Area Forecast Discussion
Issued by NWS St. Louis, MO
Issued by NWS St. Louis, MO
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028 FXUS63 KLSX 110817 AFDLSX Area Forecast Discussion National Weather Service Saint Louis MO 317 AM CDT Tue Jun 11 2024 .KEY MESSAGES... - Well above normal temperatures will move in by Thursday and persist through the weekend. This combined with increasing moisture will create heat indices in the 100 to 105 range by Sunday. - Severe weather is possible Thursday afternoon through evening with the main threats being large hail and damaging winds. && .SHORT TERM... (Through Late Wednesday Afternoon) Issued at 313 AM CDT Tue Jun 11 2024 Dry weather will persist through the short term. Otherwise, the surface ridge will continue to weaken and slowly slide off to the east over the next 36 to 48 hours. So surface flow will gradually shift to the south to southwest today. However, it will be a fairly weak flow thus temperatures will only be around 5 degrees warmer than yesterday with some high thin cirrus streaming in. In the meantime, a system will continue to slide east along the U.S./Canadian border today, dragging a cold front across the upper Midwest. The latest guidance has the southern end of the cold front approaching northern Missouri by this afternoon, but moisture remains limited and the front weakens and washes it out, thus no rain is expected. By Wednesday, 850mb temperatures will be rising into the upper teens, thus highs will be in the upper 80s to low 90s. Latest LREF ensemble concurs, as 40-70% of the members have highs greater than 85 degrees. Even though low level moisture will be on the increase with dewpoints rising back into the 60s from west to east, heat indices will be near actual surface temperatures on Wednesday. Byrd && .LONG TERM... (Wednesday Night through Monday) Issued at 313 AM CDT Tue Jun 11 2024 As upper level ridging continues to build across the central part of the country mid week, zonal flow along the U.S./Canadian border will remain active through the period. The next system will be moving through the upper Midwest Wednesday night into Thursday and activity associated with it should remain well north of the forecast area with complex weakening as it pushes east southeast into the lower Great Lakes Thursday morning. In the meantime, the latest deterministic as well as ensembles indicate that 850mb temperatures will be rising to between 20 and 22C on Thursday. Thus expect widespread highs in the low to mid 90s. This combined with dewpoints in the 60s will create heat indices near 100 for the first time this summer. As for rain chances Thursday afternoon through evening, with increasing instability, ML CAPEs 3000+ J/kg, 0 to 6 km bulk shear 20- 30kts and ML LR around 7.5C/km, may support the potential for supercell development initially just to our west, then transition to line segments as the activity moves east across the region. The main threats will be large hail and damaging winds. As the cold front sinks south, the activity will taper off late Thursday night. By Friday morning, the cold front will be south of the forecast area and stall out, before moving back north as a warm front on Saturday. So temperatures on Friday will be a bit cooler, but still above normal in the upper 80s to low 90s. Beyond that, there is a lot of uncertainty on additional chances of showers and storms due to the differing solutions among the deterministic and ensembles as disturbances slide along the periphery of the upper level ridge. For now the main forecast issue will be the well above normal temperatures through the weekend and into early next week. Byrd && .AVIATION... (For the 06z TAFs through 06z Tuesday Night) Issued at 1033 PM CDT Mon Jun 10 2024 Dry and VFR flight conditions will continue through the rest of the TAF period with light winds. Light and variable overnight winds will become southerly then southwesterly by Tuesday afternoon as surface high pressure shifts to the east. MMG/Glass && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX