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

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000 FXUS64 KMRX 140807 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 407 AM EDT Wed Mar 14 2018 .SHORT TERM (Today and Tonight)...
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Maintained the advisory for some light snowfall across Southwest Virginia and a small section of Northeast Tennessee this morning. Orographic lift and lapse rates in the neighborhood of 7-8 degrees C/km will allow the light snow to accumulate; mainly over the higher terrain across these areas. Kept the advisory going for the extreme northeast corner of Tennessee with temperatures a few degrees below freezing and some light accumulation impacting slightly elevated terrain as well as bridges and overpasses. Deeper moisture and lift fade away around mid to late morning as the upper trough slips east. With drier air building in there will be increasing sunshine northward through the valley. Despite the sunshine, temperatures will be a few degrees colder today with highs ranging from the lower to mid 30s north to the lower to mid 40s across the south. Lows will be in the mid to upper 20s under. .LONG TERM (Thursday through Tuesday)...Thursday has the potential to the best day of the forecast period for outdoor activities. There will be a surface boundary that stretches from a surface low along the front-range of the Rocky Mountains eastward into the Central Plains all the way to the Mid- Atlantic. Northwesterly flow aloft across the area with a trough over the Western Atlantic and a shortwave ridge over the Great Plains. The forecast area will be on the south side of the surface boundary with temperatures warming into the mid 50s to low 60s for most locations on Thursday afternoon. The surface boundary will slowly sink southward Thursday night into Friday as the upper level ridge flattens. Overnight lows on Thursday night will range from mid 30s to low 40s. Models indicate some weak lift along the boundary late Thursday night and have continued a small chance for precip. across NE TN and SW VA during this timeframe. Models continue to push back the timing of the precip. and could see this period being dry in future forecast. Models are fairly consistent with precipitation developing along the boundary by Friday. PW values will increase into the 0.6-0.8 inch range along the boundary. Precipitation should be light and only expecting around a tenth to a quarter of an inch. Highs on Friday will vary greatly across the forecast area with the front bisecting the area. Highs will range from mid 40s to low 50s on the north side of the boundary in SW VA and NE TN to upper 50s and low 60s in SE TN and SW NC. The surface boundary will nudge to the north as the low level ridge moves to the east with southwesterly to westerly flow in the low levels. Warm air advection will lead to increasing temperatures during the overnight period Friday night and into Saturday morning. Due to this, went with a raw model blend during this timeframe. Temperatures should be warm enough to keep precipitation in the form of rain. Warm air advection will continue on Saturday as an upper level trough passes to the north across the Ohio River Valley. Surface based instability will creep up into the area and have gone with a chance for a few thunderstorms. As the upper level trough passes to the north the front will slowly drift southward. Models differ on how far south the front progresses. Regardless, it looks like PoPs will continue throughout the weekend with the boundary stalling over or just to the south of the forecast area. The pattern remains progressive as a more robust upper level trough moves across the Central Plains early next week. The surface boundary will surge back to the north early next week with chance for thunderstorms forecast again on Monday. Temperatures throughout the extended forecast will be closer to seasonal averages.
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Chattanooga Airport, TN 47 32 63 43 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 42 30 61 42 / 10 0 0 10 Oak Ridge, TN 42 29 61 41 / 0 0 0 10 Tri Cities Airport, TN 37 26 55 37 / 20 10 10 20
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...Winter Weather Advisory until 11 AM EDT this morning for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Unicoi. Winter Weather Advisory until 9 AM EDT this morning for Claiborne-Hancock-Hawkins-Northwest Carter-Northwest Greene- Sullivan-Washington TN. VA...Winter Weather Advisory until 11 AM EDT this morning for Lee- Russell-Scott-Washington-Wise. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.