Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 260833
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
333 AM CDT Tue Mar 26 2024

.KEY MESSAGES...

- Below normal temperatures are still expected through early Thursday
  morning. The coldest temperatures look to be Tuesday night into
  early Wednesday morning with lows ranging from the mid-20s to
  low-30s. A hard freeze is favored (50-90%) over central and
  northeast Missouri into west-central Illinois. Another freeze
  and perhaps a frost is expected Wednesday night into Thursday
  morning with 50-90% chance of freezing temperatures (<=32F).

- A warm-up commences on Thursday with above normal temperatures
  through the weekend into early next week, and shower and
  thunderstorm chances returning on Friday and continuing into
  Monday.

&&

.SHORT TERM...  (Through Late Wednesday Afternoon)
Issued at 316 AM CDT Tue Mar 26 2024

The rain band associated with the warm conveyor belt and large scale
forcing has moved to the east of the CWA early this morning in
tandem with the progression of the upper trof. The attendant cold
front has pushed into central MO at 08z, and will move eastward
through eastern MO and western IL this morning providing the
potential for isold-scattered showers as it advances, exiting the
CWA by late morning. An additional chance of light rain and
perhaps a stray wet snowflake will impact northeast MO this
morning as the wrap-around precipitation lifts northeast. Today
will be a big change from yesterday with much cooler temperatures
owing to with good post-frontal CAA via gusty southwest to west
winds and extensive stratus.

The main story tonight through Wednesday night will be the colder
temperatures. The broad deep trof will meander eastward with another
short wave rotating through it to our north bringing a thrust of
even colder air into the area tonight as our winds shift to the
northwest. There is some uncertainty how low the post-frontal
stratus will persist, and odds are if it clears anywhere it will
be through central MO. Clouds or not, the air mass will bring
freezing temperatures tonight into early Wednesday morning for a
good portion if not all of the CWA. Perhaps the only area there is
a question whether we see mins aob 32F is from downtown St. Louis
into southwest IL where the NBM has probabilities for <= 32F
around 25-60%. Elsewhere the probability is high for not only a
freeze but a hard freeze with the NBM probabilities of <= 28F
averaging 50-90+% across central MO and portions of eastern MO and
west-central IL.

Temperatures will remain below normal on Wednesday with the surface
high pressure system settling into the Mid MS Valley, and any
lingering stratus on Wednesday morning gradually diminishing and
clearing eastward.

Glass

&&

.LONG TERM...  (Wednesday Night through Monday)
Issued at 316 AM CDT Tue Mar 26 2024

We will have to worry about one more cold night on Wednesday
night into early Thursday morning. The expansive surface high
will ooze east but still dominate the CWA. Although some of the
winds may begin to come around to the southwest overnight, they
look quite light and I think we should still have good radiational
cooling. The mins probably won`t be as uniform as tonight with
lows of 27-33F and some areas seeing a hard freeze. NBM
probabilities of mins <=32f range from 55-90%. There is decent
frost potential as well with light winds.

On Thursday we say goodbye to the cold, hopefully until next fall. A
pattern change will begin to get underway with height rises aloft as
the upper trof begins to depart through the eastern U.S. and upper
ridging advances into the area from the Plains. In response the
anticyclone retreats south-southeast and low-level WAA gets underway
marking the beginning of a good warm-up and return of above normal
temperatures with highs Thursday some 10-15 degrees warmer than
Wed.

The pattern change proceeds heading into the weekend as a deep
positively tilted upper trof evolves off West Coast and eventually
moves into the western CONUS, while some assembalance of broad
mid- upper ridging becomes established through the Nation`s
midsection. This will allow the warm-up to proceed but how warm is
in question as a west-east frontal boundary will move into the
CWA on Saturday and then waver about into early next week. The NBM
interquartile range is entirely above normal but the spread is as
much as 12-20 degrees with the upper quartile in the 80s. The
boundary will provide the potential for showers and thunderstorms
Saturday into Monday, however at this juncture it appears there
could be plenty of dry time. The high heights aloft appear to be
resulting in a good deal of CIN for surface-based convection,
however the LLJ and perhaps passing weak disturbances aloft could
provide the impetus for elevated storms.

Glass

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1019 PM CDT Mon Mar 25 2024

Rain is pushing out from west to east and should clear south-
central Illinois over the next 3-4 hours roughly. The cold front
is forecast to move through overnight tonight into early Tuesday
morning. Cannot rule out a some showers with this front, but
coverage is too low to mention anything in the TAFs. The winds
should shift from the south/southeast to the southwest behind the
front, with some gusts around 25 knots. These gusts should subside
late afternoon. Ceilings will also drop behind the front, with
bases around 1500-2500 feet AGL. These ceilings will gradually
rise throughout the day, with VFR conditions areawide likely by
late afternoon/early evening on Tuesday.

Gosselin

&&

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

$$

WFO LSX


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