Monthly Archives: December 2018

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

[su_box title=”Forecast update Sunday 8 AM” box_color=”#defcdc” title_color=”#000000″]Warm air retuning in the mid levels of the atmosphere is causing this layer of altostratus this morning. Light snow has developed with this pseudo-warm front feature. None of the models had picked up this feature. These clouds should dissipate by late morning. High temperatures 42-44.[/su_box]

The current pattern can be summarized as cold air remaining in Canada with small dips in the jet bringing colder air over the Northeast, which then alternates with a warmer southwesterly flow of moisture bringing rain.

Low pressure will move off the coast tonight and weak high pressure will build in. The flow will remain cyclonic from the departing low through Saturday afternoon.   Saturday will be fairly windy and cooler.  Highs about 48-50.

[su_note note_color=”#d9f2da”]Fri 11PM Update: Saturday high temps 45-47[/su_note]

Winds 15 mph with gusts.  Following some sun early, the cyclonic flow will cause some altocumulus cloudiness during the mid day hours into the afternoon, then will dissipate as winds subside.

For Sunday, weak high pressure will provide mostly sunny skies and more seasonably cool temperatures.  Highs 42-44.

High clouds move in late in the afternoon on Sunday as the next wave of warmer air and rain approaches for late Monday into New Years Eve. (Bravo to the new FV3-GFS which predicted this bad weather for New Years Eve well over a week ago, although it was originally predicting a snow storm two weeks ago. )

Things chill down toward the end of the week, as the GFS has the possibility another brush with rain or light snow Thurs evening.

 

Philadelphia Weather Outlook

WEEKEND WEATHER OUTLOOK

All models are on-board with a low pressure system that moves in late Thursday into Friday.  Rain, possibly heavy (more than 1″), is very likely for much of Friday.  It will  be very mild. High temperature near 60.

Saturday dries out and it will be colder and closer to seasonable.  There may be instability clouds.

There’s a wide range of model forecasts for Sunday, as a low pressure system tracks to our south. We may get some light precip Sunday if the low tracks a bit further north.  Type will depend on timing, but mostly like very light rain showers.

The storm I mentioned a week ago for New Years  Eve/Day is on track to be a rain-storm.

[su_note note_color=”#d9f2da”]Right now, I don’t see much in the way of snowy winter weather.

There’s no giant slug of cold air predicted to descend into the central US.

Cold intrusions will repeatedly occur in the North Eastern section of the US that will effectively block storms coming up the coast.

These cold intrusions will alternate with mild air and wet flows. Things would have to change big-time for my colder-than-normal climate forecast from late November to become a reality. [/su_note]

 

 

 

Winter Weather

INTERESTING FORECAST FOR SUNDAY NIGHT

[su_box title=”Forecast update Sunday 11pm” box_color=”#defcdc” title_color=”#000000″]Too warm for snow tonight and the NAM has reduced the QPF in Phladelphia to zero. [/su_box]

First, will the Eagles win again with Foles?  Yes.

That said, let’s turn to tonight’s forecast which may be a more difficult call. A front will pass through tonight between midnight and daybreak.  Weak low pressure is predicted to move along the front.  Each model run has increased the intensity of this wave of low pressure.

The models are consistent with low temperatures being above freezing (36 degrees in Blue Bell).  The latest NAM has several critical temperatures of the atmosphere supporting snow, except for the lowest level.  QPF values are now 0.07 inches water.  Currently the models have a general consensus of light snow with a slight grassy coating in the areas in blue –

P-Type
Current Model P-type prediction after midnight Sunday.

If there is further strengthening of the low, dynamic cooling may move this area of snow closer to the city.  Right now, the areas shown are the best bet, but it wouldn’t surprise me if there’s some very light snow falling closer to the city.  Since it will occur before daybreak, we’ll have to see if anything is left on grassy surfaces.  This is the best we can do this year for a white Christmas.

[su_note note_color=”#d9f2da”]Of more interest is the period around New Years Day.  For almost a week,  the GFS and FV3-GFS have been showing some sort of major storm (rain, ice or snow) in the Jan 1-2 timeframe.  Something I’m watching. [/su_note]