Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 151750
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1250 PM CDT Mon Sep 15 2014

.SHORT TERM:  (Through Late This Afternoon)
Issued at 329 AM CDT Mon Sep 15 2014

Shower and thunderstorm trends are the primary forecast problem for
today.  Definite lack of activity so far in our CWA as of 08z,
however impact of the veering low level jet and moisture advection
is just now starting in earnest over our CWA, so still believe that
elevated storms that developed in sw IA around 06z will be trying to
build south with time with some of this precipitation area impacting
northern sections of our CWA.  The latest HRRR, local WRF, as well
as some of the 00z synoptic models are also suggesting lesser/much
spottier development is also possible further south along and south
of the I-70 corridor over the next few hours, and don`t think this
consensus can be totally discounted with some showers currently
south of SGF.

With the primary zone of warm advection/isentropic ascent shifting
to our east during the afternoon, southward pushing cold front
should be the primary trigger for additional showers and
thunderstorms.  I have held onto a zone of likely PoPs in the
vicinity of the front, but it may be these values will be a bit too
high, especially if the warm layer depicted by the GFS between
700-750mb comes to fruition.

Have used a variety of 3 hourly temperature guidance trying to
capture impacts of the aforementioned precip trends as well as that
of the cold front over northern sections of the CWA.  Highs are
expected to range from the middle 60s in our n counties to the 75-80
degree range south of the Missouri River.

Truett

.LONG TERM:  (Tonight through Sunday)
Issued at 329 AM CDT Mon Sep 15 2014

Cold front should make it southeastward to around STL by 00z
Tuesday. There will be scattered showers along and just behind
this front as it continues to move southeastward through southeast
MO and southwest IL this evening. It does not appear that there
will be much precipitation left by late tonight as a surface ridge
builds southeastward into our area behind the front with cooler
and drier air filtering into MO and IL. It should be dry for
Tuesday and Tuesday evening, then showers may return to at least
portions of central and southeast MO late Tuesday night and
Wednesday as weak low-mid level warm air advection ahead of a weak
northwest flow shortwave intercepts return low level moisture on
the backside of the surface ridge shifting east of our area. The
eastward extent of this precipitation is in question. The models
keep most of their qpf west of the Mississippi river. Warmer
temperatures are expected for Friday as as upper level ridge over
the southwestern US shifts eastward into our area along with
strengthening surface/low level southerly winds. Convection should
return to the region Saturday afternoon and night as a strong
shortwave breaks down the upper level ridge and sends a cold front
southeastward through our forecast area Saturday night and Sunday
morning. Prefer the ECMWF model during this time period as the GFS
has some feedback problems and generates a surface low along the
front that is likely too deep and has too much qpf.

GKS

&&

.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1239 PM CDT Mon Sep 15 2014

Approaching cdfnt will bring a chance for TSRA to COU/SUS/CPS this
afternoon. With lack of insolation ahead of the fnt, there is a
lot of uncertainty regarding coverage of storms. Have kept VCTS
mention for now. Upstream obs and guidance suggests low MVFR to
IFR cigs will move into the region behind the fnt with winds
becoming nly. Clouds shud clear this eve for UIN/COU which shud
allow for FG to develop. Have kept vsbys in the MVFR range for now
as some question as to how low vsbys will get with the nly wind.
FG shud clear out by mid morning on Tues. For SUS/CPS, guidance
suggests cigs will lower this eve to IFR and remain into Tues
morning. Believe these cigs will clear out quickly with some
diurnal CU possible, but shud remain SCT.

Specifics for KSTL: Approaching cdfnt will bring a chance for TSRA
this afternoon. With lack of insolation ahead of the fnt, there is
a lot of uncertainty regarding coverage of storms. Have kept VCTS
mention for now. Upstream obs and guidance suggests low MVFR to
IFR cigs will move into the region behind the fnt with winds
becoming nly. Guidance suggests cigs will lower this eve to IFR
and remain into Tues morning. Believe these cigs will clear out
quickly with some diurnal CU possible, but shud remain SCT.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX





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