Area Forecast Discussion
Issued by NWS Springfield, MO
Issued by NWS Springfield, MO
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448 FXUS63 KSGF 231122 AFDSGF Area Forecast Discussion National Weather Service Springfield MO 622 AM CDT Mon Sep 23 2024 .KEY MESSAGES... - Marginal (1 of 5) Risk for severe thunderstorms today in across the eastern Ozarks. Main hazards will be damaging wind gusts up to 60 mph, small hail with isolated instances up to a quarter inch, and brief heavy downpours. - Multiple rounds of widespread showers and thunderstorms are expected through tonight (60-85% chance). Most locations will see an additional 0.25 to 1.5 inches of rainfall through tonight, with localized amounts up to 3 to 5 inches. - Much cooler temperatures will occur this week with highs in the 70s. - Rainfall chances (50-70%) continue to increase for late in the week as confidence increases on track of the next system. There is the potential for widespread and prolonged rainfall with this system. && .SHORT TERM /THROUGH TUESDAY NIGHT/... Issued at 345 AM CDT Mon Sep 23 2024 Current water vapor imagery depicts the positively-tilted shortwave trough still situated over the central Plains. Height falls and associated positive vorticity advection over the last few hours have provided enough ascent for scattered showers and thunderstorms to develop across the area. These are expected to increase in coverage through the morning as the trough progresses eastward. Noted on SPC Mesoanalysis, a 60-80 kt upper-level jet over KS/MO is synoptically forcing weak surface cyclogenesis in NW AR along a cold front currently analyzed from Michigan, down into SE MO, and through NW AR, SE OK, and central TX. This will create a high temperature gradient across our CWA. Highs will be in the mid-60s NW of I-44 and in the mid-70s SE of I-44. This front and surface low and their exact positions during the day will be the focus for additional thunderstorm development this afternoon, some potentially being strong to severe. Marginal (1 of 5) Risk for severe thunderstorms today: As noted in our 00Z observed sounding, deep cloud cover is keeping environmental lapse rates rather meager in the 5.5-6.5 C/km range. The clouds are not expected to go anywhere today, which will continue to keep shallow lapse rates across the region. However, surface low cyclogenesis along the AR/MO border will reorient the cold front to more SSW-NNE, and should provide just enough moisture advection ahead of that front to generate 500-1500 J/kg of MLCAPE characterized by skinny instability profiles. As heights fall with the approaching shortwave, thunderstorm development should occur along the front in an area bounded by east of Hwy 65 and south of I-44. This could occur as early as 12 PM today. Ahead of the shortwave, 0-6 km shear will increase to 25-35 kts, characterized by unidirectional hodographs. With this overlapping the marginal instability, some of these thunderstorms this afternoon in the eastern Ozarks could become severe (5% chance). Wind gusts up to 60 mph and hail up to the size of quarters will be the main hazards. Coverage of these storms will be determined by the degree of instability. If enough cloud breaks occur in areas across the eastern Ozarks (increasing low-level lapse rates), and colder air in the mid-levels advects in with the height falls (increasing mid-level lapse rates), it seems plausible that higher coverage of robust updrafts could develop across the eastern Ozarks. Interacting with the higher range of bulk shear (30-35 kts), some multicells could cluster into lines, otherwise, downbursts would be the main wind threats. These storms would all still have wind gusts up to 60 mph and hail up to the size of quarters as the main threats. 0.25 to 1.5 inches of additional rainfall through tonight: A northern-stream shortwave trough digging into the Northern Plains will modestly amplify the shortwave across our region and prompt it to slowly progress eastward. With a large zone of increasing synoptic-scale ascent spread across our area, several rounds of showers and thunderstorms are expected to continue to develop and move through our area (60-85% chance). Since the shortwave will slowly progress eastward, some areas, especially in the eastern Ozarks, could see multiple thunderstorms. As such, many areas will see an additional 0.25-1.5" with HREF LPMMs highlighting some localized areas receiving up to 3-5". This will introduce a minor and localized flooding threat across the eastern Ozarks where there`s a better chance of multiple thunderstorms moving over the same area and there are less dry conditions. Lingering rain chances into Tuesday: The front will finally kick through the rest of the region Monday night and lows will drop into the upper 50s and lower 60s. With the surface low lifting through east MO and into Illinois, backside light showers could impact areas toward central MO (20-40% chance). Additionally, the aforementioned northern-stream shortwave will dig into the central Plains through Tuesday. A strong N-S oriented 100-120 kt upper-level jet will drop through NE and KS. Left-entrance region synoptic ascent will overspread a small corridor of weak elevated instability associated with the cold- core system. This could bring some elevated showers and thunderstorms into the MO/KS border vicinity Tuesday afternoon and evening (15-20% chance). Then, lows Tuesday night will be slightly cooler in the lower to middle 50s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Issued at 345 AM CDT Mon Sep 23 2024 Much cooler temperatures this week with highs in the 60s and 70s: The deep shortwave will settle over the eastern CONUS through mid-week, bringing high pressure in behind the cold front. This will bring cooler temperatures with highs in the lower to middle 70s Wednesday and Thursday. Ensemble cluster analysis shows members starting to come into good agreement with the shortwave cutting off from the main flow aloft, and sitting somewhere over the southern/central CONUS. The cold core of the upper- level low would decrease highs into the upper 60s and lower 70s Friday through Sunday. However, if the cut-off low does not develop, or stays out of our region, highs could be closer to the middle 70s. Lows during this whole time period will consistently be in the 50s. Rainfall chances (50-70%) continue to increase for late week: As previously mentioned, models are coming into better agreement on the scenario discussed in the last two forecast packages about an upper-level cut-off low squatting somewhere around our region late this week. Ensemble cluster analysis reveals that 85% of members are now favoring this scenario since the GEFS has caught onto it (though exact location and intensity of the upper-level low is still uncertain). Additionally, GFS/ECMWF/CMC ensemble spaghetti plots of Invest-97L in the Gulf all have the mean track wrapping into the upper-level low, which would provide a boost in deep moisture. This scenario could produce widespread and prolonged rainfall somewhere in the east/central CONUS late this week, including potentially our CWA (50-70% chances Thursday through Sunday). The Extreme Forecast Index is already hitting on our CWA this far out with a value of 0.59 and 1-2 shifts of the statistical tail for QPF, signaling a potential abnormal precipitation event. Adding confidence, the WPC has a Slight (2 of 5) Risk for excessive rainfall in our SE counties for Day 5 (Friday). NBM mean 72-hour precipitation ending Saturday night has amounts in the 2-5" range. Everything mentioned above is adding confidence to this scenario. That being said, any small shift in track and/or intensity will change rainfall chances and amounts across our region. For example, a more northward and/or eastward shift could leave us with less than half an inch of rain (~25th NBM percentile). Whereas a more westward and/or southward shift could bring more than 5 inches to portions of the region (~75th NBM percentile). Trends will continue to be monitored in the coming days, but consider this a heads-up for a potentially widespread and prolonged rainfall event late this week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 523 AM CDT Mon Sep 23 2024 At the moment, TAF sites are oscillating between LIFR and IFR ceilings. There is medium-high confidence that conditions will oscillate between MVFR, IFR, and LIFR throughout the TAF period at all TAF sites as there is a 70-90% chance of ceilings staying below 1 kft through the period. There is a good chance (50-70%) that TAF sites fall into LIFR, especially before 14Z and after 03Z. Additionally, there is a 70-90% chance that showers and/or thunderstorms will impact the TAF sites at some point during the period. Confidence on timing is increasing after the first round of storms has moved through. Expect another round to move through between the 15-21Z timeframe for JLN and 18-00Z timeframe for SGF and BBG. Brief heavy downpours, lightning, and isolated downbursts up to 40-50 mph are possible with any storm, especially in SGF and BBG. Otherwise, winds will remain relatively calm at 3-8 kts out of the north. && .SGF WATCHES/WARNINGS/ADVISORIES... KS...None. MO...None. && $$ SHORT TERM...Price LONG TERM...Price AVIATION...Price