Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 291804
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1204 PM CST Wed Jan 29 2020

.SHORT TERM...  (Through Late Tonight)
Issued at 406 AM CST Wed Jan 29 2020

Southern stream system beginning to affect forecast area with mostly
light snow, though do have some sleet and freezing rain over
portions of southeast MO where a warm nose aloft, about +2C, is
causing melting of the ice crystals. Little or no ice accumulation
is expected. Eventually this warm layer will cool and precipitation
in this area will transition to all snow by mid morning. Rest of
region will just have light snow this morning. Will see anywhere
from a dusting to half an inch accumulation through midday. In the
meantime, northern stream system is fairly weak and lacking decent
moisture, so amounts remain on the light side for northern portions
of forecast area as it moves through today.

Latest CAMs are indicating a secondary vort max will slide through
southern portions of forecast area this afternoon with a second
round of light snow from mid afternoon through the evening rush
hour, with an additional half inch of snowfall possible. So raised
pops for portions of east central/southeast MO and southwestern IL
during this period before tapering off after 02z Thursday. Will
see some mix of light snow and rain this afternoon as temperatures
warm up above freezing, mainly over portions of southwestern IL.

With light snow affecting the St. Louis metro area during the
morning and evening commutes now, decided to add this area to the
ongoing winter weather advisory and extend the advisory to 00z
Thursday. MODOT cameras showing some coverage on roadways along and
south of I-70 as of 3 AM. Total snowfall amounts will an inch or
less when all is said and done.

As for temperatures, highs will be in the upper 20s to mid 30s with
lows tonight in the upper teens to upper 20s.

Byrd

.LONG TERM...  (Thursday through Tuesday)
Issued at 406 AM CST Wed Jan 29 2020

No major changes to the extended with dry weather prevailing for
much of the long term forecast, our next chance for precipitation
still looks to be early next week. Temperatures will moderate
through the week, peaking in the 50s to low 60s by Sunday and
Monday, 15 to 20 degrees above normal.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1133 AM CST Wed Jan 29 2020

IFR stratus has briefly given way to MVFR stratus at KCOU and
KUIN. IFR stratus is expected to return imminently as cool, moist
air continues to be advected into the terminals. Light snow will
return to KCOU as another wave of snow moves through the terminal
early this afternoon. Fog is likely tonight into tomorrow morning
at KCOU and KUIN as today`s light snow cover and the moist low
levels allow the low stratus to build down. Given these conditions
and cool temperatures overnight patches of freezing fog or drizzle
are possible, but confidence is too low at this point to include
in the TAFs.

SPECIFICS FOR KSTL, KCPS, KSUS:

At KSTL, KCPS, and KSUS MVFR stratus will prevail into the late
afternoon until IFR stratus once again builds back into the area.
Light snow remains possible until late afternoon as well. Fog
will build into the metro terminals overnight and persist until
the mid morning. As with the other terminals freezing fog or
drizzle is possible at the metro terminals given the moist low
layers, fog, and cool temperatures overnight, but confidence isn`t
yet high enough to include in the TAFs.

MRM

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until 6 PM CST this evening for Boone MO-
     Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Madison MO-Moniteau MO-Montgomery MO-
     Osage MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Warren MO-Washington MO.

IL...Winter Weather Advisory until 6 PM CST this evening for Madison
     IL-Monroe IL-Randolph IL-Saint Clair IL.

&&

$$

WFO LSX


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