Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
666 FXUS64 KMRX 311100 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 700 AM EDT Fri Jul 31 2026 ...New AVIATION... .KEY MESSAGES... Updated at 645 AM EDT Fri Jul 31 2026 - Dry weather with seasonable temperatures and relatively comfortable humidity Friday. - A low chance for a few strong storms Saturday evening/night, with localized flooding also possible. - The wet pattern that sets up this weekend may continue well into next week. && .DISCUSSION... Issued at 118 AM EDT Fri Jul 31 2026 Surface high pressure centered to our north will provide us with another dry day Friday as it slides slowly east. A mostly sunny sky and relatively comfortable temperatures/humidity for late July can be expected Friday, although high temperatures will be a couple degrees warmer than they were Thursday. Models are struggling with the weekend system, with a somewhat uneven but noticeable trend to keep the low pressure system and better forcing a bit further north. With the poor model consistency, the confidence level in the details is still lacking. At this time, models generally show deep moisture increasing Saturday with PWAT values approaching or exceeding 2 inches across much of the area as a low pressure system tracks into the Ohio Valley and/or southern Great Lakes Region. This system pulls a cold front toward us during the day, with it likely moving through our area Saturday night/early Sunday. This scenario would likely result in an initial round of showers/storms that moves in during the morning with the passage of a shortwave trough, with this convection possibly elevated and likely sub-severe. A line of convection then would form in the afternoon to our west near the cold front and closer to the main upper trough axis. The NAM (which has much more CAPE than the GFS) is quite vigorous in developing this convection as it crosses Middle TN, but by the time the convection reaches our area (well after sunset) the NAM shows a significant weakening trend as it moves into our area with the decreasing CAPE, the main upper jet support well to our north, and downslope low level flow off the eastern mountains. While there is some deep layer shear present, the nighttime arrival would limit surface-based instability. Ensemble joint probability of CAPE > 500 J/kg and effective shear > 30 kt is under 20% in our area Saturday evening into Saturday night. Thus, the severe risk appears still appears to be low at this time. Flooding may be more of a concern especially if heavy rain occurs with the morning round, followed by additional heavy rain in the same areas during the evening/overnight round given the abundant deep moisture. The ensemble approach of the NBM still has high chances for showers and storms Sunday with just a gradual lowering of chances as we move through the Monday through Thursday time frame. This wet pattern is favored by many of the models which have been leaving behind a weak upper low as the main trough exits. This upper low then meanders slowly and eventually fills over the region. However, it should be noted that the models typically struggle with the location of these types of weak cutoff lows several days out. A somewhat drier scenario is favored by some models, with the cutoff upper low located further to the north and/or northeast or the upper trough cleanly exiting with upper ridge edging slowly in from the west. We will have to see which scenario plays out, but for now the forecast will be low confidence but still following the wetter NBM for next week. && .AVIATION... (12Z TAFS) Issued at 645 AM EDT Fri Jul 31 2026 VFR conditions are expected. Light winds will become more southerly late in the period. High clouds will move into the region tonight. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 91 72 86 72 / 0 20 90 90 Knoxville McGhee Tyson Airport, TN 89 69 86 72 / 0 10 60 90 Oak Ridge, TN 88 69 84 70 / 0 10 70 90 Tri Cities Airport, TN 84 64 84 69 / 0 0 30 60 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ DISCUSSION...99 AVIATION...McD