Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 251140
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
540 AM CST Sun Feb 25 2018

.SHORT TERM...  (Through Late Tonight)
Issued at 250 AM CST Sun Feb 25 2018

Welcome tranquil and dry weather for central and eastern Missouri as
well as central and southern Illinois today and tonight.  A
sprawling high pressure system is building east from the Great
Plains this morning.  Current blustery winds will diminish to 10 to
15 mph by mid morning as the high builds builds into the lower and
middle Mississippi Valley.  The airmass associated with this high
isn`t particularly cold...in fact highs today should jump back up
into the 50s across the forecast area under increasingly strong late
February sunshine.  This will be about 5 to 10 degrees above normal.

The surface high will expand eastward into the Ohio Valley tonight,
but the ridge axis will stay entrenched across southern Missouri and
Illinois.  Light wind combined with relatively dry air and only some
thin high clouds should produce good radiational cooling conditions,
particularly for areas south of the I-70 corridor in Missouri and
along and south of I-64 in Illinois where the wind should be flat
calm.  Dewpoint temperatures will be in the mid 20s over most of the
area, but I recent rains will put a damper on the potential full
effect of the radiational cooling and only allow temperatures to
fall into the low to mid 30s for most locations.

Carney

.LONG TERM...  (Monday through Saturday)
Issued at 250 AM CST Sun Feb 25 2018

The period of dry and tranquil weather continues Monday through
Tuesday will above average and warming temperatures. Height rises
aloft are forecast as a low-amplitude ridge builds, occurring in
response to the departure of a weak short wave and in concert
with large scale amplification as an upper trof digs along the
west coast. The onset of south-southwest low level flow and WAA
will be gradual but skies should be relatively cloud-free
supporting a good moderation over temps forecast for today.
Temperatures will continue to warm to well above average levels on
Tuesday as the flow aloft backs to southwesterly in response to
the upstream digging trof, and as low level south-southwest flow
increases strengthening the WAA.

Wet weather in the form of showers and maybe even a rumble of
thunder will return on Tuesday night as a weak impulse traverses the
area in the southwest flow aloft, and as a veering southwesterly LLJ
produces lift and moisture transport into the area. The ECWMF and
GFS came into better agreement with features mid-late week with the
12Z model cycle, but have reversed course with the 00Z cycle and now
show rather significant differences handling the east-northeast
ejection of the western trof through the Plains into the Mid MS
Valley. Fortunately the impacts are not overwhelming on the forecast
of sensible weather. Given the consistency of the GFS and support
from many of the GEFS members, we are leaning towards its solution.
The western upper trof will eject into the Plains Wednesday with the
accompanying surface low moving into south central KS and warm
front lifting through southern MO. I think much of Wednesday will
be void of precipitation given the current model suite solutions,
however there should be a big increase in showers and a few
thunderstorms over western MO heading thru the afternoon in
response to lift via the LLJ and the leading edge of lift
associated with the upper system. The entire system will deepen as
it moves northeast into the MS Valley on Wednesday night bringing
showers and a few thunderstorms to the area. The upper trof and
surface low will continue to move east into the lower Great Lakes
region on Thursday with gusty west-northwest winds in its wake and
possibly some trailing wrap-around showers. Dry weather and
slightly above normal temperatures should then dominate Friday
into Saturday as surface high pressure shifts across the region
and ridging builds aloft.

Glass

&&

.AVIATION...  (For the 12z TAFs through 12z Monday Morning)
Issued at 537 AM CST Sun Feb 25 2018

VFR flight conditions are expected to prevail across the forecast
area through Monday morning as high pressure builds across the
Mississippi Valley. West-southwest wind will diminish through the
day and become light and variable over much of central, east
central and southeast Missouri as well as southern Illinois tonight.

SPECIFICS FOR KSTL:

VFR flight conditions are expected to prevail at Lambert through
Monday morning. West-southwest flow will continue to diminish
through the day, becoming light and variable this evening.

Carney

&&

.PRELIMINARY POINT TEMPS/POPS...
Saint Louis     53  36  61  40 /   0   0   0   0
Quincy          48  30  57  37 /   0   0   0   0
Columbia        52  31  61  38 /   0   0   0   0
Jefferson City  53  30  62  38 /   0   0   0   0
Salem           52  33  59  37 /   0   0   0   0
Farmington      56  32  61  37 /   0   0   0   0

&&

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

$$

WFO LSX



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