Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 020542
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1142 PM CST Thu Dec 1 2016

.UPDATE...
Issued at 850 PM CST Thu Dec 1 2016

Forecast mostly on track and only had to make a few minor
adjustments. Clouds in the north have been stubborn since sunset,
and with cloud level flow veering more with time from W to NW,
this is only going to serve to maintain their coverage more-or-
less where they are at now. A cloudy night will keep temps up, and
have edged a bit higher into the lower 30s for areas around UIN
with mid to upper 20s still looking likely elsewhere. Some clouds
should build in across southern MO into the eastern Ozarks but not
of the same coverage as up north.

TES

&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 337 PM CST Thu Dec 1 2016

The synoptic pattern early this afternoon features a broad trough
across much of the CONUS.  Heights will build over the South and
Midwest on Friday as ridging re-establishes itself across the
Southeast.

Mainly a temperature/cloud forecast this period as the
aforementioned ridging aloft keeps the region precipitation free
through the period.  Low-level stratus continues to slowly shift
east/northeast due to the combination of daytime mixing and westerly
925-850mb flow.  However, as we go through this evening, the 925-
850mb flow will turn a bit more northwesterly once again, which
should stall the cloud shield across the far northern CWA in extreme
northeast MO into western IL.  Additionally, mid/high clouds will
move into central and southeast MO overnight.  These clouds will
make for a tricky temperature forecast tonight.  Latest indications
are that areas along the I-70 corridor will likely be cloud-free the
longest, thus have gone a bit cooler in these areas (in the mid
20s).  Expect lows in the upper 20s/low 30s elsewhere.

On Friday, expect a slow increase in mid/upper level clouds ahead of
a system organizing across the Four Corners region.  With building
heights aloft, expect temperatures a bit warmer than today, with
highs in the mid 40s to lower 50s.

Walsh

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 337 PM CST Thu Dec 1 2016

Dry and seasonably cold conditions are expected Friday night as a
1030 mb surface ridge moves through the region.  Rain will spread
into parts of central and southeast MO Saturday afternoon on the
northern fringes of a precipitation shield associated with a surface
low over the southern Plains, and ahead of an approaching shortwave.
The NAM model appears a little too quick in spreading rain into our
forecast area with an initially very dry boundary layer on the
western periphery of the surface ridge shifting east of the region.
Rain should overspread the entire area Saturday night with favorable
upper level divergence over our region ahead of the upper level
trough moving eastward through the northern Plains, and in the right
entrance region of an upper level jet steak over the Great Lakes and
Ohio Valley regions. The NAM model is a little colder than the GFS
with forecast soundings around FAM depicting the potential for snow
late Saturday night.  It still appears that most of the
precipitation Saturday night and Sunday morning will be in the form
of liquid rain, but could not rule out a brief period of light snow
or snow mixed with rain late Saturday night/early Sunday morning as
the freezing level lowers.  No accumulation is expected due to the
light intensity of the precipitation along with air temperatures and
ground/surface temperatures above the freezing mark.  Only a brief
break in the precipitation Sunday night, then a second round of rain
will move northeastward through our forecast area Monday and Monday
night as a southern stream upper level trough/low and associated
surface low move northeastward through eastern AR and southeast MO
and southern IL.  It appears that this precipitation will be in the
form of liguid rain.  The model solutions diverge after Tuesday with
the GFS model bringing in much colder air already by Tuesday night
and Wednesday as a strong surface ridge builds into our area.  The
ECMWF model develops a strong winter storm which would bring
precipitation to our area Wednesday and Wednesday night, followed by
much colder temperatures. If the ECMWF model verifies there could be
a little accumulating snow for northeast and central MO, although
most of the snow would occur northwest of the forecast area.  For
now will forecast a chance of rain Wednesday changing to snow
Wednesday night before ending as the temperatures rapidly fall with
unseasonably cold conditions on Thursday.

GKS

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1142 PM CST Thu Dec 1 2016

UIN:  MVFR and low-end VFR CIGs over northern MO and central IL--
affecting the UIN terminal--continue to linger and have made a tad
slower retreat to the north than previously anticipated. It now
looks like these clouds will linger thru midday before scattering
as the cloud-level flow becomes more favorable for some
reinforcement from IA overnight. VFR after that with light winds
and dry wx.

Elsewhere (COU and STL Metro): VFR conditions, light winds and
dry wx are expected.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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