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

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000 FXUS64 KMRX 230735 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 335 AM EDT Tue May 23 2017 .SHORT TERM (Today and Tonight)...
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Latest water vapor imagery and RAP upper air analysis indicates shortwave trough over northern Alabama/Georgia that will continue to move NE into central NC by this afternoon. Stalled surface front is along the SE TN border extending NE into SW NC this morning. Combination of this shortwave and the surface boundary is helping to enhance rainfall out ahead of it, mainly over NE Georgia and Western Carolina this morning. As steady rain is beginning to wind down across the southern Valley and Plateau, expect this pcpn shield to continue to move NE through today with greatest pcpn potential in our area continuing along the western slopes of the Appalachian Mtns in East TN through mid day. POPs decrease to chance area wide by this evening ahead of an approaching front that will once again bring another round of pcpn by Wednesday morning. Latest 12 hour MRMS pcpn total indicates greatest rainfall amounts of 0.5 to 1.0 inches over portions of Polk and Monroe counties in SE TN with radar indicating more spotty areas of pcpn moving into those areas for this morning. With models indicating some middle level drying behind the shortwave this afternoon, PWs dropping to near 1.0 inch, additional rainfall potential for this area over the next 24 hours should be limited to 0.5 inches or less. With expected 24 hour totals well below current flash flood guidance, do not expect to see any flooding issues through the period. Continued cloud cover and pcpn will keep temperatures slightly below or about 4-6 degrees cooler than late May normals and in very close agreement with NAM/GFS MOS as well as the Super Blend. .LONG TERM (Wednesday through Monday)... Main feature will be a deep upper trough digging southeast into the Tennessee Valley for Wednesday. Strong upper jet will rotate out of the trough across the east Tennessee Valley during the day Wednesday producing strong upper divergence. The strong forcing along with marginal instability will produce widespread showers and thunderstorms. Main concern in the morning will be locally heavy rainfall. Depending if enough breaks occur behind this initial wave, scattered storms will likely develop later in the day. Given the cold air aloft associated with upper trough producing low WBZ, some of these storms could produce hail from the mid-afternoon through early evening. For Thursday, upper trough axis will be moving east of the area, but cold air aloft remains across southwest Virginia/northeast Tennessee. Scattered showers and thunderstorms are expected to redevelop there with small hail once again possible given the low WBZ. For Thursday night and Friday, upper trough moves east of the area with weak ridging developing across the region. Mostly dry conditions are expected with warmer temperatures. For Saturday, southerly flow returns pulling a moist/unstable air back into the region. Isentropic lift along with jet energy will focus the instability to produce scattered thunderstorms. Some of these storms could be strong to severe with the main concern being downbursts damaging winds and hail. For Sunday and Monday, confidence is low on timing of convection. GFS wants to develop a MCS over the mid-Mississippi Valley Saturday night, then move across the Tennessee Valley. Concerned for active severe storms for Sunday and Monday due to favorable jet dynamics. Later shifts will need to watch closely for this development/evolution.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 76 62 73 55 / 70 60 80 60 Knoxville McGhee Tyson Airport, TN 73 60 72 55 / 80 50 80 70 Oak Ridge, TN 74 60 73 55 / 70 60 70 60 Tri Cities Airport, TN 71 57 71 54 / 90 40 80 70
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ EJH/DH

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