FXUS63 KLSX 151126 AFDLSX Area Forecast Discussion National Weather Service St Louis MO 626 AM CDT Thu Oct 15 2026 .KEY MESSAGES... - Widespread showers and thunderstorms are expected through the first half of the day, becoming isolated to scattered this afternoon and evening. There is a low potential for isolated damaging winds, and lower potential for a brief, week tornado. - A strong cold front brings much cooler and drier conditions Friday through Sunday morning. A gradual warming trend begin Sunday and continues into next week. && .SHORT TERM /THROUGH FRIDAY/... Issued at 259 AM CDT Thu Oct 15 2026 Showers and thunderstorms approach the area early this morning out of the southwest and continue advancing northeast over the CWA through early this afternoon. A strong cold front then quickly moves west to east with much cooler air spilling into the area overnight into Friday. The area being monitored for the next round of showers and thunderstorms is currently over sections of eastern OK. This activity is being driven by a shortwave trough and corresponding surface low in advance of the upper level low over CO. The surface low parallels I-44 on its northeast track with broad scale ascent, lifting the stationary boundary northward through the area through the morning. A broad area of showers and embedded thunderstorms accompany the warm front with HRRR/NAMNest indicating a few strong cells in close proximity to the warm front and surface low. HREF ensembles show mean CAPE values of 1000-1500 J/kg with around 40 knots of shear and backed surface winds near the boundary resulting in curved hodographs. These indicators would normally raise some concern, but in this case, showers and embedded thunderstorms enter the southwest CWA between 10-12z and near the MS River around 15z. RAP model soundings show a capping inversion just below 850mb, CAPE below 500 J/kg, and mid-level lapse rates below 6C. The system and front moves relatively quickly, placing the warm front north of I-70 around 18-19z. The issue then, is to monitor the warm sector over southeast MO and southwest IL, where HREF shows roughly 20-40 percent probabilities for cloud cover of great than 50 percent. This leaves much to be desired with respect to severe potential with low confidence that severe weather will materialize. Instability will have a very short window of 3-4 hours (2-6PM) for recovery at a time of year with lower sun angle and earlier sunset, considering that enough clearing occurs quickly enough. Therefore, while we are messaging the marginal risk, the threat for severe weather looks very low and isolated at best. Damaging winds would be the primary threat. The low tornado potential is also limited in aerial coverage (along and north of I-70 and east of I-55). A strong cold front trails the system and races west to east late this evening and overnight as the system moves into the the Great Lakes and is wrapped into a vigorous northern stream Canadian upper trough. Scattered showers and an isolated thunderstorm are possible along the front as upper ascent evacuates to the northeast. There is not much concern for severe potential along the front itself as much of the atmosphere is work over and we enter the diurnal downward trend. The front should be east of the CWA around or just after midnight with a surface ridging beginning to build in from the northwest. Strong cold air advection drops temperatures overnight with cold air continuing to advect in through the day Friday. The surface high remain departed enough to the west that the upper trough exhibits more influence in terms of moisture. Though we may briefly see partial clearing early Friday, higher RH advects southeastward with the amplified upper trough overhead and surface ridge to the west.Clouds will build back in Friday in conjunction with continuing cold air advection. It is expected to be the coolest day of the fall so far. Highs today will range from the 70s over northern sections of the CWA to the mid-80s over southeast MO and southwest IL. Lows tonight drop into the 40s behind the cold front. Highs Friday will be in the 50s, even struggling reach 60 degrees across far southeast MO. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Issued at 259 AM CDT Thu Oct 15 2026 The fall chill will continue into Saturday before temperatures begin to moderate Sunday into next week. A long stretch of dry weather is expected through much of next week. The amplified trough shifts east of the area Friday night into Saturday with a longwave upper ridge over the western 2/3rds of the CONUS. Northwesterly flow continues aloft as the surface ridge moves southeastward and its orientation varies between RAP/NAM and long range suites. These vary from a slanted ridge axis to a more formidable, consolidated surface high. Though minor, range solutions may be the difference between a decent frost and cold, morning dew on the lawn. The orientation, placement of the ridge, and resulting surface flow suggest that while temperatures will be the coolest of the season, so far, NBM is likely too cool, leaning at or just below the 25th percentile of the IQR. LREF guidance has not only tightened in its IQR range (3-4 degrees), it has consistently shown morning lows in the upper 30s to low-40s with locally cooler temperatures in the well-known microclimates (e.g. Freedom, and Rose Bud, MO). The scenario is slightly different for Sunday as the high positions overhead and winds become light and variable. Sunday looks like the cooler of the two, barring how quickly the high moves east and return flow commences. General speaking, morning lows in the low in the upper 30s to low-40s will represent a large majority of the area. Locally cooler temperatures will support better frost potential with mid-30s. Upper ridging moves eastward and envelops the region Sunday into next week. The pattern look void of any formidable systems and drives the northern stream track into the northern CONUS/southern Canada. Another surface ridges moves west to east near the Canadian border with dry easterly flow through the midweek period. NBM has suggested high temperatures in the upper 70s to near 80 degrees through the midweek stretch, but has since come down to more reasonable levels (low to mid-70s). Morning lows will follow suit with temperatures doing a daily stair step from the upper 30s/40s early in the week to 50s by Friday. && .AVIATION /12Z TAFS THROUGH 18Z FRIDAY/... Issued at 626 AM CDT Thu Oct 15 2026 A warm front will lift northeast over the terminals this morning through early afternoon. The front includes a broken line of heavier showers resulting in vsby restrictions locally as low as 1 3/4SM. Lightning has been limited/isolated due to lower instability this morning though thunder potential increases this afternoon. By that time, the warm front lifts north of the metro terminals to near KUIN. Rain chances lower slightly after the first round of showers move northward along and north of the warm front. This afternoon brings the concern for isolated strong to severe thunderstorms with a very short window of opportunity, mainly around metro terminals. The system initially approaches KCOU/KJEF by early afternoon and before instability returns. The system quickly moves northeast, affecting the metro sites in the later half of the day. -TSRA was included in PROB30 groups with some uncertainty in how well instability recovers behind this morning's initial wave. Thunderstorms that develop should move east of the metro terminals this evening. Isolated showersremain possible until the front clears from west to east. Evening SHRA potential was not included at this time given the limited coverage. A mix of MVFR/IFR covers much of the period with gradual improvement overnight, though northwesterly winds are expected to gust on occasion. && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ SHORT TERM...Maples LONG TERM...Maples AVIATION...Maples