FXUS63 KLSX 031929

AFDLSX



Area Forecast Discussion

National Weather Service Saint Louis MO

229 PM CDT Thu Jul 3 2025



.KEY MESSAGES...



- Seasonably warm and relatively humid conditions will persist

  through Saturday with afternoon heat index values reaching the

  mid-90s to near 100 F.



- Largely dry conditions will persist into Saturday, including 

  the 4th of July. Saturday evening into next week, there will be 

  multiple opportunities for showers and thunderstorms.





&&



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

Issued at 221 PM CDT Thu Jul 3 2025



An upper-level ridge, currently positioned over the Central/Northern 

Plains this afternoon, will shift eastward into the Mississippi 

River Valley tonight through Friday/4th of July. Large-scale 

subsidence generated by this incoming ridge and a capping 

inversion will keep the chance of any isolated afternoon shower or

thunderstorm low (less than 15 percent) with "convection" likely 

limited to just diurnal cumulus and altocumulus this afternoon/ 

evening and Friday. As a surface anticyclone departs, low-level 

flow will also become more southerly by Friday, aiding the ongoing

gradual warming trend with high temperatures around 90 to the 

mid-90s F nearly CWA-wide. With increasing moisture, dewpoints 

will also be slightly rising overall, but deep BL mixing during 

the afternoon will limit peak heat index values in the mid-90s to 

near 100 F.



Pfahler



&&



.LONG TERM...  (Saturday through Next Thursday)

Issued at 221 PM CDT Thu Jul 3 2025



The upper-level ridge will continue eastward into the Great Lakes 

and Mid-Atlantic while de-amplifying over the holiday weekend, 

allowing a weakening trough to traverse the Mid-Mississippi River 

Valley late Saturday into Sunday, accompanied by a weak cold front 

on Sunday. Around 20 to 40 percent of ensemble model membership have 

showers and thunderstorms reaching/developing across central, 

northeastern MO and west-central IL Saturday evening into night. 

However, on Sunday more focused low-level forcing with the cold 

front and less convective inhibition leads to 40 to 60 percent of

membership depicting showers and thunderstorms over a larger 

portion of the CWA. That being said, it is not particularly clear 

what the coverage will be given that large-scale forcing will not 

be strong. With very weak deep-layer wind shear (~10 kt), 

unorganized, pulse thunderstorms are expected which could contain 

localized gusty winds and downpours, but organized severe 

thunderstorms are unlikely. Saturday's temperatures are forecast 

to be similar to Friday, except slightly cooler across 

northeastern, central MO and west-central IL with greater clouds 

and shallower BL mixing. On Sunday, high temperatures should be 

slightly cooler across much of the CWA but confidence in exact 

values is lower due to the presence of the front and showers and 

thunderstorms.



Through next week, global model guidance is in general agreement 

that time-mean upper/mid-level flow will make a gradual transition 

from quasi-zonal to northwesterly with some semblance of Sunday's 

front wavering around the Mid-Mississippi River Valley. This pattern 

will be favor multiple opportunities for showers and 

thunderstorms as a series of mid-level perturbations or MCVs 

traverse this flow; however, the timing of these features and the 

location of the front at any given time is uncertain. Throughout 

next week ensemble model-based probabilities of showers and 

thunderstorms vary between 20 and 60 percent, although there 

appears to be a relative minimum Monday night/Tuesday morning with

a signal for the front to shift south of the CWA and the region 

to be between waves. NBM interquartile high temperature ranges 

have narrowed for next week to around 3 to 5 F, closing in on 

approximately average, but if there are more widespread 

precipitation and clouds any of those days, temperatures could 

easily end up even cooler.



Pfahler



&&



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

Issued at 1228 PM CDT Thu Jul 3 2025



Dry and VFR flight conditions will persist through the TAF period 

with largely diurnal cumulus overhead, and nighttime conditions less 

favorable for river valley fog. Winds will remain light but become 

more southerly on Friday behind a departing surface high pressure 

center.



Pfahler



&&



.LSX WATCHES/WARNINGS/ADVISORIES...

MO...None.

IL...None.

&&



$$



WFO LSX