Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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028 FXUS64 KMRX 051804 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 204 PM EDT Fri Jul 5 2024 ...New AVIATION... .UPDATE... Issued at 1130 AM EDT Fri Jul 5 2024 Line of showers and thunderstorms are moving onto the plateau late this morning and are whats left of an MCS that was moving across middle TN earlier this morning. Our airmass is moist and unstable with mixed layer CAPE values are 1500 to 2500 J/KG ahead of the convection. Precipitable water values are very high too 1.7 to 2.2. Dew points are in the mid 70s. The flow is weaker but scattered to numerous showers and storms are expected to develop with a risk for damaging wind gusts and wet microbursts. A slight risk for severe storms was added to the day 1 outlook across NE TN and SW VA. With warnings issued already in eastern KY there could be some by early to mid afternoon across northern sections. Late morning temperatures are in the upper 80s to lower 90s already and heat index values are in the mid 90s to just over 100. Expecting highest heat index values next couple hours ahead of the thunderstorms. A few locations in the central and southern valley will like reach around 105 heat indexes. Have updated rain chances to lower them slightly to around 70 percent with line and increased dew points slightly. Updated forecast sent. May need to update again as more storms develop at early afternoon. && .SHORT TERM... (Today and tonight) Issued at 303 AM EDT Fri Jul 5 2024 Key Messages: 1. Scattered to numerous showers and thunderstorms expected today ahead of a cold front. Marginally severe storms are possible, mainly in the afternoon. 2. Another hot, humid day is expected today but with increasing cloud cover and rain chances, we are not expected to reach Heat Advisory criteria. 3. Some fog development is possible tonight in locations that received rainfall. Discussion: A trough is moving into the Midwest. Weak troughing will be over the Tennessee Valley today and tonight. At the surface, a cold front will move through the region late tonight or early Saturday with a shift to northerly winds. POPs start to increase late this morning but the best chance for showers and thunderstorms will be this afternoon and evening. NBM guidance seems to be running high on POPs compared to the HREF but this latest run is a little closer. HRRR guidance has more activity north of I-40 and along the mountains. With good instability (CAPE over 2000 J/kg) and plenty of low level moisture in place, there will be a marginal risk for severe storms mainly in the afternoon during max heating. With increasing clouds and rain chances, Heat Advisory criteria will likely not be reached today. Although, it will be hot and humid with heat indices around 100 for much of the Southern Valley with highs in the lower 90s and dew points in the mid 70s. Some showers and storms may linger into the evening hours but mostly dry weather is expected after midnight. Fog development is possible but will likely be limited to places that receive rain. && .LONG TERM... (Saturday through Thursday) Issued at 303 AM EDT Fri Jul 5 2024 Key Messages: 1. Not quite as hot, but still slightly above normal through much of the long term. 2. Mostly dry conditions expected across of the area this weekend in the wake of a front Friday night into Saturday morning. 3. Diurnal showers and thunderstorms increase early next week especially across the higher elevations. Discussion: In general throughout the entire extended, trend PoPs lower each day compared to NBM guidance and deterministic models due to the drought conditions developing over much of the area. Also, overall chances of convection have been too high by ensembles and deterministic models. For Saturday, frontal boundary moves east of the Appalachians with drier air advecting into the region. Any chance of convection will be confided mainly over the far east Tennessee mountains and southwest North Carolina. NBM probabilities remain highest there for measurable rainfall. For Sunday, ridge of higher theta-e remain across the southern Appalachian mountains, especially over the Carolina`s. A low chance of convection is expected over the far east Tennessee Mountains and southwest North Caroline but overall dry conditions. For Monday, boundary layer flow becomes more southeast/southerly allowing for moisture return with theta-e ridge axis pulling into east Tennessee. Better chance of diurnal convection especially for the Mountains and Plateau as forcing orographic. For Tuesday, Wednesday and Thursday, diurnal orographically forced convection will continue. Continue to believe that the NBM PoPs are too high due to the aforementioned above. There is a potential by Thursday that some of the moisture from BERYL may move into the Tennessee valley. && .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 74 92 72 95 / 50 20 10 10 Knoxville McGhee Tyson Airport, TN 74 90 69 92 / 60 20 10 10 Oak Ridge, TN 72 90 68 92 / 50 10 0 10 Tri Cities Airport, TN 71 87 67 90 / 70 30 10 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...TD LONG TERM....DH AVIATION...TD