Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250925
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
425 AM CDT Mon Mar 25 2024

.KEY MESSAGES...

- Widespread, beneficial rainfall is expected (100%) today through
  early Tuesday. Rainfall totals of 1-1.5 inches are forecast
  over a broad area with locally higher amounts possible.

- Southeast winds will increase this morning, becoming sustained
  at 20 to 30 mph and gusting up to 45 mph at times. A Wind
  Advisory has been issued from 7AM through 7PM today.

- Below normal temperatures are expected through midweek. The
  coldest temperatures look to be Tuesday night into Wednesday
  morning with lows ranging from the mid-20s to low-30s. A hard
  freeze is favored (50-70%) over central and northeast Missouri
  into west-central Illinois.


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 412 AM CDT Mon Mar 25 2024

Regional analysis depicts a broad upper trough digging into the
central Plains with surface low pressure centered over central Kansas
early this morning. Water vapor and IR satellite imagery show
moisture being ejected northward out of the western Gulf with a
growing mass of cloud cover running from northeast Texas through
southern Iowa. As of 09z, surface dewpoints climb from the upper
20s and low-30s over the mid-Mississippi Valley to the mid-50s
over Kansas and Oklahoma. Already, surface winds are beginning to
gust early this morning and are expected to continue to strengthen
as the pressure gradient tightens over the area today. Gusts as
high as 45 mph are possible with a Wind Advisory going into effect
at 7AM.

The surface low will continue to track northeast today, entering
northwest Missouri/southern Iowa by Monday morning. As mentioned in
prior AFDs, widespread rainfall is expected to be focused along a
pre-frontal trough as the actual cold front lags back to the
west. Latest trends in all of the hi-res guidance have been
showing a broader shield of rainfall initializing slightly further
westward (central Missouri) before moving east/northeast today
into tonight. The north-south oriented tongue of higher moisture
will gradually work its way into the mid-Mississippi Valley with
deep saturation (10k ft. or greater) over much of the area. Given
the depth of the system, several pieces of vorticity spoke round
the upper level trough, providing ample upper ascent as mid-level
flow strengthens over top the pre-frontal trough. PWAT values
climb to 1-1.4 inches over any given location in the forecast
area for an approximately 6-9 hour duration. MUCAPEs have
consistently been forecast to be in the 100-400 J/kg range,
showing the possibility for a few rumbles of thunder and maybe a
localized brief heavy downpour embedded within the overall shield
of precipitation. While a large chunk of the forecast area will
land in the 1-1.5 inch range for total rainfall, the setup makes
it plausible that some locations could end up with locally higher
amounts. CAMs are picking up on the potential for a narrow stripe
of higher totals generally running southwest to northeast from
Jefferson City to Quincy. PMM/LPMM usually do a good job at
retaining the potential for higher totals, which depict upwards of
2 inches or slightly more within this band.

Widespread rain will begin to shut off from west to east late
tonight into early Tuesday morning. However, the actual cold front
doesn`t arrive until early Tuesday. Therefore, a few isolated
showers could linger into the morning hours as fragmented
vorticity rotates around the departing low. Cold air will then begin
advecting into the region from the west and northwest. Tuesday
will likely be quite chilly with cold air advection accompanied by
gusty westerly surface winds gusting to around 35 mph. Its likely
that the warmest temperatures will be earlier in the day with
40s working in from west to east.

Maples

&&

.LONG TERM...  (Tuesday Night through Sunday)
Issued at 412 AM CDT Mon Mar 25 2024

The initial issue in the long term portion of the forecast will be
the cold nighttime temperatures Tuesday night into Wednesday morning
and again Wednesday night into Thursday morning. The key Tuesday
night will be how quickly skies can clear as surface high pressure
builds southeastward from the northern Plains. Global deterministic
guidance shows drier air moving in from the northwest with mid-level
moisture eroding from west to east Wednesday morning. Grand ensemble
probabilities for 28 degrees or colder are 50-70 percent over
sections of central and northeast Missouri, where clearing may be
quick enough to allow for better radiational cooling. The surface
high builds overhead through Wednesday, but we may actually be a
touch colder with mid-level ridging drawing in slightly warmer air
out of the southwest.

A warming trend begins Thursday with a return to above normal
temperatures Friday into next weekend. The question will be just how
far above normal temperatures climb. While there is a tight
clustering in NBM temperatures through Saturday, data quickly spread
Sunday into next week. The diverging data largely stems from the
handling of the mid-level ridge and position. GFS deterministic
guidance shows a strong mid-level ridge setting up over the
southeast CONUS, which eventually pushes 850mb temperatures near 20C
next weekend. On the other hand, the ECMWF was less pronounce with
the mid-level ridging pattern, even holding onto sub-zero air in the
mid-levels. The latest ECMWF run has backed off this solution
somewhat and while it is colder, it`s not as cool. Still, NBM
25th/75th quartiles quickly spread from 10 to 20 degrees Sunday into
Monday (60s vs. 80s), presenting quite a bit of uncertainty on the
magnitude of the warmth.

The pattern does look active heading into next week, however, as
global deterministic guidance shows a weak system passing through
the mid-Mississippi Valley late in the weekend with a slow-moving
cold front stalling somewhere in the region. A couple of shortwaves
eject eastward from a cutoff upper level low over the southwest
CONUS, which rides over a surface/mid-level boundary, resulting in
the potential for additional rainfall early next week.


Maples

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1053 PM CDT Sun Mar 24 2024

As the low level jet continues to ramp up with gusts diminishing
during the overnight hours, low level wind shear is likely. If gusts
persist, low level wind shear is not expected. Otherwise, southerly
winds will increase again on Monday morning and continue through
Monday evening with gusts upwards to 40 knots at times.

A weather system, bringing rain showers with embedded
thunderstorms will move across the region on Monday. KCOU and KJEF
will have a better likelihood of seeing embedded thunderstorms
Monday afternoon, however a few embedded thunderstorms cannot be
ruled out at KUIN, KSUS, KCPS, and KUIN. All terminals can expect
MVFR flight conditions with the passage of the weather system. IFR
ceilings are increasingly likely Monday evening as the showers
and embedded thunderstorms end.

MMG/Kimble

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Wind Advisory until 7 PM CDT this evening for Audrain MO-Boone
     MO-Callaway MO-Cole MO-Crawford MO-Franklin MO-Gasconade MO-
     Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-
     Marion MO-Moniteau MO-Monroe MO-Montgomery MO-Osage MO-Pike
     MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-
     Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-
     Shelby MO-Warren MO-Washington MO.

IL...Wind Advisory until 7 PM CDT this evening for Adams IL-Bond IL-
     Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey
     IL-Macoupin IL-Madison IL-Marion IL-Monroe IL-Montgomery IL-
     Pike IL-Randolph IL-Saint Clair IL-Washington IL.

&&

$$

WFO LSX


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