708
FXUS63 KLSX 120749
AFDLSX

Area Forecast Discussion
National Weather Service Saint Louis MO
249 AM CDT Mon May 12 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms are expected today mainly
  across southeastern Missouri and Southwestern Illinois. There is
  a low chance (30%) for isolated showers and thunderstorms
  tomorrow.

- While temperatures will be mostly seasonable Monday and
  Tuesday, they will warm notably Wednesday and especially on
  Thursday, when afternoon highs around 90 degrees are forecast.


&&

.SHORT TERM... (Through Tuesday Night)
Issued at 247 AM CDT Mon May 12 2025

Water vapor imagery this morning shows that the Rex Block that has
been driving our weather the last couple of days is beginning to
break down as the block`s cutoff is moving northward toward the
Middle Mississippi Valley as a trough edges into the ridge across
the Intermountain West. With the northward drift of the cutoff,
moisture is deepening and lift is increasing across the CWA,
resulting in the arcing band of showers and thunderstorms moving
into the area from the southeast. As the cutoff moves north-
northeastward through the day, scattered showers and thunderstorms
will continue to move southeast to northwest across the CWA, with
the greatest coverage expected across southeastern Missouri and
southwestern Illinois where moisture and lift are greatest.

As the greater lift moves eastward this evening and instability
wanes with the setting sun, convective coverage will decrease, with
a lull expected overnight. With the cutoff drifting into the Ohio
Valley tomorrow and weakening, lift will continue to decrease across
the CWA. However, there may be enough lift paired with afternoon
instability to produce widely scattered showers and perhaps a
thunderstorm if convection can break the cap noted in several model
soundings. As with Monday, convection will diminish as instability
decreases with the onset of evening.

Elmore

&&

.LONG TERM... (Wednesday through Sunday)
Issued at 247 AM CDT Mon May 12 2025

As the cutoff continues to move northeastward away from the region
on Wednesday, southwesterly flow will become increasingly
established over the Middle Mississippi Valley. Within this
southwesterly flow, warmer air will advect into the region aloft,
with 850 mb temperatures climbing to right around 15 degrees C per
ensemble means. This is a degree or two cooler than previous
initializations, and surface temperatures have correspondingly come
down as well, with ensembles clustering in the mid 80s for most
locations Wednesday afternoon. Heat only builds on Thursday as 850
mb temperatures surge to around 20 degrees C ahead of a system
moving through the Midwest, correlating with surface temperatures
around 90 degrees.

The system on Thursday continues to be reflected in the majority of
guidance, as a leading shortwave within an upper-level trough
quickly moves through the Northern Plains and Upper-Midwest, its
surface low following a similar trajectory. A Pacific cold front
associated with this low is set to sweep through the Middle
Mississippi Valley during the day Thursday. Ahead of this front,
guidance consensus remains that SBCAPE could climb as high as 3,000-
4,000 J/kg among deep layer shear of 40 kts or more - a potent
environment for severe thunderstorms. However, there still remain
several limiting factors for convective initiation, such as capping,
poor low-level lapse rates, lack of moisture in the low to mid-
levels, and upper-level clouds seen in several soundings. Therefore,
confidence in convective initiation, and therefore severe
thunderstorms, remains very low. However, if storms are able to
form, the environment will support strong to severe storms.

The trough continues to phase eastward on Friday as subsequent
shortwaves round its base. A second cold front looks to move through
the region, but whether or not convection forms along it in our CWA
will depend on its speed and thusly, its location during peak
heating or when the low level jet ramps up in the evening.
Confidence is increasing that this cold front will make it through
the CWA Friday before it stalls, as ensemble means continue to cool
temperatures Friday through Sunday relative to Thursday`s warmth.
Given quazi-zonal flow aloft through the weekend, the front is
likely to drift about the region, leading a threat for repeated
rounds of convection if the front is close enough to the region.

Elmore

&&

.AVIATION...  (For the 06z TAFs through 06z Monday Night)
Issued at 1048 PM CDT Sun May 11 2025

MVFR ceilings will overspread southeast and east central Missouri
as well as southwest and south central Illinois beginning around
09Z and continuing through 15-17Z. Some IFR ceilings are also
likely across the higher terrain of the eastern Ozarks Monday
morning. Scattered showers will also spread to the northwest
along with the low clouds through the morning. A few waves of
scattered showers and isolated thunderstorms will continue into
the afternoon. Rain should mostly dissipate by 00Z or shortly
thereafter. MVFR ceilings are expected to improve to VFR during
the late afternoon/early evening.

Carney

&&

.CLIMATE...
Issued at 1048 PM CDT Sun May 11 2025

Record maximum temperatures and warmest minimum temperatures
for May 14 and 15.

                MAY 14      MAY 15

ST Louis:
MAXIMUM         93 2013     94 1944
WARMEST MIN     73 1915     72 2013


Columbia:
MAXIMUM         90 2022     90 1944
WARMEST MIN     67 1941     71 1941


Quincy:
MAXIMUM         94 1915     93 1944
WARMEST MIN     66 1932     69 1962


&&

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

$$

WFO LSX