Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 242025 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 325 PM EST Fri Feb 24 2017 .SHORT TERM... Upper level low centered over central Iowa this afternoon will lift NE toward the Great Lakes overnight tonight. At the surface, associated 995 mb low centered over central Illinois will also lift NE into the eastern Great Lakes by Saturday morning. Associated cold front moving toward the Mississippi Valley this afternoon will push east across TN tonight before moving east of the area Saturday morning. Ahead of the front, an intensifying LLJ will move across the Plateau and into the Tennessee Valley during the overnight hours. Over the Plateau, ML CAPE of 700-900 J/kg coupled with bulk shear values of 45-60 kts will allow the line of convection to remain organized with the real possibility of some strong to severe storms as it pushes through the area during the overnight. Timing looks to be a little more delayed than previous model runs with both hires HRRR and RAP13 indicating that convection will push through the area during mainly the midnight to 6 am time frame. This agrees well with the NAM that has also slowed the progression of this front as well. With presence of the near unidirectional wind profiles, strong to severe straight line winds look to be the dominant threat with this event. Any overnight severe weather event poses an additional risk. Given that people are not as connected to latest weather information as they typically are during normal waking hours, people should be extra diligent to ensure they have access to the latest watch and warning information from the NWS. Further east of the front tonight in the eastern portions of the cwa, a tightening pressure gradient is expected to increase winds for areas of the Smoky Mtns above 3000 ft in Cocke, Sevier, and Blount counties. These winds will decrease with the frontal passage on Saturday morning. A Wind Advisory has been issued for the those areas from 7 pm tonight until 7 am on Saturday. As the front moves out on Saturday conditions should gradually improve through the afternoon. Gusty west winds and a daytime high in the lower to middle 50s that will slowly drop during the day will make it feel a bit more like winter. Especially after the record breaking late week warmth we have been experiencing. With the gusty winds tomorrow, consideration was given to a wind advisory behind the front, but 850 mb winds weaken precipitously by afternoon. However, do expect to see marginal advisory level gusts, particularly near mid-day and a Special Weather Statement may be necessary by morning to alert users to the winds gusting 25 to 35 mph behind the front. .LONG TERM...The long term forecast will follow the slower ECMWF modeling rather than the quicker GFS suggestion of a frontal passage for the week ahead. Dry and cold advection brings an end to the precipitation Saturday night with a zonal westerly flow regime gradually becoming southerly again ahead of another amplified long wave Mid America trough at mid week. In this scenario, isentropic lift with a moist, southerly component will lead to the development of showers Monday into Tuesday. The atmosphere will be destabilizing in the moistening pattern by Tuesday and so some thunderstorms could be part of the mix at this time. But the better chance for convection will be Tuesday night into Wednesday ahead of another relatively strong cold front due in the Southern Appalachian Region later Wednesday afternoon and evening. Kept the remainder of the long term dry behind this system with a prevailing west to northwesterly flow building in with higher surface pressure. The new week`s temperature forecast features another most pleasant warm up into mid week with highs back in the upper 60s and lower 70s followed by a return to more typical early March weather. $$ && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 50 56 31 57 / 70 20 0 0 Knoxville McGhee Tyson Airport, TN 50 53 29 53 / 80 40 0 0 Oak Ridge, TN 49 52 27 53 / 80 30 0 0 Tri Cities Airport, TN 50 55 26 49 / 80 60 10 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...Wind Advisory from 7 PM this evening to 7 AM EST Saturday for Blount Smoky Mountains-Cocke Smoky Mountains-Sevier Smoky Mountains. VA...None. && $$

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