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

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000 FXUS64 KMRX 261929 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 329 PM EDT Sat May 26 2018 .SHORT TERM...
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(Tonight and Sunday)... Upper ridging continues to hold across the deep south this afternoon, while modest sly llv flow advects moisture northward into the TN valley and southern Appalachian regions. A mid/late morning H85 convergence axis along with sufficient elevated instability led to a broad rain shield atop portions of northeast TN and southwest VA. Weak steering flow and occasional training of cells did yield upward of 2-3 inches of rainfall through noon today, which in turn led to some isolated flooding issues. Through the remainder of the day, said H85 convergence axis looks to have lifted slightly northeast giving some relief for these aforementioned zones. However, ample heating and somewhat steep lapse rates aloft have supported additional convective initiation back to the west. In addition, weak downsloping llv flow across the lower 81 corridor has allowed for backed winds and thus another narrow convergence axis to setup, thus yielding persistent development of convection. All in all, think broad likely level pops are warranted, perhaps with the lowest confidence southward near the GA state line where less llv forcing is present. As for threats, given elevated PWATs of around 1.6-1.7 inches, weak steering flow, and a persistent threat of training, think additional isolated flash flooding is possible (especially across northeast TN and southwest VA). Will continue to highlight such in the HWO. Moving on into tonight and Sunday, given continued elevated cape (per model soundings) and aforementioned moisture, wouldn`t be suprised to see at least a few iso/sct showers through the night. Decoupling of the moist PBL will favor patchy fog, perhaps with some dense fog in the earlier saturated regions. Sunday looks not all that different regarding the overall flow regime and upper pattern, perhaps with relatively drier profiles amidst a brief dry slot ahead of the next moisture band advected northward from TC Alberto into Monday. Therefore, am favoring a slightly more diurnal trend with pops topping out in the high chance to low likely range. With little change in the flow regime as well as degrading antecedent conditions, think the threat for isolated flash flooding presents itself yet again on Sunday. .LONG TERM...(Sunday night through Saturday)... The extended will be wet with tropical moisture as the remnants of Subtropical Storm Alberto move inland across the Southeast CONUS. On Sunday night and Monday, a quick moving trough will move off of the Northeast coast with a trailing boundary across the Central and Southern Appalachians. Models continue to show a convergence axis located near or over our forecast area which could be a focus for convection and heavy rainfall. PW values of around 1.75 to 2.0 inches will be near the climatological max for this time of year. The abundant moisture will continue through the week with a continued chance for heavy rainfall and localized flooding. With southerly/southeasterly winds ahead of Alberto, upslope flow along the southern Cumberland Plateau and along the eastern slopes of the Southern Appalachians may produce enhanced rainfall totals in these areas. In addition to the localized flash flooding threat from heavy rain, will have to monitor rivers that originate in western NC as runoff may lead to river rises toward the middle to late part of the week. The ECMWF and GFS continue to show the remnant center of Alberto moving northward across Middle/West TN Tuesday night and Wednesday and moving into the Great Lakes region by Thursday and Friday. This would lead to some drier weather and lower PoPs late in the week. There is still a lot of uncertainty with the exact evolution and track of the tropical remnants as well as any late week diurnal convection.
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&& .PRELIMINARY POINT TEMPS/POPS...
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Chattanooga Airport, TN 69 85 70 83 / 50 60 60 60 Knoxville McGhee Tyson Airport, TN 68 84 68 82 / 50 60 40 50 Oak Ridge, TN 68 85 69 83 / 50 60 40 50 Tri Cities Airport, TN 65 82 65 80 / 60 60 40 50
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&& .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ CDG/JB

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