FXUS64 KMRX 081724 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1224 PM EST Fri Dec 8 2023 ...New AVIATION... .UPDATE... Issued at 1016 AM EST Fri Dec 8 2023 No significant changes to the forecast this morning. Main adjustment was editing hourly temps and dewpoints. Several obs were running quite a bit cooler on temperature compared to the forecast. The sites that were cooler still have calm winds. Once mixing ensues, temps will start to climb more quickly. No changes to today's max temp. && .SHORT TERM... (Today and tonight) Issued at 134 AM EST Fri Dec 8 2023 Key Messages: 1. Dry and warmer today. 2. Tonight southerly winds will increase in the higher elevations of the East TN mountains and Cumberland Plateau ahead of an approaching system. Some showers will move into the region, mainly after midnight. Discussion: Ridging and high pressure remain over the Southeast today bringing dry weather and a warming trend due to southerly flow. Highs will be 7 or 8 degrees above normal. Tonight, the ridge starts to break down as the trough over the Midwest and Great Plains begins to move east. Some showers will likely develop over the region, mainly after midnight as the surface cold front approaches the Mississippi River. Southerly winds will increase tonight in the higher elevations of the East TN mountains and the Cumberland Plateau as the 850mb jet moves into the region. The 850mb jet will be strongest over the Plateau counties of Morgan, Scott and Campbell at 40 to 45 knots. Elsewhere, the 850mb jet will be closer to 35 knots. The wind direction may be favorable for downslope wind enhancement in the East TN mountains and the NBM is picking up on that potential late tonight. However, winds will likely stay below advisory criteria during this time frame. Gusts will likely top out around 30 mph in the aforementioned Plateau counties and may be only slightly higher in the mountains and foothills of East TN since wind direction may be more southwesterly and less favorable for downslope wind enhancement. && .LONG TERM... (Saturday through Thursday) Issued at 134 AM EST Fri Dec 8 2023 Key Messages: 1. A strong system is expected Saturday through Sunday night. Threats include: High winds and mountain wave winds, widespread rainfall with embedded thunderstorms, and northwest flow snowfall. 2. Dry conditions expected Monday through Friday with high pressure across the region. Discussion: Shortwave trough across the Great Plains will move eastward on Saturday with amplifying longwave troughing across the Mississippi Valley. At the surface, a strengthening surface low will move into the western Great Lakes with a trailing cold front from Michigan southwestward across the Mississippi River. Across our forecast area, we'll be within an area of deep southwest flow with unseasonably warm temperatures and increasing clouds and chances for light rain showers due to isentropic lift. Breezy conditions are possible during the day, especially across the Cumberland Plateau, as 850mb winds increase to around 30 kt. The cold front shifts eastward and will be across our region by 12z Sunday. Ahead of the front, 850mb winds will increase to around 50 kt with some mountain wave winds expected across the mountains and foothills on Saturday night into Sunday morning. We will continue to monitor the potential for a High Wind Watch of Wind Advisory across the mountains and foothills with the forecast update later today. We are also expecting to see quite a bit of rainfall across the region with this system with at least 1 to 2 inches across most of the forecast area. Lower totals will be possible near the western foothills of the mountains where downslope flow will limit overall rainfall totals. On the other hand, locally higher totals near 3 inches will be possible across the southern and western counties in our forecast area near the Cumberland Plateau. Behind the cold front, troughing amplifies and cold air will advect into the region. We will see temperatures quickly drop Sunday afternoon with a non-diurnal temperatures trend. This will change lingering rain showers across the higher elevations over to snow showers and rime ice as northwest flow of 15 to 20 kt provides ample orographic lift for continued light precipitation across the higher terrain. We won't be saturated through a great depth with this system with drier air near the -10C level and above. However, it is expected to be enough some some rime ice and snow showers across the mountains on Sunday afternoon through Monday morning. Most model guidance continues to suggest 1 to 2 inches across the higher elevations above 2500 or 3000 feet with the potential for locally higher amounts across the highest elevations such as Mt.LeConte. High pressure builds in early next week with a clear sky and dry weather. Temperatures will be below normal early in the week with longwave troughing and a cold surface airmass across the region. A moderating airmass and return of mid to upper level ridging will result in warming conditions mid to late week with temperatures back near or slightly above normal. && .AVIATION... (18Z TAFS) Issued at 1212 PM EST Fri Dec 8 2023 VFR at CHA through midnight then MVFR through the rest of the period with a PROB30 for IFR tomorrow morning. TYS and TRI will be VFR through the period but PROB30 for MVFR tomorrow morning. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 51 65 50 60 / 70 70 100 80 Knoxville McGhee Tyson Airport, TN 47 66 52 61 / 50 50 100 90 Oak Ridge, TN 47 64 49 60 / 60 60 100 90 Tri Cities Airport, TN 39 66 52 61 / 30 30 90 100 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM... LONG TERM....JB AVIATION...