Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 091735

1135 AM CST TUE FEB 9 2016

.SHORT TERM:  (Through Late This Afternoon)
Issued at 320 AM CST Tue Feb 9 2016

We have been seeing a pretty steady light and accumulating snow
since midnight across parts of eastern MO and western IL. Just
measured 0.4 inches of very fluffy snow at LSX with high ratios
and very low liquid water content. Driving mechanism appears to be
a vort max centered in extreme northeast MO. This feature is
forecast to continuing driving south/southeast this morning within
the cyclonic flow about the large upper vortex centered in the
lower Great Lakes region. Present indications are light measurable
snowfall will remain likely from east central MO into southwest IL
during the first half of the morning ahead of the vort, with
flurries further west. In fact we may see flurries continue until
the low stratus eventual clears later today. Otherwise expect
another blustry and cold day with well below normal temperatures.


.LONG TERM:  (Tonight through Monday)
Issued at 320 AM CST Tue Feb 9 2016

Heights aloft will rise slowly tonight as the upper trof axis
nudges east, with lower clouds gradually clearing west to east.
Not completely sure if they will totally clear our south central
IL counties before daybreak on Wednesday, and by that time we will
see high clouds spreading in from the northwest ahead of the next
system. A northwest flow clipper system will impact the region
Wednesday into Wednesday night and the models have really been
yo-yoing with this wave the last 4-5 days. Have increased pops and
coverage a tad, and ultimately if the recent trend continues and
confidence grows, then they will need to be increased quite a bit
more. Strong WAA and the presence of a tight thermal gradient
will produce strong low-mid level frontogenetic forcing, which
should support a NNW-SSE oriented band of snow nosing into the
region Wed. afternoon and continuing into the evening. Potential
seems to be there even at this early juncture for a couple of
inches of snow. In the wake of this clipper we will see reinforcing
cold air and a nice high pressure system nose into the area.

Yet another clipper will impact parts of the Midwest on Friday,
however backing upper flow as the deep upper trof broadens
suggests that any pcpn most likely will remain north/northeast of
the CWA from eastern IA into northern IL. Another formidable surge
of Arctic air will overspread the area in the wake of this system.

There have been some fairly large model differences the last 3 or
so days with regards to a Sunday/Monday storm system. Now there
appears to be growing support from the ECMWF, CMC GEM, and GEFS
that we will see another snow event on Sunday/Sunday night. This
one could be our first good accumulating snow. Still far out but
encouraging if you like snow.



.AVIATION:  (For the 18z TAFs through 18z Wednesday Afternoon)
Issued at 1123 AM CST Tue Feb 9 2016

MVFR ceilings will prevail along and east of the Mississippi river
this afternoon and into the evening. Light snow showers or
flurries will occasionally lower the visibility to 3-5SM where
clouds persist this afternoon as well. Expect ceilings over much
of central Missouri and some of northeast Missouri to scatter out
over the next few hours. Guidance suggests that most of the area
will go VFR between 06Z and 10Z tonight, but low clouds will
probably hang around thorugh most of Wednesday morning over south
central Illinois. Northwest wind will continue...but should
diminish Wednesday morning.

Specifics for KSTL:

Surface obs are showing MVFR ceilings upstream all the way through
eastern Iowa. Should see the ceilings clear out tonight...though
timing is uncertain at this time. Given the time of year and
continued lift in the atmosphere due to low pressure aloft, I
leaned more pessimistic on the ceiling forecast. Northwest flow
will continue, but should diminish Wednesday morning. Current
thinking on Wedenesday`s potential snow is that the majority of it
will be southeast of the terminal...and not until late afternoon
or early evening so have left mention of additional snow out of
the terminal forecast for this issuance.





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