FXUS63 KLSX 020917 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 417 AM CDT Wed Apr 2 2025 .KEY MESSAGES... - Severe thunderstorms are likely today. All hazards are possible including damaging winds in excess of 70 mph, hail in excess of 2 inches in diameter, and a few tornadoes, some possible strong (EF-2+). - Periods of heavy rain are expected Thursday through Saturday. Significant river and flash flooding are possible across parts of southeast Missouri and southwest/south central Illinois where a Flash Flood Watch is in effect for Thursday through Saturday evening. - Gusty southerly winds are forecast today, with peak gusts of 40-45 mph expected. A Wind Advisory is in effect for eastern Missouri and southwest/south central Illinois. && .SHORT TERM... (Through Late This Afternoon) Issued at 416 AM CDT Wed Apr 2 2025 Low pressure centered over eastern Kansas will lift northeast into the Upper Midwest today. The warm front associated with this low is moving into central and southeast Missouri at this time, and should lift through the remainder of the area by 14-16Z. The strong pressure gradient between storm system lifting northeast and strong/deep ridging over the eastern U.S. and into the western Atlantic will produce very strong wind fields through the depth of the atmosphere today. This sets the stage for 1) strong surface winds today...sustained in the 20-30kt range, with gusts in exess of 40kts. The Wind Advisory therefore looks in good shape, and no changes are expected at the moment. Attention turns to convection today. All CAMs show the broken line of thunderstorms over eastern Kansas/northwest Missouri moving into our northeast Missouri counties around 11-12Z. Forecast soundings as well as plan view CINH plots have been very consistently showing that these storms will be elevated, with the primary threat being large hail. However, the strong wind fields will make it impossible to rule out an isolated damgaging wind threat. CAMs show the morning convection weakening, although not entirely dissipating. This potential for clouds and showers limiting daytime heating remains the one potential issue with storms restrengthening in the afternoon. However, the models are pretty insistent that this will NOT be a hinderance, and instability will increase this afternoon ahead of the front. The boundary itself will not be moving very quickly due to the parent low pressure's northeastward movement, and the strong south-southwest flow ahead of it. RAP and GFS show destabilization ahead of the front between 16-19Z west of the Mississippi River, and CINH decreasing to nearly nothing in the same area due to a combination of heating and subtle cooling aloft. The RAP is showing around 1700 J/Kg MLCAPE and 60-70kts of 0-6km shear at that time. While the majority of the shear is linnear, hodographs do show a little curvature in the lowest kilometer of the sounding, and 0-1km helicity 200-300 m2/s2. With these kinematics and thermodynamics in play, all severe threats are on the table including damging winds in excess of 70 mph, hail in excess of 2 inches, and tornadoes, some strong (EF2+). The linnear 0-6km hodographs hint there will be lots of storm splits and mergers so this still looks messy, with few if any discrete storms. More likely are lines and clusters of supercells that move east through the afternoon. While the strongest storms will likely be out of our area by 00Z or shortly there after, convection may linger across parts of south central Illinois well into the evening until the slow- moving boundary finally clears the area. Carney && .LONG TERM... (Tonight through Tuesday) Issued at 416 AM CDT Wed Apr 2 2025 The primary concern beyond today remains the threat for waves of heavy rain and flooding Thursday through Saturday. Little has changed in the forecast for this time period. The effective boundary gets pushed into Arkansas/Tennessee tonight where it takes on an east-west orientation and becomes quasi-stationary. The deep long wave trough over the Desert Southwest ejects several subtle waves in mid-upper level southwest flow across the lower/mid Mississippi Valley which ride over the boundary. These short waves combined with strong and persistent warm/moist low level flow from the Gulf overrunning the boundary will produce waves of showers and thunderstorms. The first, and probably least impactful wave of rain still looks to develop and move into the forecast area on Thursday, and persist into Thursday night. Latest QPF from WPC shows less than an inch in our area for this first round which matches well with guidance. While we should be able to absorb this much rainfall pretty easily, it will prime the pump so to speak for Friday and Saturday. The persistent southerly low level flow pushes the boundary up into northern Arkansas/southern Missouri on Friday morning, bringing another surge of moisture with it. The true heavy rainfall threat begins at this point, and it looks like nearly continuous rain for most of the area along and south of I-70 until Sunday morning. Highest rainfall amounts are still focused generally along and southeast of I-44 in Missouri and I-70 in Illinois where WPC QPF is 5-9 inches. This agrees well with 5+ inch probabilities from ensemble guidance. Locally higher amounts are certainly possible and moderate to major river flooding in southeast Missouri continues to be a threat along with significant flash flooding. The Flash Flood Watch still looks like it's in good shape, but it may need to be expanded northward if the axis of heavy rain shifts. Briefly, for Sunday through Tuesday... The long wave trough over the southwest U.S. finally shifts east across the country which finally brings the rain to an end on Sunday. THe trough in the latest guidance doesn't look quite as persistent over the eastern U.S. as in previous runs...so the warm up next week could be faster than forecast. However, freezing temperatures for parts of the area remain in the forecast for Monday and Tuesday morning. Carney && .AVIATION... (For the 06z TAFs through 06z Wednesday Night) Issued at 1116 PM CDT Tue Apr 1 2025 Breezy southeasterly winds with intermittent gusts will continue overnight, veering to southerly Wednesday morning as a warm front lifts northward. Scattered thunderstorms could possibly traverse northeastern MO and west-central IL overnight with impacts to KUIN. However, a more widespread, broken line of thunderstorms, currently across KS, will arrive across central/northeastern MO and west- central IL Wednesday morning with a period of MVFR to IFR flight conditions at KCOU, KJEF, and KUIN. These thunderstorms should be generally weakening by that time, but hail or gusty winds cannot be ruled out. In addition to thunderstorms, areas of MVFR stratus are expected to develop early Wednesday morning along with strong southerly wind gusts of 35 to 40 kt during the afternoon and evening. Showers and thunderstorms will continue eastward and restrengthen and redevelop across east-central/southeastern MO and southwestern IL during the afternoon and evening, with a PROB30 group capturing the potential for impacts at St. Louis metro terminals. However, the timing and coverage of these thunderstorms are not exactly clear, but they will have a greater chance of being severe. Flight conditions will improve from west to east Wednesday evening as showers and thunderstorms exit and a weak cold front passes, accompanied by winds veering toward the west and quickly slackening. Pfahler && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Wind Advisory from noon today to 7 PM CDT this evening for Franklin MO-Iron MO-Jefferson MO-Knox MO-Lewis MO-Lincoln MO-Madison MO-Marion MO-Pike MO-Ralls MO-Reynolds MO-Saint Charles MO-Saint Francois MO-Saint Louis City MO-Saint Louis MO-Sainte Genevieve MO-Warren MO-Washington MO. Flood Watch from Thursday morning through late Saturday night for Crawford MO-Iron MO-Jefferson MO-Madison MO-Reynolds MO- Saint Francois MO-Sainte Genevieve MO-Washington MO. IL...Wind Advisory from noon today to 7 PM CDT this evening for Adams IL-Bond IL-Brown IL-Calhoun IL-Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-Madison IL-Marion IL-Monroe IL- Montgomery IL-Pike IL-Randolph IL-Saint Clair IL-Washington IL. Flood Watch from Thursday morning through late Saturday night for Bond IL-Clinton IL-Fayette IL-Marion IL-Monroe IL- Randolph IL-Saint Clair IL-Washington IL. && $$ WFO LSX