Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 281747
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1247 PM CDT THU APR 28 2016

.SHORT TERM...  (Through Late This Afternoon)
Issued at 333 AM CDT Thu Apr 28 2016

A stacked storm system was centered over western IA early this
morning.  At the surface, an occluded front extends southeast from
this storm center to a triple point in southwest IL, where a cold
front extends further south from there and a warm front extends east
from the triple point.  Temperatures were in the 60s ahead of the
cold front in southern IL, and have fallen into the 50s elsewhere.
Skies had also cleared over most areas, but some wraparound clouds
have recently moved back into sections of northwest MO.  A small
area of dense fog has developed just north of the front and triple
point, but the favorability to sustain this fog should decrease
heading towards dawn as the fronts move thru and the triple point
pulls away.

The surface triple point is expected to move out of the forecast
area into east-central IL by 12z this morning, taking the other
fronts out of the forecast area as well, leaving westerly flow in
its wake, and a surface TROF just to our north in southern IA and
central IL.  During this time, the storm center will track from
western IA into northeast IA with an upper level disturbance
will rotate thru southern IA by this afternoon.

The combination of some weak upper support and a surface boundary
and residual moisture should be enough for isolated to scattered
showers to develop with the heating of the day, but this all should
be just north of the forecast area.  Otherwise, clear skies are
expected for much of the area with additonal clouds in northeast MO
and west-central IL.  Westerly flow will support deep mixing,
resulting in max temps from the 60s in northern MO and central IL to
the 70s elsewhere.

TES

.LONG TERM...  (Tonight through Wednesday)
Issued at 333 AM CDT Thu Apr 28 2016

A weak sfc ridge builds into the area tonight, keeping the area dry
and cooler thru Fri morning.

The leading s/w may spread precip into the region as early as Fri
afternoon. Mdl differences continue with this system, but have
trended twd the slightly faster/more nrly ECMWF/NAM/local WRF solns.
This system will keep precip in the area thru much of the weekend,
tho Fri night thru Sat night still appears to be the bulk of the
precip. Given the mdl differences, uncertainty remains, but can not
rule out a severe threat on Sat. This threat will largely depend
upon where the sfc fnt sets up and if precip from overnight Fri can
move out of the area early enough for recovery.

Next week and beyond, sfc ridge builds into the area, keeping the
remainder of the forecast period largely dry. A secondary cdfnt
pushes thru the area sometime Wed. Mdls suggest this fnt will have
enuf moisture to generate precip, tho timing differences remain.
With Gulf cut off, do not believe enuf moisture will exist for
precip, but have kept low PoPs in for now.

Tilly

&&

.AVIATION...  (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1235 PM CDT Thu Apr 28 2016

A rather large area of stratus covered the Upper MS Valley and
northern Plains into northern MO and through a good portion of
northern and central IL. The southern extent impacting KUIN was
located within cyclonic westerly low level flow, and stretched
just north and west of KCOU. KUIN will continue to see MVFR flight
conditions this afternoon which are expected to improve to VFR by
00z. Overnight however lower stratus and some light fog will
likely move back into KUIN and persist into Friday morning.
Elsewhere predominately VFR flight conditions are expected with
potential for MVFR stratus on and off at KCOU through late
afternoon.

Specifics for KSTL:

VFR flight conditions are expected through the forecast TAF
period. Westerly winds this afternoon will become light this
evening and veer with time.

Glass

&&

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

$$

WFO LSX



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