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

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000 FXUS64 KMRX 191945 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 245 PM EST Fri Jan 19 2018 .SHORT TERM...
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(Tonight and Saturday)... The thaw has begun across the Southern Appalchians. Temperatures early this afternoon are generally in the 40s across the forecast area. Current water vapor imagery and RAP upper air analysis indicates a weak upper level trough across the Northern Gulf Coast. There are a few showers associated with this system along the Texas Gulf Coast but not seeing anything else at this time. In the lower levels, high pressure is located to the south with southwesterly to westerly flow across the area. Seeings clouds to the southwest on visible satellite imagery across the Lower Mississippi River Valley and expect these clouds will move into the forecast area late tonight. Due to this, lows will be warmer to the west across the Plateau and range from the mid 20s to low 30s areawide. Isentropic lift will keep cloud cover in the forecast throughout the morning on Saturday. Some of the models indicate enough lift for some light precipitation with this cloud cover. For now, have left the forecast dry. The best chance for light precipitation would be over the mountains where there will be additional orographic lift. If precipitation does occur Saturday morning, it would be in the form of freezing drizzle/drizzle. Again, not forecasting any precipitation at this time but will continue to monitor observations and radar trends throughout the night. The warming trend will continue on Saturday with highs in the mid 40s to low 50s. .LONG TERM...(Saturday night through Thursday)... Low level moisture and weak isentropic lift in the 285-295 K layer will keep broken to overcast cloud cover across the area to start the period. Moisture appears shallow enough in model soundings to leave precip out of the forecast Sat night and Sunday, and the GFS MOS has trended strongly in a drier direction with the latest run. Sunday will open with mostly cloudy skies with decreasing clouds through the afternoon with mixing and a mild SW flow. Model guidance has trended warmer for Sunday, and highs will be above normal, reaching the upper 50s to mid 60s south. A closed low will be tracking from the central Plains to the upper MS Valley on Monday, with its trailing cold front crossing TN through the day. Rain chances will rise from chances in the morning to categorical in the afternoon. There will be good forcing in association with the upper jet, but instability remains too far to our south to warrant any mention of thunderstorms or severe threat at this time. But this will bear watching with later model runs. ECMWF is a little slower with the fropa Monday night than the GFS, but we should see a drying trend during that period. Cold temps aloft under the closed low may skirt our northern sections on Tuesday, with just a slight chance of rain or snow showers in SW VA. Temps will be colder on Tuesday but still not far from normal, with highs in the mid to upper 40s. The rest of the period is expected to be dry with slow warming trend as surface high pressure will be the dominant feature across the eastern Conus, with a weak ridge building aloft. $$
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 29 54 37 64 / 0 0 10 0 Knoxville McGhee Tyson Airport, TN 29 51 38 59 / 0 0 10 10 Oak Ridge, TN 29 50 38 58 / 0 0 10 10 Tri Cities Airport, TN 25 49 36 57 / 10 10 10 10
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ MA/DGS

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