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

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000 FXUS64 KMRX 170854 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 354 AM EST Tue Jan 17 2017 .SHORT TERM (Today and Tonight)... Seeing a couple of upper level features that will be important in the short-term portion of the forecast. Current water vapor imagery and RAP upper air analysis indicates s shortwave trough moving northeast into the Great Lakes region with the second shortwave trough moving to the southeast across the Northern Plains. At the surface, a low pressure center is directly underneath the first shortwave trough near Chicago with an associated cold front stretching southward towards Memphis and further southwestward towards Houston. Current radar imagery depicts widespread showers across Middle and Western TN and northwards into Kentucky. The area of showers has made little progress to the east but should begin to see that closer to daybreak as the first trough pushes more to the east. Timing of the precipitation will be the main forecast challenge today. The atmosphere will be highly saturated with PW values near maximum levels observed for mid-January ranging from 1.1- 1.4 inches. Looks like the first batch of precipitation should move through mid-morning as the first trough pushes off to the east. It looks as though there will be a brief break in the precipitation late this morning into early this afternoon between the two systems. Precipitation should move in again ahead of the front later this afternoon and evening as the second trough passes just to the north. Models indicate some weak instability with MUCAPE values generally <250 J/Kg. Therefore, expect there could be a few rumbles of thunder through midnight or so. The cold front will be approaching the mountains late in the Short-Term forecast with cooler air moving into the Plateau and Southwest VA. The cold air advection behind the system is not overly impressive and lows behind the front will only drop down into the low to mid 40s across the Plateau and Southwest VA. .LONG TERM (Wednesday through Monday)... High pressure tries to build south behind a cold front later Wednesday and Wednesday evening. Drier air behind the front will lower temperatures briefly but not clear skies significantly before increased moisture with surface low moving up from the lower Mississippi Valley spreads more clouds and rain from the southwest late Wednesday night and Thursday. Increased instability...strong low level jet...upper level divergence in warm moist air mass later Thursday and continuing Friday ahead of this slow moving system will allow a few thunderstorms to develop. High temperatures both days will be in the mild upper 50s to lower 60s Thursday and lower to mid 60s Friday. The frontal system will move east of the region later Friday. Rain will end Friday night and be mostly dry into the first half of Saturday. Then yet another system will move into the Mississippi Valleys Saturday and deepening Sunday spreading another wave of showers north from the Gulf. Temperatures still mild with a chance of thunderstorms again Sunday possibly lingering into Monday as this system moves slowly east. Colder air finally poised to move in behind this system Monday night cooling temperatures into the 30s to lower 40s && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 69 54 61 49 / 70 70 20 40 Knoxville McGhee Tyson Airport, TN 67 51 58 44 / 70 60 20 20 Oak Ridge, TN 66 49 58 44 / 70 60 20 20 Tri Cities Airport, TN 64 48 56 35 / 70 70 30 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MA/TD is the U.S. government's official web portal to all federal, state and local government web resources and services.