Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 140454
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1154 PM CDT Fri Oct 13 2017

.SHORT TERM...  (Through Late Saturday Afternoon)
Issued at 238 PM CDT Fri Oct 13 2017

Much of the cloud cover over our forecast area has dissipated
this afternoon allowing the temperatures to finally make a
significant rise, although there was still patchy cloudiness
across central MO. A cold front extended from WI southwest to a
surface low over eastern KS. This front will make a slight shift
southeastward toward our area tonight, then lift back northward on
Saturday. There may be scattered showers and thunderstorms
tonight across northeast MO and west central IL due to low-mid
level warm air advection ahead of weak southwest flow shortwaves.
There will also be low level convergence on the nose of a
southwest low level jet over northwest MO. Lows will be warmer
tonight due to southerly surface winds, at least some cloud cover
especially across northeast MO and west central IL, and higher
surface dew points. Although unseasonably warm highs are expected
on Saturday, cloud cover may hinder warming enough that record
highs won`t be reached. Highs should be about 15 to 20 degrees
above normal for mid October. There will continue to be convection
across northeast MO and west central IL.

GKS

.LONG TERM...  (Saturday Night through Next Friday)
Issued at 238 PM CDT Fri Oct 13 2017

Convection will spread southeastward through our entire forecast
area Saturday night and Sunday morning as an upper level trough
moves eastward through the northern Plains and into the Great
Lakes region and sends a cold front southeastward through our
forecast area Saturday night. There may be severe storms, mainly
across northeast MO and west central IL, and mainly Saturday
evening as the wind shear increases due to a strong southwest low
level jet and a mid level wind max in the base of the upper level
trough. The primary threat will be damaging winds as the
convection will be mainly linear along the front. The convection
will likely weaken some overnight as it moves through east central
and southeast MO and southwest IL. There will be lingering post
frontal showers across southeast MO and southwest IL Sunday
morning, with clearing Sunday afternoon as a surface ridge builds
eastward into our area. Much cooler temperatures can be expected
Sunday and Sunday night with strong cold air advection behind the
front. The models drop the 850 mb temperatures down to around 2 to
4 degrees C Sunday night. With a clear sky and diminishing
surface wind the lows may be cold enough for some light, patchy
frost late Sunday night and early Monday morning in the colder
locations. It looks dry for the remainder of the forecast with a
warming trend beginning Tuesday as upper level height begin to
rise, and southerly surface winds return as the surface ridge
shifts east of the region.

GKS

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1134 PM CDT Fri Oct 13 2017

VFR conditions for all terminals through Sat evening. Dry
conditions and south winds before cold front passage Sat evening
for all TAF sites but UIN, which has slight chance for precip
thru sunrise Sat associated with retreating warm front in
northern MO. Ceilings are expected to remain VFR with the frontal
passage on Sat but lower visibilities can expected with the
showers and thunderstorms forecast.

SPECIFICS FOR KSTL:

Dry VFR conditions for STL through Sat late evening. Mid level
clouds are expected to form around sunrise Sat but will stay
above VFR limits. Cold front will move through the terminal area
late Sat/early Sun. With this frontal passage thunderstorms and
reduced visibilities are expected along with LLWS. Ceilings will
drop after the front as a low stratus cloud deck with IFR
conditions around 9Z expected.

Walsh

&&

.CLIMATE...
Record max temperatures for Saturday, 14 October...

Saint Louis:  90/1899
Columbia:     92/1899
Quincy:       91/1938


&&

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

$$

WFO LSX



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