Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262045
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
345 PM CDT Thu Apr 26 2018

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 344 PM CDT Thu Apr 26 2018

A ridge over northeast Illinois will continue to slide east of the
forecast area this evening. A weak dry cold front will move through
the area  overnight with only a light wind switch to west-southwest
noted just ahead of the front, then shift back to northwest  and
remain light behind the front. There will not be much an airmass
change behind the weak cold front as 850mb temperatures will only
drop 2-3C behind the front. Temperatures tonight and tomorrow will
remain near climatological ranges with lows tonight across the area
in the 40s and highs tomorrow in the upper 60s to lower 70s.  High
pressure over the northern Plains will slide east and provide more
dry weather and light winds through Friday.

Kelly

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 344 PM CDT Thu Apr 26 2018

A ridge of high pressure over the northern Plains on Friday night
will very slowly drift east southeast into the Ohio Valley by Sunday
afternoon. The ridge of high pressure will move off the southeast
coast of the US by Monday afternoon, but its influence will still
provide dry weather and light winds through Monday over the forecast
area. A cold front will begin to move toward the area Tuesday and
into the forecast area on late Tuesday night.

An active period of weather is possible during the middle of the
week as a cold front will move into the area on Wednesday. A strip
of 1000 to 2000 J/kg of surface-based CAPE will setup ahead of the
cold front on Wednesday afternoon over the western two thirds of the
area.  The combination of favorable shear and steep lapse rates will
be for more than sufficient for severe weather over the area on
Wednesday afternoon and evening. The severe weather potential could
possible linger into Thursday afternoon over parts of southeast
Missouri into southwestern Illinois if the ECMWF solution is
correct. There are a number of factors that could hamper severe
weather potential on Wednesday into Thursday. The first would be
convective cloud debris from previous convection over the central
and southern plains from Tuesday afternoon and evening and again on
Wednesday afternoon and evening overspreading the area on both days.
Also, frontal placement would influence the setup of dynamics which
could hamper or promote severe potential on both days over the
forecast area. High pressure and northwest flow will set up behind
the front over the area by Friday.

Temperatures will be around normal values this weekend, then
trending to at or above normal through the end of the forecast
period.

Kelly

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1225 PM CDT Thu Apr 26 2018
Dry and VFR conditions are expected through Friday afternoon over
the forecast area. A weak cold front will move through the
forecast area late tonight. Light northwest winds will briefly
shift out of the west- southwest late tonight just ahead of the
frontal passage. Winds behind the weak cold front will remain
light and out of the northwest through Friday morning before
picking up to around 10kts by 18z.

SPECIFICS FOR KSTL:

Dry and VFR conditions will persist at the terminal through
Friday afternoon. A weak cold front will pass over the terminal
around midnight. A brief light wind shift from northwest to west-
southwest will occur just ahead of the frontal passage. Light
northwest winds are expected behind the front through Friday
morning before picking up to around 10kts by 18z.

Kelly

&&

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

$$

WFO LSX


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