Christmas week has arrived, bringing along rain, wind, and mild temperatures. Despite starting with chilly mornings and clear skies, December 2024 has turned unexpectedly warmer and wetter. Currently, we are experiencing temperatures that are 2° above normal, which can be attributed to the unusually high temperatures we’ve been having for the past 10 days.
Lately, we have experienced mild and rainy weather as a result of a Pacific jet stream targeting the West Coast. This weather pattern brings ample cloud cover, which helps to maintain above-freezing temperatures during the night. Now, let’s take a look at what lies ahead.
A FEW KEY POINTS
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- I count six “shortwave troughs” moving through the region in the next 7 days. Those are little “dips” in the jet stream, often preceded by an organized frontal system (a mix of cold/warm/occluded fronts) with clouds and steady rain/snow. This is an active weather pattern ahead!
- These systems will be a bit stronger later Christmas Day through Sunday, leading to heavier rain and possibly stronger wind. Over the past week, we’ve been getting most of the storms in their “decaying” phase. They are much stronger 100s of miles offshore and weaken as they approach the coastline. The formation area for these storms will be a bit closer later this week.
- At this point I don’t see a major pineapple express or atmospheric river sitting over our region for 2 or more days. Thus the likelihood of widespread flooding is still low. But soils will be getting saturated, rivers will be running high, and possibility of mudslides increases.
- We’ll be watching development of low pressure centers very closely, since in this pattern a small little low can sudden appear with just 2-3 days warning. BUT AT THIS MOMENT, we don’t see a windstorm for the western valleys of OR/WA
- All models are pointing toward a pattern change toward cooler and a little drier. Note that’s not DRY, but drier.
- It’s clear there will be no lowland snow west of the Cascades the next 9 days. That will wrap up December AND 2024.
The holiday season brings with it a delightful and festive graphic that perfectly captures the spirit of this time of year.
Another powerful storm is expected to form within the next 24 hours, known as a bomb cyclone. However, this storm will remain well offshore and pose no immediate danger. According to the Euro model, the atmospheric pressure of this low-pressure system is forecasted to decrease from 994mb around sunrise on Monday to 960mb by 10pm later that day. This rapid drop of 34 millibars is expected to occur in less than 18 hours. Tomorrow, we can expect a period of strong easterly winds, followed by southerly winds along the coastline in the evening. It’s important to note that this storm is too far offshore to cause a windstorm.
Two additional deep low-pressure systems will develop and approach Vancouver Island on Thursday and Saturday. Fortunately, these systems are not expected to bring any significant wind damage to our coastlines and valleys.
However, I am keeping a close eye on a frontal zone that is expected to linger near the coastline during the latter half of the week and weekend. There is a possibility that a low-pressure system could suddenly form just offshore or move onto the Washington coastline. At this point, there are no indications of any imminent threats.
Get ready for some rainy days! From Thursday to Sunday, we can expect a substantial amount of rainfall. The western valleys could receive around 2-3 inches during this period.
However, there is a possibility that certain areas might experience even more precipitation. The models suggest that an atmospheric river may hover over southern Oregon throughout this time, and it could even extend into next Monday. The Euro model has consistently shown this pattern in the 5-day rainfall forecast from Thursday to Monday.
This evening, the GFS and GEM models indicate a significant increase in rainfall, particularly in the southern half of western Oregon.
The Canadian GEM model and the GFS model both predict even heavier rainfall, with the model ensemble mean suggesting that the Willamette Valley could receive up to 4 inches of rain by Monday.
This is not going to break any records or cause a guaranteed flood, but it would be the wettest weather we’ve experienced this season.
I’m closely monitoring this situation as well. It’s always difficult to predict where a frontal boundary will stall for a couple of days, if it does happen. This concentrated flow of moisture has a tendency to change direction unexpectedly.
The ski season in the mountains is in need of some assistance. Although there was a significant snowfall a week ago, the recent temperatures in the 30s and 40s have compressed and softened the snow.
Skibowl opened briefly last Thursday, but had to close the next day due to the limited remaining snow on the lower slopes, which is currently only about 18″. At a higher elevation of 5,000 feet, the base has decreased from 46″ to 28″.
While there is a substantial amount of moisture expected for the Cascades, the snow levels will tend to be slightly higher than ideal. This doesn’t mean it will be as warm as a pineapple express, but the storms will be just a little warmer than desired.
As a result, we can expect approximately a foot of snow in the upcoming week at Government Camp, with rainy or mixed periods as well. Higher up at Timberline and Meadows, there may be up to 3 feet of snow.
When it comes to travel weather, there’s some good news. You won’t have to worry about crossing the Coast Range until next weekend, thanks to the high snow levels.
The Columbia River Gorge will remain clear, and even the Blue Mountains over Meacham won’t be too difficult to navigate.
There might be some light snow mixed with rain at times. As for I-5 through the Siskiyous and Mt. Shasta heading to California, it should be mainly okay. However, it’s important to keep an eye on Thursday as a wet storm could bring snow down to those elevations.
WAY OUT THERE
There are indications that an upper-level ridge may form over or west of the West Coast in the first week of 2025. The location of this ridge is crucial in determining the weather conditions in the Pacific Northwest.
If the ridge forms directly overhead, we can expect a dry and cool pattern with the development of inversions, similar to what we experienced in early December. However, if the ridge develops farther west, it could open the door for cold Canadian air to move southward.
Currently, most models and their ensembles suggest that the first option is more likely, although it is still around 10-15 days away. At this point, it is fair to say that the situation is as follows:
The end of December 2024 was relatively mild, but as we move into 2025, there is a likelihood of cooler and potentially drier weather ahead. However, it is uncertain if it will become much colder.
The first half of this cool season has been marked by mild temperatures and above-average rainfall. As we move into the second half, we may experience colder and wetter conditions typical of La Niña winters.
However, only time will tell. In the meantime, let’s enjoy Christmas and any other holiday or tradition we celebrate. Here’s a look at the weather forecast for the next three days: