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

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000 FXUS64 KMRX 210920 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 420 AM EST Tue Feb 21 2017 .SHORT TERM (Today and Tonight)...
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Cirrus clouds have streamed into the area ahead of the next approaching upper level system. Current water vapor imagery and RAP upper air analysis indicates a closed low across Eastern Texas with moisture streaming northward from the Gulf of Mexico into the Mid- Mississippi River Valley. The ridge axis has now passed to the east but upper level heights remain elevated. At the surface, a weak low pressure center can be noted near Memphis with a weak boundary stretching to the southeast across Central Alabama and into Southern Georgia. in addition, there is a broad area of low pressure across Eastern Texas near the upper low. For today, the atmosphere will slowly saturate ahead of the slow moving upper level low. Clouds will increase across the Southern Appalachians. Due to the slow nature of the system, expect the morning and most of the afternoon will be dry. Models indicate that the moisture advection picks up across the region around 21z. PW values will eventually top out around 1.2-1.4 inches later tonight. These reading represent values over the maximum observed for late February. At the same time, the upper level low will become cut off and track to the southeast across the Northern Gulf of Mexico. Therefore, there are still some question to just how much precipitation will occur. The models indicate that convection along the Northern Gulf could cut the area off from the best moisture advection. In addition, winds in the low-levels will be from the south to southeast and could lead to some downsloping. Overall, forecast rainfall amounts are around 0.10-0.25 inches. For now, have PoPs around 70-80 for tonight but could see these increased in later forecast issuances. Well above normal temperatures are forecast again today with warm air advection highs will range from the upper 60s to lower 70s. Widespread cloud cover and rainfall tonight will keep lows in the upper 40s to mid 50s tonight. .LONG TERM (Wednesday through Monday)... Upper low over Gulf moves east southeast still slower than previous model runs with showers lingering Wednesday. Weak trough will bring drier air into the region during the afternoon Wednesday. Rain showers end by evening with partial clearing overnight Wednesday. Followed drier GFS with no rain Wednesday night. A weak midlevel shortwave trough still to cross region Thursday afternoon and evening. With some instability and warm temperatures and some moisture about a 30 percent chance of showers possible. Added slight chance of thunderstorms too. Surface low develops over Plains Thursday night and decreasing clouds over the Tennessee Valley as weak ridging moves across the southeast. The low deepens across the midwest and upper Mississippi Valley into Friday. A cold front will then cross the Mississippi Valley Friday and move into the Tennessee Valley Friday afternoon and night. Very warm temperatures will likely occur with deep southwest flow aloft. Increased upper level winds and instability will set the stage for showers and thunderstorms Friday night with some storms possibly severe. Will continue mention in the HWO. Behind this system a big drop in temperatures back to near normal 50s and even colder Sunday in the 40s to mid 50s. Showers move out Saturday and skies clear Saturday night and continue Sunday. A weak system to move southeast from the northwest Sunday night into Monday with temperatures warming into the 50s to lower 60s.
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Chattanooga Airport, TN 67 55 68 54 / 70 70 50 10 Knoxville McGhee Tyson Airport, TN 69 53 65 52 / 30 70 60 10 Oak Ridge, TN 70 53 66 53 / 30 70 60 10 Tri Cities Airport, TN 68 48 63 49 / 10 70 80 10
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