Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 282357

557 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 00z TAFs through 00z Saturday Evening)
Issued at 557 PM CST Fri Nov 28 2014

Primary focus is on potential for stratus development with a
secondary concern for LLWS from a low level jet. The latest model
data, where it was unanimously in favor of stratus development
previously, is beginning to diverge on timing and extent of
stratus now. Very little is probably going to develop by 03z,
giving us little observational reason to depart from current
forecast, and this may still be the case at 06z for the next
TAF package. Have begun to scale down on the stratus forecast by
shortening the timing of it and going more of a BKN forecast
versus OVC. There is additional data that suggests much of what
does develop will get shunted to the east, enough to perhaps
prevent it from ever getting to COU and UIN, with STL metro sites
more on the edge than previously thought. Still indications that
CIGs may still dip into IFR range, but these are on increasingly
shaky ground with doubts emerging on whether there will be any
CIGs at all. Again, trended the previous forecast towards a more
optimistic outlook while retaining the meat of it for now.
Otherwise, look for southerly winds to persist thru the period.
LLWS conditions still expected to be met and have tweaked the
specifics in the latest forecasts.

Specifics for KSTL: Confidence on stratus not as high as what it
may have been previously and have begun a trend of scaling the
forecast back on both extent and timing while retaining the
essential elements of the previous forecast for now. Will bear
close watching down in AR late this evening to see what develops
and adjust as needed, with a positive indicator meaning perhaps
IFR CIGs, while a negative indicator meaning perhaps no CIGs at
all. Otherwise, LLWS still expected for late this evening and into
mid Saturday morning.





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