Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 302139

Area Forecast Discussion
National Weather Service Saint Louis MO
339 PM CST Wed Nov 30 2016

.SHORT TERM...  (Through Late Thursday Afternoon)
Issued at 337 PM CST Wed Nov 30 2016

Stacked LOW system located over western WI continues to dominate our
upper flow, only having drifted slightly to the east over the past
24 hours.  An extensive area of stratocumulus clouds has built into
our region, save in the southernmost parts of MO and IL, with temps
having steadied out for many locales in the upper 30s and lower 40s
with moderately strong west winds.

The stacked LOW system will continue to move away to the northeast
thru Thursday, gradually losing its influence over our region, as
much of the deep cyclonic flow is gone by midday Thursday.
Otherwise, a bone dry atmospheric column will prevail over our
region with at best weak lifting mechanisms passing thru, which
should maintain dry wx and near nil pcpn chances.

Steadily rising heights in a W-NW flow should result in a slowly
retreating southern cloud shield edge later tonight, recovering some
to the south early Thursday morning to then retreat again on
Thursday.  While low clouds can be tough to clear out this time of
year, especially with steady flow, we should see some partial
clearing tonight with additional breaks on Thursday, with southern
MO and IL in the best positions to see clearing.

MOS min temps tonight in the upper 20s and lower 30s look
reasonable, but with some measure of error potentially with
questions surrounding cloud amounts and how fast some areas may
clear out versus others.  Leaned below MOS values for the northern
forecast area, near and north of I-70, due to higher cloud amounts,
and trended towards a MOS blend in the south.


.LONG TERM...  (Thursday Night through Next Wednesday)
Issued at 337 PM CST Wed Nov 30 2016

Continued dry and cold conditions Thursday night through Friday
night with surface ridging over the area.  Rain should spread into
at least parts of central and southeast MO Saturday afternoon ahead
of an approaching shortwave.  The NAM model appears a little too
quick bringing rain into our forecast area with an initially very
dry atmosphere on the western periphery of the surface ridge.  Rain
should overspread the entire forecast area by late Saturday night as
the low-mid levels of the atmosphere saturate.  Most of the
precipitation should shift east of the forecast area by Sunday
afternoon.  Could not rule out a little snow mixed in with the rain
late Saturday night/early Sunday morning as the surface layer cools,
but no accumulation is expected due to air temperatures above the
freezing mark, light precipitation intensity, and relatively warm
surface/ground temperatures.  Another batch of rain will shift
northeastward through our area Monday afternoon and night as an
upper level trough and warm front move through the region.  The
ECMWF model is a little stronger with this system compared to the
GFS and has an upper level low and associated surface low.  It also
generates more QPF than the GFS model.  Temperatures will be warm
enough that the precipitation should all be in the form of liquid
rain.  A third round of precipitation is expected on Wednesday as a
deep upper level trough approaches with an associated surface low
and trailing cold front.  The ECMWF model is further southeast with
the track of the surface low compared to the GFS model with
accumulating snow possible northwest of the forecast area.



.AVIATION...  (For the 18z TAFs through 18z Thursday Afternoon)
Issued at 1140 AM CST Wed Nov 30 2016

MVFR CIGs from a cloud shield over UIN and COU and entering the
STL metro area during the past hour is VFR along its edges and VFR
should gradually take over for the MVFR during the afternoon
hours, with the southern edge of this cloud shield sliding
northward towards the I-70 corridor and then north of it tonight,
but currently thinking it will hang in there over UIN but scatter
out for COU and STL metro sites. Otherwise, gusty westerly winds
will diminish this evening and more or less continue at its
current speed with some slight strengthening into Thursday.





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