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

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444 FXUS64 KMRX 210648 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 248 AM EDT Fri Jul 21 2017 .SHORT TERM...(Today and tonight)...A hot day in store today as mid level ridge remains over the region, centered just to our west. Model sounding continue to look on the dry side and weak capping may limit convection especially in valley areas. Will continue with the slight chance PoPs for most valley areas with low chance in the mountains for this afternoon and evening, although would not be suprised if even that may be overdone. Temperatures will be in the 90s for the valley areas, and heat index values expected to be around 100 in the southern valley and should approach 100 up into the central valley for a few hours this afternoon. However, should stay below heat advisory levels. .LONG TERM...(Saturday through Thursday)...At the beginning of this period (Saturday morning), the upper ridge is still holding on while at the surface our weak moist flow from the Gulf of Mexico continues. An upper level shortwave is tracking through the northern plains. It looks like there will be enough instability to induce some isolated to scattered diurnal showers and storms on Saturday. By Sunday, this shortwave moves southeastward into the Great Lakes and the southern end of this shortwave starts carving pretty heavily into our ridge. The front associated with this system will still be to our north on Sunday, but models agree that a weak wave of lift will be coming into the area that will increase the chances of showers and storms. By Monday as the front approaches, a leeside trough also develops in the Carolinas, that splits the organization of this system--with some organization along the W-E oriented front as it sags into our area, but also there is some organization along the NNE-SSW oriented lee trough. For Tuesday through Thursday, models start to diverge on the placement of the front as well as whether we stay under the influence of the Great Lakes trough (keeping better chances of rain in the area )or if the ridge from the Plains builds back over our area (that would tend to dry us out again). In general, there is enough agreement that the front will probably sag south of the area and take the better rain chances south, so our higher POPs will be in our southern areas. With the aforementioned pattern changes, the hot and steamy thermal conditions over the past several days will be subsiding as the upper ridge fades. Saturday will still be very steamy, but staying below heat advisory levels, Sunday not quite as hot, and then for Monday through the rest of the forecast, the Heat Index will be closer to seasonal normals. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 96 75 93 75 / 20 20 30 20 Knoxville McGhee Tyson Airport, TN 94 73 92 74 / 20 20 30 20 Oak Ridge, TN 95 73 92 75 / 20 20 30 20 Tri Cities Airport, TN 93 70 91 71 / 20 20 30 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ LW/GM is the U.S. government's official web portal to all federal, state and local government web resources and services.