Category Archives: Philadelphia Weather Outlook

REMNANTS OF ZETA TO AFFECT PHILADELPHIA AREA

A complex weather scenario involving a strong upper airclosed low”, a surface low, and the remnants of Hurricane Zeta will affect our weather from Thursday into at least early Friday.

The complexity of this setup can’t be over-emphasized and it’s likely that no existing weather model can accurately forecast how this will finally come together. Despite the complexity, the models are in relatively good agreement right now.

GFS 7 PM Thursday forecast with 1 hour rain forecast.

It appears that the upper air low and the tropical remnants will remain separate, preventing explosive development like we had with tropical storm Isaias. However, things could change and that possibility will need to be watched.

The models currently show a heavy rain event, starting Thursday morning and lasting into very early Friday morning. The CMC and GFS models have total rainfall amounts in the 2.0″ to 3.5″ range for the Philadelphia area.

As early as last Friday, the German ICON model was ahead of our GFS the Canadian models in predicting Zeta’s formation. The ICON model did very well with Isais’s precip totals. Here’s the latest ICON model cumulative precipitation forecast for the storm—

Icon Model storm total cumulative rain forecast

I expect changes in the forecast. Stay tuned.

WEEKEND WEATHER OUTLOOK

The stagnant, very mild pattern we’ve been in should continue, as I would describe the current overall situation as a “lack of very cold air” to our north.

Whatever blob of cold air exists in Canada will sag into the western/central US over the next few days, but  our area will still be on the relatively mild side of things. No very cold outbreaks in sight right now, although a weak front will bring in cooler temps for Sunday.

The Short Range Ensemble Forecast Model (SREF) sums it up well with the “540 thickness line”  (RED) staying north of our area—

SREF Model Sunday noon with “540 thickness line” (RED) and other upper air 0ºC lines (magenta, violet)    (Click on image for a larger view.)

Saturday—

As for the specifics for this weekend, a weak cold front will approach on Saturday about noontime, but upper air support is lacking and the front will fizzle out.   Showers with the front far west of the Philadelphia area are expected to reduce to some widely scattered sprinkles.

Speaking of  forecast specifics, it’s been difficult to predict when the low clouds level would lift each morning.  Over the past week, the higher resolution meso-scale models have been a bit too cloudy and the GFS has been useless, as it rarely showed the low clouds and fog that developed each early morning.  Saturday’s forecast is a bit different since clearing skies are expected during the afternoon after the frontal passage according to the model blend.  (Some models have slower clearing through the afternoon. ) Still mild with highs near 73º.

Sunday—

Sunny early.  High pressure moves off to our north and an easterly wind flow will bring in cooler temps and clouds late morning and cloudiness will increase during the afternoon.  Highs only 55º

Fri 03:36 PM Update — latest models have showers early evening Sunday.

Current seasonal average highs are 61º and average lows are 41º.

 

WEEKEND WEATHER OUTLOOK

Thursday 6:40 AM Update— All the models have clear skies by Saturday morning.

A strong cold front with a possible coastal low will move through Friday and clear the coastline by Saturday morning. Following the rain on Friday, the weekend looks good.

The Canadian model is somewhat faster with the front moving through than the GFS and  NBM (model blend). Even the models that show a slower movement of the front have the clouds clearing by mid morning Saturday.

The latest SREF model prolongs the rain and has slower clearing on Saturday. So a bit more uncertainty about Saturday’s forecast.

Here’s the current Canadian CMC Global model forecast for Saturday morning showing a high pressure building in from the northwest—

CMC GDPS forecast Saturday 5 AM   (Click on image for a larger view.)

Saturday should be mostly sunny and windy in the morning.  High temps near 57º, so it will be somewhat cool, especially with the windy conditions.

Sunday should be sunny, milder and less windy with high temps in the low 60s.

We’ll see if things progress as currently forecast.