Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 132035
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
335 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 cental 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 18z TAFs through 18z Saturday Afternoon)
Issued at 1120 AM CDT Fri Oct 13 2017

A surface ridge was centered over the TN Valley region, while a
nearly stationary front extended from a surface low over eastern
KS northeast through extreme northwestern MO to central WI. This
front will remain north-northwest of the taf sites through the
period. South-southeasterly surface winds will continue this
afternoon and tonight, then become more south-southwesterly on
Saturday. A southwesterly low level jet centered over northwest MO
tonight will bring some LLWS to the taf sites, particularly UIN
and COU, but it does not look quite strong enough to include in
the tafs. Patchy, VFR low-mid level cloudiness will continue
through the period. Could not rule out isolated, elevated
convection late tonight and Saturday morning, especially in the
UIN area, but will probably leave the tafs dry for now.

SPECIFICS FOR KSTL: A surface ridge was centered over the TN Valley
region, while a nearly stationary front extended from a surface
low over eastern KS northeast through extreme northwestern MO to
central WI. This front will remain well north-northwest of the
STL area through the period. South-southeasterly surface winds
will continue this afternoon and tonight, then become more south-
southwesterly on Saturday. A southwesterly low level jet centered
over northwest MO tonight will bring some LLWS to the STL area,
but it does not look quite strong enough to include in the taf.
Patchy, VFR low-mid level cloudiness will continue through the
period. Could not rule out isolated, elevated convection late
tonight and Saturday morning, but will probably leave the taf dry
for now.

GKS

&&

.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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