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

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000 FXUS64 KMRX 080748 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 248 AM EST Thu Dec 8 2016 .SHORT TERM (Today and Tonight)...A short wave trough will move east from the Lower Mississippi Valley across the Southern Appalachian Region today and will exit off the Southeast Atlantic Coast by early this evening. Weak lift and limited moisture depth will keep this system from generating any precipitation. Drier air should be building into the forecast area on increasing low level northwesterly flow by late morning. The lower stratus and alto stratus decks will be gradually clearing, leaving behind a thinning cirrus layer into the afternoon hours. So, some sunshine will be returning to the area but warming will be limited with strengthening cold air advection during the afternoon. Therefore, not a significant rise in temperatures expected today with highs a good ten to twelve degrees colder than Wednesday`s highs. The loss of any significant protective cloud cover tonight will allow temperatures to drop into the lower and middle 20s over most of the forecast area by daybreak Friday. .LONG TERM (Friday through Wednesday)...A few flurries will be possible Friday morning as the NAM still shows some moisture between 925-850 mb, aided by a 20 kt upslope wind. Cold advection through the day will keep high temperatures in the 30s for most spots on Friday. With the surface high settling over the area Friday night, lows will drop into the teens in most locations. The low level ridge shifts east on Saturday, allowing temps to recover into the lower to mid 40s, and mid 40s to near 50 on Sunday. Although there are some timing differences, the models generally agree on a pattern of a shortwave trough crossing the lower Great Lakes on Monday. In response, the low level SW flow strengthens and advects moisture into our area, but the greatest forcing for lift is to our north. Models appear to be less enthusiastic about our rain chances compared to yesterday`s runs, so there is some uncertainty. Will not make significant changes to the going forecast with this system, and maintain likely POPs Sunday night. Uncertainty continues to rise for the rest of the forecast period as the GFS and ECMWF show very different patterns, and have shown poor run-to-run consistency. The ECMWF maintains a broad trough over the eastern CONUS, while the GFS shows a more amplified pattern with a deep trough and strong cold front moving through on Tuesday night/Wednesday. Will keep low to sight chance POPs and a cooling trend going in those periods, but with low confidence. && .POINT TEMPS/POPS... Chattanooga Airport, TN 44 23 40 21 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 43 23 34 19 / 0 0 0 0 Oak Ridge, TN 44 22 35 19 / 0 0 0 0 Tri Cities Airport, TN 41 19 33 16 / 0 0 10 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$

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