Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 290553

1153 PM CST Fri Nov 28 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 354 PM CST Fri Nov 28 2014

Warm front currently over eastern Missouri will lift northeast of
the CWA this evening.  Models show rapid advection of low level
moisture into the area later tonight which should bring some stratus
into the area after midnight.  Combination of the clouds and south
winds should keep temperatures warmer than previous nights.


.LONG TERM:  (Saturday through Next Friday)
Issued at 354 PM CST Fri Nov 28 2014

(Saturday through Monday)

Main focus during this period will be the potential for some
freezing rain on Sunday night into Monday.  Still appears that highs
will be above average this weekend as south winds will be advecting
warmer air into the area and 850mb temperatures will be around
+10C.  Given that lows tonight will only be in the mid 30s to the
lower 40s, a diurnal range of 20 degrees is reasonable with warm air
advection even with some stratus during the morning hours.  Lows on
Saturday night will likely not fall much given the breezy conditions
and increasing mid and high clouds.

By Sunday a sharp cold front will enter the CWA from the northwest
by late morning, and exit the southern CWA by early evening.  Models
are in generally good agreement that the surface temperatures will
fall below freezing from northwest to southeast on Sunday night.
Some light precipitation is still expected to develop mainly over
the southeast half of the CWA during the day on Sunday and continue
into Monday in response to both mid and low level frontogenesis and
some ascent associated with a shortwave trough that will move
through the area late on Monday.  The rain will change to freezing
rain as the surface temperatures drop below freezing.  At this point
only expect a light glazing in some areas over southeast Missouri
into southwest Illinois as we expect above normal temperatures over
the week and only expect light precipitation with this event.
Temperatures on Monday will be quite cold with brisk northwest winds
with highs only in the mid 20s to around 30.

(Tuesday through Friday)

Confidence in the forecast for next week is not high as GFS and
ECMWF have different upper flow patterns as soon as Wednesday which
results in the GFS having precipitation and the ECMWF not having any.
Overall prefer the ECMWF at least early on because of it`s
run-to-run continuity.  Will keep Tuesday and Wednesday dry for now
as surface high moves from the northern Plains into the Mississippi
Valley.  Precipitation chances will increase on Thursday as moisture
increases from the south as the surface high moves east.  The chance
will continue into Friday as another shortwave trough moves across
the area.  Temperatures will be close to normal during the period,
but will slowly warm a few degrees as the surface high moves off to
the east.



.AVIATION:  (For the 06z TAFs through 06z Saturday Night)
Issued at 1145 PM CST Fri Nov 28 2014

Primary focus remains on expected stratus development later
tonight. Have latched on to model data that depicts the
development of the stratus a bit later...with most sites not
seeing it until close to 12z. The main push coming from LA and
southern AR will likely take it east of most TAF sites, but still
think broken coverage will still form for several hours during the
morning for areas further west. By 18z, the stratus is expected to
have cleared out from the TAF sites, remaining in a holding
pattern to the east. With the flare up of the low level jet again
on Saturday night, this stratus will likely again expand to the
west, but after 06z. Otherwise, look for southerly winds to
persist thru the period. LLWS conditions ongoing until mid
Saturday morning, with another round of LLWS possible for STL
metro sites later Saturday night, but marginal enough to preclude
mention at this time.

Specifics for KSTL: Based on current satellite info, the bulk of
the stratus will likely form to the east and a bit later on
timing. Have adjusted primarily for the timing, with a more broken
coverage in stratus still expected to develop even for areas
further west over the terminal but will be more short-lived than
originally thought. Will likely see another round later on
Saturday night with low level jet re-firing. Otherwise, LLWS
ongoing until late morning with another event possible again
Saturday night.





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