Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 190445
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1045 PM CST Thu Jan 18 2018

.UPDATE...
Issued at 857 PM CST Thu Jan 18 2018

Lots of high cloudiness upstream from a deamplifying upper RIDGE
continue to pour into our region and have adjusted the cloud
forecast to account for this, with a mostly clear to partly cloudy
sky now anticipated. This will also have a minor effect on our
temps when combined with the moderate and steady SW flow already
in place and the effective loss of snow cover for many areas, and
have bumped up forecast mins by a category or so as a result, with
min temps now expected to be in the 25-30 range.

Mostly thin high cloudiness will continue into Friday, but a
warmer day versus persistence is anticipated, with 50-55 for the
I-70 corridor between STL metro and COU/JEF with upper 40s for
most of the rest of the region.

TES

&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 259 PM CST Thu Jan 18 2018

Despite the warmer southerly winds returning to the region, clear
skies will allow temps to drop back below freezing, into the 20s
tonight.

On Friday, upper level trof moves off to the east and will see
warmer temps aloft move in and mix down, so south to southwest
surface winds to pickup a bit under sunny skies and allow temps to
rise into the mid 40s to low 50s, about 10 to 15 degrees above
normal.

Byrd

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 259 PM CST Thu Jan 18 2018

Warmer weather to persist through the weekend due to the south to
southwest winds. So highs will be 10 to 20 degrees above normal.

Some concern about fog formation late Friday night/early Saturday
morning and again Saturday night, for portions of the area, as this
warmer and more moist air flows across the cold ground. So will add
mention of fog for this period. All of these ingredients could lead
to patchy drizzle as well, especially Saturday morning, for now left
mention out.

Better chances of rain will begin Saturday night with scattered
light rain in warm sector. Then by Sunday, models are a bit slower
with deepening system as it lifts northeast towards region. Surface
low to track from southern plains north northeastward through Kansas
and into Iowa by early Monday. In the meantime, showers and a few
storms expected to develop in warm sector along prefrontal trof and
slide through region Sunday evening and into the overnight hours.

The activity quickly gets dry slotted as cold front sweeps through
and system picks up speed and lifts into the Great Lakes region.
Still could see some wrap around light rain, mixed with then change
over to all snow for areas along and north of Interstate 70, before
tapering off Monday night.

Colder air to filter in with temps back to near normal values by
Tuesday.

Byrd

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1045 PM CST Thu Jan 18 2018

VFR conditions, dry weather, and a persistent S-SW surface wind
will prevail thru the valid period. LLWS conditions approaching
(but not meeting) thresholds with around a 40kt jet at 2000ft
overnight and have kept out of TAF mention at this time. Stratus
is expected to build to our south late Friday evening and attempt
to push north and overspread our region just beyond the valid
period.

SPECIFICS FOR KSTL: Wind directions are the main issue here and
how they pertain to the crosswind direction of 210. It still looks
like the wind will lean ever so slightly from 220 until around 15z
when it will then lean toward 190-200 for the remainder of the
valid period. Stratus may reach the terminal before the end of the
valid period but even the most aggressive model guidance suggests
by 10-11z so for now will defer to next shift which will extend
the valid period to 18z/Sat.

TES

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX



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