Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 200828
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
320 AM CDT Fri Apr 20 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 320 AM CDT Fri Apr 20 2018

A frost advisory continues for portions of Southeast Missouri and
Southwest Illinois. Latest surface analysis reflects temperatures
ranging from the lower 30s to the lower 40s. As of 07z, the
coldest locations are in Southeast Missouri, where winds are
calm/light, temperatures are in the lower 30s and dewpoint
depressions are only 1-3 degrees. This may be the best potential
for frost, as most locations outside of Southeast Missouri are
still several degrees milder. Light and variable wind may stay up
just enough the limit any widespread frost through early morning,
especially in warmer areas.

Surface high pressure over the Upper Midwest will remain in
control through Friday. As the high continues its slow eastward
progress, surface flow will shift out of the east-southeast with
an upper ridge building overhead through the course of the day.
Plenty of dry air is in place, so the main question is related to
any high clouds for late Friday afternoon. Should clouds hold
off, given lower surface dewpoints, dry surface and limited
green- up, it is conceivable that high temperatures could go a
few degrees above the going forecast. Overall, a pleasant spring
day is in store for the bi-state region.

Maples

.LONG TERM...  (Saturday through Thursday)
Issued at 320 AM CDT Fri Apr 20 2018

Limited concerns exist in the extended forecast with the potential
for a couple of quick hits of light rain and slightly below normal
temperatures.

The longwave pattern shifts east, bringing an upper low out of the
Southwest CONUS and into the plains Saturday afternoon. A strong
surface high over the Great Lakes could play a role in the
northern extend of the rain shield. Plenty of dry, easterly flow
continues to pump into the region on the northern periphery of the
low. This should keep measurable precipitation south of I-70 with
the deepest moisture profiles lined up near and south of
Farmington in Missouri. The main question is in regard to the slow
eastward exit of the low, as it remains cut off from the main flow.
Low chances for showers could extend into early Monday over southern
sections of Missouri and Illinois.

Further north, a ribbon of drier air could keep Northeast Missouri
and Central Illinois rain-free Monday through the first half of
Tuesday. We then become enveloped in northwest flow as a longwave
trough develops over the eastern CONUS. The next potential for
widespread rain originates out of the Pacific Northwest, diving
southeast through the northern plain on the western side of the
trough. Chances for showers are greatest late Tuesday into
Wednesday.

Maples

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1144 PM CDT Thu Apr 19 2018

Sfc ridge currently extends across srn MN into ern IA and will
move east tonight. As it does, winds will veer overnight to
become ely to ssely Fri morning. Winds will increase but expected
to remain at or below 10 kts. VFR conditions expected thru the
TAF period with only few to sct CI expected across the region.

Tilly

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Frost Advisory until 9 AM CDT this morning for Boone MO-Callaway
     MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-Iron MO-
     Jefferson MO-Lincoln MO-Madison MO-Moniteau MO-Montgomery
     MO-Osage MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Warren MO-Washington MO.

IL...Frost Advisory until 9 AM CDT this morning for Bond IL-Calhoun
     IL-Clinton IL-Jersey IL-Madison IL-Monroe IL-Randolph IL-
     Saint Clair IL-Washington IL.

     Freeze Warning until 9 AM CDT this morning for Fayette IL-Marion
     IL.

&&

$$

WFO LSX



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