Area Forecast Discussion

515
FXUS63 KLSX 030848
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
248 AM CST Sat Jan 3 2026

.KEY MESSAGES...

- Near to slightly above average temperatures will persist this
  weekend, before temperatures warm to well-above average Monday
  onward.

- Flurries, sprinkles, or a few sleet pellets are possible this
  morning, but the next significant opportunity for rain will be
  Wednesday night into early Friday (40 to 60 percent chance).


&&

.SHORT TERM...  (Through Late Sunday Afternoon)
Issued at 244 AM CST Sat Jan 3 2026

Although the coverage of stratus is minimal this morning compared to
Friday morning, widespread mid-level clouds still blanket the CWA to
start the day. An upper-level shortwave trough, evident upstream on
water vapor imagery, will traverse MO this morning. Sprinkles,
flurries, and a few sleet pellets that have been observed so far
this morning will continue to be possible ahead of this trough.
However, a layer of dry air below weakly forced, precipitating
clouds will limit the amount of hydrometeors reaching the surface
with any measurable/accumulating precipitation very unlikely (less
than 10 percent chance per HREF). Clouds will clear across most of
the CWA by the afternoon as subsidence behind the shortwave trough
arrives and drier northwesterly flow prevails. With increasing
insolation, high temperatures are anticipated to be warmer than
Friday and in the mid-30s to low-40s F.

A surface high pressure center will dominate the Mid-Mississippi
River Valley tonight. Upper-level clouds will likely be overhead but
should be thin and permitting enough radiational cooling for low
temperatures in the low-20s F by Sunday morning. As the high
pressure center shifts to the east on Sunday, low-level flow is
anticipated to become more southeasterly to southerly through the
day, enduring WAA. This WAA will be competing with thick upper-level
clouds associated with a passing subtle shortwave trough, but the
NBM is tightly clustered on temperatures a couple degrees F warmer
than today.

Pfahler

&&

.LONG TERM...  (Sunday Night through Friday)
Issued at 244 AM CST Sat Jan 3 2026

Upper-level flow will transition from northwesterly to broadly
anticyclonic Sunday into Monday, permitting low-level flow to become
southwesterly with strengthening WAA that persists through Tuesday.
This evolution will result in substantially warmer temperatures
Monday through Tuesday with high temperatures in the 50s to around
60 F on Monday and upper 50s to mid-60s F on Tuesday as 850-hPa
temperatures rise above the 90th climatological percentile. NBM
interquartile ranges (IQRs) of temperatures are also 5 F or less,
increasing confidence in these temperatures. The temperature
forecast is slightly less certain after Tuesday with NBM IQRs
increasing as a result of a weak cold front entering the CWA
sometime late Tuesday and potentially lingering. That being said,
even the 25th percentile remains well-above average beyond Tuesday.

Global model guidance is consistent with the upper-level flow
pattern across the CONUS amplifying as longwave troughing occurs
above the Intermountain West, favoring deep southwesterly flow
across the central CONUS. Within this flow, one or more shortwave
troughs are projected to quickly track across the Mid-Mississippi
River Valley, providing the next opportunity for substantial
rainfall across the region. The timing, amplitude, and track of the
shortwave troughs vary among model guidance, but ensemble model-
derived 24-hour probabilities of measurable rainfall are now 60 to
90 percent in a window from Wednesday night through Friday morning.
NBM probabilities of over 0.5" of rainfall are also highest across
the southeastern half of the CWA at 50 to 60 percent. The threat of
thunderstorms will also need to be monitored with deterministic
model guidance advertising up to 500 J/kg of MUCAPE.

Pfahler

&&

.AVIATION...  (For the 06z TAFs through 06z Saturday Night)
Issued at 1039 PM CST Fri Jan 2 2026

Predominantly dry and VFR flight conditions are expected throughout
the TAF period; however, there is a 50 percent chance of a brief
period of MVFR ceilings at KCOU and KJEF Saturday morning and a few
sprinkles, flurries, or sleet pellets cannot be ruled out as well.
Light northeasterly winds will back to northerly on Saturday.

Pfahler

&&

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

$$

WFO LSX

NWS LSX Office Area Forecast Discussion