Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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587 FXUS63 KLSX 291709 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1209 PM CDT Mon Apr 29 2024 .KEY MESSAGES... - Lingering showers along with a few thunderstorms are forecast through much of the day today in parts of southeast Missouri and southwest Illinois. Further northwest, dry weather is expected. - Temperatures will remain above-normal through the work week, with on/off rain chances. The highest chance for rain will accompany a cold front in the Thursday - Friday timeframe. && .SHORT TERM... (Through Late Tuesday Afternoon) Issued at 343 AM CDT Mon Apr 29 2024 (Today) Widespread showers and embedded thunderstorms continues to push eastward along with an area of low-level moisture convergence. This forcing is expected to weaken by 1200 UTC, so the expectation is for the intensity of the convection and associated rainfall rates to decrease across southeast Missouri and southwest Illinois as well. The synoptic cold front still lags to the west a bit, located near a KCOU>>KIRK axis as of 0700 UTC. This front is expected to wash out over the next several hours. However, look for showers along with a few thunderstorms to remain possible most of the day in parts of southeast Missouri and southwest Illinois as a midlevel shortwave trough moves across the mid south this afternoon. Nothing strong to severe is expected, but some brief downpours are possible. High temperatures today are expected to be similar to yesterday in most locations, generally in the low to mid 70s. The coolest locations are forecast to be in parts of northeast Missouri behind the cold front and in parts of southeast Missouri/southwest Illinois where clouds will be prevalent into the afternoon hours. (Tonight - Tuesday) Decreasing cloudiness is forecast across southeast Missouri and southwest Illinois this evening, with a clear sky overnight for the entire area. Light/variable winds along with this clear sky should allow for temperatures to cool back into the low to mid 50s for overnight lows. These values are near the 25th percentile of available model guidance. Given that these lows or below afternoon crossover temperatures, would think fog may be a concern. This will especially be true in favored river valleys and where there is excess surface moisture from recent heavy rainfall. A quick warmup is expected during the day on Tuesday as low-level warm air advection strengthens. Highs in the upper 70s to low 80s are forecast, or about 10 degrees above normal for the last day of April. Gosselin && .LONG TERM... (Tuesday Night through Sunday) Issued at 343 AM CDT Mon Apr 29 2024 (Tuesday Night - Wednesday Night) Deterministic models show a midlevel shortwave trough moving quickly across the Upper Midwest Tuesday night, with a surface low north of the Twin Cities at 0600 UTC Wednesday. An attendant cold front will be draped to its south, with this frontal boundary nearing parts of northeast and central Missouri. This will bring a chance of showers and thunderstorms to this part of the CWA in the 0600-1200 UTC time period, with chances rapidly decreasing by Wednesday morning as the mid/upper level forcing for ascent is becomes even more displaced to the north and the surface cold front washes out. Mostly dry weather is forecast on Wednesday, before the chances of showers and thunderstorms returns to parts of central and northeast Missouri as well as west-central Illinois Wednesday night. Similar to Tuesday night, this area gets brushed with mid/upper level ascent southeast of the track of a midlevel shortwave trough. However, the better chances of elevated convection reside further to the north where the warm front should reside and the stronger low-level moisture convergence. Temperature wise, the well-above normal values will continue, with lows in the low 60s each night and highs Wednesday afternoon mostly in the low 80s. (Thursday - Friday) The period with the best chances of showers and thunderstorms (60- 80%) remains Thursday through Friday. The broad time period is due to uncertainty with the timing of a cold frontal passage across the region. Ahead of this front, the continuation of well-above normal temperatures day and night is expected. There is more uncertainty with Friday`s high temperatures across much of the area due to the differences in frontal timing. Differences between the 25th/75th percentile of the NBM increase more toward 6-10F degrees in most locations. (Friday Night - Sunday) There is high uncertainty in sensible weather heading into next weekend. WPC 500-hPa height clusters show vastly different solutions across the central CONUS, ranging from continued southwest flow aloft to much cooler weather behind a stronger cold front. Slightly above normal temperatures with PoPs below climatological normals are forecast at this time, but confidence is very low. Gosselin && .AVIATION... (For the 18z TAFs through 18z Tuesday Afternoon) Issued at 1204 PM CDT Mon Apr 29 2024 The IFR/MVFR stratus is continuing to push eastward ahead of a cold front. The western edge of the stratus has started to scatter, speeding up clearing even further. The St. Louis metro sites are the only terminals remaining at MVFR and will be VFR by the early afternoon. Ceilings will remain VFR through the remainder of the TAF period. However, a clear sky tonight combine with high low level moisture and weak surface winds increases the potential for fog overnight. Widespread fog is most likely southeast of the St. Louis metro terminals, but sites near rivers (KCOU, KJEF, KSUS, and KCPS) will be at risk for IFR fog overnight and into the early morning hours. Winds will become west to northwesterly today behind the approaching cold front, becoming increasingly light and variable this evening and overnight as a surface high pushes through the area. MRM && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX