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

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783 FXUS64 KMRX 160752 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 352 AM EDT Fri Mar 16 2018 .SHORT TERM...
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(Today through Saturday night)...Surface and upper ridging will produce another dry and mild day across the Tennessee Valley and southern Appalachians. Main concern today will be the low afternoon relative humidities. For Tonight...An upper low over the mid-section of the nation will move slowly toward the Ohio Valley with increasing southwesterly boundary layer flow. The southwest flow will increase the isentropic lift over a warm front boundary and spread moisture back into the region. The surface warm front will move across the Plateau and southeast Tennessee Saturday morning with enough elevated instability to include a chance of thunderstorms. For Saturday...Warm front will continue to lift northeast across the regon with showers and elevated thunderstorms likely for the first half of the day. For the afternoon, the central and southern valley will likely have a lull in the convection as the lift moves north. However, as the upper trough moves toward the east Ohio and northern Tennessee Valleys late afternoon and evening, scattered showers and storms will redevelop. The NAM, GFS, and ECMWF all differ on the amount of low-level moisture available during the afternoon. Will follow the more moist NAM/ECMWF solutions for now and expect scattered to broken convection to develop. Model soundings show the potential of large hail and damaging winds. MLCAPES of 1000-1500 J/kg, Hail CAPES of 300-600 J/Kg, lapse rates near 7 C/km, and WBZ Heights near 7kft support large hail. The 0-6km shear of 60kts also support rotating storms with more sustain updrafts. SHIP values between 1 and 1.5. As for the convective damaging winds, melting hail, plenty of dry mid-level entrainment and mid-level winds of 30-40kts supports potential of damaging winds. The potential strong convection will emain during the evening hours with showers diminishing after midnight. .Long Term (Sunday through Thursday)...After what appears to be a dry Sunday, weak short wave energy, moisture advection, and lifting ahead of a warm front could allow for the development of a few showers across mainly the southern half of the forecast area Sunday night into Monday. A stronger wave with a relatively deep surface low will move into the Southern Appalachian region Monday night into Tuesday bringing a very good chance for showers. The stronger wind field associated with this system and sufficient instability may allow for some convection which would mainly impact the southern half of the forecast area. This Spring type weather will give way to a colder regime to end the long term period as two or three short wave features dive into the back side of an Eastern United States long wave trough resulting in a rather amplified pattern Wednesday and Thursday. Model solutions indicate these short wave systems may have enough moisture for a chance of rain showers mainly on Wednesday with decreasing probability Wednesday night into Thursday. The temperature profile could be cold enough for the possibility of some snow showers in the higher terrain during this period, and maybe even in valley locations across Southwest Virginia and Northeast Tennessee as the system gradually moves away to the east Wednesday night and Thursday morning. Forecast highs will be near normal for mid March early in the long term, but will be a good ten degrees below normal during the end of the period.
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Chattanooga Airport, TN 69 54 76 50 / 10 70 50 30 Knoxville McGhee Tyson Airport, TN 62 50 74 48 / 0 60 50 50 Oak Ridge, TN 62 49 74 48 / 0 70 60 40 Tri Cities Airport, TN 57 39 67 44 / 0 60 70 60
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