FXUS63 KLSX 271900

AFDLSX



Area Forecast Discussion

National Weather Service Saint Louis MO

200 PM CDT Mon Oct 27 2025



.KEY MESSAGES...



- Widespread beneficial rain is expected (90 - 100% chance)

  tomorrow through Wednesday. Most of the area has a 70 - 80% 

  chance at seeing 0.50" or more rain.



- Cool, dry weather will end this week.





&&



.SHORT TERM...  (Through Late Tuesday Night)

Issued at 156 PM CDT Mon Oct 27 2025



Tonight will be the warmest night through at least late this week as 

low cloud cover keeps the region insulated. Most locations will see 

lows in the 40s, which, despite feeling chilly, is actually 5 - 10 

degrees above average for late October. The nightly "warmth" won't 

last long, however, as our next system will usher in cooler air as 

well as widespread rain.



Water vapor imagery shows the beginnings of our aforementioned next 

system in the form of an upper-level trough swirling over the 

northern Plains and Pacific Northwest. This feature will dig into 

the central Plains and Mid-Mississippi Valley overnight, while at 

the surface a cold front gains intensity and approaches Missouri 

from the west. Cyclogenesis along the front caused by upper level 

dynamics will result in the front tilting from near vertical to a 

more northwesterly-southeasterly orientation as it enters the CWA 

late Tuesday afternoon into evening. The deepening surface low is 

forecast to track either in our southern CWA or just south of it, 

leaving at least our southern counties below the system's warm 

conveyor belt by Wednesday morning. In this region, the better 

dynamics will support heavier rainfall and perhaps a rumble of 

thunder. The LREF and NBM ensembles reflect this, showing that 

locations within the warm conveyor belt (depicted as south of I-44, 

but subject to change based on where the low tracks) have up to a 

50% chance of seeing 1.00" of rain over a 24 hour period with the 

system. Though the probabilities for 1.00" drop dramatically 

elsewhere, the entire CWA has a high chance (70 - 80%) of seeing >= 

0.50" of rain in the 24 hours between Tuesday and Wednesday evening. 

This will be beneficial considering the vast majority of the CWA is 

in moderate or severe drought.



The cooler air ushered in with the front won't be extremely potent. 

850 mb temperatures are only forecast to drop about 4C, which will 

translate to us dropping from about 55 - 60 degree highs on Tuesday 

to 50 - 55 degree highs on Wednesday. It will likely feel much 

cooler to anyone unfortunate enough to step outside, however, given 

the cool rain and gusty (25 - 30 mph) pressure gradient winds.



Jaja



&&



.LONG TERM...  (Wednesday through Next Monday)

Issued at 156 PM CDT Mon Oct 27 2025



Thursday through Saturday are forecast to be dry and cool with highs 

largely in the 50s and lows in the 30s. Depending on how a surface 

high in the Plains behaves late this week into this weekend, winds 

may become light enough at night to support frost again. This is not 

written in stone yet, but is a possibility considering the 50 - 60% 

NBM probabilities of temperatures less than 36 degrees in portions 

of the area each morning.



Another cold front is forecast to dive through the region this 

weekend, but rain chances with this frontal passage are minimal. 

Most of the moisture in our CWA will be scoured out behind the mid-

week system, leaving this weekend's cold front little to work with. 

The cold front does look to usher in another bout of cool air, 

though uncertainty lies in how potent and long-lasting it is. This 

is reflected well in a 10 degree spread in the NBM high temperature 

interquartile range for Sunday.



Jaja



&&



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)

Issued at 1230 PM CDT Mon Oct 27 2025



Periods of drizzle are expected to dissipate early this

afternoon, leaving dry conditions until at least tomorrow morning.

Widespread rain is expected to near central Missouri tomorrow, so

added PROB30s for the end of the period. 



More notably, pesky stratus continues to sit atop the CWA with the

gradient between MVFR and IFR sitting basically right over the St.

Louis metropolitan terminals. For this reason, ceilings may bounce

between sub-1000 ft and 1000-1500 ft until late tonight when IFR

ceilings spread north again. Models suggest widespread LIFR 

overnight, but holding off on locking that in until newer guidance

comes in.



Jaja



&&



.LSX WATCHES/WARNINGS/ADVISORIES...

MO...None.

IL...None.

&&



$$



WFO LSX