Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151203

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
703 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.


.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.



.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 635 AM CDT Sun Apr 15 2018

SPECIFICS FOR KUIN, KCOU: A slow-moving upper disturbance was
located over the region at TAF issuance. Extensive cloudiness
will remain in place for at least the first 0-9 hours of the TAF
period at KCOU and likely for at least the first 0-12 hours of the
TAF period at KUIN as the disturbance moves eastward. IFR
ceilings are possible, particularly between 12-18z. Scattered rain
and snow showers are expected across the area, especially near
KUIN. Gusty west to northwest winds will continue through the
period at all terminals.

SPECIFICS FOR KSTL, KSUS, KCPS: Extensive MVFR cloudiness will
remain in place for at least the first 0-9 hours of the TAF
period. Brief periods of IFR ceilings are possible before 18z.
Scattered rain showers are expected across the area but the
precipitation coverage should be better farther north of the
terminals. Gusty west to northwest winds will continue through the



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.



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