Monthly Archives: February 2016

Weather Updates

Light wet snow possible before daybreak Friday

The models had shown a developing wave along the front that just moved through yesterday missing us, but as mentioned last night,  over the past few model runs, the NAM and the NAVGEM have extended the precipitation from this wave of low pressure further westward as a trend, now reaching PHL.

They latest NAM has 0.17 inches water (QPF) falling as rain, then snow, between midnight Thursday night and daybreak Friday.  Ground temperatures are warm and the surface temperatures are expected to be a bit above freezing, so any snow that falls will have a challenge accumulating, especially in the city. 

This is a difficult forecast.  Further westward movement of the precipitation will interact with colder air in the western suburbs, allowing more snow accumulation.   Still looking at just a coating to an inch west of PHL, if anything.  (The NAVGEM is predicting even more for PHL, west and north, lasting into the mid morning.).  But clearly, the modeling of the intensity of this coastal wave has been less than stellar to this point.    Won’t really know details until later today or this evening.

While I’m looking at the NAVGEM, (previously called the NOGAPS model) it’s showing a very different movement of the coastal low for Monday.  (The other models have it moving out to sea.). It has the low moving up the coast, giving us possibly significant snowfall by Monday morning.

I’m not big on the NAVGEM model except for hurricane prediction, but if it predicts tomorrow’s snow correctly, we’ll need to consider its solution more closely for Monday.

Philadelphia Weather Outlook

Philly Winter Weather Update

Wednesday 10pm:  Latest NAM model has light rain showers possibly mixed with light snow late Thursday night for eastern portions of South Jersey, ending early Friday morning, as a wave of low pressure moves a stalled frontal boundary off the coast. The trend has moved this precipitation westward. The NAVGEM model had shown this westward extent yesterday and now shows light snow as far west as Philadelphia late Thursday night into Friday morning.  Stay tuned .

The model predictions continue to change in the period beyond 5 days.

I’ve been monitoring the coastal storm that is expected to form Sunday night off the southeast coast.  The track of this storm has continued to shift south and east, missing us in the latest GFS model.

The clipper system that was expected to spawn a secondary low off the coast, giving us snow late Monday now appears to transfer its energy to the above mentioned low pressure system far off the coast.  As mentioned, these northern stream clipper systems often fizzle out and this is the current trend with this system.

So what looked like another possible snowstorm for the Monday timeframe now appears to be less likely.  Possibly some light snow or snowshowers is all that may occur.   Things may change again, so stay tuned.

The cold outbreak for next week still looks likely.

Philadelphia Weather Outlook

Colder and Uncertain Forecast- Wednesday

As has been the case all winter (with the exception of the “blizzard”), the model forecasts beyond 4-5 days has been anything but consistent.

The models had been suggesting a deep surface low to develop Monday in the southeast and move up the coast.  HOWEVER, the latest trend is for this track to be off-shore and  miss us.

A new wrinkle in the forecast is a clipper-type system to move in later Monday from the northwest and undergo secondary cyclogenesis off  the coast, possibly giving us snow later Monday.   But these types of scenarios are the least predictable of all storms- they can often fizzle or development occurs too far north and east.

So, some snow is certainly possible in the Monday time frame, but it doesn’t appear to be the type of storm that is any more than a nuisance.    Still very low confidence forecast.

One thing that seems consistent is an expected outbreak of very cold weather for next week, as the jet stream takes a deep dive.  If that plays out, we’ll have our coldest weather of the winter next week which will dig as far south as Florida.