031
FXUS63 KLSX 181113
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
613 AM CDT Tue Mar 18 2025

.KEY MESSAGES...

- Unseasonably warm temperatures are expected today as highs reach
  into the upper 70s to low 80s.

- Critical fire danger is forecast again for parts of central and southeast
  Missouri this afternoon due to the combination of gusty
  southerly winds, low relative humidity values, and dry fuels.
  Elevated fire danger is expected for the remainder of the area.

- Another strong storm system will move through the region
  Wednesday/Wednesday night. Very strong wind gusts of 40-50+ mph
  are expected.


&&

.SHORT TERM... (Through Thursday)
Issued at 320 AM CDT Tue Mar 18 2025

Unseasonably warm conditions are forecast today as the 850-hPa
thermal ridge moves overhead and surface winds veer slightly more to
the southwest. With early morning low temperatures running about 25
degrees warmer than yesterday and sunshine this afternoon, readings
should have no problem climbing into the upper 70s to low 80s. Daily
records at both St. Louis (82F-2012) and Columbia (81F-1921) are in
jeopardy today.

Gusty southwesterly winds are expected this afternoon, with peak
gusts in the 35-40 mph range. The combination of these gusty winds,
low relative humidity values, and dry fuels are expected to yield
critical fire danger in portions of central and southeastern
Missouri. Elsewhere, relative humidity values are a bit higher and
elevated fire danger is likely.

Very mild conditions are forecast tonight with continued strong
southerly surface winds and increasing cloud cover. Lows areawide
are expected to range from the mid 50s to near 60 degrees, or about
20-25 degrees above normal for the date.

A strong surface low will move into the mid-Missouri Valley early
Wednesday morning and move eastward through the day. A cold front is
expected to move through the bi-state region during the day, with
veering winds and sharply falling temperatures in its wake. Very
strong winds will be the main story on Wednesday. Deterministic
models show a very strong pressure gradient, with soundings showing
deep mixing to around 750 hPa and winds at the top of the mixed
layer of 55-70 knots. In addition, winds are unidirectional within
the boundary layer, suggesting efficient transport of the higher
winds aloft to the surface. Sustained winds of 20-30 mph and gusts
of 40-50 mph are forecast areawide. A wind advisory likely will be
needed for this time period. High wind warning (60+ mph) gusts are
possible, but likely would be isolated with the EPS shows 10-20%
probabilities for 60+ mph wind gusts.

The cold front is forecast to pass through mostly dry, with only
moderate convergence along the boundary and capping aloft delaying
convective initiation. Isolated showers and thunderstorms are
possible in south-central Illinois, but better chances exist to our
east. Very limited (<300 J/kg) instability is forecast in our
eastern counties due to dewpoints only near 50 degrees and very weak
midlevel lapse rates.

A secondary cold front is forecast to move through Wednesday evening-
early overnight. A broad area of light precipitation is forecast to
move eastward across the CWA associated with the deformation zone
of the cyclone. Initially, the precipitation will fall as light
rain but should turnover to snow as surface temperatures drop into
the mid 30s. The chances of measurable snow is pretty high
(40-80%) northwest of of I-44 in Missouri and I-55 in Illinois
from the LREF. Chances for 1+" drops to 10-20% however in
northeast Missouri. Regardless, any snow should have no impact as
it will be falling with temperatures at or above freezing. In
addition, ground/road temperatures will be much warmer given a day
in the 70s/80s on Tuesday. Any snow that does fall is expected to
exclusively accumulate on elevated and grassy surfaces. By late
Thursday morning, any traces of this snow should be gone as
readings warm into the 40s.


Gosselin

&&

.LONG TERM... (Thursday Night through Monday)
Issued at 320 AM CDT Tue Mar 18 2025

A weak surface ridge is expected to move across the mid-Mississippi
Valley Thursday night, with southerly winds increasing through
Friday. Another midlevel shortwave trough is expected to pass east
through the bi-state region Friday afternoon/evening. This system
has even less to work with than its predecessor, with weak moisture
return ahead of the system. Chances of measurable rainfall only peak
out in the 30-50% range, with odds of a tenth of an inch dropping to
~10%. In other words, no substantial rainfall is expected with
this system.

Near normal temperatures are generally forecast for the end of the
week through this weekend, with highs in the upper 50s to mid 60s
and lows in the 30s to low 40s. The next chance of rain is centered
on Sunday as clusters of the 500-hPa height pattern show another
midlevel shortwave trough crossing the Upper Midwest. There are more
timing/track/strength differences with this feature, but there are
signs that there will be a bit more moisture to work with and
stronger mid/upper level forcing for ascent with this system.
Therefore, PoPs are already pretty high, in the 50-60% range. The
LREF also shows some pretty respectable probabilities for at least a
quarter inch of rain, ranging from 30-50%.


Gosselin

&&

.AVIATION...  (For the 12z TAFs through 12z Wednesday Morning)
Issued at 611 AM CDT Tue Mar 18 2025

Southerly winds will increase quickly this morning and continue
through tonight. Highest gusts of around 30 knots are expected
this afternoon before some weakening occurs this evening.
Otherwise, look for a mostly clear sky with just SCT cirrus
overhead.

Gosselin

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Red Flag Warning from noon today to 8 PM CDT this evening for
     Boone MO-Callaway MO-Cole MO-Crawford MO-Dent MO-Franklin
     MO-Gasconade MO-Iron MO-Madison MO-Moniteau MO-Osage MO-
     Reynolds MO-Saint Francois MO-Washington MO.

IL...None.
&&

$$

WFO LSX