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

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000 FXUS64 KMRX 221929 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 329 PM EDT Sun Apr 22 2018 .SHORT TERM (Tonight through Monday night)... Overall the going forecast captures the expected trends pretty well. Rain associated with frontogenetic forcing will be slowly spreading across the area through the night, with highest QPF amounts in the south, while the mountain shadow effect from downslope winds will delay precip and lighten QPF totals in the northern half. 850 mb winds from the SE at 60 kts will produce an ideal setup for mountain waves overnight and Monday, as as this tends to produce strong winds in the foothills as well, a Wind Advisory will be added for the row of counties in the lee of the mountains, as well as Washington and Russell counties in SW VA. Precip will be trending downward Monday morning as strong forcing moves NE and a dry slot moves over the area. The NAM shows convection developing in the dry slot, which seems possible given the steepening lapse rates under the approaching upper low. Will mention a slight chance of thunder on Monday. The upper low rotating across the area will keep numerous showers going through Monday night as well. Storm total QPF amounts in the range of 1 to 2.5 inches are expected through Monday night. .LONG TERM (Tuesday through Saturday)... An active weather pattern continues through the extended with a closed low meandering over the area on Tuesday. As the low shifts slowly eastward, winds shift from a more southerly direction to the WNW on Tuesday afternoon. This will lead to some upslope flow along the western slopes of the higher elevations and may help to orographically force some additional rain showers across the higher elevations and foothills in the afternoon. Additionally, the upper low positioned over the area will result in relatively steep mid- level lapse rates and boost MUCAPE to between 500 and 1000 J/kg, according to NAM and GFS forecast soundings, across the northern two- thirds of the forecast area. May have some scattered thunderstorms develop during the afternoon. The severe threat appears low, but with cold air aloft, cannot rule out some small, sub-severe hail. Don`t expect widespread precipitation all day on Tuesday, but it appears likely that many locations will experience scattered precip during the day. The next shortwave will dive southeastward across the Northern Plains and Mid Mississippi Valley on Tuesday night and Wednesday which will help accelerate the closed low northeastward away from our region. This will provide some shortwave ridging over the forecast area with a brief break in most precipitation. The GFS and ECMWF both are keeping this shortwave and vort max south of our forecast area across the Gulf Coast which should keep the bulk of the precip to our south. Still, will have some slight chance/chance PoPs across the region on Wednesday and Thursday. Global models diverge late week with the GFS bringing another cold front quickly through the region on Friday morning with the ECMWF being slower with fropa on Friday night. Models differ with the upper-level pattern and position of the main upper-level low expected to affect our area. These differences mean low confidence late in the week and next weekend. Temperatures late week are expected to be near or slightly below normal with a more zonal upper pattern briefly between troughs. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 55 69 55 71 / 100 70 70 50 Knoxville McGhee Tyson Airport, TN 54 67 54 69 / 90 90 80 60 Oak Ridge, TN 54 66 54 70 / 100 80 80 60 Tri Cities Airport, TN 52 64 50 66 / 60 90 80 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...Wind Advisory from 8 PM this evening to 7 AM EDT Monday for Cherokee-Clay. TN...Wind Advisory from 11 PM this evening to 2 AM EDT Tuesday for Jefferson-NW Blount-North Sevier-Northwest Carter-Northwest Cocke-Northwest Greene-Northwest Monroe-Sullivan-Washington TN. High Wind Warning from 11 PM this evening to 2 AM EDT Tuesday for Blount Smoky Mountains-Cocke Smoky Mountains-Johnson- Sevier Smoky Mountains-Southeast Carter-Southeast Greene- Southeast Monroe-Unicoi. Wind Advisory from 8 PM EDT /7 PM CDT/ this evening to 7 AM EDT /6 AM CDT/ Monday for Bledsoe-Bradley-East Polk-Hamilton- Marion-McMinn-Meigs-Rhea-Sequatchie-West Polk. VA...Wind Advisory from 11 PM this evening to 2 AM EDT Tuesday for Russell-Washington. && $$ DGS/JB

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