FXUS64 KMRX 190532 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 132 AM EDT Fri Apr 19 2024 ...New AVIATION... .UPDATE... Issued at 906 PM EDT Thu Apr 18 2024 Will slow the forecast arrival of showers and storms tonight based on latest radar and hi-res CAM trends. Otherwise the forecast for tonight generally still looks to be on track, so the only other changes will be minor tweaks to temps and dew points. && .SHORT TERM... (This evening through Friday) Issued at 246 PM EDT Thu Apr 18 2024 1. Showers and thunderstorms expected overnight, stronger storms more likely, but not a certainty, west of Knoxville. 2. A second chance for scattered strong thunderstorms exists Friday afternoon across the Tennessee valley. Gusty winds and large hail possible with the afternoon thunderstorms. Discussion: Cold front begins the period across Missouri and will march eastwards with time until making it to Tennessee by the end of the short term Friday evening. A couple rounds of showers and thunderstorms will exist in the warm sector ahead of the front. First round of showers and thunderstorms is expected overnight tonight. This means that the remainder of the evening today is expected to remain dry, so that's good news. Guidance indicates showers and storms tonight will generally ride the midlevel heights axis as the ridge continues to move off to our east by Friday morning. Given the time of the day being the most unfavorable for thunderstorm intensity and the ability of storms to mix winds down to the surface, not feeling aggressive with the idea of strong storms overnight. Additionally, the more recent CAM runs have backed off on storm cell intensity and organization for overnight. HRRR has trended towards an even more scattered, unorganized, depiction for overnight into morning storms. Still, a few rumbles of thunder are possible given elevated CAPE as the remnants of the convection from Western Kentucky and Middle Tennessee move into East Tennessee. Convection should exit or dissipate by mid-morning, yielding a few hour pause until the second round during the afternoon. An approaching 500 mb speed max moves from west to east across Tennessee heading into peak daytime heating, increasing flow aloft from 30 knots to 50 knots. Some of the guidance (notably the HRRR and high res NAM) depict a quick and robust recovery into Friday afternoon, along with a favorable convective initiation in the Tennessee valley to take advantage of their modeled environments. Hodograph shapes are fairly linear, and given the increasing flow providing plenty of effective shear, a risk for damaging winds and severe hail is possible. One big uncertainty is cloud cover is expected to be present in the morning through the afternoon storms, so not certain how that hinders the convective environment. Still, the environment will need to be watched for strong thunderstorms. && .LONG TERM... (Friday night through next Thursday) Issued at 246 PM EDT Thu Apr 18 2024 Key Messages: 1. Outside of rain chances on Sunday, drier and cooler conditions are expected into early next week, especially on Monday. 2. Rain chances and more seasonal temperatures will return by Wednesday and Thursday. Friday Night through Monday At the start of the period, subtle troughing will be in place across the eastern U.S. with a strong upper jet to our north. A cold front will be moving through the area ahead of high pressure expanding from the northwest. During this time, lingering showers and storms from the short term period will be exiting the area west to east with a shift to northwesterly flow. This will advect cooler and drier conditions into the area heading into the day on Saturday. Subsidence and efficient mixing will certainly allow for a drop in RH's into the 30s, but luckily low-level winds will be fairly light, not to mention the return of vegetation in most places. Heading towards Sunday morning, focus will turn towards a developing Gulf low, following the recent CAA. During the daytime, a shortwave will approach from the west with increasing upper divergence as the jet becomes centered over the northeast. The result will be increasing PoPs, especially further south where better moisture exists. By Monday morning, high pressure will be expanding from the west again, which will produce additional subsidence. Depending on how much cloud cover and MSLP gradient-induced winds linger, patchy frost will be at least possible in the morning hours. Notable height falls and recent CAA will keep temperatures fairly cool. Tuesday through Thursday High pressure will keep the area dry and mild on Tuesday. Heading towards Wednesday, another shortwave will pass to the north with a surface front also drifting southeastward from the central Plains. This will lead to an increase in rain chances Wednesday and Thursday. The overall pattern currently indicates a setup supportive of showers with only limited thunder coverage due to fairly cool low- levels. Moisture will also be fairly limited for the time of year, given PWATs of only around 1 inch. && .AVIATION... (06Z TAFS) Issued at 100 AM EDT Fri Apr 19 2024 Mostly VFR conditions through sunrise. However, TEMPO MVFR in at TYS and CHA as showers and storms begin to develop and move into the region. The TEMPO MVFR may end up being too aggressive as recent Hi-Res models runs don't show as much coverage across the area as earlier runs did. TEMPO MVFR at TRI not until late morning. Then, VFR through this afternoon but with a PROB30 MVFR at all sites as additional showers and storms move through the area. MVFR toward the end of the period at CHA and TYS. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 80 57 73 51 / 50 10 20 30 Knoxville McGhee Tyson Airport, TN 75 54 68 48 / 80 20 10 20 Oak Ridge, TN 77 53 69 48 / 70 10 10 20 Tri Cities Airport, TN 73 51 66 44 / 100 20 10 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM... LONG TERM....BW AVIATION...