Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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416 FXUS64 KMRX 221541 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1041 AM EST Fri Nov 22 2024 ...New UPDATE... .UPDATE... Issued at 1026 AM EST Fri Nov 22 2024 The Winter Weather Advisory set to expire at 10 AM EST this morning, was allowed to expire. However, the Winter Weather Advisory through 7 AM EST Saturday is still in effect for isolated 2 to 4 inches of additional snow accumulation this evening across the highest elevations of the Southern Appalachians and southwest Virginia. Many reports received of a half inch to the 2 inch range of snowfall accumulation across much of the advisory area, but places such as Roan Mountain and Mount LeConte saw anywhere between 4 to 5 inches of snow. Snow has tapered for the most part for now, and cloud breaks are allowing some sunshine. We expect cloud cover to return, as well as another round of moisture this evening and overnight, hence the Winter Weather Advisory for additional accumulation for parts of the Southern Appalachians mountain zones and the counties of Wise, Russell, and Washington in southwest Virginia. KS && .SHORT TERM... (Today and tonight) Issued at 240 AM EST Fri Nov 22 2024 Key Messages: 1. Breezy winds expected today. Widespread gusts between 20-30 mph in the afternoon. Higher elevations of the East Tennessee mountains may approach 40 mph at times. 2. Snow showers are expected to bring 1-3 inches of snow to portions of southwest Virginia and the East Tennessee mountains today and tonight, with isolated totals between 3-6 inches in the highest peaks and ridgetops. Discussion: Not much has changed in the forecast thinking in the past 12 hours. As expected, we are currently in the period heaviest snowfall, associated with a trough axis rotating around the closed low over the Mid Atlantic region. Cold temperatures aloft under this trough will continue to produce widespread snow showers in the northern half of the area through 12Z. Accumulations through sunrise will be mainly in SW VA and the mountains where temperatures are at or below freezing. During the day, the trough moves to our east and dry air aloft builds in, cutting off moisture above -10C. Upslope NW winds will keep a chance of light snow accumulations in the mountains through the day, but the wind speeds at 850 mb drop to around 20 kt. Boundary layer mixing and downslope winds off the Plateau will create some partial clearing of clouds in some Valley locations this afternoon. A second surge of snow showers is expected to arrive late this afternoon and evening as we get an increase in 850 mb wind speeds to around 40 kt in association with an upper jet streak rounding the western side of the closed low. Moisture depth increases slightly with saturation near 10C, so additional light accumulations are likely from ~21Z to ~06Z. Temperatures during this time will support an additional 1-3 inches of accumulation in the mountains of SW VA and NE TN during this period. Forecast snow amounts have not changed significantly with this forecast package. However, with the expected round of additional snow accumulation this evening, the Winter Weather Advisory will be extended through tonight for the mountains and parts of SW VA. && .LONG TERM... (Saturday through Thursday) Issued at 240 AM EST Fri Nov 22 2024 Key Messages: 1. Snow ends Saturday morning as northwest flow winds down. Gusty winds decrease in the morning across higher elevations of the southern Appalachian Mountains. Gusts of 30 mph still possible through late Saturday morning northeast Tennessee mountains. 2. A return to above normal temperatures for late November on Sunday. 3. Rain returns Monday afternoon and night to start the week. 4. More significant system moves in late Wednesday and through Thanksgiving. One to two inches of rain possible with this system. Discussion: Northwest flow snowfall continues across the extreme northeast into Saturday morning across higher elevations of the southwest VA mountains. Only trace amounts possible, mostly flurries into mid to late morning as the moisture dries up with upper low and trough moving east. The gusty winds should decrease over the higher elevations of northeast Tennessee and southwest Virginia during the late morning as the pressure gradient decreases. High pressure builds in from the west Saturday as the upper trough shifts east. Clouds will linger most of the day across northeast Tennessee and southwest Virginia but become sunny over the central and southern sections of east Tennessee and southwest North Carolina by afternoon. Temperatures will range from 50s lower elevations central and southern valley in the sunshine to 40s northeast and higher elevations, except 30s highest elevations where clouds linger. The coldest night of the week will be Sunday morning with lighter winds and cold airmass. Lows mostly upper 20s to lower 30s except mid 30s extreme south and southwest. Sunday even more warming as surface high shifts quickly eastward in a almost zonal flow aloft. Highs reach mid to upper 50s northeast to lower 60s central and south to mid 60s at Chattanooga. The next system will quickly approach and move through later Monday into Tuesday afternoon. This system looks weak in the mid levels and cold front produces only light rain of about 0.10 to 0.20 inches at the surface. Temperatures are warm enough for the precipitation to be all rain. A somewhat cooler and drier air mass moves in Tuesday. The next system will move into the region later Wednesday and through Thanksgiving. This system looks much stronger than the Monday system but the timing and development of the system is still uncertain. Rainfall amounts are expected to be over 1 inch to around 2 inches and more significant colder air moving in behind it Friday. Stay tuned as the evolution of the system may change in the coming days. && .AVIATION... (12Z TAFS) Issued at 609 AM EST Fri Nov 22 2024 Gusty winds are expected at all sites through the day, mainly from a W-NW direction. Snow showers will bring MVFR vis and cigs to TRI this morning, with periods of IFR possible with heavier snow. Snow will exit by mid to late morning, but another round is expected in the evening at TRI. MVFR conditions will return at TRI and TYS after 00Z. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 50 36 57 35 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 47 37 53 32 / 20 10 0 0 Oak Ridge, TN 47 37 54 32 / 10 0 0 0 Tri Cities Airport, TN 41 36 47 30 / 40 30 10 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...Winter Weather Advisory until 7 AM EST Saturday for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson-Sevier Smoky Mountains-Southeast Carter-Southeast Greene-Unicoi. VA...Winter Weather Advisory until 7 AM EST Saturday for Russell- Washington VA-Wise. && $$ SHORT TERM...DGS LONG TERM....TD AVIATION...DGS