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

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554 FXUS64 KMRX 200854 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 354 AM EST Fri Jan 20 2017 .SHORT TERM /Today and Tonight/...
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A negatively tilting upper-trough over the central Plains has pushed a weak cold front and a broad area of moderate to locally heavy showers over the eastern Tennessee Valley. The last of this activity is currently exiting the Cumberland Plateau and is moving into the I-75 corridor of the central/southern Valleys as of 0830Z. Over the next 3-4 hours, this activity will spread NE across the region, before exiting into NC/VA after 12-13Z. Drier air will quickly shift into the region today as an upper- level ridge axis shifts into the area by midday. Low stratus will be slow to dissipate this morning, thanks to residual moisture remaining trapped in the boundary layer. However, by 18z, drier air will begin to help create some breaks in the clouds over much of the Valley. This heating, along with some southerly winds will help to push highs well into the mid to upper 60s in most spots. A partly cloudy sky will linger through the evening and most of the night, before another round of clouds increase late tonight ahead of an approaching warm front from the SW. Another round of showers is possible across the far south late tonight, but most of the shower and thunderstorm activity will hold off until late Saturday morning. .LONG TERM /Saturday through Thursday/... An active weekend is shaping up in the weather department across the Southern Appalachians. Saturday should start off dry, but clouds will increase throughout the morning hours as gulf moisture begins to stream into the area. By afternoon, showers are likely across much of the area with PWAT values increasing to near 1.0 inch. Enough instability will be in place across the southern half of the forecast area to spark some afternoon thunderstorms. There is a chance that a few storms could strengthen and become severe, especially during the late afternoon and evening hours as a warm front approaches the area and shear increases. Model soundings at KCHA show a backed wind profile at the surface, strong 0-1 km speed shear, good directional shear in the 0-3 km layer (indicative by the looped hodograph depicted on the 00z GFS run). This shear, combined with a NE advancing warm front could result in a very isolated tornado threat across the S. Plateau/Valley Saturday afternoon/evening. Will make a mention in the HWO. An upper level closed low will rotate into the southeast US on Sunday, bringing another chance for thunderstorms and heavy rain. At this point, the center of the low is progged to cross to our southeast. However, we will need to keep a close eye on this track. If the center of the low shifts just slightly further north, this would put portions of our forecast area in position for another round of strong to severe storms Sunday night. Rain chances will continue into Monday night as the low tracks across the Carolinas and continues to sling moisture back into our area. Weak ridging builds in for Tuesday into Wednesday, bringing a brief period of drier conditions. From here, model solutions diverge, but the general consensus is another cold front will bring some showers as it pushes through the region Wednesday into Thursday. Have carried widespread slight chance to chance PoPs for this period. For most of the extended period, mild temperatures will prevail, with highs in the 50s and 60s. Cooler air may finally return to the area for the second half of next week following the Wednesday/Thursday frontal passage.
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Chattanooga Airport, TN 69 54 69 55 / 20 20 70 80 Knoxville McGhee Tyson Airport, TN 66 54 68 52 / 30 10 60 70 Oak Ridge, TN 66 54 67 52 / 30 10 60 70 Tri Cities Airport, TN 65 49 65 50 / 50 10 40 60
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