Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 022018

318 PM CDT FRI OCT 2 2015

.SHORT TERM:  (Through Late Tonight)
Issued at 318 PM CDT Fri Oct 2 2015

Primary concern for tonight will be the chance for some light or
sprinkles over parts of south central Illinois tonight.  A large
cutoff low centered over northwest Florida is pushing moisture
around its northern periphery from the Ohio Valley back toward the
Mississippi Valley.  Showing some weak 850mb moisture convergence
overnight along with a lobe of vorticity swinging through Illinois
which produces some very light qpf.  MOS PoPs are between 30-50
percent over our south central Illinois counties, which looks a
little high.  Since the models have been pretty consistently
producing chance/slight chance PoPs, I went ahead and added in some
15-30 PoPs.  Temperatures will likely be similar to last night`s
with lows mainly in the mid 40s to low 50s.


.LONG TERM:  (Tonight through Thursday)
Issued at 311 AM CDT Fri Oct 2 2015

Cutoff low forming over the southeast U.S. in the base of the
eastern CONUS longwave trof is forecast to wobble southeast over the
next few days and nights, and eventually interact with Joaquin as it
works its was north from the Bahamas.  The very slow eastward
progression of this feature. along with the development of the upper
low over the southwestern U.S., means very little movement of
weather features across the central CONUS over the next few days and
nights. This atmospheric traffic jam will keep surface ridging
locked over the area tonight into Monday.

Low level moisture which begins to work into the area today should
increase tonight and into the weekend due to an intensification
of the easterly flow produced by the increase of the pressure
gradient between aforementioned surface ridge and lowering
pressures over the southeast U.S. 00z guidance supports earlier
model trends of indicating a westward surge of this low level
moisture, and plan view RH progs as well as forecast soundings
suggest this cloudiness gradually spreading west across the FA
tonight into Sunday morning. Have attempted to tweak temp trends
to reflect this increase in cloudiness, with clouds tending to
limit the diurnal swing in the mercury as they move into an area.

Can`t totally rule out a slight threat of showers with increase of
low level moisture, but at this point will keep forecast dry as
moisture is rather stratified with an apparent lack of any
pronounced dynamics/lift over the mid-Mississippi Valley.

Upper pattern over the CONUS should become progressive once again early
next week as the combo of Joaquin and southeast U.S. cutoff begin
to propagate up the east coast and into the western Atlantic.
Specifics of medium range forecasts remain rather chaotic, but
there does seem to be some agreement that remnants of low over the
southwest U.S. will press into the central CONUS by Wednesday
night/Thursday, so have continued some low PoPs during this time



.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 102 PM CDT Fri Oct 2 2015

MVFR ceilings have moved out of KUIN and the St. Louis metro TAF
sites, but have moved into the KCOU. Expect these clouds to move
out of KCOU by 20Z. Expect some gusts this afternoon into the
18-25KT range with mixing before they diminish by 00Z with loss of
daytime heating. Clouds will move back into the area late tonight
and early Saturday with VFR ceilings. Gusty northeast winds are
expected once again by mid morning Saturday.

Specifics for KSTL: Scattered clouds through this evening before
broken VFR ceilings move back into the area from the east
overnight. Gusty northeast winds will diminish this evening with
loss of daytime heating, but then increase again by mid morning



Saint Louis     51  64  52  69 /  10  10  10  10
Quincy          44  64  48  65 /   5   5  10  10
Columbia        44  65  47  66 /   5   5  10   5
Jefferson City  44  66  48  66 /   5   5  10   5
Salem           52  62  52  71 /  30  20  20  20
Farmington      48  63  50  66 /  10  10  10  10




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