088 FXUS63 KLSX 252302 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 602 PM CDT Sun Sep 25 2022 .SHORT TERM... (Through Late Monday Night) Issued at 214 PM CDT Sun Sep 25 2022 Dry, tranquil fall weather is forecast again Monday. An upper-level longwave trough will continue to very slowly move eastward over Ontario, Quebec, and the eastern Great Lakes through Monday. This trough, in part with an upper-level ridge over the Rocky Mountains, will maintain deep northwesterly flow over the Midwest that was established today. A mid-level shortwave trough rounding the longwave trough is progged to force a very weak cold front southward through the CWA late this evening and overnight. Since moisture will be quite limited (PW <0.5") in addition to synoptic-scale ascent, this front will be dry with its only impact expected to be some passing upper-level clouds and post-frontal low- level CAA. As a result, 850-hPa temps will fall into the mid to upper single digits C by Monday, leading to high temps around 10 F cooler than today or in the mid-60s and low-70s F with ample insolation and mixing between passing upper-level clouds. This diurnal mixing will also combine with a relatively tight surface pressure gradient to yield occasional northwesterly wind gusts of 20 to 28 kt once again Monday afternoon. Pfahler .LONG TERM... (Tuesday through Next Sunday) Issued at 214 PM CDT Sun Sep 25 2022 In few words; dry, tranquil fall weather will continue through much of the upcoming week. But if you are interested in hearing this message in more words, read below. The upper-level wave pattern across North America will remain similar Tuesday into Wednesday but with slow eastward propagation. This evolution will favor mid-level height rises across the Midwest at the western flank of the upper-level longwave trough and arrival of a strengthening, increasingly anomalous (central MSLP exceeding 99th percentile of climatology) surface/low-level anticyclone to the upper Midwest and Great Lakes. With the CWA anticipated to be at the south side of the anticyclone through Wednesday, low-level northerly to northeasterly flow will favor additional CAA during that time. Therefore, seasonably cool temps will cool further into Wednesday with high temps forecast to only be in the 60s or around 70 F CWA- wide. The established cool airmass, nearby anticyclone, and mostly clear skies could also facilitate efficient radiational cooling into Wednesday and Thursday mornings. Low temps these mornings may fall into the upper 30s F in portions of the northern half of the CWA. In fact, NBM probability of low temps less than or equal to 36 F are around 40 percent at Kirksville, MO but are 5 percent or less at Quincy, IL. Therefore, the potential for patchy frost will need to be monitored across primarily parts of northeastern MO Wednesday and Thursday mornings. Thursday through Friday, an upper-level ridge is anticipated to traverse the Midwest to Northeast. At the same time, model guidance indicate that TC Ian will continue advancing northward through the Gulf of Mexico before making landfall and moving inland through the Southeast. After briefly slowing as TC Ian encounters the ridge, the TC should move northward more quickly and eventually curve toward the east at the end of the workweek into next weekend as it moves around the west side of the ridge and interacts with a potential upper-level trough upstream of the ridge. However, WPC Cluster Analysis EOFs for this time period highlight differences in timing and amplitude of the ridge and trough, dictating TC Ian's exact track. At this juncture, it appears the main influence the TC will have is its associated subsidence reinforcing a branch of the surface/low-level anticyclone across or near the Midwest, west of the TC's most likely track. Even in the absence of appreciable low- level temp advection coincident with the anticyclone branch, NBM 25th and 75th percentiles both gradually warm after Wednesday as repeated days of considerable insolation modify the cool airmass in place. Pfahler && .AVIATION... (For the 00z TAFs through 00z Monday Evening) Issued at 600 PM CDT Sun Sep 25 2022 Wind gusts and diurnal cumulus will dissipate after sunset, resulting in quiet conditions overnight. Winds will begin to increase again Monday, becoming gusty during late morning through the afternoon. Wind gusts of 20+ kts are expected at all terminals. Dry, VFR conditions will prevail during the TAF period otherwise. Jaja && .PRELIMINARY POINT TEMPS/POPS... Saint Louis 54 71 50 73 / 0 0 0 0 Quincy 50 68 46 68 / 0 0 0 0 Columbia 49 73 47 74 / 0 0 0 0 Jefferson City 49 72 47 75 / 0 0 0 0 Salem 49 70 44 70 / 0 0 0 0 Farmington 49 71 46 73 / 0 0 0 0 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX