Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150854
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
354 AM CDT Sun Apr 15 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 351 AM CDT Sun Apr 15 2018

A closed upper low will slowly move across the region today,
bringing extensive cloudiness and periods of light rain or snow to
parts of MO/IL.

The combination of CAA, a cold start to the day, and extensive
stratus across most of the area will limit diurnal rises. Highs may
struggle to reach 40 degrees across central and northeast MO where
the cloud cover will be thickest and will persist the longest.
Farther east, a dry slot should permit enough sunshine for
temperatures to climb into the 40s over southwestern IL before the
stratus deck arrives. Overnight lows are expected to fall into the
upper 20s to lower 30s. A Freeze Warning has been issued for tonight
for counties in which the growing season has already begun.

Although the surface low was located well to the east of the LSX
CWA, the pressure gradient remains tight across the area and this
will produce another day of breezy conditions.

Weak PV anomalies rotating around the closed upper low will produce
sufficient lift to support light precipitation at times. Light snow
could produce up to one-half inch of accumulation over parts of
northeast MO. Flurries are possible elsewhere but the ground should
be too warm for accumulations.

Kanofsky

.LONG TERM...  (Monday through Saturday)
Issued at 351 AM CDT Sun Apr 15 2018

It still appears that Monday through Friday will be mainly dry.
GFS/ECMWF/Canadian are all showing that an upper ridge will build
into Missouri and Illinois late Monday and Tuesday as the upper low
moves east.  Temperatures will stay below normal on Monday as 850mb
temperatures will fall to around -10C.  Will need to watch for the
possibility of a freeze warning or frost advisory on Monday night as
the surface high moves across the area which will setup strong
radiational cooling.  Temperatures will return to near normal on
Tuesday and Wednesday as a warm front moves north into the area.
Temperatures will then cool back down behind a cold front that will
move through Missouri and Illinois on Wednesday. This front will
pass through dry as the best dynamics with the associated upper low
will be to the north and there will be ridging along Gulf which will
cut off moisture. Cooler air will move in behind the front
causing temperatures to fall back below normal on Thursday and
Friday at the same time another upper ridge builds in from the
west for late in the week. All of the global models show a deep
upper low moving into the Plains by next weekend that will bring a
chance of showers to the area on Saturday.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1204 AM CDT Sun Apr 15 2018

VFR conditions will likely hold through early morning for most
TAF sites with bkn/ovc cigs varying from 5-10k ft. IR satellite
imagery continue to show a north/south oriented dry slot running
just about parallel with the Mississippi River. Meanwhile, MVFR
cigs are just beginning to move into KCOU as a result of wrap-
around moisture funneling in behind the system. Kept westerly
winds a bit higher as it has been reluctant to drop below 10 kts
this evening. If trend continue with the dry slot, we may see more
clearing for locations further east from KCOU for a few hours
overnight.

Main concern continues to be gusty westerly winds Sunday, along
with IFR cigs for points north of KSTL through the mid-morning
hours. Any precip should remain light with snow mainly affecting
KCOU and briefly mixing in at KUIN.

SPECIFICS FOR KSTL:
VFR condition persist overnight with westerly winds around
floating around 10 kts. We may have a brief lull in winds after
06z, but this won`t last long as it kick up again Sunday. Westerly
gusts will reach into the 20-25 kt range much of the day Sunday.
Best chances for light rain and MVFR cigs will come in after
12-13z with the moisture wrapping in around the area of low
pressure. Expected gradual improvement Sunday evening, but west
and northwesterly gusts could extend well into the evening until
the system departs to the northeast. Cigs may return to VFR late
in the TAF period.

Maples

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Freeze Warning from 1 AM to 9 AM CDT Monday 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...Freeze Warning from 1 AM to 9 AM CDT Monday for Bond IL-Calhoun
     IL-Clinton IL-Fayette IL-Jersey IL-Madison IL-Marion IL-
     Monroe IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX



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