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

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664 FXUS64 KMRX 210730 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 330 AM EDT Fri Apr 21 2017 .SHORT TERM (Today and Tonight)...
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A weak wave is moving across the northern half of the area producing scattered showers and isolated thunder. This wave will exit the area early this morning. A frontal boundary will move into the northern half of Tennessee and southwest Virginia by this afternoon. Airmass along and ahead of the boundary will become unstable with MLCAPES of 1000-1300 J/Kg. Due to dry air in the mid-levels and below cloud base, isolated strong to damaging winds are possible with the stronger storms. Hail CAPE will be enough to support isolated hail up to quarter size. PWs will increase to 1.35 inches which is near the 90th percentile of climatology. Since storm motions will be nearly parallel with the frontal boundary, training of thunderstorms with heavy rain is possible. Localized flash flooding is a concern. The convection will weaken by sunset, but given frontal boundary across the area, scattered convection will remain through the night. .LONG TERM (Saturday through Thursday)... Frontal boundary will still be stalled out in our vicinity as we start the weekend. Current forecasts have it draped across the Kentucky/Tennessee border by Saturday morning. Along this boundary (especially south of it) there will be good chances to see thunderstorms on Saturday. High PWAT values of over 1.25 inches will combine with CAPE values of over 1000 J/Kg and decent shear through the atmosphere. This combination will lend itself to possibly seeing some strong to possibly severe storms Saturday. The biggest threat with a few storms would be strong winds.. Additionally winds in the mid to upper levels of the atmosphere will be moving generally west to east, parallel to the boundary at the surface. This will increase the chances of training storms and we could see some flooding problems if several storms move over the same area. Precipitation chances will stick around through the weekend as the low pressure system slowly swings south of us before moving off the Atlantic seaboard. As this system slides along the stationary boundary near us rain wrapped up with the low will continue through Monday night. Another frontal system will make a run at us from the northwest but a strengthening high pressure system will build in from off the East Coast. This high pressure system will win out and we will see several days of clear skies and very warm temperatures. Towards the end of the work week high temperatures are expected to be around the mid 80`s for most of our forecast area.
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Chattanooga Airport, TN 83 61 80 59 / 50 50 40 80 Knoxville McGhee Tyson Airport, TN 81 60 74 57 / 70 70 50 70 Oak Ridge, TN 80 60 73 57 / 80 80 60 80 Tri Cities Airport, TN 77 56 71 53 / 80 80 60 70
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