Saturday will be sunny and chilly. (Cancel the windy conditions.) High temperatures 42-43.
Sunday now looks to have some cloudiness in the morning, then sunny until later in the afternoon, when clouds move in. High 40. Rain, possibly starting with a few flakes of snow, in the evening/night (GFS).
There are differences between the NAM and GFS regarding QPF, but when it rains, nobody really cares if we get 0.10inches of rain or 0.30 inches.
Details from earlier today…
Let me preface this by noting that today was supposed to be cloudy. The models didn’t do too well yesterday. Let’s see how they do for the weekend.
A frontal system will move through early evening tonight. Only some cloudiness and a low chance of a sprinkle will accompany the front.
Colder air moves in for Saturday. It will be mostly sunny and windy. High 41.
On Sunday, a weak and poorly organized low pressure system moves in later in the day. Sunday starts with some sun, but expect clouds to move in during the late morning. There are some timing differences with the models with the NAM having some light precip in the afternoon, while the GFS is later, into the evening.
Both the GFS and NAM are similar with QPF values of about 0.12 inches water. The precipitation will likely fall as rain or possibly rain mixed with snow, as high temperatures are expected to be about 39 and critical temperatures in the upper atmosphere are borderline too warm for snow.
There are enough model differences with this system, that I expect the forecast to change. Stay tuned.
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.
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.
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.
So…the NAM did well last night with the predicted QPF resulting in about 1 inch of snow in and around Philadelphia. However, the precipitation started earlier and ended later than the NAM forecast. The snow shield also extended further north than expected. The NBM and GFS did poorly with this clipper.
For the weekend, the upper air pattern moves away from the highly amplified cold flow we have had since Wednesday.
Skies clear tonight and it will be mostly sunny Saturday with high pressure building in. Winds will be very light and temperatures will feel warmer than the expected high of 36-38 34 on Saturday.
Sunny skies continue on Sunday and temperatures warm to 46- 48. Clouds move in late Sunday.
For the long range outlook, the extended forecast seem to change every few days. After a warmup during the early part of the coming week, things cool down later in the week but not as much as had been previously forecast. Currently, any storms in the long range are showing as rain for us, not as snow.
High pressure that moved in on Friday will linger into Saturday morning. Milder air aloft will approach during the day on Saturday as winds become southeasterly. In effect, a weak warm front. Disturbances (vorticities) in the upper flow may give us additional clouds on Sunday.
Saturday will start mostly sunny, but mid-level cloudiness will increase during the day. The GFS is showing a significant layer of altocumulus and altostratus cloudiness by afternoon. High will be near 35. Low about 25.
Sunday will be milder, with some sunshine, but it appears that these weak disturbances in the upper flow may also result in some cloudiness. High 42-44.
A potentially interesting situation for Tuesday into Wednesday- The European ECMWF has been consistently showing a coastal low developing along an arctic front as it moves through our area. This would mean snow for us.. This has been supported by the Canadian CMC model. However the GFS and FV3-GFS do NOT show this low pressure development. Something to watch. Stay tuned.