Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 011058

458 AM CST Sun Feb 1 2015

.SHORT TERM: (Today and into this evening)
Issued at 419 AM CST Sun Feb 1 2015

Precip is blanketing the CWA early this morning in the zone of
strong WAA ahead of surface low...currently over east central KS.
Low is expected to track just a bit north of east, and our
forecast takes the low to near KUIN by 18z.  Heavy snow has been
falling over our extreme northern counties since late Saturday
evening. Although ground truth has been hard to come by overnight,
it appears 6+ inches has already fallen over Knox County. However,
the snowfall gradient appears to be quite sharp, with only a few
inches one or two counties south. It would appear that most of the
precip in this area will remain as snow today, although with
surface low getting so close it`s certainly possible that the snow
could switch back to some rain for a bit around midday before the
cold air and strong north winds in the wake of the low changes the
precip back to all snow. Based on the snow that has already fallen
and the expected snow today and into this evening, decided to
expand the Winter Storm Warning into Shelby and Marion Counties.
By the time the snow winds down this evening, some locations in
Knox and Lewis Counties should have snowfall totals around 10 inches.
In addition to the snow, falling temperatures and increasing
northerly winds are expected in the warning area during the
afternoon. Since much of the snowfall today will be fairly wet
don`t expect too much of a blowing snow problem, although the snow
that falls late today will be much more prone to being moved
around as it should be much "lighter".

While the forecast for our north is fairly clear cut, it is a
muddled mess over the central third of the CWA. Evaporative
cooling has dropped the freezing level enough to turn the rain
over to snow from mid MO to just W and NW of STL metro. However,
as the surface low tracks east this morning warmer air will
return to this part of the FA and change the snow back to rain
and likely melting any early day accumulation, with cold advection
then transitioning precip during the mid-late afternoon back to
snow from mid MO to just N of STL. Briefly considered expanding
the advisory to cover some of this morning snowfall, but given the
expected warmup and change back to rain decided to issue an SPS to
cover this area and maintain the southern edge of the advisory from
Monroe into Pike County IL...where ptype will likely remain snow
and snowfalls should be higher.

Expect some light snow with minor accumulations to linger over the
northwest two-thirds of the CWA into the early evening, with the
snow ending or tapering off to flurries by midnight. The cold air
surging south behind the storm will make for a windy and cold
night, with temperatures bottoming in out in the single digits and
teens by Monday morning.

Obviously, this is a very tricky forecast, and short term trends
could force adjustments to headlines as the day progresses. Will
also need to keep an eye on the impact of light snow and sharply
falling temperatures on the wet roadways as we head into the early
evening hours.


.LONG TERM: (Monday through Saturday)
Issued at 419 AM CST Sun Feb 1 2015

Going forecast through midweek looks pretty good, so only a few
minor changes were made to going trends. In general. expecting a
cold day on Monday, with a brief moderation on Tuesday followed by
another surge of cold air by Wednesday. There is some
some uncertainties on timing and placement of precipitation on
backside of the cold front with GFS faster than the ECMWF. For
now will side with the faster GFS and keep slight chance/low
chance pops for northern half of forecast area on Wednesday, then
spread south across rest of forecast area Wednesday night with
some accumulating snow possible with this system. Then dry and
moderating temperatures expected for the last part of the work
week and into next weekend.



.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.



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


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.



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