Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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577 FXUS64 KMRX 171719 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 119 PM EDT Sat Aug 17 2024 ...New AVIATION... .UPDATE... Issued at 1030 AM EDT Sat Aug 17 2024 Confidence is low regarding the timing and location of convective development today. Satellite shows a lot of low cloud cover, suggesting plentiful low level moisture, but the 12Z OHX sounding hasa dry layer around 700 mb that suggests dry air entrainment will be a limiting factor that will need to be overcome for development. There is also some low level stability in the OHX sounding and NAM forecast soundings. A more favorable factor will be an entrance region of a jet streak that will be moving across E KY and WV this afternoon, providing some upper divergence. The general expectation is that convection will be developing in the early and mid afternoon hours in the Plateau, with scattered to isolated coverge as it moves east into the TN Valley. Gusty winds are possible with storms but the threat of damaging wind is low. A better chance of showers/storms comes tonight with a more well- defined midlevel shortwave trough and jet streak providing better synoptic forcing. This overnight round may also have a better potential for severe storms; this will be more closely analyzed once the 12Z models come in. && .SHORT TERM... (Today and tonight) Issued at 302 AM EDT Sat Aug 17 2024 Key Messages: 1. Scattered showers and thunderstorms are expected this afternoon and evening. Some storms may be severe with the primary threat damaging winds. 2. Showers and storms will continue tonight but coverage will be more isolated. Discussion: A trough is deepening over the Ohio Valley today into tonight. Multiple rounds of showers and thunderstorms will be possible today and tonight but coverage looks highest late afternoon and evening as a shortwave moves through the region. The upper low and surface low will be vertically stacked over the Great Lakes today. The cold front will move through Sunday morning. Isolated showers and thunderstorms will continue this morning. This afternoon activity will become more scattered although still somewhat hit and miss. CAMs and the NBM are favoring the late afternoon and evening timeframe for best coverage. CAPE will be highest in the afternoon around 1000 to 2000 J/Kg. Shear will be highest in the evening around 40 knots. By the time the shear increases, instability will be much lower. Still, severe parameters look good enough for a marginal damaging wind threat in the afternoon and evening. After midnight tonight, CAMs agree that coverage will be more isolated. With a later start to thunderstorms expected in most locations this afternoon, minimal cloud cover will allow highs to reach 90 in much of the Tennessee Valley. && .LONG TERM... (Sunday through Friday) Issued at 302 AM EDT Sat Aug 17 2024 Key Messages: 1. Shower and thunderstorm chances continue through Monday, mostly confined to northeast TN/southwest VA, but storms are expected to be weaker. 2. Dry weather and near to below normal temperatures expected for much of next week. Discussion: Sunday night into Monday will be the final chances for precipitation for the next several days as we continue to sit towards the base of the slow moving trough/low over the eastern United States. Best chance to see storms will be north of Interstate 40, and especially near the TN/VA border, however there will be much less moisture in the atmosphere for storms to tap into and overall QPF amounts should be fairly light for those places that do see a quick round of rain heading into Monday. For the majority of people the main weather story for the end of the weekend and into next week will be the cooler temperatures and lower dew points. Sunday will likely be the last day of widespread 90+ degree temperatures for several days as we sit on the eastern edge of a strengthening ridge over the central United States, which will lead to generally drier air out of the north/northwest across the eastern Tennessee Valley. Not only will this help keep temperatures several degrees below seasonal normals, it will also keep the dew point values much lower than we`ve seen over the weekend. So the main story for the upcoming week ahead (once we get past Mondays storm potential) will be a unusually pleasant and cool back half of August. Next best chance for precipitation might not come until after the weekend, but large model variances does not lead to high confidence at this time. && .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 72 90 68 / 40 30 10 0 Knoxville McGhee Tyson Airport, TN 90 70 86 66 / 30 40 40 20 Oak Ridge, TN 88 69 84 66 / 30 40 40 10 Tri Cities Airport, TN 86 66 79 64 / 30 60 60 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...DGS AVIATION...DGS