Saturday

A cold front and upper air trough moves through about noontime. While temperatures will be well above freezing at the surface, temperatures at critical levels above ground will support snow. Snow showers or squall will move through about noon to 3 PM. A dusting accumulation is possible in northwest suburbs. (Some high resolution models show some additional, earlier light snow flurries in the late morning.)

• Sunny early, then increasing clouds
• Snow showers between noon and 3 PM with gusty winds.
• Clearing and increasingly cold for the balance of Saturday.
• Windy
• High temp 43.3º ± 1.6º NBM model Blue Bell. Windy conditions will keep apparent temperatures (wind chill) in the low 30s.

Sunday

High pressure builds in

• Sunny breezy and cold. A period of clouds late morning.
• High Temp 37.7º ± 0.8º NBM model Blue Bell.
• Breezy causing lower wind chills in the 30s.

Monday

Sunny and milder

Update Sun @ 11:07 AM — The models continue to indicate another wave of low pressure to continue affect us through 2 PM today with more light snow. With the higher February sun angle, solar insolation through clouds will provide enough thermal effect to prevent much additional accumulation on roadways and dark surfaces. Grassy surfaces may have additional 1/2-1.5″ accumulation.

As of 3:47  PM

...Bucks County...
Doylestown                   3.5 in    1121 AM 02/13   Public
Lower Makefield Twp          3.5 in    1236 PM 02/13   Public
Yardley                      3.0 in    0749 AM 02/13   Public
Jamison                      3.0 in    0200 PM 02/13   Public
2 NE Springtown              2.9 in    0700 AM 02/13   CO-OP Observer
Trumbauersville              2.8 in    0120 PM 02/13   Public
Levittown                    2.5 in    0130 PM 02/13   Trained Spotter
2 NW New Britain             2.4 in    0140 PM 02/13   Trained Spotter
Furlong                      2.3 in    0147 PM 02/13   Trained Spotter
2 WSW Langhorne              2.2 in    1243 PM 02/13   Trained Spotter
Jamison                      2.0 in    0729 AM 02/13   Public
1 SE Chalfont                2.0 in    0142 PM 02/13   Public
1 SSW Fricks                 1.5 in    0900 AM 02/13   Public
Hilltown Twp                 1.4 in    0650 AM 02/13   Trained Spotter
1 SSW Sellersville           1.0 in    0700 AM 02/13   CO-OP Observer
Warminster                   1.0 in    0746 AM 02/13   Public

...Delaware County...
Upper Darby                  2.3 in    0310 PM 02/13   Public
Boothwyn                     2.0 in    0140 PM 02/13   Trained Spotter
Aston Twp.                   2.0 in    0144 PM 02/13   Trained Spotter
Chadds Ford Twp              1.3 in    0730 AM 02/13   Trained Spotter
Broomall                     1.0 in    0755 AM 02/13   Trained Spotter
Thornton                     0.5 in    0933 AM 02/13   Public
Folsom                       0.4 in    0631 AM 02/13   Public\

...Montgomery County...
New Hanover Twp              3.5 in    0145 PM 02/13   Trained Spotter
Norristown                   3.3 in    1255 PM 02/13   Trained Spotter
Lower Moreland Twp           3.3 in    0120 PM 02/13   Public
Upper Dublin Twp             3.0 in    0230 PM 02/13   Public
Salford Twp                  2.5 in    0200 PM 02/13   Trained Spotter
Horsham                      2.5 in    0251 PM 02/13   Public
1 W Ambler                   1.5 in    0110 PM 02/13   Trained Spotter
Lansdale                     1.2 in    1200 PM 02/13   Trained Spotter

 
...Philadelphia County...
Shawmont                     2.0 in    1140 AM 02/13   Public
Fox Chase                    1.3 in    0800 AM 02/13   Trained Spotter
Philadelphia International   0.4 in    0125 PM 02/13   ASOS

Update Sat @ 11:15 PM — Tonight’s GFS has the bulk of precipitation coming through before temperatures drop. As a result, the GFS has considerably less snow accumulation. (less than an inch) Wish I could tell if it’s correct.

Update Sat @ 10:15 PM —Tonight’s early models have become available. The trend is for a generalized 1.5-3″ snowfall in the immediate Philadelphia area.

Snow tapers in the morning, but models show continued intermittent snow showers possible during the afternoon.

Clouds linger well into the mid to late afternoon. High temp 36º± 2.1º (NBM model Blue Bell)

Here’s another high resolution model snow accumulation forecast—

Update Sat @ 6:03 PM — This afternoon’s models have become available. As usual, there’s a wide range of snow totals. The GFS remains on the low side with less than 1 inch in most areas.

What is difficult about this particular forecast: several models are suggesting a relatively narrow band of higher precipitation. Additionally, there are different snow algorithms regarding wet snow accumulation on relatively warm surfaces.

This will initially be a very wet snowfall, until temperatures drop to freezing about 5 AM.

The trend for this afternoon has been for that narrow band of higher precipitation to be falling over Philadelphia and its western suburbs.

After reviewing several models, I’m going to invoke my mantra, “Never ignore the NAM”. The NAM has consistently been on the high end of snow accumulations. So it might be prudent to understand that the NAM might be over-doing it.

Added 7:40 PM: It appears that the models with the lower snow totals have surface temperatures warmer than the NAM.

The latest NAM—

Update Sat @ 11:22 AM — The latest Canadian RGEM—

Update Sat @ 10:23 AM — After reviewing last night’s models as well as some of this morning’s models, here’s the current forecast trend:

• More snow is possible than had been previously predicted. While the previous forecasts had predicted a coating to 1″, the latest models are predicting in the range of 1-2 inches with some having as much as 3 inches accumulation in some areas.
• The light snow, instead of ending in the mid-morning, may be with us into early afternoon.
• Accumulations may be highly varied  by location.

The trends have been more consistent with the NAM model’s forecast over the past day or so. The GFS, which had been predicting close to zero, is now back on board with over 1″. The ECMWF has also increased its snow totals and has the light snow extending past noon.

I’ll try to narrow it down this evening. Stay tuned…

Previously Posted Fri 6:13 PM —

A surface cold front will move through about 8 AM Saturday morning. Winds will shift to the WNW with the frontal passage, but not much cold air will move in with this first front. Saturday will be mild.

Low pressure develops in West Virginia and moves along the front late Saturday night. Cold air moves in during the day Sunday.

I’m leaning towards the Canadian RGEM this forecast. It has done well with recent frontal passages and rain-> snow forecasts.

Saturday

The cold front moves through in the morning. Clouds in the morning break for sunshine in the afternoon. Somewhat windy. Clouds move back in during the evening. High temp 56.9º ± 2.1º Blue Bell (NBM model)

Low pressure develops in West Virginia around midnight.

Sunday

Light rain changing to light snow 2-4 AM Sunday morning. By daybreak, all light snow. Snow tapers and ends 8 – 11 AM.

A coating to 1.8″ possible. Uncertainty remains regarding location of highest amounts at this time. The NBM and Canadian RGEM are leaning towards lighter amounts. (about 3/4 of an inch)

High Temp 35.0º ± 2.0º Blue Bell (NBM model)

Update Sat @ 10:48 PM — Tonight’s models continue to show Monday evening’s coastal storm barely brushing the Philadelphia area during the early evening. Thermal profiles are trending warmer—too warm for snow.

Update Sat @ 9:48 AM — No significant change in this weekend’s forecast.

The coastal system expected to move near us later Monday night into Tuesday morning is still expected to brush us with precipitation.

Temperatures in the immediate PHL area will be marginally too warm, so any precipitation will fall as wet snow/ rain mix at best; moisture extending beyond the immediate Philadelphia area may fall as snow flurries or light snow showers. While there is currently good agreement with the models, the trend over the past two days has been to be slightly closer to the coast. I’ll keep an eye on it.

Saturday

Fair and very cold, with windy conditions, especially in the afternoon. High temperature 29.1º ± 0.9º. Wind chills will be in the teens. NBM model, Blue Bell.