Monthly Archives: February 2019

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

[su_box title=”Weather Update Fri 10:30PM” box_color=”#defcdc” title_color=”#000000″]Tonight’s NAM has a QPF of 0.13 water falling as light snow Sunday evening ending before daybreak Monday. This translates into 1-2 inches.[/su_box]

High pressure builds in for Saturday and most of Sunday.  As mentioned previously this week, the frontal boundary remains not far to our south.  A disturbance will move along this front bringing light snow to our area Sunday evening and night.

Saturday will be sunny and cold.  It will be windy with high temperatures 33-35.  Clear and cold Saturday night.

Sunday will start sunny, but the aforementioned disturbance approaches Sunday and cloudiness will become significant by about noon.  High temperatures near 38.

Light snow is expected Sunday evening and night. Currently, the GFS gives us a coating, the NAM and ECMWF about 1 inch, slightly more south of Philadelphia.

[su_note note_color=”#d9f2da”]On the horizon is a more significant storm expected to move to our west on Tuesday and spawn a weaker coastal low off the New England coast.

Warm, moist air overspreading cold air at the surface will allow snow to develop Monday night but the snow will change to sleet and freezing rain Tuesday morning, likely early. Then all rain.

An extended period of freezing rain and sleet is possible in the northwest suburbs into Tuesday morning as a “cold air damming” effect occurs. A changeover to all rain will occur in all areas, but later further north. [/su_note]

Winter Weather

WINTER WEATHER OUTLOOK

[su_box title=”Weather Update Fri 8 AM” box_color=”#defcdc” title_color=”#000000″]So, yesterday’s models were significantly off about the amount of rain we had early this morning. (We had double the amount.) Can we depend on them for a 5 day forecast?

The current trend for Sunday night: the NAM maintains about a 2-3 inch brief snowfall before daybreak Monday. The GFS has very little. I’m going with the NAM at this time.

For Monday night into Tuesday, it appears it will be briefly snow changing to freezing rain and then all rain for most of the storm. The secondary low coastal formation doesn’t appear to be very strong. Stay tuned.[/su_box]

from yesterday…

As mentioned in my previous post, high pressure will move in for the weekend behind a cold front that moves through Friday morning. The frontal boundary will stall to our south.

For Saturday and most of Sunday, we will have mostly sunny skies but with temperatures below average, in the 30s.

The stalled frontal boundary will become associated with a developing low pressure system in the Midwest and will redevelop as a warm front, moving slowly north as it tries to displace the cold air at the surface.

Warm air will start to overrun the cold air with an initial weak impulse that may bring some light snow late Sunday night or before daybreak Monday.  (This looks to be very insignificant.)
[su_note note_color=”#d9f2da”]Thursday evening 2/7- Latest NAM has 1-3 inches of snow Sunday night. [/su_note]

As the warm front slowly approaches Tuesday, snow may develop Monday night into Tuesday, but it appears that it will mix with sleet and change to all rain sometime Tuesday. This is the most likely scenario.

But, there’s significant disagreement among the models with this system. While the change to all rain (after some freezing rain) is the most likely scenario, the GFS and FV3-GFS suggest a secondary low develops along the Delmarva coast, possibly allowing more snow. The Canadian model is similar but maintains much more cold air, with more snow.  The European model has a much later development into Wednesday, with the secondary low developing north in New England, giving us mostly rain.  

The Tuesday through Wednesday timeframe looks interesting.  Stay tuned.