Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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241 FXUS64 KMRX 221922 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 322 PM EDT Sat Apr 22 2017 .SHORT TERM /Tonight and Sunday/... Another round of showers and thunderstorms have begun to fire west of the MRX CWA across Middle TN and into portions of the northern Plateau. This activity is firing along the remnant boundary/front in place roughly along the I-40 corridor. North of I-40, which has remained overcast and wet for most of the day, a capped, more stable environment remains in place. However, places along and south of the I-40/I-81 corridor have seen some sunshine over the last 2-3 hours. This has helped destabilize things, with MLCAPE values in the 1000-1500 J/kg range across the Southern Plateau and Valley -- and in the 500-1000 J/kg across the central Valley and along the Great Smoky Mountains. As a result, am expecting the potential for some strong to marginally severe storms - particularly in Slight Risk area between 4 to 9 PM EDT this afternoon and evening. The main threats with this activity will be straight-line damaging winds, along with some marginally severe hail. However, the primary impact from this activity will be the threat for locally heavy rainfall and flash flooding -- along with a risk for lightning for the folks with outdoor plans. As mentioned, there is a favorable set-up for flash flooding tonight into Sunday, particularly across the northern Plateau and portions of southwest Virginia and far northeast Tennessee which has already seen heavy rain today and last night (1-2 inches), and could see an additional 2-3 inches through Sunday evening. Adding to the threat are high PWAT values up to 1.5 inches, a deep warm cloud layer with some CAPE to work with, and the potential for training for the mean flow potentially moving parallel to the boundary overnight. Then, another round(s) of locally heavy showers will re-develop and move across portions of East Tennessee and Southwest Virginia tomorrow ahead of the upper-low passage as it moves across the state on Sunday. There is really not a specific time more favored for rainfall Sunday, though things should begin to die down as the feature moves east after 21z. As a result, have maintained the Flash Flood Watch for the entire region until 21z on Sunday. May have to look at extending this in time based on model and radar trends this evening and overnight. .LONG TERM /Sunday Night through Saturday/... Residual showers will slowly exit the Southern Appalachian Region Sunday night into Monday as an upper level low pulls away from the area. High pressure builds in late Monday into Tuesday for dry conditions and a warming trended for mid week. Model consistency quite poor Thursday through the rest of the period...but overall trend is for an unsettled end of the period with a weakening frontal boundary progged to move through on Thursday and another system approaching the area around the Friday/Saturday time frame. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 57 64 53 71 / 90 80 40 10 Knoxville McGhee Tyson Airport, TN 56 60 51 69 / 90 90 50 10 Oak Ridge, TN 56 61 51 69 / 90 80 50 10 Tri Cities Airport, TN 53 58 47 67 / 90 100 80 30 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Flash Flood Watch through Sunday afternoon for Cherokee-Clay. TN...Flash Flood Watch through Sunday afternoon for Anderson-Bledsoe- Blount Smoky Mountains-Bradley-Campbell-Claiborne-Cocke Smoky Mountains-East Polk-Grainger-Hamblen-Hamilton-Hancock- Hawkins-Jefferson-Johnson-Knox-Loudon-Marion-McMinn-Meigs- Morgan-NW Blount-North Sevier-Northwest Carter-Northwest Cocke-Northwest Greene-Northwest Monroe-Rhea-Roane-Scott TN- Sequatchie-Sevier Smoky Mountains-Southeast Carter- Southeast Greene-Southeast Monroe-Sullivan-Unicoi-Union- Washington TN-West Polk. VA...Flash Flood Watch through Sunday afternoon for Lee-Russell-Scott- Washington-Wise. && $$ AMP/MJB

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