Dry & Cold Week Ahead

FastCast—Monday, Dec. 12 to Saturday, Dec. 17:

After a chilly and wetter than average beginning of December, a stark change is ahead, with dry and cold weather expected for the entire week. A large high pressure ridge will build over Western BC and the Gulf of Alaska, pushing weather systems away from the Pacific Northwest. Expect decreasing clouds from Monday to Wednesday (with a chance of fog), with partly to mostly sunny conditions from Thursday into next weekend. In an abnormal twist for mid December, no rain is expected for the next week. Temperatures will be chilly, with highs only reaching the upper 30s to low 40s. Overnight lows will be cold, in the mid 20s to low 30s in the lowlands. It will be downright frigid in Eastern Washington, with highs in the low 20s to mid 30s and hazardous lows in the single digits to upper teens, with the potential for lows of -5 to -10º. Stay tuned as this cold pattern continues!

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A much different pattern is ahead for the Pacific Northwest, as cold and dry weather will establish itself over the next week, with little to no rain in sight. Let’s take a look at the forecast!

First up is the reason why this pattern is happening. Below is the European model forecast showing the massive high pressure ridge that will develop by midweek.

Notice the massive ridge over Western BC and the Gulf of Alaska. This ridge will influence weather over the Pacific Northwest, deflecting storms away from the region and allowing us to stay cold & dry.

How cold will it be? Let’s take a look at the European model forecast for Wednesday morning lows.

Expect lows in Western Washington in the upper 20s to low 30s, warmest near the water. Eastern Washington will be getting very cold, with overnight lows dipping into the low teens to mid 20s. Colder weather will be found later in the week…so stay tuned.

High temperatures will also be on the chilly side. Below is the European model forecast for high temperatures on Tuesday, though they will be similar all week.

Expect Western Washington’s highs to be in the upper 30s to low 40s, except into the mid 40s on the coast. Eastern Washington won’t get above freezing, with most of Eastern WA not getting out of the mid 20s.

Let’s take a look to see what’s in store for the extended forecast, as seen in outlooks from the NWS Climate Prediction Center for December 17-21. 

First, the temperature outlook, seen below.

This outlook shows a 60-90% probability of below average temperatures from this upcoming weekend to the next week.

The precipitation outlook confirms the cold and dry pattern that we talked about earlier.

This outlook shows a 40-50% probability of below average precipitation through next week. 

Cold weather is in the forecast for at least the next week…so stay tuned for more information!

Rain & Mountain Snow Through Saturday, Colder & Drier Ahead

FastCast—Friday, Dec. 9 to Monday, Dec. 12:

The next system is ahead for Western Washington later on Friday through Saturday, bringing lowland rain, mountain snow, windy conditions at times, and a chance of lowland snow in Whatcom County and near Hood Canal. For the lowlands, expect 0.5-1.25 inches of rain with this system, mainly from midday Friday to midday Saturday. The coast will receive 1.5-3 inches. With snow levels remaining relatively low at 1,000-2,000 feet, the passes and ski areas will pick up 8-18 inches of snow. Expect delays over the passes, especially from midday Friday through Saturday night. There is a slight chance of 1-2 inches of lowland snow near Hood Canal and in Whatcom County, mainly from late Friday to early Saturday. Winds with this system will peak from Friday night to early Saturday morning. Gusts will range from 25-35 mph in the lowlands to 45-55 mph on the coast and from Everett northward. A significant change will begin on Sunday, with no rain expected in the extended forecast. Conditions will remain cloudy through Monday. For the entire period, expect highs in the mid 40s and lows in the mid to upper 30s. 

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A typical winter weather system is ahead for Western Washington, with lowland rain, heavy mountain snow, and gusty winds, plus a chance of localized lowland snow. 

Let’s start with the European model forecast for rain through late Saturday night. Expect rain to start midday Friday, getting showery by midday Saturday.

The European model shows 0.75-1.25 inches of rain across the lowlands, with 0.4-0.9 inches north of Skagit County. Expect 1.5-3 inches on the coast.

Now let’s take a look at the NAM high-resolution forecast for rain through late Saturday night.

The NAM shows 0.5-1.25 inches across the lowlands, with less in the North Sound. The coast will pick up 1.5-3 inches.

Now for the mountain snow. Below is the European model forecast for snow through late Saturday night.

Expect 8-18 inches of snow at the passes and ski areas, with a potential for up to 24 inches. Most of Eastern Washington will get snow, with 6-14 inches around Wenatchee, 3-7 inches near Spokane and Yakima, and 1-4 inches in the Tri-Cities.

Brief accumulating snow of a dusting to 2 inches is possible around Hood Canal, Whatcom County, and in the Coastal Mountains.

Now for snow on the high-resolution NAM model’s snow forecast through late Saturday night.

The NAM forecast shows 8-18 inches at the passes/ski areas and 1-5 inches for most of Eastern Washington, except 5-10 inches north of US-2 and near Wenatchee, especially in mountain valleys. 

The NAM shows a dusting to 3 inches of snow around Hood Canal and between the Canadian Border and Vancouver BC, but not in Whatcom County.

Winds are expected with this system as well, with gusts of 25-35 mph in the lowlands and 45-55 mph on the coast and from Everett northward. Winds will peak from Friday evening through Saturday morning.

Finally, there is a big change ahead in the extended forecasts. This has even changed since the last blog post. Models are honing in on a colder and drier pattern next week, and that is reflected in the NWS Climate Prediction Center extended outlooks from December 14-18.

Below is the CPC temperature probability outlook for December 14-18.

This outlook shows a 60-90% probability of below average temperatures in mid-December.

Next, the precipitation probability outlook for December 14-18.

This is a new trend versus previous outlooks. This shows a 40-50% probability of below average precipitation into mid-December. 

Overall, this shows that a cold and dry pattern is likely starting sometime next week, so stay tuned for more details. 

Cool & Rainy Rest of the Week

FastCast—Wednesday, Dec. 7 to Friday, Dec. 9:

The FastCast is back! What a crazy past week, with super localized snow that caused lots of problems for lots of people, but never a widespread event! Thanks to all of you who followed along on my blog and Twitter during this event. We have transitioned back to a “normal,” albeit cold, pattern. It will be a typical pattern for the rest of the week. A system will impact the area from late Wednesday through Thursday, bringing lowland rain, mountain snow, and breezy conditions. Expect 0.2-0.4 inches of rain for the lowlands, 4-8 inches of snow at the passes, and winds gusting up to 30-35 mph, except up to 45 mph around Admiralty Inlet and Whatcom/San Juan Counties. Areas of showers will continue through Thursday and Friday. By late Friday, rain will total 0.5-1 inch in the lowlands (most near Everett), 1-3 inches on the coast, and 0.9-1.25 inches from Olympia south. Highs will be on the chilly side, only reaching the low to mid 40s through Friday, with lows in the mid to upper 30s. Some forecasts are beginning to show another bout of colder weather next week, so stay tuned.

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After a cold and snowy past week (for most) we have transitioned back to a typical winter pattern, but on the chillier side. Below is the European model forecast for total rain through 10 PM Friday.

Expect rain to begin late Wednesday, becoming showery on Thursday, with showers continuing on Friday. Totals for the lowlands will be 0.5-1 inch, most near Everett, with 1-3 inches on the coast and 0.9-1.25 inches from Olympia southward. Eastern Washington will pick up 0.1-0.5 inches, but most of this will be in the form of snow (especially north of I-90) as temperatures remain chilly.

Next, we’ll look at expected mountain snow through Thursday evening from the HRRR model.

The HRRR shows that the passes will get 4-8 inches through Thursday evening, so be prepared for delays when crossing the state. Additionally, Eastern Washington will receive a trace to inch of snow (except in the Lower Columbia Basin), and 1-6 inches north of US-2.

Below is the European model forecast for Wednesday’s highs. Wednesday is expected to be the warmest day of the week for the lowlands.

As you can see, “warmest” is used loosely. Highs across Western Washington will struggle to hit 45º, with Eastern Washington will reach the low 40s in the south and get very close to or just above freezing in the north.

Now, let’s take a look at the extended temperature and precipitation probabilities from the NWS Climate Prediction Center.

Below is the temperature probability outlook for December 12-16.

The CPC shows a 40-70% probability of below average temperatures for Washington, with the highest probability for the eastern tier of the state.

Next, the precipitation probability outlook for December 12-16.

This outlook shows a 33-40% probability of above average precipitation for most of Washington state into mid-December. This isn’t a very high probability, so precipitation near normal is a good expectation.

Overall, chillier and slightly wetter weather is expected through mid-December. Stay tuned!