FXUS64 KMRX 021427 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1027 AM EDT Fri May 2 2025 ...New UPDATE... .UPDATE... Issued at 1020 AM EDT Fri May 2 2025 Not much change to earlier thinking for today with the severe storm threat later during the day/evening. This update will primarily be to make minor adjustments to PoPs/Weather based on latest radar trends and CAMS, along with a few other tweaks. && .SHORT TERM... (Today and tonight) Issued at 345 AM EDT Fri May 2 2025 Key Messages: 1. Another period of showers and storms are expected late this afternoon and evening, some of which are expected to be severe. Damaging wind gusts and large hail will be the primary severe weather threats, with confidence greatest along and west of I-75. Discussion: Currently an upper trough is in place over the Great Plains with an upper ridge over the western and eastern coasts. Shortwave energy is lifting northward through the Great Lakes region with a few isolated showers and rumbles of thunder owing largely to an enhanced area of upper divergence. A few showers and rumbles of thunder will remain possible overnight but no severe impacts are expected due to a lack of instability, though brief downpours and maybe some small hail across the southern valley. An additional shortwave is expected to round the trough as we head into the afternoon hours, driving a surface cold front into portions of the southern Mississippi and western Tennessee River valleys. Frontal forcing and and effective shear near 30-35kts will allow for an organized line of thunderstorms to translate across Tennessee, reaching our forecast area by the late afternoon into the evening hours. While the surface front itself will remain well west of the CWA, EBWD near 35kts, MLCAPE between 1000-2000J/kg and steepening mid-level lapse rates to 6.5-7.0 C/km will promote the best chance for organized severe weather that we have seen with this recent active stretch. Latest SPC outlook has introduced an enhanced risk for areas along and west of I-75 where we are most likely to see the best alignment of convective activity with the strongest diurnal heating. The rest of the area remains under a slight risk. The primary threat is going to damaging wind gusts as DCAPE near 800-1000J/kg will enhance downdrafts. Large hail will be the secondary threat, especially in the event of any developing discrete cells ahead of the main line of storms as is suggested by latest HRRR runs. As is typical with strongly sheared environments, a tornado cannot be totally ruled out though, marginal LCL heights around 1000m will limit that threat. Some activity may linger for the first few hours into the overnight, primarily our far eastern areas, but the shortwave will continue to lift northeast with little to no severe threat for much of the overnight. && .LONG TERM... (Saturday through Thursday) Issued at 345 AM EDT Fri May 2 2025 Key Messages: 1. Widespread rain and a few thunderstorms likely on Saturday, a very low risk for a severe thunderstorm. 2. Lower chances of light rain Sunday and Monday across northeastern TN into southwestern VA. 3. Mild temperatures Sunday and Monday, followed by a very slow warming trend through next week. Discussion: Diving shortwave coming out of the Midwest is expected to push a cold front through the area Saturday evening before the shortwave itself pinches off from the upper westerlies and becomes a cutoff low, doomed to meander over the Ohio Valley for a couple of days. The most interesting weather comes on Saturday, with widespread rain showers and a few embedded thunderstorms likely Saturday. Severe chances are likely pretty low, with plenty of cloud cover, weak upper divergence helping to bring about showers apart from the thunderstorms, and questions about how much instability can build before afternoon storms can fire. The Euro ensemble seems to be the most aggressive with CAPE, and is biasing the NBM probabilities, meanwhile high res guidance and GEFS are notably less enthusiastic, likely from the more widespread rain depictions the GFS and NAM have. Given the setup, I'd probably lean to the lower end scenarios, too much to spoil the thunderstorm setup, and guidance really hasn't performed well the last few days. Depending on how today's weather plays out, there will be a low risk for flash flooding on Saturday as well. PWATs are elevated but not especially so, and skinny CAPE profiles (if we get enough CAPE) will lend favorably to rainfall efficiency on potentially more saturated soils. Beyond Saturday our upper low friend maintains its stuck position over the Ohio River Valley for a couple of days until around Tuesday when it begins to drift northwards again and eventually rejoins the westerly flow and heads out. A few scattered low topped showers may develop Sunday afternoon, but wrap-around dry and warm air throughout much of the midlevels underneath the low's center will preclude any significant weather. With the low stalled at this point heading into the start of next week, probably can't rule out a shower in southwestern Virginia Monday into Tuesday, but no significant weather expected then either. Midweek and onwards a couple subtle disturbances may provide enough spark for scattered showers and a couple thunderstorms. The larger synoptic feature by then in guidance is another upper low, this time originating from the Rockies encountering a loss of direction over the Central US and showing signs of meandering. Where that feature ends up by late into next week will influence our weather here. Model guidance tends to perform poorly in these situations, so we'll watch at this time range. && .AVIATION... (12Z TAFS) Issued at 721 AM EDT Fri May 2 2025 MVFR cigs near TRI will gradually improve this morning, though some vicinity shower and low VFR sct/bkn clouds will remain as an area of showers and isolated storms progresses across portions of the southern and central valley. Light rain and isolated thunder will remain possible at TYS as well. Main concern for aviation will additional showers and storms late this afternoon into the evening that could lead to strong to severe winds, frequent lightning, and even the potential for hail. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 84 62 73 54 / 60 70 100 60 Knoxville McGhee Tyson Airport, TN 83 61 74 56 / 50 60 90 80 Oak Ridge, TN 82 61 72 55 / 50 70 90 80 Tri Cities Airport, TN 81 58 75 56 / 40 50 80 90 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM... LONG TERM....Wellington AVIATION...KRS