591 FXUS64 KMRX 041100 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 700 AM EDT Sun Apr 4 2021 .UPDATE... FOR 12Z AVIATION. && .SHORT TERM...(Today and Tonight)... With surface high pressure and upper ridge axis to our west, expect an absolutely beautiful and pleasant Easter Sunday across the forecast area with light winds and a clear, sunny sky. With increasing 850mb temperatures, expect afternoon max temperatures to be 5 to 7 degrees warmer today for most locations. Temperatures surface ridging shifting eastward and upper ridging increasing across the area, minimum temperatures should be closer to normal tonight with any frost risk generally limited to mountain zones where the growing seasons has yet to begin. JB .LONG TERM...(Monday through Saturday)... Key Messages: 1. Monday and Tuesday will be dry with a continued warming trend. 2. Chances for showers and thunderstorms increase late on Wednesday and top out on Thursday. Low-end rain chances will linger into the weekend. 3. Localized flooding and a few marginally strong/severe storms are possible on Thursday. 4. Temperatures will be generally above normal for the whole period. Monday through Wednesday At the start of the period, shortwave ridging will be in place across the east-central U.S. with a positively tilted shortwave/ closed low over the Pacific Northwest. At the surface, broad low pressure will be in place in the Rockies with high pressure continuing across the southeast. With this initial setup, dry and mild weather will continue, evidenced by increasing heights and a thermal (1,000-500mb) ridge building from the west. As surface high pressure shifts eastward on Tuesday, increasing southerly flow helps to enhance WAA and likely allow for much of the area to reach well into the 70s. During this timeframe, the aforementioned shortwave/closed low becomes more neutral and ejects out of the Rockies with cyclogenesis taking place over the High Plains. Heading into Wednesday onward, uncertainty still remains in exact details with the system, which will inhibit confidence in PoPs. But in any case, mid/upper ridging builds into the area with significantly increasing differential WAA via higher 1,000-500mb thickness values. This is also coincident with stronger southerly flow leading to low-level moisture advection and WAA. But as was stated, details still remain unclear in the track of the system with the latest trend being for a more northerly track towards the upper Mississippi Valley/upper Great Lakes especially with the latest CMC and ECMWF deterministic models. Within the GEFS members, a normalized spread of 0.8 to 1.0 and spatial range of 500+ miles still remains in the track of the system with the mean being in line with deterministic guidance. Regarding chances for showers and thunderstorms, the latest trends keep chances more towards Wednesday night based on indications of deeper moisture. This is also ahead of the approaching cold frontal boundary as well. Based on ensemble and deterministic indications of PWATs reaching above 1.3" during this timeframe, there is some low-end concern for locally heavy rainfall, which could lead to potential for isolated flooding following repeated rainfall into Thursday. Thursday through Saturday By Thursday, the focus will be the approaching cold frontal boundary, and potential for increasing negative tilt in the trough and subsequently more notable height falls locally. This negative tilt is indicated most notably with the ECMWF and also with the CMC, but in any case, is much more notable further west. Nevertheless, the increasing cooling aloft and steepening lapse rates may be sufficient to support marginally strong/severe convection. This is also dependent upon the extent of clearing and development ahead of the front, which is seen more with the CMC and ECMWF than the GFS. Following an early look at vertical profiles, the potential for thermodynamically-driven damaging winds and isolated large hail are the main concerns. The overall tornado potential in our area does lack moreso than these threats with largely unimpressive 850mb flow of 30 kts or less. The overall marginal upper jet strength (50-70 kts) for this time of year is also an inhibiting factor for severe potential. With all of these factors considered, 60%-70% PoPs will be kept heading into Thursday and throughout the day. The overall consensus is for the cold front to occlude and not pass through the area until more towards Friday morning. Behind the front, low-level moisture and some continued vertical ascent will keep rain chances in the area for Friday. By Saturday, confidence is lower for rain chances based on varying indications for embedded shortwave energy. BW && .AVIATION... 12Z TAF DISCUSSION. High pressure will result in VFR conditions and light winds through the period at all sites. JB && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 71 45 75 49 75 / 0 0 0 0 0 Knoxville McGhee Tyson Airport, TN 70 44 72 48 73 / 0 0 0 0 0 Oak Ridge, TN 71 43 73 47 74 / 0 0 0 0 0 Tri Cities Airport, TN 67 40 70 45 72 / 0 0 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Frost Advisory until 9 AM EDT this morning for Cherokee-Clay. TN...Frost Advisory until 9 AM EDT /8 AM CDT/ this morning for Anderson-Bledsoe-Bradley-Campbell-Claiborne-East Polk- Grainger-Hamblen-Hamilton-Hancock-Hawkins-Jefferson-Knox- Loudon-Marion-McMinn-Meigs-Morgan-North Sevier-Northwest Blount-Northwest Carter-Northwest Cocke-Northwest Greene- Northwest Monroe-Rhea-Roane-Scott-Sequatchie-Sullivan-Union- Washington-West Polk. VA...Frost Advisory until 9 AM EDT this morning for Lee-Russell-Scott- Washington-Wise. && $$