535 FXUS63 KLSX 131127 AFDLSXArea Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 627 AM CDT Mon Oct 13 2025
.KEY MESSAGES...
- Near to above normal temperatures hold through at least Friday. A cold front brings progressively cooler air through the weekend.
- A majority of the week remains rain-free through Friday afternoon. Rain chances increase Friday night into Saturday (50-60%).
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.SHORT TERM... (Through Late Tuesday Afternoon) Issued at 320 AM CDT Mon Oct 13 2025
The narrow corridor of ridging that maintained mostly clear skies yesterday has shifted east and now extends from the Great Lakes through the Ohio and Tennessee Valleys into the northern Gulf. The elongated ridge is hugged by trough to its east and west. The eastward shift in the synoptic pattern has allowed the western ridge to lean far enough east to bring clouds and a few showers to parts of the region late last evening into this morning.
IR satellite shows broken cloud cover as far east as the Illinois and Indian border with radar mosaics plotting showers from west- central Illinois through central and southwest Missouri. A weak surface low over eastern Kansas is making a play on the stalled boundary, returning it north as a weak warm front. The warm front marks the divide between temperatures in the upper 50s/near 60 degrees and upper 60s/low-70s from central Missouri westward. Drier air (dewpoints in the 40s) to the east gives way to relatively moist air (dewpoints near 60 degrees) to the west. These elements will be the primary factors in today`s forecast.
The weak surface disturbance shows little movement as it is suppressed by another surface ridge building in from the northern Plains. Additionally, the lack of upper ascent and dry, more stable air to the east will impeded the eastward extend of showers this morning. Probabilities (15-40%) for showers will continue to decrease through late morning.
The biggest change in the last 24 hours is the adjustment in high temperatures. Thicker cloud cover lingers over central Missouri into sections of west-central Illinois as moisture is fed northeastward and increasing wrapped around the mid-level ridge with time. Thicker cloud cover keeps temperatures 3-5 degrees cooler (mid-70s) over central Missouri. To the north and south, clouds give way to a little more sunshine with highs in the upper 70s to low-80s. Clouds are stubborn to move as the mid-level pattern is nearly parked overhead. This keep the northwest quadrant of the CWA milder (low- 60s) with mid to upper 50s under mostly clear/partly cloudy skies in southeast Missouri through southwest Illinois.
Tuesday brings a modest warming trend with a return to widespread low-80s with clearing. As the surface ridge builds in from central Plains, easterly surface flow around the eastern side of the ridge pushes drier air from east to west. HREF temperatures spreads (due to questions with cloud cover) have decreased across the north, leaning into the warmer solutions that will bring upper 70s as far north as Quincy, while the cooler (low-70s) shift toward the Iowa and Missouri border.
Maples
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.LONG TERM... (Tuesday Night through Sunday) Issued at 320 AM CDT Mon Oct 13 2025
Upper level longwave ridging continues to steer the active weather through the Plains and northern CONUS late Tuesday through Friday. Meanwhile, guidance shows mid-level moisture continuing to eject out of the southwest and wrapping around and into the ridge. This initially makes a small, but noteworthy play on temperatures over the northern sections of the CWA Wednesday with upper 70s extending across northern Missouri into central Illinois. Conditions remain dry with gradual warming Thursday with more sunshine.
The upper ridging pattern begins to show signs of change late Wednesday into Thursday, losing some amplitude and shifting east of the region by Friday. A longwave trough shifts east in tandem as an upper low ejects out of the Intermountain West into Canada. Southwesterly flow strengthens through the day Friday, drawing 15- 20C H8 air in from the southern Plains in what is likely to be the warmest day of the week (low/mid-80s).
The long-awaited question is the rainfall potential considering how dry is has been in recent weeks. Ensemble data remains fairly well clustered through the day Friday before diverging Saturday into Sunday. Guidance is in better agreement than previous days, but timing issues remain. General consensus bring the cold front into the region late Friday night into early Saturday morning, then quickly moves it southeast Sunday morning. This mainly impacts the start and end times of measurable precipitation with blending between guidance likely too dispersive. Per usual, this is likely to be fine-tuned in coming days with better consensus among the ensembles as medium range guidance can better resolve potential vort lobe rotating around the parent upper level low and over top the surface boundary.
As of now, trends are looking a little more favorable for rainfall, but it is more likely to be a progressive hit rather than a long duration, soaking that we need. Through much of the week, the moisture source out of the Pacific (uncommon) is cutoff, transitioning to the western Gulf. One key is how quickly we can transition to Gulf moisture as the front advances from the northwest. Fortunately, long range deterministic solutions show strong moisture advection drawing 60 degree dewpoints into the mid- Mississippi Valley ahead of the front. Additionally, we may finally have a low level jet to work in light of the tightening pressure gradient. If current trends stick, we may be able to squeeze out a reasonable amount of rainfall to hold use over for a few days. LREF guidance shows 50-70% probabilities for measurable rainfall lining the front Saturday morning through Sunday morning. Amounts are dispersed roughly between 0.25" to 1" in the interquartile range (25th-75th percentile).
While these aren`t impressive numbers that would put a dent in drought conditions, the pattern may become more active and cooler beyond the end of the long range period. It might be the first step to additional chances further out. Cooler, more seasonal temperatures follow (mid-60s/low-70s).
Maples
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.AVIATION... (For the 12z TAFs through 12z Tuesday Morning) Issued at 619 AM CDT Mon Oct 13 2025
Light rain continues to line up from northeast Missouri through central Missouri early this morning. Rain is falling from mid- level cloud bases that is running into drier air and high pressure to the east, which will limit potential to central Missouri terminals (KCOU/KJEF) and KUIN. Not much impact is expected considering the light nature of the precipitation. What currently exists is expected to fade through mid to late morning.
VFR conditions are expected to continue otherwise. There are indications that a brief stint of patchy fog is possible over central sections of Missouri late tonight into early Tuesday morning. This was not included in this TAF package as the potential may be able to be handled with TEMPO groups in later updates.
Maples
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.LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. &&
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WFO LSX
NWS LSX Office Area Forecast Discussion