Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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316 FXUS63 KLSX 301735 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1235 PM CDT Thu May 30 2024 .KEY MESSAGES... - The next best chance of rain will be Friday evening through Saturday, with limited thunderstorm potential. - The region returns to a warm and active pattern for the work week. && .SHORT TERM... (Through Late Friday Night) Issued at 253 AM CDT Thu May 30 2024 Mid-level water vapor imagery shows a trough over the Great Lakes region, extending into the Ohio River Valley, and a ridge across the central CONUS. A shortwave is evident in the western side of the ridge, and a weak surface low has formed across western Kansas this morning. The current northwesterly mid-level flow will turn southwesterly today with the approach of the ridge axis and the shortwave. The southwesterly flow will push a warm front northeast through the forecast area today, bringing warm, moist air into the region ahead of the surface low and associated precipitation. Today will be a few degrees warmer than yesterday, while the approach of the ridge axis will keep the area dry. The surface low will approach the region overnight tonight into tomorrow morning, and warm air advection precipitation is possible as early as late morning Friday across central Missouri. The best chance for rain will be near the surface low as it pushes through Friday evening into Saturday, as this is where the best ascent will be. Thunderstorms will be largely isolated as instability will be greatly limited (generally less than 200 J/kg of MUCAPE), but I can`t rule out a few rumbles of thunder. Given the lack of widespread instability, I expect rain to be more uniform in distribution rather than showery. QPF amounts will be beneficial but not concerning, given the lack of instability. By Sunday evening the probability of 0.5 inches of total precipitation is 50-80%, while the probabilities of 1 inch of rain or more peak near 40% across central Missouri. MRM && .LONG TERM... (Saturday through Wednesday) Issued at 253 AM CDT Thu May 30 2024 The surface low and associated precipitation will continue its march northeastward in step with the movement of the mid-level shortwave. Mid- and low-level subsidence in the wake of the shortwave will help to clear precipitation from the region Saturday, but showers could still linger into the afternoon hours. A weak surface high will build into the region overnight, but it will quickly move east and put the region back into southerly surface flow. Southerly flow and daytime heating may be enough to generate some instability across the region during the day Sunday, deterministic global guidance shows anywhere from 100-1400 J/kg (that`s not a typo) of MUCAPE Sunday afternoon. Areas that see instability on the higher end of that wide spectrum could see a few pop-up showers and thunderstorms during the afternoon hours. Despite this chance for isolated precipitation, most areas will be dry through the day Sunday. In the wake of the weekend shortwave the mid-level pattern will become quasi-zonal, leaving the region open to multiple shortwaves to move through the mid-Mississippi Valley. There are differences in the timing, location, and intensity of these shortwaves across the ensembles, which accounts for the isolated to numerous mention of showers and thunderstorms in the forecast through the work week. While there is uncertainty in the timing of precipitation, confidence is high that under this flow regime temperatures will warm to near or above normal and instability will return to the region. This reintroduces the potential for strong to severe thunderstorms across the region, which is highlighted in the CIPS and CSU guidance, which begin to highlight the mid-Mississippi Valley for severe thunderstorm potential on days 6 and 7. MRM && .AVIATION... (For the 18z TAFs through 18z Friday Afternoon) Issued at 1230 PM CDT Thu May 30 2024 Dry and VFR conditions are expected through the end of the period. The only exception is that there is a chance of showers and thunderstorms over central Missouri after 15Z on Friday morning and at STL on Friday afternoon. These chances are too low to include in the TAFs at this time. Winds will remain out of the southeast at around 10 knots through the period. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX