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

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000 FXUS64 KMRX 190854 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 354 AM EST Thu Jan 19 2017 .SHORT TERM...
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(Today and Tonight)... Low pressure has moved into Louisiana along old frontal boundary and is forecast to lift slowly northeast into the Ohio Valley over the next 24 hours. Upper level ridging over the northern Gulf of Mexico and Florida is being flattened as closed upper level low over the southern Plains moves into the upper Mississippi Valley. Subtropical moisture is being lifted northeast toward southeast Tennessee north of the front with rain now developing across the southern Plateau and southern Valley at this hour. Short range models show this trend continuing the next few hours then after a brief break late this morning and early afternoon then more rain moving in late afternoon and evening. Precipitable Water values will be high and with the southerly flow and shortwave energy rainfall amounts of one to two inches are possible across southeast Tennessee tonight. Some localized flooding could occur. Enough instability will be present for a few thunderstorms late afternoon and evening. Highs today will be again mild in the 60s. Lows tonight still mild with showers and storms and southerly flow. Most locations lower to mid 50s except upper 40s northeast Tennessee valley. .LONG TERM...(Friday through Wednesday)... An active weather pattern will feature throughout the long-term forecast with a few breaks in the precipitation from time to time. In addition, above average temperatures will continue throughout the forecast period with precip. all in the liquid form. An exiting trough to the northeast and a shortwave ridge moving across the Southern Appalachians will start the extended forecast period on Friday. A few lingering showers will be possible early in the day but significant drying in the mid and upper levels should bring any leftover precipitation to a quick end. PW values will drop down into the 0.6-0.7 inch range Friday into Friday night. These values are still well above normal for late January but the lack of any upper level support will give the area a brief break in the precipitation Friday afternoon into Saturday morning. A series of shortwave troughs will move through the Southern Appalachians over the weekend keeping elevated chances for showers and thunderstorms throughout the period. The first shortwave trough will move into the region early Saturday with warm air and moisture advection ahead of the trough. PW values will increase into the 0.8- 1.0 inch range on Saturday. These values are near the 90th percentile for late January. Models also depict a secondary warm front moving into the Southern Valley and Southern Plateau counties during the afternoon. SBCAPE values to the south of this boundary are as high as 1000 J/Kg with decent directional low-level shear along the boundary with 0-1 km SRH values around 150-250 m2/sr. Based on this, will continue with threat for strong to severe storms in the HWO for Saturday afternoon mainly over the Southern Plateau and Southern Valley. Expect any strong or severe storms will weaken during the overnight period as the low level winds weaken and the low level boundary becomes less defined. Another shortwave trough will move across the region Saturday night and expect widespread showers will continue with a few thunderstorms. An upper level closed low will move eastward across the Southeastern U.S. on Sunday. The latest models have been further south and faster with the track of the closed low on Sunday. In this scenario, the track of the low would not be favorable for strong to severe storms across the region. However, MUCAPE values will generally be < 500 J/Kg, 0-6 km bulk shear around 50-70 kts with weak low level 0-1 km SRH only around 50-150 m2/s2. Based on this, there still appears to be at least a threat for strong to marginally severe storms and will continue the wording in the HWO for now. Atmospheric profiles remain highly saturated as the closed low takes a northern turn across the Mid-Atlantic Sunday night into Monday. Lower rain chances will continue on Tuesday as the system tracks up the Eastern Seaboard. Cooler temperatures are expected to start the work week thanks to the closed low, but temperatures will still run around 8-12 degrees above average. No PoPs are forecast for Tuesday night as another system moves into the area by Wednesday.
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Chattanooga Airport, TN 65 55 69 54 / 80 100 30 10 Knoxville McGhee Tyson Airport, TN 62 53 67 54 / 50 90 40 10 Oak Ridge, TN 62 52 67 54 / 60 90 30 10 Tri Cities Airport, TN 63 46 64 47 / 20 90 50 10
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