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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
1121 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 warm air advection 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 County Warning Area. However,
the key to total snowfalls with this storm will likely be tied to
how quickly the warm air advection 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 warm air advection 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 warm air advection 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 County Warning Area 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 18z tafs through 18z Saturday afternoon)
issued at 1114 am CST Fri Jan 30 2015

VFR flight conditions will prevail for the valid forecast period.
High clouds will steadily increase across the region this
afternoon and tonight as a large surface high slowly retreats
eastward. Mid and eventually lower clouds will begin spreading
into the area on Saturday morning. The onset of precipitation with
the next storm system is a bit tricky in timing. At most
terminals the onset will be after the valid taf forecast period,
however light rain will probably develop at kcou between 15-18z
Sat 31 Jan.

Specifics for kstl:

VFR flight conditions will prevail for the valid forecast period.
High clouds will steadily increase this afternoon and tonight as
a large surface high slowly retreats eastward. Mid clouds will
begin spreading into the area on Saturday morning with lower clouds
on Saturday afternoon. The onset of precipitation with the next
storm system is a bit tricky, but current thoughts are light rain
will probably develop at kstl around 21z Sat 31 Jan.

Glass

&&

Lsx watches/warnings/advisories:
MO...Winter Storm Watch from Saturday evening through Sunday
afternoon for Knox MO-Lewis MO-Marion MO-Shelby MO.

Illinois...Winter Storm Watch from Saturday evening through Sunday
afternoon for Adams Illinois-Brown Illinois-Pike Illinois.

&&

$$

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