279 FXUS64 KMRX 210724 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 324 AM EDT Sat Aug 21 2021 .SHORT TERM (Today and Tonight)... Key Messages: 1. Isolated to scattered showers and thunderstorms are expected this afternoon and into the evening with the best coverage in the southern Valley/Plateau. 2. Highs will be well in the 80s with tonight's lows in the 60s to near 70. Today Currently, a mid/upper closed low and shortwave are centered to our east with surface high pressure along the northern Gulf. A weak frontal boundary is also in place from northwest to southeast in central portions of the area. Shower activity continues to our west with notable boundary layer moisture making the case for fog development into the early morning hours. Otherwise, the main story for the day will be resulting northerly flow aloft and fairly weak flow in the lower levels. There are indications of weak upper divergence, PVA, and better overall moisture in the southern Plateau/southern Valley. As such, this will be the focus for better convective coverage. Elsewhere, coverage will be largely isolated and largely driven by orographic means. Also, with generally weaker flow in the lower levels, locally heavy rainfall does remain possible with any stronger storm. Tonight Heading into tonight, the closed low/shortwave will shift slightly eastward with slight height rises locally. With a loss of diurnal instability and continued weak forcing, any lingering showers and thunderstorms should dissipate in the evening. Places that see rainfall will have better chances for fog forming late in the night. Otherwise, the night will be quiet overall. BW .LONG TERM (Sunday through Friday Night)... Key Messages: 1. A ridge will build into the region Sunday and Monday. A more seasonal diurnal convective pattern is expected all week along with warmer temperatures. 2. Guidance shows a weakening in the ridge late week with potential for more widespread scattered convection. Discussion: Upper level ridging begins to build across the region on Sunday and Monday as an upper-level trough across the Mid-Atlantic absorbs TC Henri and shifts northeastward. Increased heights and subsidence will limit PoPs and increase temperatures across the region. A diurnal trends in convective coverage is forecast with highest PoPs each day across the higher elevations. Late week, guidance indicates a potential retrograde of the ridge as a tropical low moves WNW across the Southeast CONUS. This would bring an increase in convective coverage to the area with weaker subsidence. However, confidence in location and timing of this potential tropical low pressure system is high and forecast certainty is low late in the period. JB && .AVIATION... 06Z TAF DISCUSSION. MVFR/IFR fog is expected at the 3 sites with the most significant reductions likely at TRI. This will likely take place over the next few hours and continue some time after sunrise. Otherwise, VFR will likely prevail throughout the day with potential for TSRA at CHA. Any ceilings that develop outside of convection would likely remain VFR. Winds will also be light and fairly variable. BW && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 82 71 90 71 93 / 60 30 30 0 10 Knoxville McGhee Tyson Airport, TN 86 70 90 69 92 / 10 20 20 0 10 Oak Ridge, TN 86 69 90 69 91 / 20 20 20 0 10 Tri Cities Airport, TN 87 65 88 65 90 / 10 10 10 0 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$