Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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795 FXUS64 KMRX 151453 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1053 AM EDT Thu Aug 15 2024 ...New UPDATE... .UPDATE... Issued at 1030 AM EDT Thu Aug 15 2024 A couple of light showers have developed over Greene County within the past hour or so. Expect this trend to continue through the afternoon and early evening where light showers and maybe a thunderstorm possible over and adjacent to the Appalachians. A couple hundredths to a couple tenths of an inch did fall over isolated parts of the higher terrain yesterday. Inherited forecast check out okay, only minor tweaks to some PoP and cloud cover, mostly. KS && .SHORT TERM... (Today and tonight) Issued at 314 AM EDT Thu Aug 15 2024 Key Messages: 1. Dry weather to continue, humidity a little higher today. Discussion: Narrow upper ridge axis will be sliding overhead today, with sinking air over the wider region. 00z CAMs are quiet with most forming light returns over the mountains, whereas the most recent HREF had at least some activity dotting both the mountains and the rim of the Plateau. Left a slight chance for a shower in over the East Tennessee Mountains, where the better low level CAPE might allow for a brief shower during peak heating. Very unlikely for anyone in the valleys to see rainfall once again today. Otherwise low level winds will finally pivot to a more southerly to southwesterly flow, and while they`ll remain weak, it marks the beginning of low level moisture flowing northwards once more. Depending on cloud coverage tonight, it might also allow for another round of patchy fog, especially with guidance keeping rain at bay through sunrise on Friday. && .LONG TERM... (Friday through Wednesday) Issued at 314 AM EDT Thu Aug 15 2024 Key Messages: 1. Scattered to numerous showers and storms Friday and Saturday, with some strong to severe storms possible. 2. More scattered showers/storms possible Sunday and Monday, with better coverage across the north. 3. Dry Tuesday and Wednesday. Discussion: Models are in general agreement that an upper low over the western Great Lakes region early Friday will move east/southeast with multiple short waves dropping southeast around the back side, carving out a significant upper trough over the eastern CONUS by early in the week. However, the models differ significantly in the details and have been rather inconsistent. Timing and strength of the individual short waves is uncertain as is the timing of a cold front that will drop southeast across our area sometime in the Saturday/Saturday night time frame, which leads to uncertainties in how the convection will unfold. The overall environment continues to show significant effective bulk shear for this time of year although latest runs have generally trended a bit lower for Friday with values more in the 15 to 25 kt range, and show the higher values of 20 to 30+ kt for Saturday. Models vary widely on how much convective energy will be available as well, but perusing the HREF and SREF ensemble means would suggest SBCAPES will be in the 500-1500 J/kg range Friday and more like 1000-2000 J/kg Saturday. Overall the atmosphere looks supportive of more organized convection with some strong to severe storms possible both Friday into Friday evening and again Saturday. Damaging winds will be the primary severe threat with these storms. In addition, any areas that see repeated and/or prolonged rounds of heavy rainfall may experience localized flooding. Poor agreement in the CAMS does not lend high confidence to timing of convection Friday, but current thinking is it will be focused more late morning into the evening hours and this will likely be the case for Saturday as well. Additional upper short wave features are expected to be moving through the upper trough and are expected to bring additional showers/storms Sunday and to a lesser extent Monday with the better coverage across the north. Cooler air will also be moving in behind the front, with temperatures likely below normal both days. Surface high pressure will build in from the north Tuesday as the trough axis shifts further east, providing dry weather both Tuesday and Wednesday along with a slight warming trend. && .AVIATION... (12Z TAFS) Issued at 652 AM EDT Thu Aug 15 2024 Though an isolated shower is possible in the wider region today, no impacts to the terminals are expected. Dry weather and VFR should persist through the TAF period once more. Winds will go from calm to light southerly or southwesterly flow today. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 91 72 93 73 / 10 10 40 50 Knoxville McGhee Tyson Airport, TN 90 71 90 71 / 10 10 50 70 Oak Ridge, TN 89 70 89 70 / 10 10 50 70 Tri Cities Airport, TN 86 66 85 69 / 10 10 50 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...Wellington AVIATION...Wellington