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

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000 FXUS64 KMRX 200735 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 335 AM EDT Thu Apr 20 2017 .SHORT TERM...
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(Today and Tonight)... Patchy fog/low stratus is possible early this morning due to partly clear skies and residual ground moisture from this week`s rain. Some isolated showers are possible this morning, but most areas should stay dry into this afternoon. Scattered showers and thunderstorms are expected to develop this afternoon with winds out of the south-southwest advecting Gulf moisture into the area (PWATS near 1") and a bit of instability (MLCAPE values generally under 800 J/kg). With very little shear to work with and the only forcing being orographic lift, we`re not expecting many strong storms, but there is the potential for an isolated strong to severe storm producing some strong winds or small hail. Again, with the orographic lift being pretty much the only forcing, the best chance for storms will be over the higher elevations. Convection will fizzle out after sunset. Tonight should be mainly dry, but northern portions of the forecast area will begin seeing increased cloud cover and potentially a shower/thunderstorm as a frontal boundary slowly approaches the area. Temperatures will be quite warm today, reaching the lower 80s in many locations. Lows tonight will hover near 60 degrees. .LONG TERM...(Friday through Wednesday)... Zonal flow aloft dominates Friday and Saturday ahead of a digging Plains trough that swings through the area Sunday with weak ridging behind it through Wednesday. At the surface, frontal boundary approaches the area Friday morning becoming nearly stationary across the area Friday night. Boundary then begins to lift north Saturday ahead of a well defined low pressure system that will finally kick east of the area on Sunday afternoon and allow for high pressure and an extended period of drier conditions through Wednesday. Frontal boundary on Friday will serve as a focusing mechanism for showers and thunderstorms once again. With model indicated PWs of 1.4 inches, MLCAPE values nearing 1000 J/kg and sufficient deep layer shear, some of these storms could become organized enough to produce an isolated strong to locally severe threat across the area. Additionally, orientation of sfc boundary parallel to the deep layer flow could cause training cells and the possibility of heavy rainfall in training cells. Rain threat will persist overnight Friday before diminishing some over the southern half of the area early Saturday as warm front ahead of the approaching low Saturday night, shifts north of the area. This is followed by another potential bout with severe thunderstorms Saturday night as a 30-40 kt low level jet develops ahead of the approaching front. As the upper level trough begins to rotate through the area, some shortwave energy and sufficient deep layer shear could once again act to support a primary threat of large hail and damaging winds. Although, latest consensus of models indicates that greatest threat for severe will likely lie further west over NW Mississippi and the southern third of Middle TN, low level forcing of the associated front could act as a focal point for severe weather as it moves through East TN Saturday night. Forecast then sees a prolonged period of clearer skies and drier conditions Monday through Wednesday. With a surface ridge nosing southeast from New England and an upper level ridge finally able to establish itself over the area, we can expect seasonal temperatures gradually warming about 4-8 degrees above normal by Wednesday. $$
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 83 62 83 62 / 30 20 60 50 Knoxville McGhee Tyson Airport, TN 83 62 80 61 / 30 20 60 50 Oak Ridge, TN 84 61 79 61 / 30 30 60 60 Tri Cities Airport, TN 79 58 77 57 / 50 30 70 60
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ EMH/EJH

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