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Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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278 FXUS64 KMRX 171902 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 302 PM EDT Sat Aug 17 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Sunday) Issued at 301 PM EDT Sat Aug 17 2024 Key Messages: 1. Scattered to numerous showers/storms through the afternoon and tonight, with a few severe storms possible. 2. Scattered to numerous showers tomorrow in northern sections under a broad trough. Discussion: Mesoanalysis shows ample instability across northern AL and southern Middle TN and the southern TN Valley that will drive thunderstorms for the next few hours. The presence of some weak shear will pose a threat of severe storms, with damaging winds behind the main concern, and a lesser concern for large hail. Meanwhile, convection is blossoming across KY near and ahead of a cold front. This activity will be moving E-SE through an unstable environment as it approaches our area, and it will likely expand into a line of convection. Expect that it will enter our KY border counties in the 23-03Z time frame, with a threat of damaging wind gusts. With some upper dynamic support from a jet streak, it could maintain its intensity past sunset as it crosses NE TN and SW VA through midnight. These storms should exit the area between 06-09Z with the passage of a shortwave trough axis and weak surface cold front. We will continue to have a broad cyclonic mid/upper level flow across the region on Sunday, with another embedded shortwave trough moving around the broad trough during the day. Low level instability will be weak behind the surface frontal passage, but lower temps aloft under the trough and ample moisture depth will support convective showers and a few isolated thunderstorms in the afternoon, mainly north of I-40. Temperatures in northern sections will be in the 70s to lower 80s with the expected precip and cloud cover, while southern sections will be in the 85 to 90 range under mostly sunny skies. && .LONG TERM... (Sunday night through next Saturday) Issued at 301 PM EDT Sat Aug 17 2024 Key Messages: 1. Shower and thunderstorm chances continue Sunday evening through Monday behind cold front, but will be mostly across the northeast half of east TN and southwest VA. Showers and thunderstorms will not be as strong. 2. Dry weather and near to below normal temperatures expected Tuesday through about Thursday. 3. Upper ridging shifts east from the central states beginning later Thursday and continues into the weekend. A more southerly flow will warm temperatures back to near normal with very little chance of rain through Saturday. Discussion: Sunday night into Monday will be the last chance to see showers and or storms for several days as the forecast area will lie near the base of a slow moving upper trough and low over the eastern United States. The best chance to see convection for the early periods will be north of Interstate 40, and especially near the TN/VA border and into southwest Virginia and far northeast Tennessee. Much less moisture will be present in the atmosphere behind a cold front moving south of the region Sunday evening for thunderstorms to tap into and the overall rainfall amounts should be lighter for locations that see a quick round of rain Sunday evening and night and into Monday. The main weather news in the extended this week will be the cooler temperatures starting Monday and much lower dew points through the week after Monday. Sunday night and Monday the forecast area will still be on the edge of upper trough over the eastern third of the US with shortwave energy triggering some scattered showers and storms across the northeast half of the area. There will be more clouds in the northeast and temperatures Monday in the 70s to lower 80s with mountain locations staying in the 60s. Only the southern valley will stay warmer in the mid 80s and little chance of rain. A drier airmass will be settling in from the northwest late Monday and Monday night. The forecast area will then be under the eastern edge of a strengthening upper ridge over the central United States. The drier airmass out of the north and northwest will allow temperatures to drop into the 50s to lower 60s Tuesday and mainly 50s Wednesday. Highs Tuesday and Wednesday will be below average in the 70s to mid 80s as surface high pressure will drop southeast from the upper midwest and mid Mississippi Valley towards the Ohio Valley and Great Lakes. Some long range models are trying to increase moisture east of the Appalachian crest Thursday but this looks overdone and will keep the overall trend that the hot upper ridge shifts east for the last 2 days of the extended and the surface high moves east of the Appalachians as the upper trough lifts northeast. This should warm temperatures back to near average and keep the region dry through Saturday. && .AVIATION... (18Z TAFS) Issued at 115 PM EDT Sat Aug 17 2024 Confidence is high that the TAF sites will see some showers and thunderstorms during this forecast period, but confidence is low on the timing. The pattern will favor multiple rounds of storms from this afternoon through tomorrow afternoon, with the best chances being at TRI. This afternoon, scattered coverage is expected around the area, and will have TEMPOs at CHA and TYS for this. Tonight, a disturbance will bring showers and storms to TRI, followed by IFR conditions behind the storms through the early morning. Another round of storms tomorrow will likely hold off until just after this TAF period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 91 70 90 68 / 50 30 10 10 Knoxville McGhee Tyson Airport, TN 87 69 85 66 / 20 40 40 20 Oak Ridge, TN 85 68 84 66 / 30 40 40 10 Tri Cities Airport, TN 86 66 77 64 / 30 60 60 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DGS LONG TERM....TD AVIATION...DGS