Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251154
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
654 AM CDT Thu May 25 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 333 AM CDT Thu May 25 2017

Low system, currently centered over IN/OH region at the sfc, will
continue to move ewd today. Expect cloud cover over the ern half of
the CWA to gradually clear out of the area today before mid clouds
move into the wrn portions of the CWA.

With ample insolation expected today, have trended twd the warmer
guidance despite weak advection. Have also trended twd warmer
guidance for tonight as clouds move into the region and winds
becoming sly across the region.

Expect today to remain dry as well as much of tonight. However, have
kept low PoPs late tonight across wrn and nrn portions of the CWA as
the wrmfnt lifts thru the area. There are some mdls that suggest
TSRA moving further south impacting srn portions of the CWA.
However, given the strong and deep WAA across this area, it wud seem
this area would be capped with convection remaining further north.
Mdls disagree on timing, but with a weak trof moving thru IA late
tonight into Fri morning, have focused further north late tonight.

Tilly

.LONG TERM...  (Friday through Wednesday)
Issued at 333 AM CDT Thu May 25 2017

Surface ridge to continue weakening and shift off to the east on
Friday as next system moves in. Frontal boundary associated with
system to sink south across forecast area and stall out along I-70
corridor. Low level moisture will be on the increase with moderate
instability. However, decent cap so activity will be slow to
develop, if at all. If anything does fire up by late afternoon/
early evening, it could be strong to severe.

The threat for storms will persist Saturday through Saturday night,
with models continuing to indicate very high CAPES and strong 0-1km
shear. As frontal boundary lifts north as a warm front, will see
elevated hailers during the morning hours, then transition to more
of a supercell environment for the afternoon and evening hours. SPC
has placed areas along and south of I-70 in an Enhanced risk for
Saturday/Saturday night.

As system exits, will see showers taper off on Sunday. Quieter
weather for Monday and Tuesday, though could see isolated/scattered
showers and storms as shortwaves rotate around upper low anchored
over Great Lakes region each day. Weak surface ridge builds in by
Wednesday.

As for temperatures through the period, will be near normal or just
a bit above normal.

Byrd

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 641 AM CDT Thu May 25 2017

VFR and dry thru the period. Expect some CU to develop later this
morning and dissipate late this afternoon. Nwly winds will
gradually back to become sly to sely late tonight. TSRA are
possible late tonight at KCOU and/or KUIN. Uncertainty of
impacting the terminal are too low to mention in TAF attm.

Tilly

&&

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

$$

WFO LSX



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