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

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000 FXUS64 KMRX 170751 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 351 AM EDT Sat Mar 17 2018 .SHORT TERM...(Today and Tonight)...Radar shows a line of storms moving acrosss northwest Tennessee. This line of convection is being supported by upper level divergence and isentropic lift with elevated instability. Latest high resolution models show this activity weakening but moving across the area from daybreak through mid/late morning with best coverage along and north of interstate 40. Once this activity moves east across the area, warm frontal boundary will also track northeast and become quasi-stationary over east Kentucky into southwest Virginia for late this afternoon. Model soundings show most of the region becoming capped for this afternoon by a boundary layer inversion as southwesterly winds advect warmer 800-850mb air into the southern Appalachians. This will allow for generally a warm and dry afternoon. For late this afternoon and evening, upper trough over Kentucky will approach southwest Virginia/northeast Tennessee. Models show the boundary layer capped eroding with upper forcing focusing along quasi-stationary boundary to produce strong convection from southeast kentucky into southwest Virginia. The thermodynamic profile will shows MLCAPES of 500-1000 J/kg over this Region, low and mid-level lapse rates of near 7 degree C/km, Hail CAPES of 400-600 J/kg and plenty of deep layer shear (0-6km) of 60kts+. End result indicates large hail will be a concern with WBZ of 7kft. Besides hail, melting hail, dry mid-level entrainment, and boundary winds of 30-40kts will support the potential of damaging winds. As for tornado potential, can not rule out isolated weak tornado development, especially given 0-1km shear of 25kts and location of boundary over southwest Virginia. The area of greatest severe weather concern will be over southwest Virginia and northeast Tennesse, but if cap can break, isolated severe is also possible as far south as TYS. Main concern over the southern areas will be this morning`s convection. For Tonight, showers coming to an end with upslope flow keeping chances going longer for the mountains areas. .Long Term (Sunday through Friday)...At the beginning of the forecast, the Southern Appalachian region will be in between systems with the next mid latitude cyclone on the approach through the Mid Mississippi Valley later in the day Sunday into Sunday evening. There will be an increasing chance for showers Sunday night as a warm front builds north out of the Lower Mississippi Valley. The next part of the rather strong storm system will move into the region Monday night as a surface low drives east across the Ohio Valley. The low will drag a cold front across the Southeastern U.S Monday night into Tuesday morning. Instability and the wind field ahead of the front will be sufficient for the development of thunderstorms, and some of these storms could become severe. Unfortunately, colder air will be spilling back into the Eastern U.S. behind this initial boundary on Tuesday, followed by even chillier air Wednesday into Wednesday night. Several pieces of short wave energy will be dropping southeast out of Middle America into the back side of the mean Eastern U.S. long wave trough generating rain showers on Tuesday and Wednesday. Upslope flow and increasingly colder air aloft will lead to the development of some higher terrain snow showers Tuesday night into Wednesday. Surface temperatures will be cold enough for the possibility of snow showers in valley locations Wednesday night as the final short wavelength feature exits to the east. A brief period of dry advection and ridging may allow for a dry Thursday and Friday with the next spring time system building in Friday night with more showers. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 75 49 68 53 / 30 20 0 70 Knoxville McGhee Tyson Airport, TN 74 48 64 50 / 30 30 0 70 Oak Ridge, TN 73 48 65 49 / 40 40 0 60 Tri Cities Airport, TN 68 44 61 45 / 60 70 0 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.