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

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000 FXUS64 KMRX 201951 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 251 PM EST Mon Feb 20 2017 .SHORT TERM...
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(Tonight through Tomorrow night)...High pressure will remain in control tonight but will be slowly moving off to our east due to an incoming closed off low. A cirrus layer will remain over the area tonight which will yield mostly clear conditions. Overnight lows will be in the mid to upper 40s north (TRI) and upper 40s to low 50s south (CHA). Mid-level moisture begins to spread in from the west tomorrow morning as the closed off low nears the area, brining an increase in clouds. Moisture will spread from west to east through the day. It takes a while for soundings to moisten up so don`t bring pops into the area until the afternoon hours, where a slight chance/chance pop is in for the Cumberland Plateau, Southern Valley, and SWNC. Gradually spread pops from southwest to northeast through the day with increasing chances as the day progresses, Northeast TN and Southwest VA stay dry the longest. 850mb flow reveals some downsloping winds early tomorrow so tried to hold off clouds in these areas until later in the day. So the foothills of our eastern mountains should see sunshine the longest. QPF amounts look light through the day with only a few hundredths of an inch forecast. Highs will be cooler with the increased cloud cover, mid to upper 60s are expected. Low moves across to our south during the overnight hours giving the best chances of precip with deeper moisture and better lift in place. Have likely pops across the area with around 0.15 to 0.25 inches expected on average. Lows will remain mild tomorrow night with the added cloud cover. Lows will be in the upper 40s to lower 50s. .LONG TERM...(Wednesday through Monday)... The 12Z model runs have trended toward a slower departure of the low pressure system over the northern GoM, so the chance of rain Wednesday morning will be raised to likely for northeast sections as the 700 mb deformation zone remains over the mountains at 12Z. But any rain chance should be gone by the mid/late afternoon, with decreasing clouds. A weak midlevel shortwave trough is progged to cross the area on Thursday, and with forecast soundings showing a little instability present, a low to slight chance PoP will be carried in the afternoon, favoring NE sections where soundings show a weaker capping inversion. A strengthening low in the lee of the Rockies on Thursday night will provide a deep S-SW flow across the TN Valley on Friday. The jet streak rotating around the base of the closed upper low will move into West and Middle TN Friday night, becoming favorably positioned to provide strong upper divergence. Frontogentic forcing in the jet exit region peaks over our area around 06Z Saturday. The overnight timing will mean limited instability, but given the strong dynamic forcing and high shear that may be present, there appears to at least be some potential for severe storms at this point. Will add a mention of this to the HWO. High temps will peak in the lower to mid 70s on Friday before colder air arrives behind the front on Saturday. Still, it will not be a bitterly cold air mass, with highs in the mid/upper 50s Saturday and lows in the 30s Saturday night. The next chance of rain appears to come on Monday as a cold front sags slowly southward across the OH Valley and a series of weak disturbances move through a nearly zonal flow aloft.
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Chattanooga Airport, TN 51 66 54 68 / 0 50 60 30 Knoxville McGhee Tyson Airport, TN 48 69 52 64 / 0 20 60 40 Oak Ridge, TN 47 68 52 65 / 0 20 60 40 Tri Cities Airport, TN 44 67 48 64 / 0 10 60 60
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ SR/DGS is the U.S. government's official web portal to all federal, state and local government web resources and services.