Weather Headlines
*Warm and more humid conditions will offer a chance for hit-miss showers or thunderstorms through this weekend.
*A upper-level low will dominate weather conditions across the southern-central Appalachians through the upcoming work week.
Locally heavy to excessive rainfall amounts will be possible, but upper lows are notoriously difficult to predict exactly where bands forming around their swirling circulation will develop.
Waves rotating aloft around upper-level lows tend to support low-level convergence zones at the surface, with these being difficult to predict in advance of their development. Since it is impossible for air to go downward into the ground, low-level convergence mandates rising air with subsequent cooling and condensation to support precipitation formation.
If the upper low remains stationary from one day to the next, corridors that receive heaviest rain amounts during day 1 may again be impacted on day 2, especially if over terrain locations where tree leaves have fully matured and evapotranspiration is running at a maximum level to support a positive feedback for wetness.
If the upper low moves from one day to the next, the corridor that receives heaviest rainfall amounts also tends to move as the low-level convergence becomes focused, or enhanced, along a new corridor.
Interactive Surface Streamline Flow Field
The potential for heavy to excessive rainfall is enhanced if these upper-level low generated convergence zones (where air rises) phase with orographic forcing and become superimposed on air flow trajectories which are naturally forced to rise by terrain barriers.
Large run-to-run model variations for any given spot indicates the uncertainty for a given spot, but persistent replication of heavy-excessive amounts indicates that some places will tend to get much more rain (with possible high water issues) than other locations this upcoming week.
NOWCasting is a favored term used to describe this type of forecast scenario, where heavy rain potential is best resolved once rain bands begin forming during any given day around the upper low.
Near average to below average temperatures will occur mainly due to clouds and rainfall, impacting maximum temperature most relative to average.