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

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354 FXUS64 KMRX 220822 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 322 AM EST Sun Jan 22 2017 .SHORT TERM /Today through Monday/...
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Active pattern over the next 36 hours, with several rounds of precipitation to impact the region as an upper-level low pressure system moves across the Tennessee Valley. The first wave is associated with a prefrontal trough currently moving through northern Alabama and Georgia as of 3 AM. These showers and thunderstorms will continue their march into Southeast Tennessee during the predawn hours. Given some limited instability, good shear, and a MCV-like feature over NE Alabama, cannot rule out a strong to marginally severe thunderstorm -- mainly from damaging wind gusts. Over the course of the morning hours, these showers and isolated thunderstorms will weaken as they move across the Central and Northern Valleys due to the lack of instability. As the precipitation shield erodes, QPF amounts may be a little lower than originally though along and north of I-40 during the day. As the LLJ ramps up by the late afternoon and evening, the upper- low will deepen as it races into Alabama and Georgia. This will generate a second big round of showers and thunderstorms (a few of which could be strong to marginally severe) during the 21-03z timeframe. This activity will form along and ahead of the slow advancing cloud front from the west. Ahead of the boundary, a deep Gulf moisture flux will be in place -- parallel to this boundary. This could set the stage for training later on tonight and Monday morning, especially along the Mountains and the Central and Northern Valleys. Additionally, PWAT values will be at/above 1.0 inches, with mild temperatures promoting a deep, warm cloud layer. There will also be some modest instability of 500-1000 j/kg of elevated CAPE, which will help to support more robust, organized updrafts with the strongest clusters. Thus, a localized flash flood/areal flood threat is expected tonight into Monday. The threat looks to be isolated enough to hold off on a watch, but will keep the Hydrologic Outlook going to address this. Storm total QPF of 1.5 to 2.5 inches seems common, with high amounts at/above 3 inches possible along the East Tennessee and Western North Carolina Mountains. As the low shifts east across the region Monday morning, dynamic cooling will result in a lowering of the melting level to 4500 to 5000 feet along the East Tennessee Mountains. Thus, some very light snow accumulations are possible along the peaks at Newfound Gap, Mt Leconte and Clingmans Dome in Great Smoky Mountains National Park. Otherwise, the cooler air will filter in on Monday afternoon behind this system, with breezy conditions thanks to the strong pressure gradient. Highs will still be mild in the 50s as the true blast of cool will not arrive until Tuesday morning. Precipitation will taper off by the evening in the valley and over the cource of the night in the Mountains. .LONG TERM /Monday Night through Saturday/... Parent surface low will lift further northeast Monday night into Tuesday, with rain showers gradually tapering off from southwest to northeast through Tuesday afternoon. As cooler air funnels in early Tuesday morning, some flakes may mix in across the highest elevations of the Smokys. Winds will become quite breezy on the backside of the low, especially along the Smokys where winds may approach advisory levels Monday night. Will continue mention of gusty winds in the HWO. Weak ridging will build in for the second half of Tuesday, bringing a brief period of dry weather. Southwest flow on Wednesday will warm highs back into the 60s for one more day, before a cold front sweeps through the area Wednesday night into Thursday and temperatures turn colder. Model solutions continue to diverge at this point in the forecast, with the GFS showing a much wetter frontal passage than the drier ECMWF. For now, have broadbrushed slight chance to chance PoPs Wednesday and Thursday in association with this feature. A few snowflakes may mix in Thursday morning across higher elevations as colder air once again works into the area. It will turn much cooler for the end of the week with upper level troughing over the eastern US. A couple weak shortwaves will ripple through this trough through the weekend. Diving in from the midwest, there`s not a lot of moisture associated with them, but with predominately northwest flow there should be enough for some orographically driven snowfall accumulations across the higher elevations. Some snowflakes may mix in at lower elevations with temperatures dipping to near freezing at nighttime, but with temperatures rising into the upper 30s to lower 40s in the valleys during the day no accumulation is expected at this time.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 64 49 53 38 / 90 70 50 20 Knoxville McGhee Tyson Airport, TN 66 49 54 41 / 90 90 80 60 Oak Ridge, TN 64 49 54 41 / 90 90 80 60 Tri Cities Airport, TN 64 47 53 40 / 80 100 90 70
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ AMP/EMH

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