Mountain Area Forecast ( August 25-28 )
Wednesday Night Into Thursday Morning
Partly cloudy. Areas of dense valley fog. Winds S to SW at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temperatures in the upper 50s to mid-upper 60s.
Thursday Afternoon
A chance of hit-miss showers & thunderstorms. Partly cloudy. Hazy. Winds S-SW at 5-10 mph, with some higher gusts along highest ridges. Temperatures varying from the low-mid 70s in upper elevations to the lower-middle 80s.
Thursday Night Into Friday Morning
Partly to mostly clear. Areas of dense valley fog. SW winds becoming northerly into morning at 5-10 mph, with higher gusts, along mid-upper elevation mountain ridges. Temps varying from lower 60s to around 70 degrees.
Friday Afternoon
Partly to mostly sunny. Hot. Light N to NE winds. Temps varying from middle-upper 70s in upper elevations to the middle to upper 80s ( hotter south into the Great Valley ).
Friday Night Into Saturday Morning
Mostly clear. Areas of dense valley fog. Light E-SE winds. Temperatures varying from 50s in the coolest mountain valleys ( mid-upper elevations ) to the mid-upper 60s.
Saturday Afternoon
Partly sunny. Hot & humid. Chance of a hit-miss shower or thunderstorm. Light SSE-SSW winds. Temps varying from mid 70s to around 80 degrees at highest elevations to upper 80s to around 90 degrees ( hotter into the Great Valley ).
Saturday Night Into Sunday Morning
Partly cloudy. Humid. Areas of dense valley fog. Light southerly winds along mid-upper elevation ridges. Temps in the 60s to around 70 degrees.
Weather Discussion ( More Summer )
A heat ridge centered near the Great Smokies is well known climatologically as a heat maker for the Mountain Empire, even in the final days of the Meteorological Season.
Although some afternoon cumulus formed Thursday and Friday, especially along major lifting zones like the High Knob Massif, the atmosphere was clearly being dominated by subsidence aloft.
Mathematically deriving the Law Of Conservation Of Mass, from which various forms of the Continuity Equation is obtained, it is easy to develop a basic Subsidence Model for the atmosphere that clearly illustrates the relationship between rising & sinking air.
Essentially, low-level rising in one region of the atmosphere must be compensated for by large-scale sinking within another region. While we often focus on convection that forms in a ring around high pressure centers it is seldom noted how air spreading out aloft above the convection acts to support and reinforce, via compensative subsidence, the adjacent high pressure.
So even as Invest 99L struggles, and models struggle with what it will eventually do, there will be significant low-level convergence across the Gulf of Mexico into the Upper Midwest through coming days that will continue to support the large-scale subsidence of air that is dominating the Mountain Empire. The result being heat, humidity and little rain ( only localized storms in places where orographics and/or instability may briefly overcome sinking ).
Eventually, as is true of all things, this will change but for now this is the Bottom Line of the Big Picture.
*While rising-sinking ( outside of that orographically forced ) is not as coupled in mid-latitudes on the synoptic-scale as it is amid the tropics, the principle still applies and regions where synoptic high pressure is favored can be ( and often are ) aided by these processes ( since mass can be neither created nor destroyed, only rearranged in space & time and/or transformed in ways that still result in the total mass remaining unchanged ).