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

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935 FXUS64 KMRX 212006 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 306 PM EST Tue Feb 21 2017 .SHORT TERM...
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(Today thorugh Wednesday night)... Clouds continue to push across the area. Though overcast, clouds were thin enough across the north to allow some sunshine to filter through and warm locations to around 70 degrees, with some spots climbing into the low 70s. Some light rain showers this afternoon will slowly give way to steadier rain across southern portions of the forecast area as the atmosphere slowly becomes more saturated. Short term models continue to want to keep areas north of I-40 dry through at least midnight tonight. For Wednesday, conditions should slowly dry out across the south as the closed low slides east and cuts off the moisture transport to our area. In contrast, this looks to be the better setup for rain across SW VA and NE TN, and models indicate some rain through Wednesday evening over the northern half of the forecast area. Overall, rainfall amounts should be light, but south to southeast winds could lead to some areas of downsloping. With overcast skies, lows tonight will remain mild, holding in the 50s across much of the area. Cloud cover tomorrow will keep lower, especially across the north. Highs will range from the lower 60s there to the upper 60s in the southern valley where some sunshine may be able to work in by late afternoon. .LONG TERM...(Thursday through Tuesday)... A 700-500 mb shortwave trough is expected to cross the area on Thursday. Forcing with it is weak, and forecast soundings show weak instability across northern sections while southern sections remained capped. Will have just a slight chance PoP north on Thursday. Temperatures will continue their upward trend Thursday and Friday as the southerly 850 mb flow strengthens ahead of a Midwest low. Highs in the TN Valley will be in the lower 70s Thursday, and mid 70s Friday. Models have been consistent and in good agreement on the timing of a cold frontal passage late Friday night. Convection ahead of the front is expected to develop in Middle TN in the evening, and move into East TN around midnight. The overnight timing means instability should be weak, but strong shear and favorable positioning of the upper jet exit region could result in some strong to marginally severe storms. Likely PoPs with a chance of thunderstorms will be continued. With fropa expected around 12Z, Saturday should have lowering rain chances with clearing skies through the afternoon. Cooler temperatures build in over the weekend, but still only close to normal for late February - highs in the 50s and lows in the 30s. The GFS shows a fast-moving shortwave trough bringing some precip to northern areas Sunday night, but the ECMWF shows nothing. Will keep this period fry for now. We return to a mild SW flow pattern on Monday as the pattern becomes more amplified with a deepening trough over the Rockies, which will also bring a return of rain chances on Tuesday.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 57 70 55 74 / 70 40 10 10 Knoxville McGhee Tyson Airport, TN 55 67 52 73 / 70 60 20 20 Oak Ridge, TN 54 66 52 73 / 70 60 20 20 Tri Cities Airport, TN 51 62 48 72 / 70 80 30 20
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ EMH/DGS

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