Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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593 FXUS63 KLSX 150325 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1025 PM CDT Sat Sep 14 2024 .KEY MESSAGES... - The remnants of TC Francine will continue to erode through Sunday, resulting in gradual warming and drying. These conditions persist next week. && .SHORT TERM... (Through Late Sunday Night) Issued at 206 PM CDT Sat Sep 14 2024 Remnant moisture and upper-level forcing from TC Francine remains stalled across the Lower Mississippi River Valley in the absence of any appreciable steering flow to advect it east. Further north, a surface high over the Great Lakes is drawing easterly surface winds and marginally-drier dew points into the forecast area. As a result of this weak confluence in the low-levels, a narrow plume of moisture stretches across western and central Missouri stretching down through the Ozarks. This tropical moisture, along with weak mid- level vorticity maxima near Francine`s remnant low, will allow for a 15-30% chance for showers to persist along and south of the I-44 (MO)/I-64 (IL) corridor this evening. That said, any rain that does fall will be light and most of the night will remain dry. Thunderstorm chances are more scarce (up to 15%) with plenty of warm air aloft limiting instability. The moisture axis shifts west by Sunday with high surface pressure further impinging on the region from the east. This will not only shunt the 15-40% shower and thunderstorm chances west of the Mississippi River, but will also allow for more abundant sunshine (and warmer temperatures) further east. Guidance continues to struggle with this weakly-forced environment, producing far too much precipitation. The rain chances were adjusted slightly lower, but the moisture may have marginally-stronger forcing with which to work and precluded greatly reducing or removing the chances. While the gradual warming trend is most certain, exact temperatures are still unclear since they will greatly hinge on could cover and the location of the upper-level low. That said, those along and east of the river have the best chances of reaching the mid/upper 80s during the afternoon with slightly cooler temperatures further west. Temperatures stay seasonably warm overnight Sunday into Monday with clouds overhead, but rain chances will be next to zero with the upper-level wave disintegrating. MRB && .LONG TERM... (Monday through Next Saturday) Issued at 206 PM CDT Sat Sep 14 2024 While broad upper-level ridging will persist throughout most of the CONUS to start the work week, which overall favors warmer and drier weather, there is one feature that has the outside chance throw a curveball at this forecast. An organizing area of convection off the Carolina coastline has potential to form a tropical cyclone over the next few days (see the NHC Tropical Weather Outlook for more information). Regardless of whether it strengthens into a TC, this wave will drift west onshore along the southern periphery of the upper-level ridge and gradually weaken amidst this feature. What happens from here will factor into how warm we get mid-week and beyond. A sizable majority of global ensemble members keep the upper-level wave far from the Mid- Mississippi Valley, which would allow for uninhibited warming (as high as the upper 80s to low 90s) for the latter half of the work week. If the second solution, which features the wave getting close to the forecast area, comes to fruition, we`d see temperatures a little bit cooler. That said, the difference is pretty minor (as much a 5 degrees) and largely inconsequential. What the ensemble guidance seems quite certain of is that we will be entering a several-day period of dry weather under the strong ridge established over the eastern two-thirds of the CONUS. Even if the wave mentioned earlier manages to reach us, it will be very weak and moisture-starved, making it very unlikely to produce much rain at all. While the dry weather this week is preferred for outdoor activities, this forecast does not bode well for relief from the gradually-worsening drought. Coupled with warm temperatures promoting stronger evapotranspiration, and our climatologically- driest part of the year approaching, drought conditions are likely to either remain steady state or continue gradually deteriorating through the week. A strong upper-level trough will gradually expand and drift east next weekend, which forces a frontal boundary into the region. This feature, which doesn`t actually reach us in the forecast period, presents our next shot for widespread rain. MRB && .AVIATION... (For the 06z TAFs through 06z Sunday Night) Issued at 1023 PM CDT Sat Sep 14 2024 Main concern for overnight tonight is on fog as earlier shower/thunderstorm activity has diminished. River valley fog is expected with the worst conditions (IFR visibilites) expected at KSUS. Also added some MVFR fog at KJEF and KCPS. Any fog should quickly lift and dissipate within 1-2 hours after sunset. Additional scattered showers/weak thunderstorms are forecast on Sunday, mainly across portions of southeast Missouri during the afternoon hours and south of the terminals. Gosselin && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX