Freeze Warning 4, NWS St. Louis, MO

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

Hazardous Weather Outlook
National Weather Service St Louis MO
310 AM CDT Sat Apr 20 2024

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-211200-
Greene IL-Macoupin IL-Montgomery IL-Bond IL-Fayette IL-Clinton IL-
Marion IL-Washington IL-Randolph IL-Adams IL-Brown IL-Pike IL-
Calhoun IL-Jersey IL-Madison IL-Saint Clair IL-Monroe IL-Knox MO-
Lewis MO-Shelby MO-Marion MO-Monroe MO-Ralls MO-Pike MO-Boone MO-
Audrain MO-Moniteau MO-Cole MO-Osage MO-Callaway MO-Montgomery MO-
Lincoln MO-Gasconade MO-Warren MO-Saint Charles MO-Franklin MO-
Saint Louis MO-Saint Louis City MO-Jefferson MO-Crawford MO-
Washington MO-Saint Francois MO-Sainte Genevieve MO-Iron MO-
Madison MO-Reynolds MO-
310 AM CDT Sat Apr 20 2024

This Hazardous Weather Outlook is for portions of eastern and
central Missouri as well as west central and southwest Illinois.

.DAY ONE...Today and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Sunday through Friday.

There is a chance of thunderstorms over parts of the area Tuesday
through Tuesday evening with another chance of thunderstorms Thursday
afternoon through Friday.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Byrd

Preliminary Local Storm Report
National Weather Service St Louis MO
1250 PM CDT Sat Apr 20 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0558 PM     Tornado          1 SE Cahokia            38.55N 90.17W
04/18/2024                   St. Clair          IL   NWS Storm Survey

            The tornado touched down near the western
            edge of the Prairies of Cahokia Golf Course
            and moved east for about 1.1 miles where it
            lifted near the intersection of Carol Rd and
            Lynn St. Damage consisted of uprooted trees
            and broken tree limbs. Estimated peak wind
            was 76 mph. Rating EF0.

0552 PM     Tornado          3 S Standard City       39.31N 89.79W
04/18/2024                   Macoupin           IL   NWS Storm Survey

            A brief tornado touched down south of
            Standard City where it damaged the roofs of
            3 farm sheds. The tornado moved southeast
            across South Standard City Rd where it
            caused tree damage before lifting. Path
            length 0.23 miles. Estimated peak wind speed
            95 mph. Rating EF1.

&&