Update Sat @ 5:55 PM — More models are on-board with very light snow Sunday evening. The NAM and NAM-NEST have about 0.5-1″ by 1 AM Monday. The location of anything more than a coating varies by model. The HREF is provided below which shows the spotty nature of the snow forecast—

Things still uncertain for Tuesday. The NAM continues as an outlier with several inches of snow. Other models have a coating to less than 1 inch. Stay tuned.

Update Sat @ 11:19 AM — Sunday looks to be mostly sunny in the morning, increasingly cloudy during the afternoon. The weak upper air disturbance and cold front coming through Sunday night looks to have only some snow flurries, maybe a coating far western areas.

The possible storm on Tuesday is only being forecast by the NAM model. Other models have little development. This is not one of those situations where my “never ignore the NAM” mantra necessarily applies. In this sort of thing, the NAM is often off-target. But I’ll keep an eye on it.

Fri @ 10:03 PM — Forecast update highlighted below:

This weekend’s weather will be influenced by an upper air trough that has been with us for over a week. Very cold air is contained in this trough and our temperatures will be well below seasonal average through the weekend.

A low pressure system predicted to form off the coast Saturday will move off well to our south and east. Cape May NJ will be on the very northern fringe.

Originally Posted Fri 5:04 PM —

The next active period may be Tuesday into Wednesday, when a more potent disturbance in the southern stream (2) may phase with the northern stream(1) closer to the coast, but the models currently have it occurring further north and east of us—

Friday night’s models are suggesting a greater possibility of coastal storm development on Tuesday.

Update Sun @ 9:15 PM — Snow is changing over to rain. High winds possible after midnight. Temps wise to near 50 before falling back to the 30s. Rain ends before daybreak. Tonight’s models continue to forecast snow showers between 7AM and 11 AM Monday morning (mentioned in my 12:50 PM update today). Temperatures will be above freezing and little or no additional accumulation is expected.

Update Sun @ 7:15 PM — The current radar precipitation type shows that the transition to rain is lagging about an hour or so from the model forecasts. The latest HRRR and RAP models still show the transition in PHL about 8 PM, but the actual transition time may be later.

The next new major model run is the 00z run. The 00z HRRR, NAM, RAP and HIRESW will be available by 9:15. I’ll update if necessary.

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Update Sun @ 2:48 PM — Eagles Half time update—

Update Sun @ 12:50 PM — This morning’s high resolution models (HIRESW) show considerable snow shower activity Monday morning with a wet coating possible.

Update Sun @ 8:03 AM — Last night’s 06z models continue with a generally earlier start and transition to rain. Clouds move in between 11 AM and 1 PM. Some snow possible as early as 5 PM, very rapidly changing to a period of freezing rain and then rain by 8 PM in the city and shortly afterwards north and west as temperatures rise above freezing. With heavy rain (1.25-1.5”) late evening, temperatures climb to 47º-50º around midnight. Strong wind gusts about 1 AM approaching 50mph.

Rain ends about 4 AM. Cloudy Monday, windy, temps above freezing in the 30s until evening.

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Update Sat @ 9:30 PM — The major model runs are are done at 00z and 12z ( 7 PM & 7 AM EST). Some of the 00z high resolution models have become available. The changes noted in my previous update, with an earlier change to rain, are still expected. Some freezing rain possible about 8 PM.

Temperatures below freezing all day Sunday, will rise into the mid 40s after midnight! About 1.5 inches of RAIN will fall before it ends before daybreak Monday.

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Update Sat @ 5:05 PM — This afternoon’s 18z models have become available. The trend is for the system to approach earlier on Sunday. Clouds increase by late morning. Some snow develops as early as 5 PM.

The warm-up also appears to occur 2 hours earlier with a transition to sleet and rain in the city around 8 PM and moving quickly north. By 10 PM, the HREF has mostly rain for our area —

By Monday morning, little if any snow will be left after the heavy rain.

Another slight change. Non-accumulating snow flurries/showers likely Monday morning and again late afternoon.

Update Sat @ 10:01 AM — The forecast for Sunday evening’s storm is essentially unchanged from the GFS forecast from this past Wednesday. While we still have plenty of time before Sunday evening, the models have done usually well with this storm forecast so far. There weren’t the usual differences among models we often see with winter storms.

The Sunday night period is within forecast range now of the very high resolution models.

Snow starts at about 5-7 PM from south to north. Changes to rain most immediate suburbs by midnight. Here’s the latest HRRR with the snow-sleet transition line at 10 PM Sunday—

Originally Posted Fri 5:23 PM —

Very cold air will move in due to the flow around a low pressure system (that missed us) in the Atlantic today.

A storm that is has been forecast since Tuesday to form near Virginia early Sunday will move northeastward across our area. We’ll be on the warm side of the storm.

While the model forecasts for this storm have been remarkably consistent, a possibility exists that a more prolonged period of freezing rain will develop in the very far northwestern suburbs Sunday night due to cold air damming. It should all change to rain during the pre-dawn hours.

Saturday

Embedded in the upper very cold flow is an upper air disturbance. Sunny early morning. Then we’ll have mid-level cloudiness from late morning through much of the afternoon. Very cold. High temperature will be 23.2º ± 2.1º (NBM model Blue Bell, PA). It will be very windy in the morning, but winds should subside in the afternoon.