Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 202037
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
337 PM CDT Sat Sep 20 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 18z TAFs through 18z Sunday Afternoon)
Issued at 1233 PM CDT Sat Sep 20 2014

The main forecast issue is the threat of showers and thunderstorms
this afternoon and evening. A cold front will be pushing into
northern MO later this afternoon and moving southward across the
area tonight. Scattered showers and thunderstorms should develop
across northern MO into central IL this afternoon in a zone
along/ahead of the front. Coverage should be greatest from the
late afternoon into the evening and diminish overnight. Given the
low coverage of storms I have limited confidence in any direct
terminal impacts and thus have kept with VCTS in the TAFS. Gusty
southwest winds will prevail this afternoon in advance of the
front, with gusty north northwest winds on Sunday.

Specifics for KSTL:

The main forecast issue is the threat of showers and thunderstorms
this evening. A cold front will be pushing into northern MO later
this afternoon and moving southward across the area tonight.
Scattered showers and thunderstorms should develop across northern
MO into central IL this afternoon in a zone along/ahead of the
front and move southeast. Coverage should be greatest from the
late afternoon into mid evening and diminish overnight. Given the
low coverage of storms I have limited confidence in any direct
terminal impacts at KSTL and thus have kept with VCTS in the TAFS.
Gusty southwest winds will prevail this afternoon in advance of
the front, with gusty north northwest winds on Sunday.

Glass

&&

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

$$

WFO LSX





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