Area Forecast Discussion
Issued by NWS St. Louis, MO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45
000
FXUS63 KLSX 281141
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
641 AM CDT Thu Mar 28 2024

.KEY MESSAGES...

- Temperatures warm through at least Friday. Widespread 60s and
  70s are expected.

- A front stalls across the region this weekend. The front will
  serve as the dividing line between warm (near 80) weather to the
  south and cooler (in the 60s) weather to the north. It could
  also be the focus for showers and thunderstorms this weekend.

- A more organized threat for showers and thunderstorms comes
  Sunday into Monday. Strong to severe thunderstorms are possible.


&&

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 247 AM CDT Thu Mar 28 2024

Surface high pressure slides south this morning while ridging aloft
begins to move in from the west. We`ll see a rebound in temperatures
today with widespread 60s expected on a light southwest wind. The
warmest temperatures are likely in the St Louis area where
downsloping off the Ozarks aids in low level mixing. While
temperatures are rebounding, moisture return is only just beginning
across the Plains where recycled moisture will begin to push
northward today to the east of a developing lee trough. With the
last front having cleared the Gulf Coast it will take some time to
pull richer Gulf of Mexico moisture back in. The initial limited
moisture return is mainly to our west today, so we`ll see some
pretty low humidity values this afternoon. Thankfully, though, winds
remain light enough to reduce the fire weather threat. We`ll see
warmer overnight lows tonight due to the continued light winds
preventing a strong inversion tonight.

We`ll see another day of warming and another day of moisture return
on Friday, this time the moisture begins to make it into our area.
Temperatures warm into the 70s and dewpoints rise into the 40s to
near 50. Southerly winds will be noticeably breezy on Friday as the
pressure gradient tightens ahead of an approaching front. This front
is being driven by a shortwave trough passing through the northern
Plains. Moisture pushing through our area will be pulled into this
trough and bring an increased chance of showers and thunderstorms
as the cold front approaches Friday night. This threat is
greatest to our north where there is better support from mid level
lift with the shortwave trough, but some of this activity could
extend into northeast Missouri and through central Illinois as
well.

Kimble

&&

.LONG TERM...  (Friday Night through Wednesday)
Issued at 247 AM CDT Thu Mar 28 2024

As the shortwave trough moves east, the cold front will settle
southward into our region where it is expected to stall for the
next couple of days. To the west, a large trough in the
southwestern US will cause a transition to southwest flow aloft,
maintaining a lee trough in the southern High Plains and
continuing to pull Gulf of Mexico moisture northward. This
northward pull of moisture into the stalling front could lead to
some showers and thunderstorms mainly along and north of the
front. The chances are higher during the overnight hours Saturday
and especially Sunday evening as the low level jet further aids
that moisture transport. Deterministic forecast soundings are not
necessarily impressive yet, but given the synoptic situation it
would make sense for elevated instability to increase such that
some hailers would be possible Sunday night. We`ll also see a
contrast in temperatures on either side of the front. To the south
in the warm sector it will be warm and increasingly humid,
feeling more like late spring or early summer. To the north it
will be much cooler with more widespread clouds.

A more substantial shortwave trough ejects out of the southwestern
US trough on Monday. This will lead to the best rain chances of the
period as this wave will bring more large scale lift and set the
front in motion again. There`s still considerable uncertainty on how
things evolve as this shortwave moves through, mainly centered on
how quickly it moves through and where the warm sector exists during
peak heating. By this time we will have had several days of moisture
return across the southern plains, fueling instability in the warm
sector which should also push northward a bit. There will be
plenty of shear for supercells as the southwesterly mid level flow
increases over top of a southerly surface flow creating a
situation in which all severe weather hazards would be possible.
Convective initiation along the dryline in Kansas and Oklahoma
Monday afternoon would send storms northeast from there, but
there could also be storm initiation along the warm front across
northern Missouri into central Illinois, again depending on the
timing of the wave and evolution of the warm sector ahead of it.
Locally heavy rain is also possible considering the increasingly
moist air mass especially if we see multiple rounds of
thunderstorms in some areas.

While there is certainly the potential for severe thunderstorms to
affect our area on Monday into Monday evening, it`s not a slam dunk
either. If the shortwave moves in too quickly or too slowly then the
threat may not be in our area. Cloud cover could also prevent
strong destabilization in the warm sector while more sun could
just add more fuel. Either way, though, this does look like the
best chance for a more widespread rainfall, although due to the
convective nature of it we can`t guarantee everyone will see rain.

After Monday`s trough moves through it will shove a cold front
through the area bringing cooler weather for the middle of next
week.

Kimble

&&

.AVIATION...  (For the 12z TAFs through 12z Friday Morning)
Issued at 640 AM CDT Thu Mar 28 2024

Light southwest winds expected today under a mostly clear sky. A few
gusts to 15KT or so are possible during the afternoon with any gusts
diminishing this evening.

SPECIFICS FOR KSTL:

Maples

&&

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

$$

WFO LSX


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.