Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 210504
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1204 AM CDT Sun Sep 21 2014

.SHORT TERM:  (Through Late Tonight)
Issued at 335 PM CDT Sat Sep 20 2014

Main question for tonight is the convective trends and evolution.
The surface cold front is still far removed from the CWA, extending
from central Iowa through southeast Nebraska into northern Kansas at
mid afternoon. A fairly broad region of low level confluent flow is
located ahead of the front from northern IL into northern MO and
northeast KS where SBCAPE ranges from 1500-2500 j/kg. Convection
allowing models differ considerably on evolution of storms and don`t
offer much support. The visible satellite is showing agitated cu
within the confluent zone where the cirrus has been thinning. The
shortwave tracking across the upper MS Valley will bring some weak
mid level cooling further reducing any CIN, but large scale
support is largely weak or non-existent. Present thought is that
scattered thunderstorms will develop within this confluent zone
during the later part of this afternoon and evening. Can`t see
much better than scattered coverage unless we see areas of
storm/cold pool mergers. Greatest coverage should be this evening,
waning overnight with loss of instability as the cold front moves
southeastward through the area.

Glass

.LONG TERM:  (Sunday through Next Saturday)
Issued at 335 PM CDT Sat Sep 20 2014

The cold front should exit southern portions of the CWFA around
12-15Z on Sunday morning, thus ending the chance of precipitation
across the area through at least the first half of the work week.
Cooler and drier air filtering into the region in the wake of the
front Sunday will yield highs up to 10 degrees cooler for some
locations, with highs ranging from the low 70s north to near 80
degrees over far southern zones. Northwest flow will persist over the
region through the first part of the week as high pressure builds in
over the central US, with highs Monday and Tuesday only reaching the
low to middle 70s area-wide.  Beginning Wednesday, temperatures will
start to slowly rebound as surface high pressure drifts to the east
allowing for southerly flow to return, with highs reaching the upper
70s to around 80 degrees by Friday and Saturday.

A low pressure system currently off the central California coast
is still progged to come ashore and lift through the Rockies
toward the north central Plains by Tuesday night, though models
differ on the behavior of the low from that point forward. The GFS
and GEM both show the low retrograding southwestward prior to
making any impact on our area, whereas the ECMWF absorbs it into
the mean flow, lifting it quickly toward the upper Midwest and
Great Lakes. This feature could bring some increased cloud cover
and precipitation to northeast and mid Missouri in the Wednesday
night/Thursday time frame, though confidence is low until future
model runs come into better agreement. Other than this mid-week
feature, the extended looks to be dry and seasonably cool through
the start of next weekend.

Phillipson

&&

.AVIATION:  (For the 06z TAFs through 06z Sunday Night)
Issued at 1152 PM CDT Sat Sep 20 2014

Widely scattered thunderstorms may clip the 10-nm vicinity around
KCPS over the next few hours. It rained briefly at KUIN earlier in
the evening, and the additional moisture at low levels combined
with radiational cooling may continue to produce light fog over
the next few hours until wind speeds increase after fropa. VFR
conditions are expected at KCOU and KSUS. Expect winds to become
northwesterly at KSUS/KCPS/KCOU/KUIN after fropa, then gust to
around 20-25 kts with diurnal mixing. Gusts should subside after
sunset.

Specifics for KSTL: Widely scattered thunderstorms may clip the
10-nm vicinity of the terminal over the next few hours. Will
continue to monitor radar trends and amend if necessary.
Otherwise, expect winds to become northwesterly after fropa
overnight, then gust to 20-25 kts with diurnal mixing. Gusts
should subside after sunset. VFR conditions are expected outside
of thunderstorms.

42

&&

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

$$

WFO LSX






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