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Area forecast discussion...updated aviation 
National Weather Service St Louis MO
1115 PM CST Friday Feb 12 2016

issued at 842 PM CST Fri Feb 12 2016

Wind gusts have decreased somewhat with the loss of daytime
heating. The wind speeds should continue to decease through the
night as the surface ridge currently over the middle Missouri
River valley moves in from the west. Current temperature trends
support going lows, and it still looks like wind chills will fall
below zero in most areas by early morning.



Short term: (through late tonight)
issued at 237 PM CST Fri Feb 12 2016

Unseasonably cold temperatures are expected tonight as a strong
1040-1045 mb surface high over the northern plains builds
southeastward into MO and Illinois. The low level clouds across parts of
eastern MO and southwest Illinois will advect southeast of the area
early this evening, with just some mid-high level clouds spreading
back into the area later tonight. Strong and gusty northwesterly
surface winds this evening should weaken later tonight as the
surface pressure gradient gradually relaxes. With little cloud
cover for much of the night, diminishing winds, and very low
surface dewpoints minimum temperatures in the single digits are
expected for most of the area. Some light snow cover across parts
of northeast MO and west central Illinois will aid in the radiational
cooling. Wind chills will get bitterly cold late tonight down to
around 10 below zero across northeast MO and west central Illinois.


Long term: (saturday through next friday)
issued at 237 PM CST Fri Feb 12 2016

Warm air advection ahead of an approaching strong shortwave over
the northern plains will lead to a band of snow developing from
around irk southeast to near stl Saturday evening. The low levels
will be initially dry Saturday afternoon into the evening, but
should began to moisten as the forcing increases. The band of snow
will shift eastward into west central Illinois late Saturday night with
lighter snow breaking out across much of the rest of our forecast
area as a southwesterly low level jet brings increasing low level
moisture into the area as well as increasing low level warm air
advection. More widespread snow can be expected Sunday morning as
the shortwave, vort Max moves into southeast Iowa by 18z Sunday.
Should see the snow tapering off across northeast and central MO
Sunday afternoon as the shortwave begins to shift east of the
area. Could not rule out a little sleet or even rain across parts
of central and southeast MO Sunday afternoon as the surface layer
warms up as the precipitation tapers off. Most of the accumulating
snow should shift east of the entire forecast area by Sunday
evening. Preliminary snowfall totals for Saturday night through
Sunday night range from less than 1 inch in central MO to around 2
inches in much of the St Louis Metro area to 2 to 3 inches across
west central and southwest Illinois into a small portion of southeast
MO. It now appears that most of the precipitation, caused by a
secondary shortwave and an associated surface low which will pass
south of the region, will stay south of our forecast area on
Monday. Temperatures will also be much warmer on Monday. The European model (ecmwf)
model brings a northwest flow shortwave and associated surface
low southeastward through our area late Monday night and Tuesday
leading to another shot of rain or snow. The GFS is further
northeast with the track of this system, bringing it through Iowa
and northern Illinois and keeping most of the precipitation northeast
of our forecast area. Due to the uncertainty of the track, for
now will just include chance pops on Tuesday across northeast and
east central MO and west central and southwest Illinois for rain or
snow. It is still looking unseasonably warm by Thursday as an
upper level ridge moves into the area along with increasing south
or southwesterly low level winds.



Aviation: (for the 06z tafs through 06z Saturday night)
issued at 1114 PM CST Fri Feb 12 2016

Expect mainly dry and VFR conditions through Saturday afternoon.
Then chances for light snow will begin to increase at KUIN and
kcou on Saturday evening as snow moves into central and northeast
Missouri and west central Illinois from the northwest. Ceilings
will begin to slowly fall as a result. Confidence is not high
enough at this time to include in the tafs. Northerly surface
winds will veer easterly on Saturday as a surface ridge moves
through the area.

Specifics for kstl: expect mainly dry and VFR conditions through
at least Saturday evening before chances for light snow begins to
move into the terminal after 06z Saturday night. Confidence is
not high enough at this time to include in the taf. Northerly
surface winds will decrease in speed as a surface ridge passes
through and veer easterly on Saturday.



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