Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 011744
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1144 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.

Truett

.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.

Truett/Byrd

&&

.AVIATION:  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1126 AM CST Sun Feb 1 2015

IFR conditions will improve late this afternoon as surface low
pressure moves rapidly eastward. Expect visibilities to gradually
improve in snow at KUIN to MVFR by around 00Z, and IFR ceilings in
the KSTL metro TAF sites should lift to MVFR as winds shift to the
NW by around 00Z. Winds will increase rapidly at all TAF sites as
surface pressure gradient tightens dramatically early this
evening. Expect gusts in excess of 30 knots at most taf sites.
Winds will diminish quickly on Monday morning however as low
pressure area continues to move away and surface high pressure
builds in. MVFR ceilings may begin to break up by 15Z Monday as
drier air filters in.

Specifics for KSTL: IFR ceilings should lift to low end MVFR by
around 23Z as surface low pressure moves eastward. A period of
light snow will likely move through this evening, however
visibilities should remain above 3 miles. Very tight pressure
gradient behind the low will then move in early this evening and
produce strong NW winds with gusts in excess of 30 knots. Winds
will diminish farily quickly by around 12Z Monday, with MVFR
ceilings breaking by around 15Z.

Browning

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     44  14  25  23 /  80  80   5   5
Quincy          35   8  19  18 / 100  90   0  10
Columbia        41  13  25  22 /  90  80   0  10
Jefferson City  43  14  26  22 /  80  80   0  10
Salem           43  14  27  22 /  90  50   5   5
Farmington      47  15  28  23 /  60  30   0   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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