Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 240926
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
413 AM CDT Sun Mar 24 2024

.KEY MESSAGES...

- Mild temperatures will combine with strengthening winds and
relative humidity below 25% over sections of central and southeast
Missouri this afternoon, which will support rapid spread of open
flames. A Red Flag Warning will be in effect from 1 p.m. to 7 p.m.
for affected areas this afternoon. Areas outside the Red Flag
Warning iwill still have conditions supporting elevated fire danger.

- Rain chances will extend from late tonight through early Tuesday.
The highest potential (90-100%) will progress west to east Monday
morning through Monday night. Rainfall totals of 1-1.5 inches could
fall over much of the area with exception to northeast Missouri.


&&

.SHORT TERM...  (Through Late Monday Afternoon)
Issued at 407 AM CDT Sun Mar 24 2024

A broad overview of the CONUS shows an inverted surface ridge
extending south through the Great Lakes into the Tennessee
Valley. Meanwhile, surface low pressure is beginning to move east
of the central Rockies with an abundance of mid/high clouds
streaming northeastward into the southern Plains. Model soundings
indicate this will be the trend through the day with increasing
moisture in the 10k-20k ft. layer. Plenty of dry air rests below
this with dewpoint depressions widening below 10k ft. and surface
dewpoints largely in the 20s. RH values will fall below 30% west
of the Mississippi River with value over portions of central and
southeast Missouri falling below 25%. The combination of very dry
air, increasing winds and observations of dead fuels below 9%
yesterday, there was enough confidence to warrant a Red Flag Warning
from 18z- 00Z this afternoon over sections of central, south-central
and east-central Missouri. The elevated fire danger still exists for
locations outside the Red Flag Warning over much of the remainder
of the area.

The system over eastern Colorado will round the base of a broad
upper level trough and track northeast through the central Plains
today into tonight. A tongue of moisture will advect northward into
the central Plains with dewpoints rising into the 50s. The elongated
axis of moisture will encounter enough dry that runs as far west as
the Mississippi Valley, holding precipitation west of the
forecast are through late tonight. Moisture will deepen overnight
into early Monday with saturation occurring in the lowest 10k ft.
over central Missouri between 06z-12z tonight. This trend will
continue eastward as a surface to mid-level pre-frontal trough
line up almost north to south. Upper ascent increases fairly
rapidly overnight into Monday as several upper level impulses run
ahead of the system and eject northeast at the eastern edge of the
trough.

Short/medium range guidance is in good agreement showing rainfall
quickly developing over southwest Missouri, tracking to the east-
northeast and expanding in coverage in time. Several deterministic
models project a broad swath of 1-1.5 inch amounts covering much of
the CWA with exception to sections of northeast Missouri, where 0.50-
0.75 is still possible. Multi-run overviews of the ensemble guidance
(ECMWF/GFS/Canadian) shows that not only have 1+ inch totals been
consistently forecast over much of the CWA, these totals have
broaden in their westward extent. Where prior forecasts limited
totals to near 0.50 an inch near Columbia, recent runs have shifted
the access of beneficial rain slightly westward. It is notable that
the Canadian, while the outlier, does have 2-3 inch amounts within a
number of its members. While convection is expected to be
widespread, MUCAPE values of 100-400 J/kg accompany the deeper
moisture (10k ft.) and PWAT value above 1 inch. There may be brief
periods of moderate to perhaps heavy rain during the height of
the rainfall Monday into Monday evening.


Maples

&&

.LONG TERM...  (Monday Night through Saturday)
Issued at 407 AM CDT Sun Mar 24 2024

Widespread rainfall will continue into the early part of the long
term period, moving east of the Mississippi River Monday night into
Tuesday morning. While a few showers could lingering through
sunrise, measurable rainfall is expected to shutoff by mid-morning
Tuesday.

A cold front will trail the system, bringing in a cooler than
normal airmass through midweek. In fact, the upper level trough
will be broad enough to encompass almost all of the Lower 48
states Tuesday. By Wednesday, the western extent of the trough
gives way to a developing ridge that begins to amplify over the
Rockies. Surface high pressure builds into the mid-Mississippi
Valley in advance of the upper ridge, which will work eastward
through late week. As the surface high move into the southeastern
U.S., return flow at the surface will draw gradually warmer air
into the area with near to slightly above normal temperature
Thursday. The axis to a mid-level ridge and strengthening
southwesterly flow then bring much warmer air by Friday into next
weekend. What initially looked like another chance of rain Friday
is beginning to quickly trend lower. The active track seems remain
a bit further north as a weak surface low lacks moisture and any
real support for rainfall. While the NBM does have low end
(15-30%) probabilities late week into early next weekend, the
trends are drier and warmer.


Maples

&&

.AVIATION...  (For the 06z TAFs through 06z Sunday Night)
Issued at 1040 PM CDT Sat Mar 23 2024

VFR conditions continue with a southeast breeze through the night.
Some high level moisture is streaming through but very little of
this is reaching the ground and cloud bases are above 10,000 FT.
Winds pick up out of the SSE Sunday morning, gusting to 20 or 30KT
by midday for most sites. These winds continue deep into the
evening on Sunday, but if surface winds are able to diminish and a
low level inversion set up, we could see some low level wind shear
as winds aloft increase Sunday night.

Kimble

&&

.FIRE WEATHER...
Issued at 412 AM CDT Sun Mar 24 2024

A Red Flag Warning will go into effect at 1 p.m. today through
7 p.m. this evening as a result of sustained southeast winds of
20 mph, gusts up to 30 mph, minimum RH values below 25%, dry fuels
and warmer temperatures. Elsewhere, elevated fire danger is still
expected outside the Red Flag Warning for Missouri locations
through this afternoon.

Byrd


&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Red Flag Warning from 1 PM this afternoon to 7 PM CDT this
     evening for Boone MO-Callaway MO-Cole MO-Crawford MO-Dent
     MO-Franklin MO-Gasconade MO-Moniteau MO-Osage MO.

IL...None.
&&

$$

WFO LSX


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