Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 151815
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
115 PM 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 18z TAFs through 18z Monday Afternoon)
Issued at 1244 PM CDT Sun Apr 15 2018

MVFR flight conditions are expected to prevail across the forecast area
for most of the next 24 hours. Widely scattered light rain or
snow showers will continue to move east-southeast across eastern
Missouri and western Illinois. These showers may temporarily
reduce visibilities and ceilings to IFR, but IFR conditions should
be transient and short-lived. Some model guidance suggests that
ceilings could briefly pop up to VFR late this afternoon and stay
up for a few hours this evening...however there doesn`t seem to be
much support for rising ceilings in current observations. If the
ceilings to come up, they`ll likely drop back down to MVFR tonight
and stay low until mid to late morning Monday when the clouds
should lift and scatter from west to east. West-southwest wind
along and east of the Mississippi River will turn to the northwest
this afternoon. Will continue to see the possibility of wind
gusts up to around 30kts.

SPECIFICS FOR KSTL:

Watching an area of stronger radar returns about 20 miles
northwest of the terminal. Don`t have any observations under these
showers, so not sure if they`re rain or snow at this time. If the
precip holds together it will get to Lambert between 19-1930Z.
Could briefly reduce vsbys/cigs, but it shouldn`t last long.
Otherwise...expect MVFR ceilings to continue to prevail through
tonight...p As mentioned above ceilings may improve to VFR late
this afternoon into the early evening...but there is little
observational support for this improvement. Northwest wind will
continue to be strong and gusty...up to 30kts through Monday.
Should see ceilings improve Monday morning as the strong low
continues moving east.

Carney

&&

.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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