Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 220351
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1051 PM CDT Thu Mar 21 2024

.KEY MESSAGES...

- A band a light rain will move across the area Friday afternoon
  and evening (40-80% chance). A better chance (90-100%) for
  widespread rain and a few thunderstorms will be on Sunday night
  into Monday night as a cold front moves through the area.

- Temperatures will vary up to 20 degrees from normal through next
  week as a series of fronts move through the area.


&&

.SHORT TERM...  (Through Late Friday Night)
Issued at 301 PM CDT Thu Mar 21 2024

Latest surface analysis is showing a high over the Great Lakes with
a stationary from extending from low pressure over the Central High
Plains into the southeast CONUS.  Winds were southeasterly across
Missouri and Illinois keeping a cool, dry flow over the area.   The
satellite is showing some mid-high clouds moving east across the
area with radar showing a few light returns across Missouri and
Illinois.  We have received a few reports of virga today which
confirms just how dry the low levels are with the most recent
dewpoint at KSTL being 18 with a RH of 26%.

Water vapor is showing a shortwave over Montana that the HREF shows
dropping down across the CWA by late tomorrow afternoon.  The
combination of lift provided by the trough and an attendant cold
front will be enough to bring a band of light rain through the area
late tomorrow afternoon and evening.  Moisture will be limited, so
still expect any QPF amounts to be less than 0.10" with the greatest
amounts across northeast Missouri and west central Illinois during
the late afternoon and early evening. The precipitation will diminish
during the evening as the trough moves off to the east.

Temperatures tonight into tomorrow will be warmer as the wind turns
out of the south.  Highs tomorrow will be about 10-20 degrees above
normal before the front moves through.

Britt

&&

.LONG TERM...  (Saturday through Next Thursday)
Issued at 301 PM CDT Thu Mar 21 2024

Saturday still looks dry at this point as the NAM/GFS are showing a
shortwave ridge moving across Missouri and Illinois during the day.
Then we still look on track to get rain starting Saturday night and
Sunday over central and northeast Missouri into west central
Illinois as the operational models are showing an increase in mid
level ascent and low level moisture ahead of the mid-level trough
entering the Plains.  The best chance for rain and a few
thunderstorms will not come until late Monday night into Tuesday
night when a pronounced shortwave trough and an attendant front will
move across the area when PWATS climb above 1".  Moved PoPs in the
90-100% range during this time period with a slight chance of
thunderstorms, though it is unclear at this time how strong the
storms will be as forecast values of MUCAPE are <500 J/kg.  Current
forecast storm total QPF with this system is in the 0.5-1.25" as
there will be decent lift and modest moisture, but the system will
be moving through the area fairly quickly.  Also could not rule out
that there would be some wet snowflakes as the system moves into the
area Saturday night and Sunday with evaporative cooling.  Do not
expect accumulations as the surface and ground temperatures are
expected to be warm.  The operational GFS is showing a second,
stronger shortwave moving through the Mid South on Tuesday which
would develop a stronger surface low to our southeast and help
linger precipitation over our southeastern CWA on Tuesday, but this
solution is not supported by many of the GEFS members. Much of the
rest of the next week looks dry as a ridge builds into the Midwest.

Temperatures will cool down on Saturday behind Friday`s front but
will warm back up slightly on Sunday and Monday ahead of the next
front.   Temperatures Tuesday and Wednesday will be close to normal
before warming back above normal.  The NBM IQR at STL is 10 degrees
or more next week which lowers overall confidence in the forecast
for next week.

Britt

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1050 PM CDT Thu Mar 21 2024

VFR conditions continue overnight and through much of the day
tomorrow. One low pressure system slides by to our south while
another trough passes by to our north. The northern one will send
a cold front through our area during the day on Friday arriving
first at Quincy and in central Missouri before proceeding into the
St Louis metro during the evening. This will shift winds to the
north and becoming gusty through Friday night. Confidence has
increased that lower ceilings will also be observed behind the
front, likely in the MVFR range. Some light rain or drizzle is
also possible behind the front Friday night.

Kimble

&&

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

$$

WFO LSX


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