Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190454
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1154 PM CDT Tue Apr 18 2017

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 211 PM CDT Tue Apr 18 2017

Showers left over from a dying MCS over IA has dissipated before
making it into northeast MO.  Diurnal cumulus clouds have developed
across parts of the forecast area this afternoon.  Could not rule
out isolated showers across parts of southeast MO and southwest IL
late this afternoon, although it appears that any significant
diurnal convection will remain southeast of the forecast area.  A
cold front extending from a surface low over central Minnesota
southwest through southeastern Nebraska will drop southeastward to
near the northern MO border by 12Z Wednesday.  Most of the
convection associated with this front should remain north of our
forecast area, but there may be widely scattered showers/storms
across parts of northeast MO and west central IL late tonight and
Wednesday morning. This front will lift back northward on Wednesday
as an upper level trough moves eastward into the northern Plains and
another surface wave develops along the front ahead of it. Warmer
temperatures can be expected tonight and Wednesday with southerly
surface winds in the warm sector. Temperatures will be about 15
degrees above normal.

GKS

.LONG TERM...  (Wednesday Night through Next Tuesday)
Issued at 211 PM CDT Tue Apr 18 2017

GFS/NAM are consistent with moving surface low from western Iowa
into eastern Michigan on Wednesday night and Thursday. The surface
front will move southeast across Missouri and Illinois during this
same time period.  Any showers and thunderstorms that do develop
during the day and evening over the central Plains and the mid
Missouri Valley will likely become more scattered as they move into
the CWA during the late evening and overnight hours.  There will
continue to be a chance of showers and thunderstorms on Thursday
morning, but chances will increase along and south of I-70 in the
afternoon hours.  This when the GFS/NAM are showing increased low
level moisture convergence and instability.  There continues to be
the possibility for a few strong or severe thunderstorms on
Wednesday night or Thursday because of the marginally strong
instability and shear parameters.  The front will then move well
south of the area ending the shower and thunderstorm threat.

Global models are still on track to move the upper low out of the
southwest CONUS and across Missouri and Illinois over the
weekend. The Canadian has now fallen in line with the GFS and
ECMWF in keeping the track of the surface low along the MO/AR
border into the OH River Valley. Consequently, the warm sector
will also stay south of the area this weekend which will have
affect the temperatures and the coverage of thunderstorms that
will be over the area.

Then an upper ridge will begin to build into the area right behind
the trough by Sunday as the surface ridge moves through on Monday.
The models are showing another northern stream shortwave trough and
attendant cold front moving into Missouri and Illinois by next
Tuesday.

Temperatures still look like they will warm above normal ahead of
Thursday`s cold front, but then fall below normal over weekend as
850mb temperatures fall into the 0-5C range.  By Monday and Tuesday,
temperatures will climb back above normal as 850mb temperatures
climb back into the 5-10C range.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Wednesday Night)
Issued at 1146 PM CDT Tue Apr 18 2017

VFR flight conditions are expected through the forecast period.
Showers and thunderstorms are expected in the vicinity of the
IA/MO border and points northward overnight. Otherwise expect some
high and mid clouds overnight into Wednesday morning. Diurnal cu
should develop around midday with gusty southerly winds in the
afternoon. A cold front will eventually generate showers and
thunderstorms across western MO on Wednesday night but any impact
will be after the valid TAF period.

SPECIFICS FOR KSTL:

VFR flight conditions are expected through the forecast period.
High clouds will move across the area overnight into Wednesday
morning. Diurnal cu should develop around midday with gusty
southerly winds in the afternoon. A cold front will eventually
generate showers and thunderstorms across western MO on Wednesday
night but any impact at KSTL will be after daybreak Thursday.

Glass

&&

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

$$

WFO LSX



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