133 FXUS64 KMRX 010456 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1256 AM EDT Sat Apr 1 2023 ...New AVIATION... .UPDATE... Issued at 903 PM EDT Fri Mar 31 2023 Key Messages: 1. A nearly solid line of showers and storms, mainly between 3 and 6 am. Main threat will be damaging winds. 2. Isolated tornadoes mainly across the Plateau and southeast Tennessee. Tornado potential is a conditional threat depending on low-level instability and mixing becoming surface based. 3. Pressure gradient induced high winds, especially across the far east Tennessee mountains and foothills. Discussion: Currently, a warm front extends from middle Tennessee into northern Alabama and far western Georgia. How far northeast this boundary can be pulled northeast into east Tennessee will play a large role in determining tornado potential across the Plateau and southeast Tennessee. Latest HRRR model trends does suggest this boundary will be able to pull northeast with 0-3km CAPES of 40+ and mixing becoming surface based. The strong upper level dynamics is depicted by latest deterministic models and ensembles to increase over the region by 09Z producing strong upper divergence. Large scale forcing will enhance the fronto-genetic forcing allowing the current scattered storm coverage to become a nearly solid line. Due to the strong low-level jet of 65-70kts (850mb), this line will have the potential of producing localized damaging winds, especially across the Plateau and southern half of the Tennessee valley. Since the low-level jet is not mixing to the surface (except ridge tops), have delayed the wind advisory for the central and southern areas until 2 am. Otherwise, no changes to ongoing wind warning/advisories. So far, Cove Mountain has reported a gusts up to 70 mph and Camp Creek near 50 mph. Have a good night and stay safe. && .SHORT TERM... (This evening through Saturday) Issued at 259 PM EDT Fri Mar 31 2023 Key Messages: 1. A band of showers and storms will move through tonight and some storms may be strong to severe, especially along the Cumberland Plateau and into the Southern Valley. 2. The main threat with the strong to severe storms will be damaging winds, but a brief tornado is possible as well. 3. Strong and gusty winds are expected at times, with the highest winds over the TN mountains. Discussion: A powerful low pressure system will track from the Plains across the Great Lakes into the NE states by the end of the period. A prefrontal trough will move through our area tonight, and while there is some convection ahead of the main area it looks like the main band of showers and thunderstorms will move in from the west most likely after midnight. As has been advertised, the LLJ and deep- layer/low-level shear will be very impressive with the main question being how much convective energy will be available when the convection moves through. This is also limited in our area both by the time of day and less than ideal upper support. The latest HREF continues to indicate values of 250+ J/kg will be most likely along the Plateau and southern Valley areas with lower values further east, although it is worth noting that values have trended up slightly in some of the latest guidance. It still looks like the main severe threat will damaging winds. However, there remains a tornado threat especially across the Plateau and into the southern valley. The HREF continues to highlight the highest probability of helicity tracks in these areas, but a low threat does exist to the east of these areas dependent on exactly how much convective energy is available at the time. Any areas that see repeated heavy downpours may see some localized flooding although that threat appears significantly lower than the severe threat at this time. Winds will continue to increase across the mountains and foothills into tonight as the LLJ increases, and models indicate the orientation of the jet to the mountains may become briefly more favorable for some mountain wave enhancement mainly this evening/early tonight. Outside of the mountains, winds will increase tonight as well with the strongest winds likely to occur ahead of and with the band of convection. Once the convective band moves through there will likely be slight lull in the winds, however the strong surface pressure gradient, WSW 850mb winds reaching 45-50kts again, and expected deep mixing all indicate we will see windy conditions across the entire area by late Saturday morning into the afternoon. Will keep the wind advisories and warning as they are for now except to delay the start of the first wind advisory until 03Z tonight. The hi-res guidance suggests wind speeds may flirt with warning criteria even in valley locations, so cannot rule out later shifts needing to upgrade at least a portion of the wind advisory to a warning. Once any lingering convection in eastern portions of the area exits early Saturday, we will see dry conditions and plenty of sunshine along with the aforementioned winds. Temperatures will be quite warm with highs in the 70s in most valley areas. && .LONG TERM... (Saturday night through next Friday) Issued at 259 PM EDT Fri Mar 31 2023 Key Messages: 1. Below normal temperatures Saturday night/Sunday morning with patchy frost possible on the Plateau and Appalachian Mountains. 2. Shower and thunderstorm chances return beginning Tuesday as a cold front tries to move through the area. Discussion: Saturday night into Sunday will mark another chilly morning behind the front as cold air from the northwest funnels into the region. Temperatures will likely drop down into the 30's for much of the eastern TN valley, and possibly near or below freezing in the higher elevations of the Cumberland Plateau and Appalachian Mountains. In the Valley winds could calm down enough to see patchy frost with the highest chance to see frost being on the Plateau, frost/freeze products may be needed again. Surface high pressure and weak mid level ridging will begin to build in late in the weekend, which kick start a quick warm up into next week. Temperatures are expected to climb into the lower 80's by Tuesday. A weak shortwave is expected to push through the southeast to start off the work week. Still some discrepancies with the exact location of this shortwave, but areas near or south of the TN/GA state line have the highest chance to get a shower from this system. A strengthening system will develop across the plains and try to drag a cold front through the eastern US. With our area being in the warm sector expect to see scattered showers and thunderstorms develop on Tuesday and Wednesday. Some of the deterministic models are indicating that the mid week could stall out somewhere along the Tennessee Valley into the Mid Atlantic. Should this happen it would likely act as a focusing mechanism for continuous rain chances for the second half of the week and into the weekend, before finally moving out late in the weekend. Still lots of uncertainty with the location of the front this far out, but it will be worth keeping an eye on as showers and storms are expected along the front for several days next week. && .AVIATION... (06Z TAFS) Issued at 1249 AM EDT Sat Apr 1 2023 Significantly severe convection is ongoing near and west of Nashville at this hour with the line expected to maintain and continue advancing into the area from the west. The timeframe will be west to east after 07Z with conditions improving by 12Z. Just ahead of and within these storms, very strong winds are expected, especially at CHA and TYS. Depending on how strong the storms are when they reach the terminals, gusts in excess of 50kts will be possible at these sites with lesser but still strong gusts at TRI. This will also be accompanied by brief, significant visibility and/or ceiling reductions. Then, conditions should improve with winds remaining suppressed to ~20kts for at least a few hours. By the afternoon, however, very windy conditions are expected area- wide with TYS and TRI likely to see gusts approach and/or exceed 40 kts. By the end of the period, a shift to a more northwesterly direction is expected with speeds generally around 15kts or less. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 78 42 69 49 / 10 0 0 20 Knoxville McGhee Tyson Airport, TN 74 38 65 44 / 20 0 0 10 Oak Ridge, TN 75 37 65 44 / 10 0 0 10 Tri Cities Airport, TN 72 37 61 40 / 40 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Wind Advisory until 8 PM EDT this evening for Cherokee-Clay. TN...Wind Advisory until 8 PM EDT /7 PM CDT/ this evening for Anderson-Bledsoe-Bradley-Campbell-East Polk-Hamilton-Knox- Loudon-Marion-McMinn-Meigs-Morgan-North Sevier-Northwest Blount-Northwest Monroe-Rhea-Roane-Scott TN-Sequatchie- Union-West Polk. Wind Advisory from 8 AM this morning to 8 PM EDT this evening for Claiborne-Grainger-Hamblen-Hancock-Hawkins-Jefferson- Northwest Carter-Northwest Cocke-Northwest Greene-Sullivan- Washington TN. High Wind Warning until 11 PM EDT this evening for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Southeast Monroe-Unicoi. VA...Wind Advisory from 8 AM this morning to 8 PM EDT this evening for Lee-Russell-Scott VA-Washington VA-Wise. && $$ SHORT TERM...DH AVIATION...BW