174 FXUS64 KMRX 251727 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 127 PM EDT Wed May 25 2022 .UPDATE... FOR 18Z AVIATION. && .DISCUSSION... Some weak convection has been trying to move into the SW corner but has weakened. Better convection to our southwest is expected to move into our area later this afternoon/evening, and will bump PoPs up to likely in our southwest corner. Further northeast downslope flow is expected to inhibit convection and this is handled well in the current forecast. Will make a few other tweaks to temps, dew points and sky with this update. && .AVIATION... 18Z TAF DISCUSSION. Will see some showers and thunderstorms around at times during the period, but timing is still problematic. Best chance for thunder looks to be at CHA, with lesser chances further northeast. Will try to time higher probability times for thunderstorms with VCTS and prob30 groups at CHA/TYS. Will just have VCSH and prob30 for showers at TRI as thunder chances look too low to include for now. Expect MVFR level cigs at CHA for much of the period, but outside of a heavier shower/thunderstorm expect TYS and TRI to be mainly VFR. && .PREV DISCUSSION... /ISSUED 328 AM EDT Wed May 25 2022/ SHORT TERM (Today and tonight)... Key Messages: 1. Low to slight chances of showers and thunderstorms this afternoon, with partly sunny skies and warmer temperatures. 2. Increasing chances of showers late this evening as an midlevel disturbance crosses the area. Discussion: Light showers are lingering in northern sections this morning in association with a midlevel shortwave trough. Once this feature lifts north of our area by 12Z, rain chances will end and dry but mostly cloudy conditions are expected through this morning, with clouds becoming scattered in the late morning and early afternoon. This should allow temps to warm into the lower 80s in most spots. The CAMs show very little convective activity across our area today, which makes sense given the weakly capped forecast soundings and the lack of forcing. The northern Valley will be under the influence of a weak downslope flow that will further enforce the cap in that area through the day. The forecast will have low to slight chance PoPs mainly south of I-40 this afternoon, then increasing as we move into the evening hours. A 500 mb vort max is shown by the models to move from north to south across the area tonight, along with increasing upper divergence. This will increase PoPs to likely for southern sections for the first half of tonight, with a decreasing/weakening trend expected as the showers spread northward into the area of downslope flow. DGS LONG TERM (Thursday through Tuesday)... Key Messages: 1. Showers and thunderstorms are expected Thursday. Damaging winds and an isolated tornado or two are the main concerns, in addition to localized flooding. 2. Showers linger into the weekend. Temperatures back above normal by Sunday, with continued warming into next week. Discussion: The main concern of the period is the severe weather potential on Thursday. Agreement on timing looks to be a little better with the NAM now coming in slightly faster, which puts it in better agreement with the other models. If the trends hold, this would put our best chances for seeing strong to severe storms from late Thursday morning through Thursday evening. Due to the mean flow being parallel to the cold front, there will be several clusters of storms move through the area throughout the day. Because of this, it's hard to narrow down the timing of the severe threat. Setup: A quasi-cutoff upper low will make it's way out of the Great Plains on Thursday and into Western TN by Thursday evening. A strong upper jet associated with the low and will move into our area through the day. Due to the strong upper jet, combined with high pressure anchored off the coastal Carolinas, a moderate to strongly sheared environment will be in place across our area. Soundings show shear values increasing through the day as the upper jet moves further into the area. The NAM is still the most aggressive with shear values, with 0-1km shear of near 40 kts and 0-1km SRH values around 350 m2/s2 which is concerning. The GFS isn't as excited however. Looking through the CAMs on SPC's page, all of the members show a few to several 2-5km helicity tracks across our area. This is further indication of the severe/tornadic potential. Again, the main threats with these storms will be damaging winds and few isolated tornadoes. This will likely be a messy event due to several rounds/clusters of storms moving in through the day. In addition to the wind and tornado threat, isolated flooding will also be of concern due to the moderate to heavy rainfall expected with the stronger storms. The atmosphere will be very moist with PW values averaging 1.6 inches, which is at the 90th percentile for BNA sounding climatology. Also, still anticipating 30 to 40 mph wind gusts across the higher terrain of the east TN mountains through the the day Thursday due to the 40kt 850mb jet in place. The severe threat will wind down Thursday night. Friday, the upper low will slowly moves across our area. Scattered on and off showers and and few isolated storms are expected through the day. Friday should be the coldest day of the period due to the upper low being directly overhead, high temps will be in the lower to mid 70s, which is around 5 to 8 degrees below normal. The low finally begins to move to our northeast on Saturday but wrap around moisture will keep isolated/scattered showers in across northeast TN and southwest VA through Saturday afternoon. Ridging builds in from the rest from Sunday onward, with highs climbing back near 90 by Tuesday. Slight chance POP in for the east TN mountains Monday and Tuesday due to diurnal convection. SR && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 66 76 62 76 59 / 80 90 80 30 10 Knoxville McGhee Tyson Airport, TN 65 81 62 75 59 / 60 90 90 40 20 Oak Ridge, TN 64 79 61 75 57 / 70 90 90 50 30 Tri Cities Airport, TN 62 79 62 75 56 / 50 70 100 80 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$