Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 010958
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
358 AM CST Sun Feb 1 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 355 AM CST Sun Feb 1 2015

Based on overnight snowfall and expected snowfall into the evening
will be extending the winter storm warning to include Shelby and
Marion Counties in MO. No other changes to headlines attm.

Will issue a complete AFD ASAP.

Truett

.LONG TERM: (Monday through Next Saturday)
Issued at 324 PM CST Sat Jan 31 2015

(Monday-Tuesday)

The work week will start off on a cold note featuring much below
average temps with cyclonic flow and lots of remnant stratus early
Monday morning. The low clouds however should clear southward during
the morning as high pressure builds into the area. By afternoon warm
advection aloft is already underway and heights are rising in the
wake of the departing upper trof. This will be accompanied by lots
of high clouds overspreading the region from afternoon and
continuing into Monday night as the surface high retreats. The pick
day of the week should be Tuesday with a strong warm advection
regime forecast. This should result in a brief bump in highs to
above normal readings. The exception is possibly across far
northeast Missouri into west central Illinois where there will be
snow cover and a bit of high cloudiness.

(Wednesday-Saturday)

Cold weather and below average temperatures will once again take
hold during the later part of the upcoming week. The flow aloft
initially across much of the Conus will be broadly cyclonic anchored
by an upper vortex in the northern Hudson bay region. A pronounced
shortwave migrating through this flow aloft will send a rather
strong cold front through the area late Tuesday night-early
Wednesday. The biggest uncertainties during the extended forecast
time frame deal with the Wednesday-Wednesday night period in the
wake of this front. The GFS and CMC GEM both have another
progressive disturbance lagging in the cyclonic flow. They both
suggest that this disturbance and the associated forcing and
resultant frontogenesis will produce a post-frontal wnw-ese oriented
band of accumulating snow. The ECMWF on the other hand lacks this
scenario and has high pressure dominating, however suggests a warm
advection snow band may occur Thursday. At this point I have a
little more confidence in the GFS/GEM solution albeit low, and will
continue with some low pops.

By the beginning of the next weekend, heights aloft are rising as
the mean longwave trof axis shifts off the eastern seaboard and warm
advection is underway signaling moderating temperatures.

Glass

&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1121 PM CST Sat Jan 31 2015

Specifics for KUIN: An air temperature of around 34 degrees has been
sufficient for the transition from rain to snow, and various
processes in the atmosphere continue to keep the temperature
fluctuating through the low to mid 30s, which is causing the ptype
to unpredictably switch back and forth between RA and SN. With
time, the ptype should become predominantly SN. I have attempted
to convey this complexity in the TAF. Several inches of
accumulating snow are expected at the terminal, but some of the
snow could melt during periods of rain. Winds will swing around to
the northwest and become quite gusty during the afternoon and
evening hours.

Specifics for KCOU: Precipitation was starting to reach the ground
at KCOU at TAF issuance. An air temperature of around 34 degrees
has been sufficient for the transition from rain to snow over the
last few hours around the region. Various processes are causing
the temperature to fluctuate through the low to mid 30s, therefore
the ptype can switch back and forth between RA and SN
unpredictably. It is possible that a solid changeover to SN at
KCOU may not occur until the colder air arrives with the cold
front on Sunday. Winds will swing around to the northwest and
become quite gusty during the afternoon and evening hours.

Specifics for KSTL, KSUS, KCPS: Dry air has been holding its own
over the last several hours (as per the donut hole on radar over
KLSX and the 20 degree dewpoint depressions at KSTL/KSUS/KCPS).
Precipitation has been slower to reach the ground at St. Louis
metro area TAF sites than previously anticipated, so I backed off
on the rain by a couple of hours. The overall thinking is that
precipitation will be predominantly rain overnight and for most of
Sunday. It will take the arrival of the cold front on Sunday
afternoon to start changing the rain over to snow. Winds will
swing around to the northwest and become quite gusty between
02/00z and 02/03z.

Kanofsky

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     44  16  26  23 / 100  50   5   5
Quincy          35   8  19  18 / 100  70   0  10
Columbia        41  12  27  22 /  90  50   0  10
Jefferson City  43  14  29  22 / 100  50   0  10
Salem           43  18  25  22 / 100  30   5   5
Farmington      47  18  31  23 / 100  30   5   5

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...WINTER STORM WARNING until 9 PM CST this evening FOR Knox MO-
     Lewis MO-Marion MO-Shelby MO.

     WINTER WEATHER ADVISORY until 9 PM CST this evening FOR Monroe
     MO-Pike MO-Ralls MO.

IL...WINTER STORM WARNING until 9 PM CST this evening FOR Adams IL-
     Brown IL.

     WINTER WEATHER ADVISORY until 9 PM CST this evening FOR Pike IL.

&&

$$

WFO LSX





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