Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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730 FXUS64 KMRX 201424 AAB AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 1024 AM EDT Sat Jul 20 2024 ...New UPDATE... .UPDATE... Issued at 1004 AM EDT Sat Jul 20 2024 Regional radar imagery shows scattered to numerous showers along and north of the I-40 corridor this morning in east Tennessee and stretching up into our Virginia counties. South of the I-40 corridor, precip is much more difficult to come by at the moment. The NAMNest seems to be handling precip coverage quite well, matching up nicely with the break from I-40 southward into northeast AL that is currently shown on radar mosaic imagery. Guidance shows that we`re beneath the entrance region to an H3 jet streak which, when coupled with some meager elevated instability, seems to be driving the fairly uniform coverage of showers across that portion of the CWA this morning. Haven`t seen any evidence of lightning so far, and radar doesn`t show these cells to be very tall, which suggests the GFS BUFR soundings are probably assessing the environment fairly well at this time and they show only a few hundred J/kg of elevated MUCAPE. As such, expect the trend of weak convection to continue until we get into the afternoon hours and surface based instability becomes more prevalent. Made some adjustments to the PoP grids through midday or so, blending in the NAMNest with current hourly NBM PoPs. Forecast for the afternoon seems to be on track, including temperature wise, so no changes necessary there. && .SHORT TERM... (Today and tonight) Issued at 246 AM EDT Sat Jul 20 2024 Key Messages: 1. Scattered to numerous showers and a few thunderstorms are expected today. 2. Below normal temperatures will continue. Discussion: A shortwave trough remains west of the area this morning, over West TN. A plume of moisture from the Gulf extends across the TN Valley and Appalachians. PW values in the range of 1.75-2 inches will be over the area today, and soundings show a deep, skinny CAPE profile. The question is when/where forcing will enhance convetive development. The NAM shows a jet streak developing this morning over the Plateau, whcih produces some upper divergence in the area this afternoon. Expect scattered to numerous shower coverage, with mainly isolated thunderstorms. A few slow-moving or training showers may produce locally heavy rainfall, and possibly some minor flooding issues. This evening, the jet streak and trough axis lift NE of our area, which should result in decreasing rain chances. With cloud cover expected to be broken to overcast today, highs will continue to be below normal, with highs in the lower to mid 80s. && .LONG TERM... (Sunday through Friday) Issued at 246 AM EDT Sat Jul 20 2024 Key Messages: 1. An unsettled weather pattern will persist through the long term with daily mostly diurnal chances for showers and thunderstorms. Although there will still be some showers and a few storm in the overnight hours. 2. Slightly below normal temperatures expected through the extended forecast and considerable cloud cover. Discussion: A significantly strong upper level closed low will be over northeast Canada at the start of the extended forecast Sunday morning. This low moves east through Monday but new troughing develops Monday night and onward over the northeast states and the Great Lakes. A weak upper low to the southwest of the Canadian low will enhance a southwest flow over the Tennessee Valley as an upper ridge lies over Florida and the Carolina coasts Sunday into Sunday night. This low opens up and upper troughing digs southwest through the Mississippi Valley to the west of the forecast area. At the same time a stationary front over the eastern sections of TN this morning will be lifting northward towards KY Sunday morning. Rain chances will increase in the afternoons and evenings Sunday and Monday. Rainfall amounts are not expected to be that high for these 2 days. From Tuesday through Thursday a better southwest flow as the southeast US high pressure ridge strengthens will increase moisture for more significant rainfall amounts with the potential late in the week for some isolated flooding as total rainfall amounts reach 2 to 4 inches by this time. The frontal boundary will still be north and west of the region through the rest of the extended and will help to enhance rainfall amounts as well. Instability will be high each day which will help the initiation of showers and thunderstorms. Cloud cover and rain will keep temperatures in the lower to mid 80s each day across lower elevations. Lows will be in the upper 60s and lower 70s and dewpoints will stay high too making it feel sticky. With the current drought D! and D2 categories this significant rainfall will help drought conditions improve slowly. Highest rainfall amounts will be in the Appalachians along the TN border and across southwest North Carolina. High PWATS from 1.5 to possibly over 2.0 inches will enhance rainfall amounts. && .AVIATION... (12Z TAFS) Issued at 646 AM EDT Sat Jul 20 2024 Light showers will be around the area this morning. MVFR cigs are expected all sites at times. Most showers should exit by late morning, with cigs rising to VFR in the noon to 18Z time frame. Can`t rule out additional showers/storms in the afternoon, so VCTS will be mentioned with VFR conditions. Winds will be light through the period. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 84 71 86 71 / 50 30 70 50 Knoxville McGhee Tyson Airport, TN 83 70 86 69 / 70 30 70 50 Oak Ridge, TN 84 69 86 69 / 70 20 70 40 Tri Cities Airport, TN 80 66 86 67 / 70 30 60 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD LONG TERM....TD AVIATION...DGS