Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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864 FXUS64 KMRX 041939 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 339 PM EDT Thu Jul 4 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Friday) Issued at 312 PM EDT Thu Jul 4 2024 Key Messages: 1. Low chance for a shower or thunderstorm into this evening, mostly across northern portions of the forecast area. 2. Numerous to widespread showers and thunderstorms expected to impact the area tomorrow ahead of a cold frontal passage. Marginally severe storms are possible. Discussion: Showers have been very isolated this afternoon across parts of the forecast area, mainly north of I-40. Lightning hasn`t yet been observed and we are approaching the hottest part of the day so only a short window of time remains for anything to develop. If a storm does occur, there`s a chance it could be strong with heavy downpours and gusty winds. Heat indices have been hovering in the low 100s across parts of the area this afternoon. Expect the advisory to expire at 8 PM EDT as we turn cooler into the evening hours. Tomorrow: a bit of moving parts with tomorrow. A trough will pivot across the northern part of the country into tomorrow with a low pressure center pretty much stacked below it. A cold front will extend from this system bringing some relief to the area for the weekend. With increased cloud cover ahead of this system as well as a west to east draped boundary bringing precipitation ahead of the front, temperatures tomorrow will not be as hot as today. A few degrees lower, which makes a difference with how moist the atmosphere is. Therefore, heat indices will be below the advisory criteria. This could potentially change for tonight`s forecast like it did last night for higher heat indices. Numerous to widespread much needed rain and some thunderstorms will increase in probability tomorrow into the afternoon and evening. Only a marginal threat for severe weather expected as indicated by the SPC this afternoon. Ingredients-wise, CAPE will be in the neighborhood of the 1000-2000 range, more than enough moisture, and although shear not all that strong vertically, all could support organized cells and clusters of storms. The very moist airmass which makes sense for such high PWs, initiation of convection will not have an issue with the destabilization that will occur with increased day-time heating. With that being said, the main threats with any strong to possibly severe storms tomorrow will be damaging winds and heavy rain makers. We are also in that time of the year when parameters aloft don`t support the typical spring time severe set-up. && .LONG TERM... (Friday night through next Thursday) Issued at 312 PM EDT Thu Jul 4 2024 Key Messages: 1. Not quite as hot, but still slightly above normal through much of the long term. 2. Mostly dry conditions expected this weekend in the wake of a front Friday night into Saturday morning. 3. Rain chances increase notably early next week. Discussion: In general, the long term will feature a persistent troughing pattern from the Great Lakes into the Ozarks, while upper ridging remains situated from Florida up through the mid-Atlantic coast. This will leave our forecast area beneath weak, but increasingly south to southwesterly flow. Resulting lack of strong ridging will mean we`ll see a break from the mid 90s heat of late, but upper 80s to low 90s will still be on tap, especially in the south. Rain chances will be mostly confined to thunderstorms in the mountains through the weekend, but coverage of afternoon convection should take a notable uptick as we move into the Mon-Wed timeframe. Going into a bit more detail here, a front will be moving through the region Friday night into Saturday morning. It`s not a particularly strong front but models do show decreasing dewpoints on Saturday along with northwesterly low level winds. Would think this will favor a lack of convection during the daytime hours on Saturday, especially by the afternoon hours. Did leave some rain chances lingering in the mountains through late in the day but I`m not exceptionally confident in that aspect of the forecast. Low level convergent flow between the surface high to our north and southeasterly surface to H85 flow east of the Appalachians will likely result in some afternoon convection over the mountains again on Sunday but would not be surprised of this rainfall stays mostly on the NC side of things and thus expect dry conditions most places to round out the weekend. For the Monday through midweek timeframe, the aforementioned upper trough to our northwest shifts slightly closer as a plains shortwave moves through the base, and the remnants of Baryl are pulled northeast out of Texas towards the Ozarks and lower Mississippi river valley. Expect to see diurnally driven, widespread showers and thunderstorms across the southern Appalachian region as a result. && .AVIATION... (18Z TAFS) Issued at 141 PM EDT Thu Jul 4 2024 Isolated showers have started to pop over parts of the forecast area with CHA being the closest to activity currently. VCSH has been kept at all terminals this afternoon to reflect the possibility. Up near TRI will experience the best chance of being impacted by a shower or storm, but for the most part guidance has been all over the place on how today is going to lay out. Thus, confidence not all that high either as far as coverage and what could be expected. Gusty southwest winds at times can be expected at TYS and TRI through the evening before conditions turn calm overnight. There is a slim chance TRI may see MVFR fog late tonight. Kept the line added in this morning. Better chance for showers and thunderstorms appear tomorrow ahead of a cold FROPA. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 78 94 75 92 / 20 70 50 20 Knoxville McGhee Tyson Airport, TN 77 92 73 90 / 20 70 70 20 Oak Ridge, TN 75 91 72 90 / 30 70 60 10 Tri Cities Airport, TN 72 91 72 88 / 10 70 70 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for Bradley- Hamilton-Loudon-Marion-McMinn-Meigs-Northwest Blount- Northwest Monroe-Rhea-Roane-Sequatchie-West Polk. VA...NONE. && $$ SHORT TERM...KS LONG TERM....CD AVIATION...KS