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000
FXUS63 KLSX 201730
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1230 PM CDT Sat Apr 20 2024

.KEY MESSAGES...

- Seasonably cool weather is forecast through the weekend, with
frost potential both tonight and Sunday night.

- Dry weather expected until next Tuesday.


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 302 AM CDT Sat Apr 20 2024

Surface ridge will remain over the region through the weekend.
For today, colder air will continue to advect south into the area
with highs only in the low 50s to mid 60s, around 10 degrees below
normal.

In the meantime, an upper level shortwave will undercut the surface
ridge late tonight into Sunday, ushering in colder air and
increasing mid and high clouds. For tonight, despite light and
variable winds and colder temperatures, clouds (mainly across
portions of southeast Missouri and southwestern Illinois) will limit
frost formation. However, portions of northeast Missouri and west
central Illinois, where the clouds will clear out late tonight,
could see widespread frost with patchy frost elsewhere. May need to
issue a frost advisory for this area tonight, but will hold off for
now.

On Sunday, as the upper level shortwave exits the region the clouds
will clear out, allowing for plenty of sunshine. However with north
to northwest winds, temperatures will only moderate a little bit
with highs still a bit below normal in the low to mid 60s.

Byrd
&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 302 AM CDT Sat Apr 20 2024

(Sunday Night)

Sunday night despite clear skies, the surface ridge begins to slide
off to the southeast with winds backing to the west to southwest.
Thus temperatures will be a bit warmer except in valleys and
sheltered areas, where patchy frost is possible.

(Monday - Next Friday)

As the surface ridge slides off to the southeast, southerly surface
flow will return to the region early next week. So temperatures will
moderate with highs near normal once again. In the meantime, an
upper level shortwave over the western provinces of Canada will
begin to slide southeast into the Great Lakes region with an
associated cold front. Still seeing some discrepancies in the
deterministic models, though they are coming into better agreement
on the timing of the front which will slide through the area during
the day on Tuesday. QPF will be on the light side with only 20 to 30
percent of the LREF ensemble members indicating that QPF will be
over a quarter of an inch.

Then dry weather returns for mid week as a surface ridge builds in
once again. However, another system moves on shore into the Desert
Southwest with the upper trough deepening, then eventually lifting
out towards the region late in the work week. This will bring the
next chance for showers and thunderstorms, but there are major
timing, strength and location differences among the deterministic
models, so stuck with the latest NBM solution with rain chances
Thursday through Friday.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Sunday Afternoon)
Issued at 1226 PM CDT Sat Apr 20 2024

Dry, VFR conditions are forecast through Sunday morning. Some
northwest wind gusts to around 20 knots are expected today before
diminishing toward sunset. Winds may go light/variable overnight
as a surface ridge approaches from the west. The predominant
direction should become northwesterly again though by mid/late
Sunday morning but speeds should stay lighter, generally around
7-8 knots.

Gosselin

&&

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

$$

WFO LSX