Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 301143
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
543 AM CST Fri Jan 30 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 354 AM CST Fri Jan 30 2015

Surface ridge to build over region today with sc deck along and east
of Mississippi River slowly clearing out. Despite plenty of sunshine
most of the day today, temperatures will remain near normal in the
mid 30s to low 40s.

Byrd

.LONG TERM:  (Tonight through Thursday)
Issued at 354 AM CST Fri Jan 30 2015

(Tonight-Monday)

Primary concern in the short range continues to be potential for
wintry conditions Saturday-Sunday.  00z guidance has come in a bit
warmer than earlier solutions with regards to ptype, so have
judiciously trended the forecast a bit warmer...and to a slower
changeover to snow.

Precip with upcoming system should be tied to two different
features...first, the WAA in advance of the system, and secondly
some wrap around precip on Sunday as secondary shortwave drops into
the mid-Mississippi Valley in the wake of the main system.  This
secondary shortwave will likely produce some measurable snow on
Sunday...especially over the northeast half of the CWA.   However,
the key to total snowfalls with this storm will likely be tied to
how quickly the WAA precip can transition from liquid to frozen on
Saturday night/early Sunday. I`ve been a bit aggressive in the
changeover in our far north overnight Saturday night, and when you
combine this changeover to the lighter precip that should be all
snow on Sunday snowfall totals are calculated in the 5-6 inch range
over our northern counties.  This may be a bit high considering the
850mb low track is directly over our northern counties, but if
precip can change over fast enough these numbers should be in the
ball park. Snowfall totals should then drop off as you head south,
with 1-3 inches along the I-70 corridor.  In our far southern
counties persistent low level WAA should cause the changeover to all
snow to be a struggle, so snowfall totals here should be under an
inch.

Snowfall forecasts will continue to evolve over the next 24 hours as
we try to fine-tune low level thermal profiles.  Obviously, if the
changeover to snow in the WAA band is delayed these amounts will
need to be adjusted down, but as mentioned above even if this
changeover is significantly delayed Saturday night, some measurable
snow should still be expected over northeast sections of the CWA on
Sunday.

Snow should taper off early Sunday evening, with Canadian high
bringing another round of cold air and below normal temperatures
to the region Sunday night and Monday.

(Tuesday-Thursday)

Temperatures should briefly moderate on Tuesday, followed by more
cold air and below normal temperatures for the Wednesday-Thursday
time frame. Forecasts will carry some low, slight chance PoPs
Wednesday-Thursday...tied to the next frontal passage.

Truett
&&

.AVIATION:  (For the 12z TAFs through 12z Saturday Morning)
Issued at 537 AM CST Fri Jan 30 2015

Surface ridge to build in over region today with sc deck to
scatter out at all taf sites by 14z. Otherwise, north winds to
become light and variable. Then surface ridge to move off to the
east late tonight with winds becoming southerly.

Specifics for KSTL:
Surface ridge to build in over region today with sc deck to
scatter out at all taf sites by 14z. Otherwise, north winds to
become light and variable. Then surface ridge to move off to the
east late tonight with winds becoming southerly.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$
WFO LSX





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