653 FXUS64 KMRX 200701 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 301 AM EDT Fri Sep 20 2019 .SHORT TERM...(Today and Tonight)... Surface high pressure has built southwestward into the southern Appalachians helping to push the old backdoor cold front farther west into middle TN. This has lead to rapidly clearing skies and lower Td's in a light easterly flow pattern of cool and dry advection. Water vapor and IR satellite indicate a weak perturbation currently over southern PA and WV. This feature is moving southwestward on the periphery of the mid level ridge over the Mississippi Valley. With the surface high overhead, soundings are dry, so only expect some mid and high cirrus clouds over southwest VA and northeast TN late tonight through mid morning. Current low temps remain on track for the rest of the night. Temp and dew point spreads have been rather larger in recent observations, so any fog will be very isolated and will hold off until after 09Z, mainly in northeastern areas. The above mentioned H5 ridging over the Mississippi and OH Valleys will start to build over our region during the day Friday. This will lead to a slow increase in warm advection as the surface high is forced a bit farther east. Due to the dry ground, nudged highs slightly above guidance with most areas seeing mid 80's with a few upper 80's in the southern valley. The NAM, GFS, as well as some of the CAMs indicate another weak shortwave topping the building ridge in the afternoon and are trying to develop a few showers in the east TN mountains. The surface high will still be in the vicinity, and the soundings still show a dry profile, so have not included any pops at this time. The relatively dry airmass continuing will bring lows Friday night similar to past nights with upper 50's/low 60's and only very spotty pockets of fog. .LONG TERM...(Saturday through Thursday)... Overall, persistent pattern of upper and surface ridging will remain over the southern Appalachians except for Monday. For Sunday night and Monday, a short-wave trough will move across the Great Lakes/upper Ohio valley pulling a frontal boundary through the area. Dynamics with this trough stays well north and airmass remains relatively dry. Due to the dry soil, will continue to go above guidance highs and on the lower end of the MOS lows. Also, lowered afternoon dewpoints a couple degrees in the afternoon. Now the specifics... For Saturday and Sunday, upper ridging is evident with forecast soundings showing a strong mid-level subsidence inversion suppressing any convection. For Monday, aforementioned trough moves well north of the area with frontal boundary sweeping through. Given the persistent dry airmass over the region, will only call for low PoPs (15-30 percent range) with the highest over the northern/western areas which is closer to the dynamics/slightly better moisture. For Tuesday through Thursday, surface and upper ridge will build back/remain across the southern Appalachians producing dry and unseasonably very warm conditions. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 87 61 88 63 / 0 0 0 0 Knoxville McGhee Tyson Airport, TN 86 62 87 62 / 0 0 0 0 Oak Ridge, TN 86 61 87 62 / 0 0 0 0 Tri Cities Airport, TN 83 58 85 58 / 0 0 0 0 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ RG/DH