Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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201 FXUS64 KMRX 212303 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 703 PM EDT Sat Sep 21 2024 ...New AVIATION... .SHORT TERM... (This evening through Sunday) Issued at 240 PM EDT Sat Sep 21 2024 Key Messages: 1. Isolated showers and possibly a thunderstorm through early evening. Greatest coverage over Plateau and southwest Virginia/northeast Tennessee. 2. Unseasonably hot conditions today and Sunday. Temperatures near 10 degrees above normal. Discussion: A weak wave is rotating around the upper ridge across the Ohio valley and central Appalachians. Meso-analysis shows best instability across the northern Plateau into southwest VA/northeast Tennessee with MLCAPES of 500-1000. These areas have the best chance of showers and possibly a thunderstorm through early this evening. Locations that see any rainfall will have a decent chance of fog development overnight. Otherwise, partly cloudy sky with a stray shower possible. For Sunday, upper ridge remains over the region allowing for another unseasonably hot day with temperatures from 5 to 10 degrees above normal. HREF and deterministic models agree with another short-wave moving toward the area during the afternoon. MLCAPES will be best across the Plateau and western sections of the Tennessee valley. Widely scattered to scattered late day showers and possibly a thunderstorm are expected. && .LONG TERM... (Sunday night through next Saturday) Issued at 240 PM EDT Sat Sep 21 2024 Key Messages: 1. Increasing chance of convection during the extended but confidence is low on probabilities and timing due to evolution of the tropical system in the gulf. 2. Can not stress enough to not focus on deterministic models on timing, strength, and location of tropical systems late this week. Main message is that the CPC is depicting a greater than 60 percent probability of tropical development in the Gulf. Discussion: For Monday through Wednesday, ensemble cluster analysis shows a slow change in the upper level pattern with a northern and southern stream short-waves weakening the upper ridge over the area. This will allow for increasing coverage of convection over the region especially along and north of interstate 40. Some much needed rainfall is possible. For Thursday through Saturday, forecast confidence decreases as CPC probabilities shows tropical development in the gulf combined with continued upper trough over the mid-section of the nation. The evolution of these systems will play a large role in the timing, direction, and strength of the tropical system and associated rainfall. && .AVIATION... (00Z TAFS) Issued at 702 PM EDT Sat Sep 21 2024 A few showers developing across east central and SE TN early tonight so expect a few hours of isolated showers/storms but not enough coverage to put in evening TAF forecast. Main concerns later tonight will be fog development late tonight/Sunday morning at TRI between 08-12Z Sunday. Due to lack of fog last night and overall dry soil, forecasting only A TEMPO MVFR. Otherwise, VFR conditions expected with weak surface pressure gradient continuing. Only light wind speeds. Isolated showers expected to develop across the Plateau counties, SW Virginia and NE Tennessee Sunday but confidence is not high enough to include in TAFs. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 70 94 70 93 / 0 10 0 20 Knoxville McGhee Tyson Airport, TN 68 92 68 90 / 10 10 20 30 Oak Ridge, TN 68 91 67 89 / 0 20 20 40 Tri Cities Airport, TN 62 88 63 84 / 0 10 20 60 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DH LONG TERM....DH AVIATION...TD