Monthly Archives: January 2020

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

Not so sure we’re going to hit 70 ° on Sunday.

Fri 10 PM Update – No significant changes. I want to emphasize the winds both Saturday and Sunday will be 15-20 mph with gusts.

The very warm temperatures predicted for this weekend have been well-advertised.   The current EKDMOS  (Ensemble Kernel Density Model Output Statistics) shows very warm temperatures: 67º for Saturday and 68º for Sunday (Blue Bell)—

O EKDMOS High Temp Forecast for Blue Bell, PA

A strong southwesterly flow of warm air ahead of an approaching cold front will bring the unseasonably mild air.   But it won’t be a blue-sky day.  With the warmth will be considerable cloudiness and some uncertainty about the amount and timing of sunshine (if any).  It will be somewhat windy.

For Saturday, depending upon the model, we have sunny skies in the morning, becoming cloudy (NAM)

or clouds early breaking for sunny skies by noon (HIRESW-ARW) then cloudy later,

or mostly cloudy all day (GFS)!

For good measure, the NAM-NEST has some widely scattered showers in the morning (not supported by the other models).

So the warmth is a certainty, the cloud cover less so.   I’m leaning toward the HIRES-ARW with clouds breaking for some sun mid-day, then clouds return.—

HIRESW-ARW-MEM2 Cloud cover forecast 1 PM Saturday.  After 1 PM, clouds start move back in. Click for larger image.

The cold front moves through Saturday night.  There may be a spotty shower early evening, then heavier rain after midnight.

For Sunday, all models have the front moving through about 7 AM with clearing afterwards.   Mostly sunny skies but windy.  High temps near 70, but that will be late morning.   Temperatures slowly fall during the afternoon.

I don’t expect any changes, but I’ll do an update later if there are,  based on the new model runs.

PHL Climate Forecasts

SO WHERE’S THE SNOW THIS WINTER?

…Update added Arctic Temperature Anomaly chart below.

When temperatures reach into the 60s this weekend (the Canadian model has us near 70!), it’s appropriate to wonder where’s the snow this winter?   I don’t have any good answers, but I have some interesting observations.

Taking last year as an example, we would have jet stream configurations and air mass positions that would suggest the possibility of coastal storm development and snow.  Most of the times last year, these model forecasts of snowstorm development would fall apart just a few days before the forecast event.  But there were possibilities.

What’s fascinating about this year’s weather pattern is that the models haven’t even projected a potential storm for us. I haven’t seen any instance of southern and northern jet stream phasing over the western Atlantic in a way that would allow a coastal low to form near the Carolinas or Virginia.

The jet stream, which really represents the “air river valley” at the periphery of cold air masses sagging southward has been broad in shape instead of a sharp dip in most cases.  Where there have been some sharp dips, they have occurred in the Western and Central US. Where there was any sort of dip, the shape was positively tilted instead of negatively tilted (tilted back westward), which induces deep storm formation and slower movement.

There has been no large blocking North Atlantic high pressure that results in these sharp dips along the coast.

Not only have there been no sharp dips along the east coast in any model projections during December or the first week in January, the current GFS which forecasts 16 days in advance shows no potential snowstorms through January 24th.

Things could change, but the Climate Prediction Center shows our area with above normal temperatures and precipitation through the spring and summer.

One more thing —the amount of cold air dropping south is dependent upon the amount of cold air that accumulates in the arctic.  Here’s December’s temperature anomaly for the arctic:

Arctic air temperature departure Dec 2019 at 925 mb height

There’s simply less cold air pooling in the arctic circle.