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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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804 FXUS64 KMRX 301720 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 120 PM EDT Sun Jun 30 2024 ...New AVIATION... .UPDATE... Issued at 841 AM EDT Sun Jun 30 2024 Showers and storms continue to weaken as they move toward the northern Cumberland Plateau from out of northern middle TN. The HRRR has been depicting this as well over the last few runs. The showers and storms to our northwest have provided quite a bit of downstream debris clouds across our area. This will delay heating and possibly initiation of afternoon convection. Previous initiation time looked like it would occur around 17 to 18Z. The latest HRRR suggest it could be as late as 20 to 21Z before coverage begins to substantially increase. This makes sense based on the amount of high clouds currently in place. As far as updates go, no big changes to the grids. Mainly just tweaking hourly temps to slow heating and bumping up sky cover a little bit. && .SHORT TERM... (Today and tonight) Issued at 256 AM EDT Sun Jun 30 2024 Key Messages: 1. Scattered to numerous showers and storms today. A few may become strong to severe. 2. Hot and humid today. 3. Cooler and drier air moving in tonight. Discussion: A cold front currently over the Great Lakes and Ohio Valley will drop southeast and move across our area later today before exiting to our southeast this evening. The atmosphere ahead of this frontal boundary will be quite moist, with models generally showing PWAT values near or above 2 inches. In addition, HREF ensemble probabilities show a 60 to 80% chance for SBCAPE to reach or exceed 2000 J/kg across much of the area. Shear will be weak, with models generally indicating 0-6km shear will remain below 20kts. While most storms are expected to remain below severe limits, a few may become strong to severe with the main threat being damaging wind gusts. It will be hot again today, although the details of exactly how hot it becomes will be tied to how any convection and associated cloud cover evolve during the day which leads to some uncertainty. Dew points are expected to be a bit higher than yesterday, and high temperatures are expected to be near or slightly lower given the expected convection. Heat index values will likely climb to near or a bit above 100 in many locations again mainly across central and especially southern valley areas. A few locations may reach a heat index value of around 105 if convection and clouds hold off long enough, but right now the probability of 105+ heat index values looks low and nearly all of the area is expected to stay below heat advisory criteria, so none will be issued at this time. Any lingering showers/storms will be moving out this evening, with drier and cooler air moving in behind the front. && .LONG TERM... (Monday through Saturday) Issued at 256 AM EDT Sun Jun 30 2024 Key Messages: 1. Brief below normal temperatures Monday followed by a return of the hot weather the remainder of the week. 2. Dry or mostly dry through Wednesday, better chances of showers and thunderstorms Thursday into the weekend. Discussion: Monday kicks off the work week with a post-frontal dry airmass, and expected afternoon temperatures near or maybe even a couple degrees below normal. With relative humidities dipping into the 35 to 40% range in the afternoon, this is by far the best day to get outdoor work done at any hour of the day. However upper heights never really drastically weaken, and as soon as the flow in the atmosphere pivots back around for Tuesday, in returns the heat and humidity. Upper ridge then parks itself through the midweek over the wider Tennessee and southeast region, peaking near 596 dm. Ensembles aren`t gung-ho on even having 500J of CAPE Wednesday afternoon, so bumped the PoPs down for then in accordance. Afternoon convection in this June heat has struggled to overcome the warm air aloft associated with the persistent upper ridge, With the return of the strong ridge, that will be a consideration in any storm chances. By late week, guidance has better moisture profiles that should allow for better convective chances. At the very tail end of the week into Saturday, guidance indicates the potential arrival of another front, which would bring about more widespread rain chances. && .AVIATION... (18Z TAFS) Issued at 116 PM EDT Sun Jun 30 2024 VFR conditions are generally expected through this evening. However, there is a chance that brief MVFR conditions could occur due to any passing shower or storm from now through this evening. High confidence in VFR conditions from this evening through the end of the period as drier air moves in behind a cold front. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 69 88 68 91 / 10 0 0 0 Knoxville McGhee Tyson Airport, TN 66 84 64 90 / 20 0 0 0 Oak Ridge, TN 64 83 63 89 / 20 0 0 0 Tri Cities Airport, TN 60 81 59 88 / 30 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM... LONG TERM....Wellington AVIATION...