


Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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468 FXUS63 KLSX 040726 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 226 AM CDT Fri Jul 4 2025 .KEY MESSAGES... - Warm and humid conditions are expected today through Saturday. Temperatures fall slightly Sunday into Monday and remain fairly steady through next week. - Mainly dry conditions are expected through Saturday before chances of showers and thunderstorms increase late Saturday into Sunday. Probabilities for additional showers and thunderstorms extend through the upcoming week. && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 224 AM CDT Fri Jul 4 2025 A look around the region shows the center of surface high pressure sliding just to the east of the local area. In response, surface winds are veering out of the southeast to south from eastern Missouri westward through eastern Kansas. The surface high is trailed by amplified mid/upper level ridging that will position overhead today through Saturday. Southerly flow at the western side of the ridge is drawing moisture northward into the eastern Plains and will eventually shift eastward into the local area in coming days. Until then, subsidence will maintain dry conditions with mostly clear to partly cloudy skies. Expect temperatures to climb into the 90s areawide with urban areas squarely in the mid-90s. Heat index values will only be a few degrees warmer than actual air temperatures, along with an increase in surface flow. This may counter the moisture somewhat, serving to cool those outdoors better than the calm/variable winds of the last 24 hours. Saturday is another warm day with much of the daylight hours remaining dry. Latest data suggests slight chances (15-20%) will nudge into the western edge of the CWA by mid-morning Saturday. If this did occur, it`s likely to be remnant activity from the west, which would be expected to be going through a dissipating phase considering it being during the diurnal lull in instability and model sounding show air quickly drying from west to east. Timing tools show the best estimate for measurable rainfall will be around 5 p.m. Saturday evening and I`d say this may be at the earlier stage of potential as LREF shows 10-30% probabilities for measurable rainfall. Regardless of rainfall, cloud cover will be thicker to the west during the day Saturday. This keeps temperatures slightly cooler from central Missouri through west-central Illinois, where upper 80s are forecast. 90s will largely be confined to southeastern and east- central Missouri and southwestern Illinois. Lows will range from the upper 60s to low-70s. Maples && .LONG TERM... (Saturday Night through Thursday) Issued at 224 AM CDT Fri Jul 4 2025 Aside from the modest spread in temperatures , ensembles have been rather tightly clustered along with consistency in deterministic long range guidance with respect to increasing rain chances Saturday night into Sunday. This is the timeframe that the upper level ridge overhead begins to move east and deamplify as a train of troughs/shortwaves traverse the northern sections of the Lower 48. Guidance continues to show the first in the series of shortwaves moving into the Great Lakes while pushing a weakening cold front southward into the region. Potential for showers and thunderstorms will increase from north to south late Saturday into Sunday. What initially arrives is likely to be in the form of showers or weakening convection as surface instability drops in the overnight period. Sunday will include an increase in cloud cover from aforementioned activity, which will hold temperatures down slightly from Saturday. The front encounters a warm, moist air mass, but one that is initially capped Sunday morning and includes weak flow/shear. Once air become uncapped, scattered showers and thunderstorms reemerge during the afternoon and evening. The stalled boundary remains the focus for additional chances in the early portion of the week with diurnally driven thunderstorms that lack any real organization as a result of weak flow. The biggest question may center on Tuesday as surface high pressure passes to the northeast but may have enough influence to reduce the potential over eastern sections of the CWA. It seems that NBM guidance may be picking up on this a little more as the broad spread of low PoPs have come down some and the relatively higher potential to the southwest form a horseshoe around the influence of the surface ridge. I expect this to be resolved in time to provide better detail to the spread and magnitude of potential as Tuesday approaches. An additional consideration will be the mean upper level flow as ridging builds westward and strengthens over the Four Corners Region through midweek. Quasi-zonal upper level flow transitions to northwest flow over the central U.S., which may be conducive for driving shortwaves around the northern periphery of the ridge and into the Plains/Mississippi Valley. This is more likely to be the case by midweek, while early week potential is attributed to the stalled surface boundary. If so, the best potential for rainfall may actually be mid to late week. Maples && .AVIATION... (For the 00z TAFs through 00z Friday Evening) Issued at 632 PM CDT Thu Jul 3 2025 High pressure over the region provides light or calm winds and VFR conditions. The main concern is the potential for valley fog, but a warm evening and relatively low dewpoints is expected to prevent significant fog from occurring. Kimble && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX