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Area Forecast Discussion
Issued by NWS Springfield, MO
Issued by NWS Springfield, MO
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608 FXUS63 KSGF 152009 AFDSGF Area Forecast Discussion National Weather Service Springfield MO 309 PM CDT Thu Aug 15 2024 .KEY MESSAGES... - Heat index values reaching 100-110 degrees today. Heat Advisory in effect from 12pm-9pm today. - Slight (2 out of 5) risk for severe thunderstorms this afternoon through tonight. Damaging wind and large hail are the main severe weather risks (15% SPC risk), with tornadoes being a lower, but nonzero risk (<=2% SPC risk). - 40-70% chance for scattered showers and thunderstorms late Friday into early Saturday, with a marginal risk for severe storms. && .MESOSCALE UPDATE... Issued at 300 PM CDT Thu Aug 15 2024 Slight risk for severe thunderstorms this afternoon and tonight: Between the last update and now, destabilization of the airmass has been progressing quicker than models anticipated, which is what we were originally thinking would happen. What`s left of the cold pool has set up an E-W oriented temperature gradient just south of Springfield (90 F in Branson and 80 F north of Springfield). Sfc obs do note some weak convergence along this boundary the extends SW into extreme NE OK and SE KS. Indeed, some showers are beginning to develop along this weak convergence line and are beginning to move into our CWA. With the cold pool and cloud cover slowly eroding, weak convergence still evident, and temperatures and dewpoints already almost fully recovered, latest thinking is that isolated to scattered thunderstorm development will occur along and SE of I-44 within the 4-7 PM timeframe. Latest CAMs suggest the higher coverage will still be east of Springfield where MLCAPE and deep-layer shear are slightly more favorable (3000-4000 J/kg MLCAPE and 25-35 kts 0-6 km bulk shear). That being said, thunderstorms will be possible (30-50% chance) along and south of I-44 as far west as extreme SE KS. After 9 PM or so, the forecast diverges. The HRRR/RAP increases coverage and training of storms along the same boundary (along I-44) before the scattered line drops SE out of our area after 3 AM. Other CAMs suggest storms in northern MO to grow into a line and drop S into the area. Either solution, thunderstorm coverage and chances for much of the area will be highest between 8 PM and 3 AM. As for hazards, they still remain largely unchanged at this time. Deep-layer shear at 25-35 kts is still expected to be marginal, and 0-3 km SRH is low at 50-100 kts. This will favor mainly multicell clusters with damaging winds up to 60 mph and hail up to quarter size given 6-7 C/km mid-level lapse rates and a moist layer above an inverted V near-surface sounding profile. However, any perturbation in this shear could support a supercell or two (indeed the supercell composite parameter is at 4-10. Given weak flow producing <25 kts of storm-relative inflow and HREF model soundings showing high RH all the way through 600 mb, any supercell will likely be mini. This will bring a very low risk for tornadoes, especially out east where dewpoints will be higher and surface winds more S`ly, as well as the higher possibility for storm-to-storm interactions. A flash flooding hazard still exists, generally east of Springfield. With the line of storms forecasted to be oriented largely E-W, and shear vectors/mean wind being W`ly, training storms look increasingly likely, especially if storms do initiate during the afternoon and last through the night. Even in shorter periods of training, PWATs in the 1.75-2.00" range and a deep moist layer will make these storms efficient rainfall producers. The eastern Ozarks will especially be under the gun with recent rainfall received there. Many areas east of Springfield will receive up to an inch of rain under any thunderstorm. Training storms could give areas of 1-2" of rain with localized amounts up to 4-6" east of Springfield (30-50% chance). The 12Z HREF LPMMs have a bullseye over Texas/Wright/Webster counties, but the highest totals could set up anywhere east of Springfield. Trends will continue to be monitored and communicated accordingly. && .SHORT TERM /THROUGH FRIDAY NIGHT/... Issued at 300 PM CDT Thu Aug 15 2024 The outflow-induced cooler air this morning is quickly overturning to higher temperatures and dewpoints. As such, the Heat Advisory is continuing, with some obs along and south of I-44 already at 100-110 F Heat Index values. The advisory will be allowed to expire at 9 PM. There are areas north of the advisory that are hitting advisory criteria, but given the short-fused nature of the advisory, have not issued to the north. Please just be wary and cautious of heat when outside, even if not in an advisory. Otherwise, lows will be mild in the upper 60s to lower 70s tonight. Highs Friday will also be quite hot in the middle to upper 90s (higher temperatures toward the MO/KS and MO/AR borders). These will produce Heat Index values up to just below 105 F, however, cloud cover from overnight convection is still uncertain, and therefore a Heat Advisory will not be issued yet. But be aware again, that temperatures will be hot and humid along our state borders. 40-70% chance of thunderstorms Friday evening and night: The cold front forcing storms tonight will stall somewhere across the area Friday into Saturday. The current WPC forecast has it sitting along the I-44 corridor. NW`ly flow aloft will be in place as well. The boundary along with subtle shortwave energy aloft will be the focus for additional showers and thunderstorms Friday evening into the overnight hours. With SBCAPE at 1000-2000 J/kg during the afternoon/evening, scattered thunderstorm development is possible, but the main focus is overnight. After 8-10 PM, the right entrance region of a 300 mb jet streak, nose of a 25-30 kt low-level jet overtop the surface boundary, 7-8 C/km mid-level lapse rates, and 1000-1500 J/kg of MUCAPE will support numerous thunderstorms during the overnight hours across SE KS and extreme SW MO. With these parameters, isolated instances of 60 mph wind gusts and hail up to the size of quarters are possible (5% SPC risk). Additionally, shear vectors and the mean wind will be parallel to the surface boundary which could promote training of storms, introducing a marginal flash flooding threat as well. Lows will be in the middle to upper 60s Friday night. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Issued at 300 PM CDT Thu Aug 15 2024 With the pattern of an amplified ridge to the west and an amplified trough to the east persisting into the long term, NW`ly flow will dominate and a NNW-SSE quasi-stationary boundary will set up to our west. This pattern could bring chances for more nocturnal showers and thunderstorms with any source of lift that occurs, whether that be a shortwave rounding the ridge or a low-level jet overlapping the stationary boundary. These chances would be highly mesoscale, so long range global models will not capture precipitation chances well. With that being said, there are 15-25% chances for showers and thunderstorms Saturday night, Sunday night, and Tuesday night. Do not be surprised if these chances increase as medium/short range models start to come into play. Other than chances for nocturnal rainfall, the weather will be quite seasonable and calm in the long term. Highs will be in the 80s (lower 80s toward central MO) with lows in the mid-50s (eastern Ozarks) to mid-60s (MO/KS border). && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 1240 PM CDT Thu Aug 15 2024 The main hazard for this TAF period will be scattered thunderstorms, some perhaps severe. These will develop around the TAF site areas after 22Z. They will generally be more isolated in the 22-04Z timeframe, with increasing coverage and chances to impact the TAF sites between the 03-08Z timeframe as a line of broken thunderstorms moves through from the NW. Be aware that there is a scenario where all three TAF sites stay completely dry (40-60% chance), especially JLN and BBG. SGF has the highest chance of being impacted by a thunderstorm (50-70% confidence). Any storm that forms will be capable of producing wind gusts up to 50 kts and hail up to the size of quarters. Otherwise, a cumulus field should develop at 7000 ft between 21-02Z with winds generally out of the SSW at 8-12 kts. There will be a shift to W`ly winds towards the end of the TAF period. && .SGF WATCHES/WARNINGS/ADVISORIES... KS...Heat Advisory until 9 PM CDT this evening for KSZ097-101. MO...Heat Advisory until 9 PM CDT this evening for MOZ077-079>082- 088>097-101>106. && $$ MESOSCALE UPDATE...Price SHORT TERM...Price LONG TERM...Price AVIATION...Price