Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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659 FXUS63 KLSX 172331 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 631 PM CDT Wed Jul 17 2024 .KEY MESSAGES... - Dry weather along with well-below normal temperatures is forecast through Saturday. - Temperatures are expected to moderate slightly heading into next week. Rain chances also return, but at this time look to be focused in the afternoon/early evening each day and largely unorganized (not widespread, low chance for heavy rainfall/flash flooding and severe weather). && .SHORT TERM... (Through Late Thursday Night) Issued at 205 PM CDT Wed Jul 17 2024 Isolated to scattered showers continue along the cold front. A few lightning strikes are also expected over parts of southeast Missouri through the late afternoon hours given 1000+ J/kg of CAPE. This boundary is progressing to the southeast, and is expected to clear the CWA just before dusk early this evening. Further to the northwest, there is a dewpoint gradient with an uptick in northerly surface winds. This lower humidity and cooler air mass will infiltrate the remainder of the area through early overnight. The strength of this incoming air mass is certainly notable for mid/late July. The surface anticyclone (1022+ hPa) over the Upper Midwest on Thursday is above the 99th percentile of climatology. In terms of 850-hPa temperatures (+9 to +12C), those values are forecast to be below the 2nd percentile. This impressively cool air mass will first enter northern sections of the area tonight, with lows in the mid 50s (~10 degrees below normal). Further southeast, lows in the low to mid 60s are expected. Thursday`s highs are expected to be in the upper 70s to near 80 degrees or about 10 degrees below normal across the entire area. Thursday night`s lows should be cooler than tonight in most locations, with more widespread mid to upper 50s forecast. Gosselin && .LONG TERM... (Friday through Next Wednesday) Issued at 205 PM CDT Wed Jul 17 2024 (Friday - Saturday) There is very little change in the synoptic pattern heading into early this weekend as the strong surface high very slowly moves eastward. Dry weather along with below normal temperatures are expected to continue, though temperatures should moderate slightly. (Saturday Night - Next Wednesday) Ensemble guidance is in good agreement that a midlevel shortwave trough will move southward out of the northern Plains Saturday night. This feature is then expected to become cutoff from the mean flow across southeast Canada and become quasi-stationary. The mid- Mississippi Valley is forecast to be downstream/east of this cutoff low, with areas of vorticity pinwheeling northeast around the eastern periphery of the midlevel anticyclone. This pattern should mean a return of shower and thunderstorm chances to the area. At this early juncture, chances will likely be at least partially influenced by daytime heating/when instability is maximized. Deterministic guidance at this time are not showing a strong low-level jet any of the nights. In addition, wind shear and instability do not look particularly high nor does precipitable water values (only slightly above normal). This all indicates likely unorganized, weaker convection that should not be a high threat for severe weather nor heavy rainfall/flash flooding. Due to the increase in cloud cover and rain chances, daytime high temperatures should stay below normal (in the 80s) though nighttime readings should moderate back into the 60s to near 70 degrees (very close to seasonal normals). Gosselin && .AVIATION... (For the 00z TAFs through 00z Thursday Evening) Issued at 629 PM CDT Wed Jul 17 2024 VFR flight conditions through the forecast period. As for winds, north winds will diminish by late this evening, then pickup from the northeast by mid morning on Thursday. Byrd && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX