Area Forecast Discussion
Issued by NWS Springfield, MO
Issued by NWS Springfield, MO
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608 FXUS63 KSGF 260903 AFDSGF Area Forecast Discussion National Weather Service Springfield MO 403 AM CDT Fri Apr 26 2024 .KEY MESSAGES... - Widespread moderate to heavy rain/thunderstorms will develop again today through the late evening. Heaviest rain, greatest chance for flooding, and conditional threat for strong to severe storms is generally east of I-49 during the late morning to mid-afternoon. - A second round of conditional strong to severe storms exists late afternoon/evening with the greatest chance for significant severe storms along and west of Highway 65. - Risk of severe storms, heavy rain, and flooding will continue to occur through Sunday night as multiple rounds of storms move through the region. Greatest severe threat appears to be Saturday evening and night. - 20-50% chances of showers and thunderstorms Tuesday through Friday. Highest chances Wednesday night into Thursday. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 400 AM CDT Fri Apr 26 2024 Recent mesoanalysis and observational trends depict an amplifying upper-level wave pattern across the central Plains as a negatively-tilted shortwave trough ejects off the Rocky Mountains. At the surface, a 994mb surface low has developed in west KS, and a sharp pressure gradient across the entire Great Plains states has strengthened. Atop this gradient, an extensive N-S 40-60 kt LLJ exists. Strong isallobaric surface winds have developed across this pressure gradient as the surface low and strong upper-level divergence vacuums in air from the ESE. Recent observations have Springfield at SE`ly sustained winds of 20-30 mph, gusting to 35-40 mph. This will begin warm air advection and highs will reach into the mid-70s. Moderate to heavy rain/thunderstorms will develop again today: As a result of the amplifying wave pattern, broad upper-level divergence and diffluence is overlapping a region of strong low- and mid-level warm air advection and isentropic upglide across our area NE of a surface warm front. Scattered showers and thunderstorms have developed within this region in east KS/west MO. These thundershowers will progress NE through the early morning, generally staying scattered in nature. A second, more widespread round of convection will begin in central OK when better synoptic scale forcing overlaps the strong LLJ and associated WAA. This convection will grow upscale into an MCS and move to the NE into west MO by mid-morning/early afternoon. Models are still having a hard time handling the evolution of this thunderstorm complex. 00Z CAMs have the MCS clearing through our area in the 8AM-2PM timeframe, while the 01-05Z HRRR runs progressively slowed the MCS to where it entered our area after 12 PM. Despite uncertainty in timing, increased coverage in moderate to heavy rain/thunderstorms looks likely (70-90%) during the mid- morning to mid-afternoon hours. These storms will progress east across the area before stalling across central MO by late afternoon as the upper-level divergence axis settles over that region. With mean-layer flow rather parallel to the axis of forcing, this will introduce a period of training thunderstorms. The training combined with high PWATs and IVTs (our 00Z balloon measured 1.28", a daily max according to the SPC sounding climatology) will produce yet another threat for excessive rainfall and potential flooding. Indeed the WPC has most of our area in a slight (2/4) risk for excessive rainfall. Many locations will receive at least a half inch of rain (60-90% chance from NBM; 50-70% chance from HREF). Locations generally along and east of Highway 65 where the band of heavy thunderstorms stalls could see 1-2 inches (20-40% chance). 00Z HREF LPMMs suggest that localized areas within the heavier thunderstorms could see amounts up to 2.5-3.5 inches. Given that some locations have already seen substantial rainfall, flooding will once again be a risk. Conditional threat for strong to severe storms today: The evolution of the previously discussed MCS will largely determine the potential for strong to severe storms across central MO during the early to mid-afternoon hours. The 00Z CAMs suite depicts a more progressive and widespread MCS over the area, developing a more substantial surface cold pool. This would limit destabilization and any subsequent severe storms across the area. However, monitoring post-00Z HRRR runs, each run slows and weakens the MCS, allowing for undisturbed MLCAPE values of 1000-2000 J/kg to advect into south-central MO by mid- afternoon. This would then allow redevelopment and intensification along the line of thunderstorms (generally along and east of Hwy 65), bringing the risk for strong to severe storms. Thus, this is a very conditional threat based on how daytime convection evolves across the area. If storms are more widespread, persistent, and progressive through the day, the severe threat will be very low to nonexistent along and east of Hwy 65. If storms are more scattered and/or less progressive, severe storms become possible along and east of Hwy 65 after 12-3 PM. In this scenario, deeply curved hodographs characterized by 40-50 kts of 0-6 km bulk shear with 25-35 kts of 0-1 km shear and 250-350 m2/s2 0-1 km SRH would introduce a tornado threat. Mid-level lapse rates >7.0 C/km with CAPE focused in the hail growth zone would also introduce a severe hail threat up to golf ball size. Wind gusts up to 60 mph would also be possible. A second conditional threat for severe storms then sets up in the late afternoon/evening hours west of Hwy 65, specifically toward the MO/KS border. West of the MCS in central MO, mid-60s dewpoints will surge northward ahead of a sharp N-S oriented dryline. This will create a corridor of 2000-3000 J/kg MLCAPE along the MO/KS border. With the surface low in Nebraska and synoptic forcing focused in NW MO/SW IA, the development of severe storms along the MO/KS border in our CWA is conditional, dependent on the strength of any capping inversion and convergence along the dryline circulation. Given the subtle forcing and shear vectors largely perpendicular to the dryline, if storms were to initiate, we`d likely be looking at a couple supercells (maybe even just one). But the environment those supercells would be in would be conducive for severe weather, perhaps significant. Shear will be better in this region at 50-60 kts of 0-6 km bulk shear characterized by veer-back-veer hodographs and enhanced low-level curvature. 0-1 km SRH at 200-300 m2/s2, LCL heights below 500m, and near-surface lapse rates >7 C/km would support a tornado threat with the possibility of a significant tornado if any supercell can mature given the weak forcing. Significant hail (up to the size of tennis balls) is also possible with HRRR analog soundings pulling a couple 3-4.5" historical hail size events. And as always, wind gusts up to 60 mph are also possible. The main timeframe for this threat would be between 5-9 PM. But once again, this threat is dependent on if storms can initiate along the dryline. There is good potential (60-70% chance) that this region stays completely dry during this timeframe. Lastly, there is signal that some overnight strong thunderstorm development could occur along the MO/AR border after midnight. With decoupling of the boundary layer, the threat with these would mainly be hail up to the size of golf balls. Risk of severe storms and flooding will continue Saturday night: Precipitation chances will clear our forecast area by the morning hours Saturday. Generally cloud cover will still be over the area, keeping lows in the mid-60s (near record high minimum). The upper-level longwave pattern will continue to keep the jet NW of our region which will keep the surface boundaries NW of our CWA. This will keep persistent S`ly low-level flow across our area, advecting in upper-60s dewpoints and temperatures in the upper 70s. This will be a muggy warm sector creating MLCAPE values of around 2500-3500 J/kg. Another shortwave impulse will eject off the Rockies during the day Saturday and force cyclogenesis once again across OK/KS. This will force a widespread severe threat across that area. The SPC has an Enhanced (3/5) risk just clipping our KS counties with a Slight (2/5) risk just past Springfield. This is mainly for storms that will move into that area from OK/KS overnight. Widespread and explosive thunderstorm development in that area is forecast to significantly amplify the upper-level wave pattern, creating very strong upper-level divergence in a coupled jet pattern along our MO/KS border. Additionally, upper-level flow will be straight south-to-north. Mean flow will then be quite parallel to the surface boundaries. This will promote training severe thunderstorms that will gradually work their way into our far western CWA after midnight. This will create a risk for flooding, especially since that area already received 3-6 inches of rain. The WPC has a moderate (3/4) risk for excessive rainfall right on the edge of our KS counties with a slight (2/4) risk along I-49. Along with the flooding threat, the training thunderstorms will likely be severe with shear off the charts. Hodographs in this region resemble the St. Louis arch with 1km flow at 60 kts creating 0-1 km shear at 40-50 kts. This will promote a tornado threat, perhaps significant, mainly for our KS counties. A significant hail threat (>2") and wind gusts up to 60 mph are also possible. This will be an overnight threat! It will be important to be aware of the weather and alerts as these storms enter our area overnight. These storms should generally decrease in intensity as they progress past the MO/KS border into the early Sunday morning hours. Lows will be mild in the mid-60s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Issued at 400 AM CDT Fri Apr 26 2024 Risk of severe storms and flooding will continue Sunday: The negatively-tilted upper-level shortwave and attendant surface low will still be lingering just off to our NW during the day Sunday. As such, the warm sector will still be settled over our region (characterized by highs in the mid-70s and dewpoints in the lower 60s). This will set the stage for our final severe threat for this weekend. The SPC has our entire CWA in a Slight (2/5; 15%) risk. There`s still quite a bit of uncertainty in the evolution of ongoing convection from Saturday night, but some destabilization ahead of the storms is possible. The best scenario looks to be redevelopment and intensification of storms within the ongoing convection as it progresses east through our CWA. Instability and deep-layer shear will remain favorable for these storms to become severe with all hazards possible. Beside the severe threat, training thunderstorms will still be an issue as the line slowly progresses eastward. This will once again introduce an excessive rainfall and flooding threat, especially along and SE of I-44 where upper-level support is more potent. While only in a slight (2/4) risk, the amount of rain we will have received up until then will make it easier for areas to flood even with "lower" QPF values. Chances of showers and thunderstorms Tuesday through Friday: Rain/thunderstorm chances (30-70%) will linger into the day Monday, mainly for south-central MO. Highs will be in the upper 70s and lows in the mid-50s. These rain chances will finally clear the area by Tuesday morning, giving a brief break from rainfall. However, there is a signal that S`ly low-level warm air advection will force several more rounds of showers/thunderstorms Tuesday through Friday. Ensemble clusters depict slight timing disparities which may be the reason for multiple days of rain chances. The most agreement looks to focus 40-50% PoPs Wednesday night into Thursday evening. Subsequent forecasts will iron down details, but the main message here is to be prepared for more rain next week. Otherwise, highs will be in the 70s and lows in the 50s Tuesday and onward. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1235 AM CDT Fri Apr 26 2024 IFR conditions will continue at all TAF sites due to <1000 ft ceilings. These ceilings should improve to MVFR after 13-15Z. Scattered thundershowers will also increase in coverage from west to east as the night goes on. Multiple cumulonimbus towers are already going up in east KS/NE OK and will gradually move into all TAF site areas. These cells will be small and scattered for the overnight hours, infrequently impacting TAF sites directly. Some thunderstorms may be heavy at times, especially within the 17-22Z timeframe when greater coverage in rainfall is forecast. The rain should clear the TAF sites by 22Z, at which point there is a 15-30% chance of an isolated strong to severe storm to be in the vicinity of one of the TAF sites. The greatest chance for one of these would be JLN, but confidence is quite low on the location of these isolated strong storms. Otherwise, moderate winds will remain SSE`ly with sustained speeds at 15-20 kts and gusts periodically up to 25 kts and perhaps an isolated 30 kt gust or two. Lastly, low-level wind shear will be right near threshold values through 18Z, and then again after 00Z. Have kept out of the TAFs for now given the spotty nature of wind shear values breaking threshold. Greater low-level wind shear will return towards the very end of this TAF period. && .CLIMATE... Issued at 1225 PM CDT Thu Apr 25 2024 Record High Minimum Temperatures: April 27: KSGF: 67/1899 April 28: KSGF: 68/1896 && .SGF WATCHES/WARNINGS/ADVISORIES... KS...None. MO...None. && $$ SHORT TERM...Price LONG TERM...Price AVIATION...Price CLIMATE...Price