Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 201137

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
637 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.


.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

The longwave pattern shifts east, bringing an upper low out of the
Southwest CONUS and into the plains by Saturday afternoon. A
strong surface high over the Great Lakes could play a role in
keeping the northern extent of the rain shield from making it too
far north. Plenty of dry, easterly flow continues to pump into
the region on the northern periphery of the moisture through the
weekend as rain develops over Southern Missouri and Illinois
Sunday. Measurable precipitation should remain south of I-70 with
the deepest moisture profiles lined up near and south of
Farmington in Missouri. The main question beyond this will be in
reference 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, light rain originates out of the Pacific Northwest in
the form of a shortwave, which dives southeast through the
western side of the longwave trough. Chances for showers are
greatest late Tuesday into Wednesday, which may linger into early



.AVIATION...  (For the 12z TAFs through 12z Saturday Morning)
Issued at 637 AM CDT Fri Apr 20 2018

VFR conditions are forecast through the period. Light easterly
winds around 10 kts or less and mostly clear skies are expected
Friday. A few high clouds may stream in from west to east late in
the day. Otherwise little/no impacts to aviation expected until
Saturday night into Sunday.



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



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