708 FXUS64 KMRX 191113 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 713 AM EDT Tue Oct 19 2021 .UPDATE... FOR 12Z AVIATION. && .SHORT TERM...(Today through Tonight)... Key Messages: 1. Valley fog this morning, and again on Wednesday morning. 2. Highs returning to above normal levels today amidst sunny skies as upper heights rise given the pivoting H5 ridge axis. Discussion: Overall not much change in the weather across the TN Valley and Southern Appalachian region today as the upper ridge axis pivots overhead, reinforcing high pressure at the surface which is generally anchored atop the region. Given a moist PBL amidst ample radiational cooling tonight (and pattern persistence noted above) did favor another morning of valley fog, perhaps impacting the metro areas of CHA/TYS/TRI a little more. Will monitor for SPS/DFA issuance. Moving on, the entire upper omega shaped pattern will be shifting east, thus the Rockies upper cyclone will eject into the Plains with lee cyclogenesis favored at the surface. Convection well to the west in association with these features looks to interact with nwly flow aloft to advect some higher cirrus into the region late in the day/evening. Otherwise, warmer given slight height rises and abundance insolation, highs returning to just above normal levels. Tonight, would expect yet another night of patchy valley fog given persistence in the pattern favoring a moist and decoupled PBL. CDG .LONG TERM...(Wednesday through Monday)... Key Messages: 1. Periods of showers and a few thunderstorms spread west to east across the region late Wed night and Thurs with temps a few degrees above normal. 2. Mainly dry Fri through Sat with temps cooling to near normal. 3. Warming trend Sun into early next week, but precip coverage and magnitude of warming is uncertain. Discussion: Wednesday through Thursday... Mid/upper shortwave ridging centered over the OH and TN Valleys will continue to provide fair and warm conditions Wed aided by southerly low-level flow on the backside of surface high pressure over the coastal Carolinas. H85 temps of 12-14 C, southerly flow, and mostly sunny skies will yield highs in the low/mid 70's. By Wed night, a weakening mid/upper low will be opening up and progressing eastward across the Upper MS Valley, reaching the lower Great Lakes Thurs while becoming absorbed into a stronger northern stream trough diving through eastern Canada. This will lower heights across the TN Valley dragging a cold front across our region Thurs. The greatest upper jet support will be displaced over the Upper OH Valley, but some diffluence aloft and a low-level jet increasing to 25-30 kts with isentropic ascent will be enough to support a line of showers spreading into the region ahead of the front. The increased low- level jet actually brings impressive dew points for late Oct into the region (mid 60's) with corresponding PWATs likely above 1.50 inches Thurs, so this warm/moist advection will make up for the lack in forcing leading to decent coverage. Added some thunder Thurs given at least weak to moderate MLCAPE. Wed night lows will remain mild in the low/upper 50's with highs Thurs staying in the low 70's. Thursday Night through Saturday Night... As the aforementioned wave over the lower Great Lakes fully phases with the northern stream Thurs night, mid/upper troughing will deepen over the central and eastern CONUS Thurs night and Fri as the cold front moves E of the region. Showers will end from W to E Thurs night as dry air and subsidence increases, and surface high pressure dropping down from the Midwest will provide dry weather Fri. A secondary shortwave will further deepen the trough Fri night as it drops through the lower OH Valley. Moisture is very limited, but given some PVA, kept NBM slight chance PoPs in NE TN and SW VA for isolated showers. Surface high pressure returns for dry conditions Sat and Sat night as it settles over the TN Valley and S Appalachians. Highs Fri and Sat will be in the upper 60's to lower 70's (near normal) with lows in the upper 40's/upper 50's Thurs night falling into the upper 40's/low 50's Fri night and Sat night. Sunday through Monday... Confidence drastically lowers in this period since deterministic and ensemble guidance are struggling to resolve the upper pattern. The GFS and CMC suggest strong amplification of ridging ahead of a strong trough moving out of the Rockies/Plains early next week leading to above normal warmth and increasing chances of convection, whereas the ECMWF briefly raises heights Sun with some light WAA/isentropic lift showers along a slowly retreating boundary, before quickly reloading a trough into the eastern CONUS by Mon. This all leads to differences in temps and rainfall coverage. For now, stayed with NBM PoPs and temps showing slow warming with increasing chances for showers and a few storms. Garuckas && .AVIATION... 12Z TAF DISCUSSION. Mostly VFR through the period as high pressure prevails across the region. As expected, fog has developed at the terminals this morning, however with the most dense (IFR) fog at CHA, with only MVFR at TYS/TRI. New tafs have been adjusted as such with recovery expected around 13z-14z. Beyond that, solid VFR with SKC and light winds. Could see some high cirrus advecting through the region this evening. Included another round of MVFR fog at CHA/TYS with IFR at TRI on Wednesday morning given pattern persistence. CDG && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 74 48 76 58 75 / 0 0 0 20 70 Knoxville McGhee Tyson Airport, TN 74 47 75 56 74 / 0 0 0 10 70 Oak Ridge, TN 72 47 74 55 73 / 0 0 0 10 70 Tri Cities Airport, TN 72 42 73 48 72 / 0 0 0 0 50 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$