Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140518

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1118 PM CST Mon Nov 13 2017

Issued at 950 PM CST Mon Nov 13 2017

Forecast on track and only made cosmetic changes, primarily to
cloud cover. Spotty light rain will move into portions of
northeast and central MO and west-central IL toward daybreak and
into Tuesday morning. This activity should fade in the afternoon
and much of the evening before a more widespread and substantial
rainfall event takes place ahead of a cold front late Tuesday

Overnight min temps tonight will range from near freezing in parts
of southwest IL to the low-mid 40s in MO underneath thicker cloud
cover and a more southerly low level flow. Only modest increases
in temps into the low 50s on Tuesday with most locations
continuing under mostly cloudy skies.



.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 323 PM CST Mon Nov 13 2017

High pressure at the surface quickly moves off to the east
overnight. Flow aloft becomes more zonal allowing for a quick
change top a southerly flow at the the surface and 850MB. Warm air
advection and some isentropic lift will bring in some changes of
light rain overnight from west to east across the area Tuesday
morning. Model pops are pretty low but would not be surprised to
see them rise a bit by Tuesday morning. Still not a significant
rain event, where it happens. Cloud forecast has and will be a
challenge. Some models want to redevelop low ceiling from the
southeast overnight. while others only bring in some lower
ceilings out to the west. Given current trends hare gone with the
latter. Clouds should temper temperatures a bit for tomorrow, but
will still be warmer than today for most areas.


.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 323 PM CST Mon Nov 13 2017

Showers and a few thunderstorms can be expected mainly late
Tuesday night and Wednesday morning as an upper level trough with
embedded shortwaves moves eastward through the northern Plains and
Great Lakes region and sends a cold front southeastward through our
forecast area Wednesday.  A southwesterly low level jet Tuesday
night will bring increasing low level moisture into our region ahead
of the approaching cold front.  Despite the morning cloud cover and
rain, highs on Wednesday should be close to seasonal normals or even
slightly above.  A surface ridge will build southward into our area
Wednesday night bringing colder and drier air into the region.
Another round of showers and a few storms can be expected late
Thursday night and Friday morning as a warm front lifts north-
northeastward into our area.  Temperatures may become steady or rise
slightly late Thursday night due to low-mid level warm air advection
as the surface/low level wind becomes southerly/southwesterly as the
surface/850 mb ridge shifts east of the region.  A third round of
convection, possibly strong will move quickly through our area
Friday afternoon or night along a strong cold front. The operational
GFS model continues to be quicker with the front, dropping it
southeastward through our forecast area Friday afternoon and
evening, while the ECMWF model was about 12 hours slower bringing it
though the region late Friday night and Saturday morning.  Due to
this timing uncertainty will keep a chance of showers going for much
of the forecast area until noon Saturday. Temperatures will be
unseasonably warm Friday ahead of the cold front, then should take a
quick drop after frontal passage as potentially strong and gusty
northwesterly winds behind the front bring colder and drier air into
the region Friday night and Saturday.  Dry and colder conditions can
be expected for Saturday afternoon through the rest of the weekend
as a surface ridge moves slowly eastward through the region.
Temperatures Saturday night through Sunday night should be around 10
degrees below normal.



.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1118 PM CST Mon Nov 13 2017

A transition to MVFR CIGs is still expected at UIN and COU late
tonight or early Tuesday morning with these lower CIGs accompanied
by some spotty light rain, which is handled via a VCSH mention.
As for the STL metro sites, VFR conditions and dry weather will
prevail thru the valid period. Light SE surface winds will
gradually veer S during the period. A high prob more widespread
rain event lurks just beyond the valid period but is covered and
mentioned in the longer 30-hour STL valid period.





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