Philly Winter Weather Outlook

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For the past week, the European model, the ECMWF, has suggested the formation of a coastal low pressure system in the Sunday to Tuesday time frame. The GFS has only gradually come onboard with this possible scenario, but last night’s GFS is developing a slow moving coastal low, bringing heavy rain and and changeover to snow late Tuesday to Wednesday.

For most of last week, the GFS advertised a warm up with cold air sequestered in Canada and the low pressure development out at sea.

The GFS is now advertising much more of an amplified jet stream and a deepening hug-the-coast storm. In fact, the jet stream becomes negatively tilted with the storm track blocked, resulting in a slow-mover (read, high precipitation)

So, the GFS has finally caught up and the NWS extended range forecasters have been on-target in anticipating this coastal low development.

Many unknowns with this as-yet undeveloped storm- the degree of amplification of the jet stream, the degree of negative tilt and the degree of blocking. What this means is that we don’t know if it will be heavy rain or heavy snow or whether this will be a slow mover.

Right now, it looks like mostly heavy rain for NJ and SE Pennsylvania, but a changeover to snow is very likely late Tuesday afternoon and Tuesday night. A couple of inches is possible and the wrap-around snow may linger into Wednesday morning. Doesn’t look like a major “stormstorm” for our area at this time but a different story for interior New England.

With this storm in the hypothesized, unformed stage, we won’t know specifics about rain-snow line and snow amounts until late Monday.

Current GFS forecast for early afternoon Tuesday
Current GFS forecast for early afternoon Tuesday

Philly Weekend Weather Forecast

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An area of low pressure will move across our area tonight and Saturday, before a front passes through before daybreak on Sunday.

Saturday will be cloudy and dismal. There may be a break in the rain early Saturday morning but heavier rain will return by early afternoon on Saturday into the evening. Winds will be from the south and it will be relatively mild. High around 50.

A cold front will move through before daybreak on Sunday. Sunday will have plenty of sunshine, but it will be windy and cold. High 44

GFS model forecast for early Sunday
GFS model forecast for early Sunday

Philly Winter Weather Outlook

Last Updated

This weekend, we are entering into a period where the weather models are showing big differences in the forecast from run to run and between different models.

The upcoming weekend looks to be cloudy and wet, particularly on Saturday, but there’s a chance of a coastal storm developing anywhere in the time period from Sunday through early Tuesday.

It appears that it will be too warm here for snow. But while wet is much more likely than white, there’s even uncertainty about how amplified the jet stream may become and how much cold air will be present.

One thing that is becoming clearer….there is a change in pattern from last year’s highly amplified jet and oppressive cold weather, with extreme dry weather in the west.

This pattern reminds me of the last solar cycle peak in 2001 where we had very warm periods in January and February and more rain than snow.

Storm Forecasts & Other Things "up in the air".