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000
FXUS63 KLSX 211706
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1206 PM CDT Sun Apr 21 2024

.KEY MESSAGES...

- We have one more cool day today with another frost or freeze
  possible in parts of the area tonight.

- The next chance of rain comes on Tuesday when mainly showers are
  expected.

- Warmer temperatures and chances for thunderstorms return later
  in the week, with the best chance for thunderstorms on Friday.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 323 AM CDT Sun Apr 21 2024

As the upper level trough exits the region today, skies will
clear out from northwest to southeast. As for highs today, despite
northwest winds around 10 mph, the sunny skies will keep high
temperatures similar to yesterday in the low 60s, especially along
and south of I-70, while the northern half of the forecast area
will be around 10 degrees warmer than yesterday.

For tonight, it will be another chilly night as temperatures dip
down into the 30s outside of the St. Louis metro area. Also, with
the center of the surface ridge anchored over the southern portions
of Missouri and Illinois, light and variable winds along with clear
skies will allow for widespread frost development in this area as
temperatures dip down into the low to mid 30s. Could see isolated
areas where temperatures drop a bit below freezing, especially in
the eastern Ozarks. So a frost advisory is likely for parts of the
area tonight, but will leave that for the day crew to take one last
look at things and to get past the current headlines first.

On Monday, after a chilly start, warm southwesterly surface winds
will allow temperatures to warm up into the mid 60s to low 70s,
which is around the 90th percentile of available model guidance.

Byrd
&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 323 AM CDT Sun Apr 21 2024

By Monday night, the upper level shortwave, as well as associated
surface low, that is sliding southeast into the Great Lakes
region will drag a cold front into northwestern Missouri by 12z
Tuesday. There continues to be good agreement among the
deterministic models with the timing of this front, with it
sliding through the area during the day on Tuesday. Showers and a
few storms are still expected with it. However, despite a 60 to 80
percent chance of precipitation across most of the region,
rainfall amounts will be on the low side, with less than 20
percent of the LREF ensemble members indicating that QPF will be
over a quarter of an inch.

Highs on Tuesday will depend on the timing of the cold front and
when the precipitation develops and moves through. For now highs
will be in the mid 60s to mid 70s.

Then dry weather returns for mid week as a surface ridge builds in
once again. However, another system is still progged to move on
shore into the Desert Southwest with the upper trough deepening,
then eventually lifting out towards the region late in the work
week.

In the meantime low level moisture will be on the increase with
showers and storms developing on the nose of a low level jet across
OK and AR and spread northward across the region during the day on
Thursday. Then as the first in a series of shortwaves (associated
with the Desert SW system) lifts northeast towards the region on
Friday, the latest cluster analysis indicates differences in
location, strength and timing of each round. So stuck with the
latest NBM solution with rain chances Friday through Saturday.

Byrd

&&

.AVIATION...  (For the 18z TAFs through 18z Monday Afternoon)
Issued at 1205 PM CDT Sun Apr 21 2024

Dry, VFR conditions are forecast through Monday morning. Northwest
winds will slacken very late this afternoon and early evening
before becoming light/variable as a surface ridge of high pressure
approaches from the west. By Monday morning, this ridge shifts off
to the southeast, with winds turning to the southwest and
increasing in speed closer to 10 knots.

Gosselin

&&

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

$$

WFO LSX