Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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882 FXUS64 KMRX 170236 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1036 PM EDT Mon Sep 16 2024 ...New UPDATE... .UPDATE... Issued at 1017 PM EDT Mon Sep 16 2024 A light rain is currently falling over the very northeastern portions of Tennessee into southernmost portions of Virginia, primarily east of Interstate 81. Dry air is clearly evident in both surface observations and radar, with forward progress of the rain on a bit of a pause for now. Still, expecting the rain shield to make progress overnight into more of East Tennessee and southwest Virginia as the atmospheric column begins to saturate. If the atmosphere moistens slower than expected, this may impact rainfall accumulations by morning and extent of rain into East Tennessee. Forecast seems to be on track for the most part, with only minor edits made to the various weather groups to match trends seen in radar, satellite, and surface obs. && .SHORT TERM... (This evening through Tuesday) Issued at 257 PM EDT Mon Sep 16 2024 Key Messages: 1. Rain will spread into northern portions of the area tonight and tomorrow with an approaching tropical low. 2. Rain amounts will be highest in the terrain along the NC border, with lower amounts in the Valley. Discussion: The tropical low near the SC coast will track NW through this period. Some light rain is currently crossing the mountains, but it is encountering a low level dry air mass in the TN Valley. Gradually, the column will moisten in NE TN and SW VA, with measurable rain likely in the Tri-Cites around 06Z. The precip shield will spread westward through Tuesday morning, reaching the Plateau before 12Z. Easterly winds at 850 mb may result in downslope drying effects in the Valley, so the highest QPF amounts will be in the higher terrain along the NC border, where 1.5-3 inches of rain are expected. In the adjacent Valley and foothills, amounts will be in the range of 0.5-1 inch, but possibly lower depending on how strong the downslope winds are. With the expected cloud cover and precip, temperatures on Tuesday will be much cooler, with highs in the upper 60s north to upper 70s south. && .LONG TERM... (Tuesday night through next Monday) Issued at 257 PM EDT Mon Sep 16 2024 Key Messages: 1. Precipitation chances continue through Wednesday. 2. Warming trend with low confidence precipitation chances expected the second half of the week 3. Dry and warm over the weekend. Discussion: Wednesday night will see the remnants of Potential Tropical Cyclone 8 spinning directly over the southern Appalachian region near northeast TN and southwest VA. The late Tuesday through Wednesday period will be some of the best chances to see widespread rainfall from this system, but there will likely be a sharp gradient between north and south of Interstate 40. Precipitation will once again be moving in from the east/north and a good portion of it will stay to the east of the mountains where upslope flow produces heavy rain on the windward side of the mountains. Rain will definitely spill over into the western side of the Appalachians, but expect the vast majority of the precipitation to remain north of Interstate 40. Currently am expecting to see over an inch of rain in northeast Tennessee and southwest Virginia, decreasing down to practically nothing around Chattanooga. Forecast becomes a bit more uncertain for the second half of the work week, mainly with regards to precipitation chances as the remnants merge into a low pressure system and the ridge tries to ride up over it leading to a continuation of the rex block set up. Deterministic models are in disagreement with how much and how widespread any showers and possibly thunderstorms would be for the second half of the week... But a general trend of higher PoPs north of I-40 is starting to emerge. QPF amounts are expected to be light, but we could see near an inch of precipitation in the northeast, and possibly higher amounts along the mountains. Otherwise expect a warming trend for the week topping out on Saturday as the warmest day with temperatures about 5 degrees above seasonal normals. Precipitation chances dry up once we move into the weekend and the && .AVIATION... (00Z TAFS) Issued at 645 PM EDT Mon Sep 16 2024 Light and fairly steady rain will pivot through the northeastern two-thirds of East Tennessee over the next 24 hours. CIGs will steadily fall overnight, with MVFR expected at both TYS and TRI after 12z. Rain may become more scattered during the daylight hours, winds will remain generally light. VIS to MVFR during the day at TRI is likely, with potential further degradations if heavier rain falls. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 62 81 63 85 / 0 10 0 20 Knoxville McGhee Tyson Airport, TN 59 75 65 80 / 40 50 30 40 Oak Ridge, TN 62 75 63 79 / 40 40 20 40 Tri Cities Airport, TN 60 71 62 75 / 70 70 60 50 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...Wellington AVIATION...Wellington