Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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382 FXUS64 KMRX 051940 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 340 PM EDT Fri Jul 5 2024 ...New SHORT TERM, LONG TERM... .SHORT TERM... (This evening through Saturday) Issued at 330 PM EDT Fri Jul 5 2024 Showers and thunderstorms have been moving across much of the forecast area this afternoon. With the moist and unstable airmass with mixed layer CAPE values 1500 to 2500 J/KG ahead of the convection some strong storms have occurred. Precipitable water values continue to be very high 1.9 to 2.2. Dew points ahead of the convection were in the mid 70s and heat index values have reached around 105 in a few locations. With the temperature drop behind the storms heat index values have dropped. The risk for more storms is now lower because of the cooling with the remaining threat just the far eastern part of the forecast area the rest of the afternoon. Highest rain chances will be this afternoon, then decreasing this evening and overnight. For tonight the front over middle TN will move across this evening and into early Saturday. Slight chance to chance showers/storms extreme east. Lows tonight will still be warm in the lower to mid 70s but cooler than this morning. Also patchy fog will form in the areas with significant rainfall. Saturday with upper ridge to the south and upper trough moving in temperatures will be cooler in the upper 80s to lower 90s. Lower dew points will be observed by all with the numbers in the mid to upper 60s so heat index values will only be in the lower to mid 90s. With the front close to the mountains a few showers and storms my form but likely move quickly east of the Appalachians. && .LONG TERM... (Saturday night through next Friday) Issued at 330 PM EDT Fri Jul 5 2024 Key Messages: 1. Mostly dry conditions continue into Sunday. 2. First half of next week looks fairly active, so confidence is a little higher for better afternoon thunderstorm coverage each day. Discussion: The Tennessee valley and southern Appalachian region will remain situated beneath southwesterly flow aloft for much of the long term period, with troughing over the mid-Mississippi and Ohio valleys and ridging off the southeast coast. In general, this will mean chances for diurnally driven showers and thunderstorms most everyday from Monday onward, with the best chances over higher terrain as is usual in the summer. We`ll be in a dry air advection regime Sat night, but by Sun morning low level flow will begin to turn out of the southeast and bring some better moisture content back our direction from the Carolinas. Upslope flow into the southern Appalachians will likely be enough for at least some isolated convection in the mountains so will keep some slight chance PoPs through the morning hours in TN mountains zones. Coverage should increase Sun afternoon with steering flow pushing storms off into the lower elevations...but the best chances will remain in the mountains. Don`t drop rain chances Sunday night as the pattern could support some nocturnal convection, but coverage should be limited. Monday through the midweek time frame should see notably higher rain chances, with southeast/southerly boundary layer flow allowing for moisture return with theta-e ridge axis pulling into east Tennessee. Best chance of diurnal convection will remain in orographically favored mountains and plateau zones on Monday and Tuesday, but outflow boundary interactions and steering flow pushing storms off the Appalachians should yield fairly decent rain chances most everywhere. By Wednesday and Thursday, persistent southwest flow and the possibility of moisture associated with Beryl being siphoned off and shot this direction should lead to a steady increase in afternoon convective coverage. && .AVIATION... (18Z TAFS) Issued at 155 PM EDT Fri Jul 5 2024 VFR conditions are expected outside of thunderstorms today. Showers and storms moving through terminals now will exit next hour or two but more could form through early evening ahead of a cold front to the west. Initial storms could have gusty winds to 30 knots or higher at TRI so have Tempo there. Later storms weaker but still possible MVFR conditions with rainfall and linger until around 01Z. Some fog/low CIGs will be possible late tonight at TYS and TRI so included brief MVFR ceiling early Saturday before VFR again. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 75 93 72 94 / 40 10 10 30 Knoxville McGhee Tyson Airport, TN 73 91 70 92 / 50 10 10 30 Oak Ridge, TN 71 92 69 93 / 30 10 0 20 Tri Cities Airport, TN 71 89 67 90 / 50 10 10 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...TD LONG TERM....CD AVIATION...TD