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

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410 FXUS64 KMRX 050822 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 322 AM EST Mon Dec 5 2016 .SHORT TERM (Today and tonight)...
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Low level saturation under a strong inversion near 850 mb will keep overcast clouds across the area this morning, but with no rain as forecast soundings show sharp drying above the inversion. The models are likely scouring out the clouds too quickly today given the strong inversion and shallow CAD-like NE flow in the Valley, especially the GFS, so will keep temps on the cool side of MOS and maintain more cloud cover through the day. Precip returns late this afternoon as the closed southern stream low over northern Mexico tracks NE. The NAM and GFS continue to have major differences in their depictions of POPs and QPF tonight, but the NAM has support from the ECMWF and SREF, and the GFS is very much an outlier in reagard to its late timing of rain onset. In addition, WV imagery shows a tropical connection to the moisture stream, so the GFS is likely underdone with its QPF. Isentropic lift will quickly spread light rain into the area after 18z, with rain intensifying in the evening as the LLJ picks up and the upper jet becomes better positioned for upper divergence. Will also mention a slight chance of thunderstorms tonight and Tuesday AM as there will be some elevated instability along with the strong forcing. Precip begins to taper off Tuesday afternoon with the passage of the 500 mb trough and ensuing dry advection aloft. Will maintain low to slight chance POPs up to 00z with the surface fropa. With a LLJ expected to be near 50 kts tonight, winds in higher elevations tonight into Tuesday morning will be near advisory criteria. However, due to the S-SW orientation of the LLJ, this does not appear to be a mountain wave event where the high winds impact the foothills and favored Valley locations. Therefore the High Wind Watch will be cut back to a Wind Advisory that will include only the TN mountain zones. .LONG TERM (Tuesday night through Sunday)... We could see a hint of lingering precipitation in Northeast Tennessee/Southwest Virginia into early Wednesday morning, but most of the precip will have already exited the area to the northeast. In place of the rain we will get dropping temperatures through the rest of the work week and into the weekend. These cold temperatures will be the main weather story for most people in the long term portion of the forecast. Our coldest time frame will be Thursday night through Friday night where temperatures will remain below freezing for the vast majority of the time. Temperatures during this time will be running about 15 - 20 degrees below normal for this time of year. The other story with the colder temperatures will the models predicting much lower precipitation chances with the frontal passage Thursday. GFS has been pretty consistent in showing little QPF with the frontal passage while the ECMWF was much more bullish until the latest run. Will be interesting to see what the new ECMWF comes in showing, but at this time I will be hedging my bets towards the more consistent GFS for this time frame. We then get into a moderate warming trend behind the front over the weekend with highs rebounding but likely remaining below climatological normal. Another system will move through Monday, at the very tail end of the 7-day forecast, and long term models are currently in decent agreement on timing/QPF with this system. It will likely be the next best chance for precipitation after Wednesday.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 55 50 62 42 / 100 100 80 10 Knoxville McGhee Tyson Airport, TN 53 46 59 41 / 60 100 90 20 Oak Ridge, TN 53 47 58 41 / 50 100 90 20 Tri Cities Airport, TN 52 45 56 39 / 20 100 100 30
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&& .MRX WATCHES/WARNINGS/ADVISORIES...
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NC...None. TN...Wind Advisory from 10 PM this evening to 4 PM EST Tuesday for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Southeast Monroe-Unicoi. VA...None.
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&& $$ DGS/ABM

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