Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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813 FXUS63 KLSX 211122 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 622 AM CDT Fri Jun 21 2024 .KEY MESSAGES... - Hot weather continues into the beginning of next week with temperatures in the mid to upper 90s most days. Humidity increases early next week creating the potential for greater heat risk Sunday thru Tuesday. - The best chance of rain comes Saturday night as a cold front coming from the north triggers some thunderstorms. Not everyone will get rain, but northern areas have the best chance (70+ percent). Although there is some potential for damaging winds with thunderstorms Saturday night, the risk remains fairly low at this time. && .SHORT TERM... (Through Late Saturday Afternoon) Issued at 221 AM CDT Fri Jun 21 2024 The large ridge of high pressure which has brought the early summer heat to much of the country is centered over the Tennessee Valley this morning on a gradual trek back to the southwest. To the north, influences from the jet have kept a parade of thunderstorms across the Dakotas into Minnesota, well out of range of our forecast area. Under full control of the ridge today we will see temperatures rise to near or slightly warmer than we saw yesterday across the region, mostly in the low to mid 90s. We`ll likely see our warmest temperatures on Saturday as low level southwest flow continues to pump in that warm air while the influence of the ridge holds on enough to keep us dry during the day. As a shortwave trough tracks through the Great Lakes on Saturday it will push a cold front south behind it. Thunderstorms are expected to form on this front Saturday afternoon and evening over Iowa before pushing south and east overnight Saturday night. We`re not sure how well these will hold together as they push into our area Saturday evening and into the overnight, but no doubt the northern areas have the best chance of being affected. Enough instability and shear exist to pose a risk for strong to severe storms with damaging winds the primary threat, but it`s unclear how far into our area this threat may extend. Thunderstorms are likely to weaken as they move southeast and may dissipate altogether before the cold front makes it into the center of our forecast area Sunday morning. Kimble && .LONG TERM... (Saturday Night through Thursday) Issued at 221 AM CDT Fri Jun 21 2024 The front slows down and stalls in or near the southern part of our forecast area on Sunday adding some uncertainty to the temperature forecast. North of the front there will be at least some cooler air and some places may only peak in the 80s. To the south of the front the heat continues with some added humidity as well, creating the instability needed for thunderstorms to redevelop along the front Sunday afternoon and evening. Where those storms form early, some heat relief will come with the rain, but until then heat and humidity south of the front pushes heat index values near 100. Sunday`s front washes out as ridging builds over the Plains on Monday helping to push the hot weather fully back into our area, accompanied by greater humidity this time. More widespread dewpoints in the 70s are expected Monday and Tuesday helping to push the heat index several degrees higher than the forecast highs. While there is some uncertainty on the temperature forecast with NBM being near the top of the available guidance, I wouldn`t get too hung up on the forecast high temperature numbers. The story will be in the heat index which is going to be climbing above 100 Monday and Tuesday due to that added humidity even if we don`t hit the more extreme air temperature values. Synoptically it makes some sense for Tuesday to be the hotter of the two days as the air mass peaks just before the arrival of the next cold front, but there is some uncertainty on that. If the trough and cold front are a little quicker, or thunderstorms develop earlier in the day, then the near-record 100+ air temperatures will be less likely. Speaking of that trough, there is strong agreement that there will be a shortwave trough moving through the center of the country Tuesday into Wednesday with an air mass changing cold front accompanying it. The uncertainty lies in the timing and strength of this wave. Thunderstorms likely accompany the front, but how strong, where, and when is still uncertain. While we do expect a significant cool down (10 degrees or so) it`s less clear how long that cool down will last. That will depend on how deep this trough develops over the southeast US and how quickly the ridge builds back in from the west behind it. If we remain more under the influence of the trough then we`ll see more days in the 80s for the latter part of next week. But the hot weather isn`t that far away and it will build back in again by the weekend. If the ridge builds back quicker then we could see those mid to upper 90s return as early as Thursday. Kimble && .AVIATION... (For the 12z TAFs through 12z Saturday Morning) Issued at 616 AM CDT Fri Jun 21 2024 VFR flight conditions and light south-southwest winds are expected to prevail through Saturday morning. Expect scattered cumulus to develop late this morning/early afternoon between 5000-7000ft. There may be enough moisture across central and northeast Missouri into west central Illinois for the cumulus to go broken at times. Low clouds should disspate during the evening. Carney && .CLIMATE... Issued at 221 AM CDT Fri Jun 21 2024 With hot temperatures forecast next week, here are some of the daily high temperature records: MON JUN 24 TUE JUN 25 ST LOUIS 102 in 1988 102 in 1954 COLUMBIA 103 in 1988 102 in 1988 QUINCY 99 in 1988 102 in 1931 && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX