Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 230945

Area Forecast Discussion
National Weather Service Saint Louis MO
345 AM CST Mon Jan 23 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 344 AM CST Mon Jan 23 2017

Extensive stratus blankets much of the region this morning within
the low level cyclonic flow about the deep low pressure system
centered in the southern Appalachians. The vertically stacked low
will track east-northeast into the Middle Atlantic Region today and
then out off the Delmarva by 12Z Tues. This low track will keep
modest northerly flow across the region this morning and into the
early afternoon with generally cloudy conditions persisting. The
weak surface/low-level ridge presently centered through the eastern
portion of the Plains will then progress into central MO by early
evening, and stretch from the eastern TN Valley through central IL
by daybreak Tuesday. While confidence is rather high that clouds
will hang tough today east of the aforementioned ridge axis, there
is a bit less confidence tonight. The new forecast is more
pessimistic maintaining clouds across much of eastern MO this
evening and then having the back edge pivot east/northeast tonight
into IL with the ridge. Temperatures will be a good deal cooler
today with weak CAA through the morning and due to the clouds. The
new forecast cuts high temps back a bit from the previous one
minimizing the diurnal range. Lows tonight while cool, will still be
above average for late January.


.LONG TERM...  (Tuesday through Sunday)
Issued at 344 AM CST Mon Jan 23 2017

Tuesday through Wednesday night

Mid level ridge passes overhead putting the region under the
influence of SW flow in advance of the next short wave. The energy
is fcst to move out of the cntrl Rockies as an open wave and then
deepen and close off as it moves across the cntrl Plain and into the
Grt Lks. At the SFC...ridge axis is fcst to be east of the FA by the
by the beginning of the prd with SErly flow already established. A
SFC low is expected to track from the cntrl Plains to the Grt Lks.
This path takes both the SFC and upper level lows N of the
CWA...keeping the FA in the warm sector until cold FROPA Tue night
into early Wed mrng. Although limited...there appears to be two
separate windows for precip chances. The first is late Tue aftn thru
Tue evng when a WAA wing of precip may lift thru the nthrn CWA.
A rumble of thunder can`t completely be ruled out but not enough
confidence yet to include. There should be a prd of diminished
chances as the low passes by late Tue night into early Wed mrng
before the potential for wrap around precip assoc with the actual
short wave requires the mention of addtnl PoPs for Wed aftn and
evng. The system lifts NE into Quebec by Thursday mrng. 1035mb SFC
ridge builds into the region out of the Rockies. Meanwhile...a
substantial 500mb ridge will be building into the Pacific NW and wrn
Canada with the resulting pattern evolving into N/NW flow across
the cntrl CONUS.

After a brief cool down on Mon...temps are expected to rebound into
the 50s again on Tue. Return flow ahead of the mid-week system and
the low level (850mb and 925mb) thermal ridge approaching the wrn
CWA drng the aftn could push temps into the lower 60s across cntrl
MO. Due to the synoptic set-up...went above SuperBlend...closer to
MOS. Clouds...possible precip and CAA drng the aftn...esp N of the
STL metro..will cause Wed to be quite a bit cooler than Tue...but
still some 5-10 degrees above avg for late Jan with highs expected
to be in the 40s. Even though high temps will be about 5 degrees
above normal across the N won`t necessarily be a nice day
since there won`t be much of a diurnal rise due to CAA with a W/WNW
wind gusting 25-30 mph.

Thursday through Sunday

In the wake of the mid-week system...the overall pattern will
undergo a change to N/NW flow for the end of the week and thru the
wknd. This prd will feature colder temps...back to normal...with
highs mid 30s N to low 40s S and lows in the 20s. Temps will be
rather stagnant due to several reinforcing shots of colder air. Even
though there are single digits PoPs thru the prd in the going
fcst...don`t be surprised if slight/chance PoPs are added at a later
date. NW flow systems are notoriously hard to fcst wrt timing and/or
strength let alone affects on the sensible wx much more than a day
in advance. There will also be plenty of low clouds assoc with each
surge...esp for the nthrn and ern portions of the FA.



.AVIATION...  (For the 00z TAFs through 00z Monday Evening)
Issued at 534 PM CST Sun Jan 22 2017

A fair amount of uncertainty exists with this forecast with not
much help from guidance and cigs of varying heights advecting
into the region from multiple directions. Believe KUIN will remain
IFR thru the night, tho do not think cigs will drop below 600 ft.
KCOU shud improve at some point this evening into low MVFR.
General trends are to improve late Mon morning thru the afternoon

SPECIFICS FOR KSTL/KSUS/KCPS: Terminals are currently under a def
zone of sorts which is helping to create breaks in clouds. While
latest obs are VFR, MVFR cigs shud move back in shortly. Cigs shud
improve late Mon morning and into the afternoon hours.





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