Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 022308

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
608 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.


.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.



.AVIATION...  (For the 00z TAFs through 00z Tuesday Evening)
Issued at 533 PM CDT Mon May 2 2016

The cloud ceiling at 2000-4000 feet should gradually rise this
evening with a few sprinkles or light showers possible as an
upper level disturbance moves through the area. Should be VFR by
late evening with even the possibility of the low level cloud
deck scattering out in places late tonight/early Tuesday morning.
There may be some patchy light fog late tonight/early Tuesday
morning. Some diurnal cumulus cloudiness is expected on Tuesday
especially in COU and the St Louis metro area with VFR
conditions. Mainly a northwest wind through the period, albeit
becoming light later this evening.

Specifics for KSTL: The MVFR cigs should become VFR later this
evening. There may be a few sprinkles early this evening. The
cloud ceiling may scatter out late tonight and early Tuesday
morning, but diurnal cumulus clouds will develop late Tuesday
morning and afternoon in the VFR catagory. These clouds should
dissipate Tuesday evening. Northwest wind will become light later
this evening, then increase to around 7 kts Tuesday afternoon. The
surface wind will back around to a southwest direction Tuesday





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