Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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078 FXUS64 KMRX 220517 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 117 AM EDT Sun Sep 22 2024 ...New AVIATION... .UPDATE... Issued at 955 PM EDT Sat Sep 21 2024 New update for the rest of the night as showers have almost ended with the last activity over the southern Tennessee Valley. Blow off clouds from upstream convection in middle Tennessee and south central Kentucky was keeping variable high clouds over the east Tennessee Valley but this has been decreasing over the last hour. Have added fog over much of the region for late tonight and early Sunday as the air mass is not quite as dry as this morning and yesterday with fog likely forming where winds are calm and skies partly cloudy. A few areas may have dense fog. Lows still expected to be in the mild 60s overnight tonight. Updated forecast already sent. && .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... (06Z TAFS) Issued at 1245 AM EDT Sun Sep 22 2024 Possible fog development is a concern mainly TRI toward sunrise although right now probability looks marginal for inclusion, so will just include an MVFR vsby group for fog toward sunrise. There may be a shower or even a thunderstorm around later today mainly CHA/TYS, but probability is low so will not include mention in TAFS. Other than the aforementioned TRI fog, will have a VFR forecast for the period all sites. Winds will generally be light. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 94 70 93 70 / 20 10 20 10 Knoxville McGhee Tyson Airport, TN 92 68 90 68 / 20 10 30 20 Oak Ridge, TN 91 67 89 67 / 20 20 40 20 Tri Cities Airport, TN 88 63 84 64 / 10 20 60 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...TD LONG TERM....DH AVIATION...