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

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000 FXUS64 KMRX 190811 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 411 AM EDT Mon Mar 19 2018 .SHORT TERM...
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(Today through Wednesday Night)...Very active through the period. A series of short-waves and associated jets will move through today and then again Tuesday and Wednesday. Enhanced threat of severe weather today for Plateau, central and southern Valley, and southwest North Carooina. The mid- week upper trough and associated cold frontal passage will bring wintry conditions back into the southern Appalachians with mountains snowfall and widespread freeze for Wednesday night/Thursday morning. For Today, a short-wave and associated 120kt upper jet will move into the lower Ohio and Tennessee Valley. The pressure falls with the upper jet will strengthen the low-level jet pulling Gulf moisture northward into the Tennessee Valley. Main question is how far north will this push of moisture and instability go before upper dynamic associated with upper jet pulls through this afternoon and evening. Model soundings plenty of instability and very strong shear to produce discrete supercells over middle Tennessee and northern Alabama this afternoon, then race quicly east northeast into the Plateau, southeast Tennessee and southwest North Carolina. The greatest tornado threat will be across these areas, but the Knoxville area could does have a threat of damaging winds and marginal severe hail. Main timing of severe storms will be between 5 and 7 pm ET Plateau to 8 and 10 pm ET central and southern Valley, 9 and 11 pm ET southwest North Carolina. The rest of the area can expect widespread showers and thunderstorms with gusty winds and heavy rainfall. Besides the convection, strong southerly winds will produce windy conditions across the mountains and foothills late afternoon and evening. For Tonight, the storms exit the area this evening with dry slot clearing sky. Clear sky, winds becoming light/calm, and wet ground will allow widespread fog to develop. Some of the fog may be dense overnight. For Tuesday and Wednesday, the upper low over Oklahoma and Kansas will move across the Ohio and Tennessee Valleys. A cold frontal passage Tuesday will produce widespread showers with enough instability for thunder across east Tennessee, mainly TRI and TYS areas. As the cold front moves through and approach of upper trough, the vertical temperature profile will become cold enough for the rain showers to change to snow showers over the higher terrain. Snow accumulations of 2 to 4 inches are possible across the far eastern Tennessee and southwest Virginia Mountains. Places like the highest elevations of the Smoky Mountains and High Knob, VA could see up to 6 inches throughout a 36 hour period. Main concern is for any hikers getting caught off guard of the cold and snowy conditions over the higher terrain. Will highlight all of these concerns within our HWO and SPS products, and DSS. .Long Term (Thursday through Sunday)...The advertised dry period still appears to be on track on Thursday with the offending deep Eastern U.S. trough slipping out to sea, followed by an amplifying upper ridge. The next low pressure system will be developing over the Plains on Friday with eastward movement into the Midwest by 12z Saturday. Typically, model solutions try to generate too much lift over the Southern Appalachian region in the warm air advection ahead of an approaching Middle America low pressure system. We see that again in this mornings model runs for the period Friday through Friday night; evidenced by a relatively high chance for showers during the day Friday along with increasing probability Friday night due to uncertainty in system timing. Tried to pull back on pops as much as possible on Friday where the chance of rain this far in advance of a developing mid latitude cyclone is rather low. The best chance for showers; and even a thunderstorm or two would be Saturday into Saturday night according to the latest modeling. Had to broadbrush a chance pop for showers into Sunday due to uncertainty in storm system timing. A welcome, but modest warming trend begins on Thursday with continuation through Saturday. Sunday may not be too unpleasant with weak cold air advection predicted behind the weekend frontal system.
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Chattanooga Airport, TN 67 52 62 36 / 80 100 60 40 Knoxville McGhee Tyson Airport, TN 67 51 60 35 / 80 100 70 70 Oak Ridge, TN 65 51 60 35 / 80 100 70 70 Tri Cities Airport, TN 65 48 63 37 / 40 100 80 90
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.