Saturday Weather Update- Unsettled Weather

Saturday 11:30 PM Update :  the models over-predicted the showers today.  Tonight’s models have some showers late morning into afternoon Sunday, as the main cold front moves through. High temp only 59.

Again, upper air lows and associated showers and clouds are often  poorly modeled. A low confidence forecast .


The bright spots we’re having this morning were expected and predicted.

The models have more low level cloudiness moving back in by this afternoon, with an increase in areal coverage of spotty showers during late morning and afternoon.

Exact placement and timing of showers with an upper air low pressure system is nearly impossible to predict.  Instability of the atmosphere is high and any breaks of sunshine become “self-destructive” with the cold pool of air present in the upper atmosphere interacting with the sun-warmed rising air from the damp ground surface.

Unsettled Weather for this Weekend

The low pressure system that brought the heavy rains to Philadelphia this morning will gradually move northeastward, as a sharp upper air trough digs down over our area.  The sharp upper trough will “pinch off” into a closed upper low pressure system by Tuesday and will be centered over the northeast. The developing closed upper low pressure system will result in very cool weather Monday into Tuesday.

Upper air lows are notoriously difficult to model, especially regarding amounts of sun vs. cloudiness and precipitation, so this forecast is a bit below average confidence. 

For Saturday, the low pressure system and cyclonic flow in the upper atmosphere will result in considerable low level cloudiness, after some early morning bright spots.  It will be breezy and mild; temperatures will reach a high of about 69.

A weak cold front approaches late Saturday afternoon with the possibility of light scattered showers. The cold front moves through early Sunday morning.

Following the frontal passage, Sunday will be have a mix of sun and clouds.  With the cold, low pressure in the upper atmosphere, any sunshine will be “self-destructive”; heating from sunshine will result in more cloudiness due to the unstable thermal profile.   Temperatures will be cool on Sunday; Highs about 60.

Cecily Tynan doesn’t know what an “Omega block” is

On today’s 6PM weather segment on Channel 6, Cecily Tynan showed a graphic of an upper trough expected to influence this weekend’s weather and incorrectly labeled and described it as an “Omega Block”.

An Omega Block is the result of high pressure and the jet stream takes the shape of the Greek letter Omega. What she showed is a plain old upper trough.

Correctly identifying an Omega Block is one of the ABCs of meteorology.