Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150901
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
401 AM CDT Mon Oct 15 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 359 AM CDT Mon Oct 15 2018

Areas of post-frontal rain (possibly mixed with a few snowflakes in
NE MO) will continue for the next several hours as a cold front
sinks southeastward through the region. Precipitation is expected to
end between 14-18z for nearly all areas; the exception is across the
extreme southern tip of the LSX CWA where light rain may continue
for a few more hours and persist into the early afternoon. High
temperatures today are expected to be around 5 degrees cooler than
yesterday within the colder post-frontal air mass and beneath mostly
cloudy skies for around half of the day. By early afternoon, some
locations should see some sun as the back edge of the cloud deck
moves through the area.

Attention then turns to what will likely be the coldest night of the
season so far. A surface high pressure center will be located over
KS/OK tonight with the ridge axis extending ENE through MO and into
IL/IN. Mostly clear skies are expected across central and NE MO, and
this is where the coolest overnight lows are currently forecast.
Frost appears likely in these areas based on the expected conditions
of light winds, mostly clear skies, and air temperatures in the low
to mid 30s. Farther to the southeast, BUFKIT time/height cross
sections show that the atmosphere is nearly saturated with respect
to ice between 20-30 kft, and models depict increasing divergence
aloft within the right entrance region of a developing jet near H25.
This suggests that a thick cirrus shield will develop tonight and
affect part of the southeastern CWA.

Conditions appear favorable for widespread frost formation across
parts of central and NE MO into west central and southwest IL.
Farther south and east, as the previous shift noted, opaque cirrus
would interfere with radiational cooling and therefore with frost
formation for the southeastern CWA. After coordination with
neighboring offices, a Frost Advisory has been issued for areas
where widespread frost is likely tonight.

Kanofsky

.LONG TERM...  (Tuesday through Sunday)
Issued at 359 AM CDT Mon Oct 15 2018

After a very cold and frosty start to the day on Tuesday, sunny
skies and warm southwest to west winds will allow temperatures to
warm up into the mid to upper 50s.

Dry and slightly below normal temperatures will persist through
Thursday before next system moves in. Surface ridge will move off to
the east by Thursday night with southern stream shortwave lifting
out of southwestern U.S. towards forecast area. This combined with
increasing low level moisture as well as a cold front sliding into
region from the northwest, will generate showers late Thursday night
through Friday evening, before coming to an end. Dry and below
normal temperatures will persist through next weekend.

Byrd
&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1042 PM CDT Sun Oct 14 2018

Cold front extending through the St Louis metro area will
continue moving southeastward. Light wind in the St Louis metro
area will strengthen from a north-northwest direction after fropa
late tonight, like it already has in UIN and COU. Rain, showers
and drizzle along and just behind the front will continue to move
through the taf sites late tonight with the cloud ceiling heights
down to as low as 500 feet at times and visibility as low as
2 miles at times in rain or drizzle. This rain will shift
southeast of the taf sites by early morning with visibilities
improving and the cloud ceiling rising into the VFR category
shortly after 12Z. Northwest surface winds will continue on Monday
as a surface ridge builds into the area from the Plains, then
becomes light Monday evening.

SPECIFICS FOR KSTL: Cold front extending through STL will
continue moving southeastward. The light wind will strengthen
from a north-northwest direction after fropa late tonight, like
it already has in UIN and COU. Rain, showers and drizzle along and
just behind the front will continue to move through the STL area
late tonight with the cloud ceiling heights down to as low as 500
feet at times and visibility as low as 2 miles at times in rain or
drizzle. This rain will shift southeast of the STL area by 12Z
with visibilities improving and the cloud ceiling rising into the
VFR category shortly after 13Z. Northwest surface winds will
continue on Monday as a surface ridge builds into the area from
the Plains, then becomes light Monday evening.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     50  39  58  42 /  20   0   0   0
Quincy          47  32  58  38 /   5   0   0   0
Columbia        47  32  58  39 /  20   0   0   0
Jefferson City  49  32  58  39 /  20   0   0   0
Salem           49  36  56  41 /  50   0   0   0
Farmington      48  35  56  40 /  50   5   0   0

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Frost Advisory from 11 PM this evening to 9 AM CDT Tuesday for
     Audrain MO-Boone MO-Callaway MO-Cole MO-Crawford MO-
     Franklin MO-Gasconade MO-Knox MO-Lewis MO-Lincoln MO-Marion
     MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike MO-
     Ralls MO-Shelby MO-Warren MO.

IL...Frost Advisory from 11 PM this evening to 9 AM CDT Tuesday for
     Adams IL-Brown IL-Calhoun IL-Greene IL-Jersey IL-Macoupin
     IL-Montgomery IL-Pike IL.

&&

$$

WFO LSX



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