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

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000 FXUS64 KMRX 241849 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 249 PM EDT Tue Apr 24 2018 .SHORT TERM...
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(Tonight and Wednesday)... A closed upper low continues to slowly shift east across the TN valley and southwest VA/NC, while at the surface weak low pressure slides along the I85 corridor region of the the Carolinas. Given abundant llw moisture streaming in ahead along sly H85 flow, sct/num showers continue to spread east through the Great Valley into extreme northeast TN and SW VA/NC this afternoon. In addition, steep low/mid lvl lapse rates beneath the rotating upper low remain overhead, therefore cannot rule out a few iso/sct thunderstorms this afternoon. In fact, latest CAM guidance favors a broken line of weak tsra forming in the next few hours along/east of the I75 corridor before pushing eastward along I81. All in all, think most of these storms will be weak, yet cannot rule out some heavy rainfall due to training and slow storm motions, as well as small sub severe hail. This system will move east throughout the overnight hours, however sufficient BL moisture will remain, therefore am expecting mostly cloudy skies tonight with low bases. In addition, surface condensation pressure deficits will be rather low amidst light surface flow, therefore cannot rule out some patchy fog. Pops will be allowed to lower regionwide overnight, with slight/chance pops holding along the high terrain given developing nwly flow which should support a few showers. A brief period of shortwave H5 ridging will overspread the region on Wednesday keeping the vast majority of the fcst area dry, albeit amidst partly/mostly cloudy skies along persistent moist nwly flow. Highs on Wednesday will top out around a category below normal levels. .LONG TERM...(Wednesday night through Monday)... There will be a number of upper level shortwave troughs across the Eastern CONUS to start the long-term period. One racing to the northeast into New England another passing to the north across the Great Lakes and a third moving into the Lower Mississippi River Valley. Precipitation should be coming to an end for most areas Wednesday night with a few wrap around showers possible in SW VA and NE TN. The next system moves in on Thursday with an upper level low moving right over the Tennessee River Valley. Yesterday the only model depicting this solution was the NAM. Since then, the GFS, ECMWF and most SREF members are all in relatively good agreement with this more northward track. Due to this, have increased PoPs during th day on Thursday and into the overnight hours. Rainfall amounts will range from around a quarter of an inch to as highs as an inch in some places. This system will race off to the northeast early Friday with precipitation chances dwindling. Another upper level low will move through the Lower Mississippi River Valley later in the day on Friday. Low level winds will remain out of the northwest ahead of this system and not seeing much in the way of moisture and have only gone with slight chance PoPs. Based on the latest model guidance, most of the day Friday may be dry. A warming trend is in the forecast for the weekend into early next week. An upper level ridge will build in from the west with temperatures rising into the upper 60s to low 70s over the weekend and into the mid to upper 70s by early next week.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 53 68 53 64 / 30 10 10 70 Knoxville McGhee Tyson Airport, TN 54 67 50 64 / 50 30 10 60 Oak Ridge, TN 53 68 49 65 / 40 30 10 50 Tri Cities Airport, TN 51 64 47 63 / 70 50 20 60
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ CDG/MA

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