The upcoming week looks to be a relatively active weather week compared to the past few weeks.
The storm expected to pass to our south on on Tuesday is showing less development and less moisture. Additionally, it now appears to move in later Monday evening and gradually exits during the day Tuesday.
Warm air appears to be brought in about 2000-3000 feet above ground level. The predominant precipitation type will be sleet/freezing rain, then light rain on Tuesday instead of snow, after a small accumulation Monday night.Total accumulations have reduced to under 1 inch for most of the immediate Philadelphia area—
It appears that light rain showers, may linger on and off into the day Tuesday, tamping down or melting some of the small accumulation we receiving Monday night. The main issue may be early Tuesday morning with some icy areas and perhaps some freezing rain in some areas—
Yet another storm is now showing moving to our south on Thursday. This storm is expected to brush us with light snow Thursday morning, however there is a possibility of greater intensification with this system—
Currently, only about 1 inch of snow is expected with this Thursday storm.
Thu 09:30 AM Update — What had been expected to be a colder, active pattern next week (title of original post) is unfolding to be a seasonably cold, uneventful pattern. A flat and zonal flow as depicted in the “540 thickness” line (RED) of the Canadian Global model captures the uneventful flow and is NOT conducive to storm development—
We’ll have a dip in the jet this weekend with an upper low affecting our area, but the original expectation for a continued amplified pattern next week has faded. As for the very cold weather, temperatures in Canada have significantly chilled, but there’s no indication at this time that it will move down to affect our area.
Addendum: Here’s the current day temperature deviation compared to the period 1979-2000—
Wed 09:48 AM Update — After looking at the latest GEFS (statistical ensemble) model as far out as it predicts -384 hours in the future – I don’t really see any intrusion of extremely cold air showing except in the far northwestern US. In fact, the jet flow is looking rather ‘flat’, (not amplified) so previous expectations of an active pattern next week may be incorrect. The flat pattern does not lend itself towards storm development. Cold air starts building in as shown below in the forecast for Sat, Jan 23rd below, but that’s a ways off—
Tue 10:52 AM Update — A plunge of cold air will cause low pressure development over our area Saturday. It looks like RAIN for our area on Saturday. Despite talk about displacement of the”the polar vortex” as suggested by signs of “stratospheric warming”, current statistical models have deep cold in Canada, but not deep or cold enough to extend into the US at this time. Current minimum temperatures from the statistical ensemble model (GEFS)—
This morning’s models are beginning to show an outbreak of very cold air around the last week of January.
Mon 06:22 PM Update — The pattern change expected over the weekend is still showing in the models. It appears it will be too warm for snow here, but there’s high uncertainty about Saturday’s forecast. Low pressure is expected to develop along the coast or slightly inland, keeping us in the warm sector, maybe with a brief changeover to snow before ending Saturday. Stay tuned.
This winter has been relatively quiet with average to above average temperatures, and with the exception of one storm, not much snow.
As mentioned in several posts over recent days, the models having been showing a strong signal towards a pattern change during the period January 16th through January 20th.
Colder air has been building in Canada and it appears that a southward plunge in this cold air will start occurring during the above timeframe, forcing a dip in the jet stream as a jet streak (1) causes the development of low pressure—
The models have not come together with exact timing and placement of this plunge. The GFS (version 16) has rain, changing to snow for this first impulse: not a big storm.
The Canadian global model is similar to the GFS 16, with snow developing Saturday morning.
I should add that the current, operational GFS (version 15.2) is faster and does NOT have this storm form until the impulse is north of us—
Either way, colder temperatures are expected next weekend.
On the horizon is another impulse (#2 above), which depending upon the model, shows the possibility of a significant nor’easter a few days later.
It’s way too early to really know specifics, but the take-away is that colder temperatures are on the way next weekend and a more active winter weather pattern likely follows.
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The latest models are just becoming available this evening. Most models have it too warm for snow in the immediate Philadelphia area. Some snow accumulation is possible far western areas. The NBM (National Blend of Models) 75 percentile snow accumulation captures it well. (75% of the constituent models and their statistical members are equal or below this accumulation amount)—
The latest HRRR and NAM, just available, is consistent with this NBM forecast. There may be some snow mixed with rain in areas that show zero accumulation towards the mid afternoon.
Rain starts around 6-8 AM Monday and ends about 3-4 PM. It may briefly mix or change to snow in the western suburbs as it ends.
As for Thursday—
The models continue to show a major storm for Wednesday into Wednesday night. It will be a stormy day by Wednesday afternoon with high gusty winds. (At one point today, it appeared that warm air might move in, but the newest models are showing significant snow accumulation for Wednesday afternoon and night.) Here’s the latest GEFS snow totals by late Wednesday night—
Here’s the NBM 75 Percentile snow totals—
Very clear is the sharp cut off in NJ as temperature will be too warm for much accumulation there.
While I’m at it, I thought I’d share the latest GEFS snow accumulation forecast for this coming Wednesday into Thursday
The dip in the jet flow that gave us the thunderstorms Monday and the colder weather today will be an ongoing feature of the weather pattern this week and this weekend.
Low pressure developing near the Gulf of Mexico at the end of the week will move up the coast this weekend. Any other year, this would be a recipe for snow with the track of this storm, but the theme of this year so far is what I call “the lack of really cold air”.
There’s much uncertainty with the development, track and timing of this low pressure system. The current GEFS model shows the low pressure system at 1 PM Saturday—
The German global ICON model has a more intensified low pressure system that takes a faster, more coastal track—
The Canadian global is somewhat similar to the GEFS—
All the models keep the storm warm enough for the precipitation to be RAIN for us on Saturday. (Some snow flurries early Sunday morning possible.)
Either way, Saturday looks stormy and Sunday looks to be windy and unsettled. This is an interesting scenario. Stay tuned.