Update Sun @ 10:09 AM — On my way out at 10 AM but it’s raining!

What about this peak at 10 AM?? Hmmm….. I guess I didn’t annotate my own meteogram closely enough.

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Update Sun @ 8:30 AM — As suspected, some of the high resolution models weren’t too great in forecasting the freezing rain. The GFS, NAM and NAM-NEST as well as the HIRESW-FV3 correctly forecast the precipitation at it’s current location—

So when will it rain?

The models also show winds getting quite gusty by the time the rain starts.

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Update Sat @ 11:03 PM —

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Update Sat @ 9:45 PM — Eagles halftime and time for a weather update.
The trend with tonight’s models is for the early slug of potential freezing rain to stay just north and west of Philadelphia. The NAM group has any freezing rain not even close by. The newer models HRRR, RAP and and HIRESW models keep the freezing rain just north and west.

Only one version of the HIRESW-ARW has some light freezing rain in Philadelphia early.

Of interest is that the morning may be relatively rain free after a quick slug of precipitation, with the main area of rain moving in about 1-3 PM.

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Update Sat @ 4:35 PM — Today’s models continue to increase the likelihood of a period of freezing rain on Sunday morning. While most of this will occur just north and west of Philadelphia, several models are showing very light freezing rain occurring around 7 AM within the city. It will changeover to rain from south to north, and by noon, and it should be all rain as far north as Quakertown.

As shown in the graphic below, the lower resolution GFS is not as aggressive with the freezing rain in Philadelphia as the HREF model because it has the precipitation coming in somewhat later, after the temps have warmed up. (The latest Canadian RGEM model is similar to the GFS, with precipitation coming in later.)

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Update Sat 7:50 AM— Saturday high temp 29.3± 1.3º. (Somewhat colder). Sunday a period of freezing rain in the morning looking more likely at this time. Sunday details.

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The weather moves to an active pattern as amplifications in the jet stream, both ridges and troughs, move through the northeastern US.

The expected pattern is described in the caption above.

Saturday

Saturday will be sunny and cold but winds should subside as a surface high will be right over us. High temp 32º ± 2º NBM Blue Bell

Sunday

The upper ridge moves over us and surface winds become southerly, bringing some moisture. The moisture will rise over cold air and a period of freezing rain is possible northern and western areas during the mid to late morning. This should all change to plain rain in the immediate suburbs, but very far northern/western areas (north of Allentown) might see a prolonged period of freezing rain . High temp 42º ± 3º (NBM Blue Bell)

Light rain through the afternoon. Winds pickup and become gusty later afternoon into evening.

A cold front moves through before midnight Sunday with gusty winds. Temperatures drop into the 20s with lower wind chills.

Very cold weather Monday through Tuesday.

Happy New Year!

Update Sat @ 10:11 PM — It hasn’t gone unnoticed that the TV/radio weather people haven’t really mentioned anything about the snow possibility for our region on Monday morning. I’m truly perplexed by it. But I guess that’s why you’re here reading this blog.

I must mention that the NAM, NAM NEST and ICON models have shown zero snow until this evening. ( They now show snow in southern NJ only.) Very strange to have such a wide divergence of forecasts.

Here’s tonight’s HRRR model, which continues to show snow, as does the NBM and the SREF.

With all these models, the most likely forecast is snow in Southern New Jersey and a rapid taper to zero just west of the city. The surprise would be if the SREF just above is correct.

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Update Sat @ 4:18 PM — I have more interesting data to share and chew on regarding snow early Monday. The most recent run of the HRRR (which forecasts out 48 hours) has more than moved in the direction of the GFS regarding possible snowfall for Monday. Here’s the latest HRRR snow totals for Monday morning—

Several models, including the Canadian GEM, the Canadian GEPS and the ICON Ensemble (ICON-EPS) have moved in the direction of the GFS with accumulating snow, especially for South Jersey. Their snow totals have a similar profile, decreasing towards Philadelphia, with maximum snow of 2.0 inches in Cape May County.

The possibility of snow has been a ongoing possibility since since I mentioned it in Tuesday’s blog post. It’s been on again, off again. The above HRRR is the latest, possibly the most extreme possibility.

If you’re just joining this this blog forecast discussion, I recommend you read the background info below.

Stay tuned.

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Update Sat @ 11:10 AM — The latest GFS model just became available minutes ago. Hard to believe (literally), but here’s the snow the GFS is predicting by Monday morning. I’m just throwing this out there —

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Update Sat @ 9:58 AM — The period between Sunday and Monday is just coming into range of the higher resolution short range models.

Saturday —rainy and mild.

Sunday- Cloudy with a thinner cloud deck into the afternoon. Very mild until the front moves through.

The front moves through between 3 and 5 PM. Gusty winds with highly scattered light sprinkles as temps begin to drop.

Despite last night’s GFS model’s snow prediction, the other models all keep any precipitation to our to our far south and east. Even the NBM has removed snow from its forecast. So no snow late Sunday night into Monday.

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Updated Sat @ 8:10 AM — No significant change in Saturday’s forecast. The spotty light rain drizzle in the morning today will become more steady by the afternoon.

The trend for late Sunday is for any measurable snow to be in Delaware and southern NJ (Cape May).

The GFS still has measurable snow here by Monday morning. The higher resolution short range models have no snow in our neck of the woods. The GFS ensemble still shows light precipitation falling as snow before daybreak south and east of the city, but no accumulation around PHL. (As was the case last week, the GFS over-predicted snow here. I’m going to lean away from the GFS this time around.)

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Previously Posted Fri 6:10 PM —

The mild weather continues through Sunday. A continuing complex scenario is expected play out Sunday into Monday as a cold front approaches from the west and low pressure develops as it stalls.

Saturday

Low pressure to our southwest will sweep another warm front through Saturday. Saturday will be rainy during the day and evening through midnight. There may be some pauses in the action, but a rainy day expected. High temp 59º ± 3.0º

Sunday

The advancing cold front approaches during the day. Showers in the morning, then mostly cloudy until late afternoon (~4 PM), when the actual cold front moves through and additional showers develop. Becoming WINDY. Additional showers during the evening. High temp 59.5º ± 5º (high spread/high uncertainty!) NBM model Blue Bell.

I’ve been focusing on the Sunday evening period since Tuesday’s blog post and and it’s been on again off again regarding low pressure development. A new wrinkle has developed with today’s models—

The cold front appears to stall late Sunday night into Monday morning. Yet another low pressure system develops before daybreak Monday to our south. The precipitation shield appears to expand enough to cover our area with light snow.

The GFS and the ensembles (GEFS and SREF) show a light snow shield over us early Monday morning. Totals appear to be less than 0.5″ near Cape May NJ.

The GFS has light snow only from 4-8 AM with just coating amounts in the immediate PHL area. The ensemble forecasts continue the possibility of light snow later into the morning with additional weak waves on the front.

This continues to be a complex scenario and a low confidence forecast. I’ll keep an eye on this. Stay tuned.

Update Sat @ 9:30 PM — Sunday’s forecast for sunshine still looks good. High 49° ± 2°. Watching the Monday forecast.

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This morning’s latest HRRR and RAP models have the sun breaking out between 2 and 3 PM in many areas.

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Updated Sat @ 7:36 AM— Merry Christmas! The forecast specifics for today remain hard to pin down time-wise. The general trend is that there will be showers early, then a break and even some sun for a bit, then more showers about noon, followed by another break and even some sun about 1-2 PM, then more clouds and showers.

High temp 55.6º ± 3.7º Blue Bell based on the latest NBM model. (The high standard deviation -3.7º reflects the uncertainty in the model forecasts for today.)

The current radar doesn’t match favorably with any model forecasts, so it’s still a lower than usual confidence forecast.

Sunday still looks sunny.

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A low pressure system in western NY state will have it’s associated warm front move through after midnight tonight (Friday). It’s associated cold front will move through during the evening Saturday. The front will stall to our south and return on Monday as a warm front. In between, Sunday will be sunny.

There’s been a lack of clarity about Saturday’s forecast details, as covered in my previous post.

Saturday

The showers associated with the warm front will move through before daybreak and into the early morning. There’s been a lack of clarity regarding the early morning showers placement, but I’m going to lean on the latest NBM to make the call.

Most models are in agreement with showers returning late morning well ahead of a weak cold front. (The main front moves through on the evening.) Showers will be light. It will become WINDY late morning. There may be some clearing after 1-2 PM although that’s not a certainty.

High temperature 56º ± 3.0º (NBM Blue Bell)

The main cold front moves in in the evening (possibly with additional showers, but a low chance.)

Sunday

The front moves to our south and fair weather moves in. It will still be mild.

High temperature 50.3º ± 2.4º (NBM Blue Bell)

Looking Ahead…

The front that moved through Saturday will return as a warm front Monday. There’s the possibility of light, non-accumulating snow early Monday morning.