Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 231100

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
500 AM CST Thu Nov 23 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 402 AM CST Thu Nov 23 2017

NW flow aloft currently prevails over our region with an imbedded
upper disturbance over central IL helping to drive a region of
clouds near and mainly east of it.  At the surface, a RIDGE of high
pressure was to our south, with a light southerly flow over our
region.  A warm front extended from western IA to southeast
Nebraska.  Temperatures ranged from around 30 for areas north of I-
70 where the southerly flow was strongest, to the lower 20s in
portions of the eastern Ozarks where winds were calm.  Some weak
radar echo was seen with a batch of mid clouds pushing into central
IL, but pcpn reports from AWOS/ASOS sites have been very hard to
come by with a rather dry layer of air below 8000-9000 feet.

Northwest flow aloft will prevail thru tonight.  The shortwave
disturbance over IL exits early this morning and will drag the
cloudiness out of our region with it, with skies becoming clear
regionwide by late morning.  The surface warm front to our west will
drag across our region this afternoon, with south winds turning from
the west.  With plenty of sunshine, and a more favorable wind
direction during the afternoon, temps should easily surge into the
50s for nearly the entire area, with 55-60F expected from a corridor
from STL to COU.

Mainly clear skies will continue into tonight as winds turn again
more back to the south.  A warmer night can be expected with min
temps in the 30s most locales, and around 40 for the STL heat


.LONG TERM...  (Friday through Wednesday)
Issued at 402 AM CST Thu Nov 23 2017

Warmer temperatures can be expected on Friday due to plenty of
sunshine during the morning and southwesterly surface winds.  Highs
on Friday will be around 15 degrees above normal.  An upper level
trough will move eastward through the northern Plains and Great
Lakes region and send a cold front southeastward through our
forecast area Friday afternoon and night.  It appears that the
measurable precipitation will be north-northeast of our forecast
area closer to the better upper level forcing, although could not
rule out sprinkles across northeast MO and west central IL Friday
afternoon and evening.  Will see cooler temperatures this weekend
due to northwesterly mid-upper level flow, and as a surface ridge
moves east-southeastward through our region, albeit highs will still
be above normal for late November.  Warmer temperatures can be
expected by Monday as an upper level ridge shifts eastward into our
area and south-southwesterly surface winds strengthen.  The
operational GFS and ECMWF model solutions diverge by Tuesday with
lowering confidence in the forecast after Monday.  The operational
GFS brings a cold front southeastward through our forecast area late
Monday night and Tuesday ahead of a positively tilted upper level
trough and generates relatively light QPF across southeast MO and
southwest IL on Tuesday.  The ECMWF model is less progressive and
does not phase the northern and southern streams. It deepens the
southern stream upper level trough leading to a weak surface low
reflection which moves eastward through our region, spreading rain
into our forecast area on Wednesday.  For now will lean toward the
ECMWF model solution and not introduce any pops into the forecast
until Wednesday afternoon and night.  It appears that temperatures
will be warm enough that the p-type will be all liquid rain.



.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 500 AM CST Thu Nov 23 2017

VFR conditions and dry weather will prevail at the TAF sites thru
the valid period. Light southerly surface winds will veer westerly
this afternoon and mildly strengthen in the wake of a dry passage
of a warm front. This will be temporary, with winds already
backing from the south later tonight but will be light.





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