsidence builds in over the area.

Temperatures will remain below normal the next few days as we will
be mainly in cold air advection and as 850mb temperatures stay
between 0-5C.  MOS guidance temperatures are in good agreement and
are mainly in the 60s.

(Friday through Monday)

Upper pattern will begin to transition late week into early next
week as the upper ridge moves across the Midwest and the upper flow
goes from northwesterly to southwesterly.   Still expect that Friday
and Saturday will be dry as the upper ridge will move across the
area. Chances for showers and thunderstorms will begin to increase
by Sunday as southwesterly low level flow begins to bring Gulf
moisture back into the area.  Both the GFS and ECMWF are showing a
frontal boundary moving south into the area by late Sunday into
Monday that will act as a focus for thunderstorm development.

Temperatures will start out near normal on Friday as the surface
high moves off to our east, but then we will then climb above normal
in the southwesterly low level flow over the weekend.  850mb
temperatures will also climb to around 15C next weekend which
supports temperatures in the upper 70s and lower 80s.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1056 PM CDT Mon May 2 2016

Surface ridge was just northwest of our area this evening with
gradual clearing from the northwest. This clearing trend should
continue overnight at UIN and the St Louis metro area. Low stratus
and fog developed quickly at COU after the sky cleared out this
evening and this may happen at the other taf sites as well. The
stratus and fog will dissipate Tuesday morning followed by the
development of diurnal cumulus cloudiness, especially in COU and
the St Louis metro area with VFR conditions. Light surface wind
late tonight, then a west-northwest wind on Tuesday.  The low
level clouds will clear out Tuesday evening with the wind backing
around to a southwest direction.

Specifics for KSTL: VFR, low level cloud ceiling may gradually
clear out overnight with the development of stratus clouds and
fog towards morning. This stratus and fog will dissipate by late
Tuesday morning followed by the development of diurnal cumulus
clouds late Tuesday morning and afternoon in the VFR catagory.
These clouds should dissipate Tuesday evening. A light surface
wind late tonight will increase to around 7 kts from a northwest
direction Tuesday afternoon. The surface wind will back around to
a southwest direction Tuesday evening.

GKS

&&

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

$$

WFO LSX



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