Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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240 FXUS63 KLSX 221712 AFDLSX Area Forecast Discussion...Updated Aviation National Weather Service Saint Louis MO 1212 PM CDT Sat Jun 22 2024 .KEY MESSAGES... - Hot weather continues today, but humidity increases early next week making it feel even hotter. The greatest heat risk will be Monday and Tuesday when Heat Index values near 105 degrees are expected. - Our best chance of rain is tonight when thunderstorms forming in Iowa move south ahead of a cold front. These storms are expected to be weakening as they arrive this evening, with the chances for rain decreasing as the front moves south through the night. Although some of the strongest storms could contain damaging winds, the severe weather threat remains low. The next chance for rain comes Tuesday into Wednesday when the next cold front approaches. && .SHORT TERM... (Through Sunday) Issued at 240 AM CDT Sat Jun 22 2024 Upper level ridging over the Lower Mississippi Valley this morning will continue to build back to the west today. We`ll be on the northern periphery of the influence of this ridge with hot temperatures expected. Low level southwesterly winds will aid in low level mixing downstream of the Ozarks helping to add a degree or two to the temperature across the Missouri Valley and into the St Louis metro. So while temperatures the last few days may have been a touch cooler than expected, confidence is greater that temperatures today will be warmer especially in that downslope affected area. Thankfully, though, humidity will not be extreme, only adding a couple of degrees to the Heat Index, peaking near 100. The best low level moisture has been pooling across Nebraska and Iowa ahead of a surface front. This has been where most of the thunderstorms have been tracking the last few days and that will be the case again this evening. A shortwave trough tracking east through the Upper Midwest will give that front a push southward tonight. Thunderstorms are expected to initiate in central and eastern Iowa this afternoon and evening in the axis of greater instability ahead of the front. As the shortwave trough moves by aloft it will add just enough wind shear into the mix to create the potential for more organized thunderstorms to develop. While individual storms and clusters will be moving east with the mid level flow, the overall line will be sinking southward as the front moves south this evening. It is likely that we`ll see at least some of this activity move into our area, but CAMs are generally in agreement that storms will be weakening and eventually dissipating as they head south and away from the better moisture and instability while the best lift with the shortwave trough pushes off to the east. There continues to be at least some risk for strong to severe storms with damaging winds the primary threat this evening, but the risk remains low as the overall convective trend will be decreasing as storms arrive. The best time window for our area to see severe storms is from about 9PM to 1AM. Unfortunately there`s a chance that most of us won`t see rain from this, but it is our best opportunity for rain in a while and our last opportunity before the heat builds again. Models continue to trend rather quick with Saturday night`s cold front, with strong agreement that it will push south of our area by Sunday morning. As a result, the forecast continues to trend a bit cooler on Sunday with thunderstorm chances along the front shifted further south and mostly out of our area by Sunday afternoon. Kimble && .LONG TERM... (Sunday Night through Friday) Issued at 240 AM CDT Sat Jun 22 2024 Upper level ridging reorganizes over the Rockies and shifts into the Plains early next week. This will push the hot weather quickly back into our area, this time accompanied by greater humidity. We still have high confidence that the greatest heat risk for our area will be Monday and Tuesday. While NBM continues to be at the top of the guidance spread in terms of air temperatures, it`s not so much the air temperature but the Heat Index that is the greater focus. Dewpoints near 70 will make this round of heat feel noticeably more intense, with heat index values peaking near 105 degrees. It is likely that we will need a Heat Advisory for much of the area on one or both days. The next trough rounding the top of the ridge and tracking east across the northern part of the country will send a cold front southward Tuesday into Wednesday. This will provide at least a brief break from the heat and our next chance for thunderstorms. While we certainly couldn`t rule out a chance for strong to severe storms at some point as the front moves through, it`s not a strong chance at this point. While instability will likely be strong in the hot and humid air mass, the bulk of the forcing and better wind shear seems more likely to remain to the north closer to the Great Lakes. So at this point I think the main story here is that this represents our next chance of rain, while the severe weather story is still murky. The cold front does provide a brief break from the heat, but it doesn`t last long. Models are coming into better agreement that the ridge builds back in rather quickly, with temperatures pushing back into the mid 90s again before the end of the week. It looks like it will also be accompanied by at least moderate humidity as well, so we may be looking at another period of greater heat risk next weekend. Kimble && .AVIATION... (For the 18z TAFs through 18z Sunday Afternoon) Issued at 1205 PM CDT Sat Jun 22 2024 Dry, VFR conditions with gusty southwest winds are forecast this afternoon. A cold front will approach by late evening, moving through KUIN just after midnight and central Missouri and metro St. Louis sites just before dawn. Scattered showers and thunderstorms are possible along/ahead of this boundary, with best chances in parts of northeast Missouri and west-central Illinois including KUIN. Did not make much in the way of changes with this TAF package, with a TEMPO at KUIN from 0400 to 0600 UTC and PROB30 groups at the metro terminals from 0700-1000 UTC. Central Missouri sites have the least chance of any showers/storms so no mention for those terminals. After the front moves through, look for winds to veer to the northwest. Some guidance also hints at a brief period (1-3 hours) of MVFR ceilings behind the front, but the signal is too weak to add a BKN025 group anywhere. However, did add a SCT025 mention at KUIN and the metro terminals for a few hours behind the frontal passage. Gosselin && .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