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

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376 FXUS64 KMRX 271933 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 233 PM EST Mon Feb 27 2017 .SHORT TERM...
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Tonight and Tuesday... The upper trough that provided light rain earlier today mostly over the southern TN Valley was translating into NC. The majority of light rainfall has moved east of the forecast area. Therefore, mostly dry conditions will occur during the first part of tonight. There will be another shortwave approaching the forecast area, however, warm air advection and strong southerly flow will occur ahead of that system. Expect increasing rain showers after 2am ET. By noon, scattered thunderstorms will be more common along the Plateau with increasing instability. Thunderstorms will spread eastward through the afternoon. At this time, these thunderstorms will bring brief heavy rain and wind gusts to 40 mph. .LONG TERM...Tuesday Night through Monday... The main focus for the long-term forecast will be the risk for severe weather Wednesday afternoon and evening. A deep upper level trough will traverse across the Great Plains Tuesday night into Wednesday with a surface low tracking from the Oklahoma panhandle to near Chicago by Wednesday morning. There are some questions about how much convection will be ongoing at the beginning of the long-term period. Model soundings indicate dry air in the mid-levels with a cap in place most of the overnight hours Tuesday into Wednesday morning. For now, have backed off on PoPs a bit during this timeframe. The main line of severe storms will approach the area during the early afternoon on Wednesday. There are still some minor timing differences but the noon to 8 pm timeframe looks to be a pretty good. A sub-tropic 300mb jet max of around 120-130 kts will be located over the Lower Mississippi River Valley Wednesday afternoon putting the forecast area in the favored left exit region of the jet. A low level jet of around 50-60 kts will develop as the cold front approaches. A warm and moist airmass will advect northward across the forecast area with upper 50s to low 60s dewpoints. These higher dewpoints will yield SBCAPE values of around 500-1000 J/Kg depending on model run variability. Low level 0-1 km SRH is around 300-400 m2/s2 but most of this is speed shear with little change in direction in the low-levels. The deep layer 0-6 km shear is around 50-70 kts. All of these parameters point to a line of severe storms with damaging winds being the main threat.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 49 68 62 73 / 30 70 40 90 Knoxville McGhee Tyson Airport, TN 47 68 61 73 / 20 70 40 90 Oak Ridge, TN 46 66 61 73 / 20 70 40 90 Tri Cities Airport, TN 41 69 56 73 / 10 60 40 90
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ AC/MA

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