Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 300934

434 AM CDT Tue Jun 30 2015

.SHORT TERM:  (Through Late This Afternoon)
Issued at 434 AM CDT Tue Jun 30 2015

Scattered showers and storms are expected mainly this afternoon and
mainly across west central and southwest IL, east of the Mississippi
River as northwest flow shortwaves move southeastward through our
area.  The atmosphere will destabilize this afternoon due to daytime
heating, especially across IL near the axis of the upper level
trough centered over the Great Lakes region where mid level
temperatures will be a little colder and hence lapse rates steeper.
High temperatures should be a little warmer today compared to Monday
and close to seasonal normals for the end of June.


.LONG TERM:  (Tonight through Monday)
Issued at 434 AM CDT Tue Jun 30 2015

Showers and thunderstorms can be expected late tonight and Wednesday
as a southwesterly low level jet brings strong low level warm air
advection and moisture convergence to our forecast area, and a
surface low approaches from KS while a front sags slowly southward
through the region.  The models were also depicting strong upper
level divergence over our forecast area ahead of a northwest flow
shortwave.  There will be the potential for heavy rainfall which
could result in more flooding.  High temperatures on Wednesday will
be cooler due to the increased cloud cover along with fairly
widspread precipitation.  As the surface low and front sag slowly
southward the best threat for convection will shift to the southern
portion of the area Wednesday night and Thursday.  A surface ridge
across the Great Lakes region will nose into northeast MO and west
central IL likely ending the chance of precipitation across this
area Thursday and Thursday night.  Another upper level trough
dropping southeastward into the region will keep the threat for
showers/storms going at least across the western and southern
portion of our area Thursday through Friday.  The GFS model is a
little stronger with the surface ridge over the Great Lakes region
and is a little further south with its QPF than the NAM and the
ECMWF models.  Upper level troffing over the region coupled with a
moist low level southerly flow should lead to at least scattered
afternoon and evening convection Saturday and Sunday.



.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1146 PM CDT Mon Jun 29 2015

Specifics for KCOU, KUIN: Radiational fog is possible at KUIN
because late afternoon rainfall has locally increased the low
level moisture, winds will be light, and skies will be mostly
clear. No fog is currently forecast at KCOU because T-Td spreads
were higher and no rain had occurred at KCOU earlier in the
period. Expect winds to back overnight and then veer again after
sunrise. Winds then become light/variable late in the TAF period.

Specifics for KSTL, KSUS, KCPS: Isolated convection continues to
percolate near and along outflow boundaries from earlier
convection. Given the light winds and nearly clear skies,
radiational fog should develop overnight in the St. Louis metro
area, especially at KSUS and KCPS where increased moisture from
rainfall during the late afternoon and mid-evening hours will
reduce the T-Td spread. Otherwise, expect winds to back overnight
and then veer again after sunrise. Rain is possible at KSTL late
in the 30-hour TAF period, but there is low confidence in the
timing or duration attm.





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