Wet Weather Returns to Western Washington

 FastCast--Thursday, April 25 to Monday, April 29:

After a relatively dry month, by Seattle standards, a rainy pattern will return to Western Washington to round out April. Thursday will be the rainiest day of the pattern, with 0.4-0.8" of rain across the lowlands. A chance of showers will persist every day through at least Monday, and likely beyond. Conditions will be overcast, except for some potential sunbreaks on Monday. High temperatures will be below average, with highs on Thursday only reaching the low to mid 50s, and remaining in the mid to upper 50s through Monday. Wetter and cloudier conditions will keep lows in the upper 40s through Sunday, decreasing to the upper 30s to low 40s by Monday. Despite a wetter pattern, snow will remain mostly above 5,000 feet, with a trace to 1" of snow possible at the higher passes through early next week.

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A wet pattern is returning to Western Washington after a relatively dry past few weeks. Let's take a look at the forecast!

We'll start with the European model forecast for rain through midday Friday.

This forecast shows areas from Seattle south and Mount Vernon north getting 0.5-0.8" of rain by midday Friday, with a rain shadow from Seattle to Mount Vernon, and west along the Strait, where 0.3-0.5" of rain is possible. The coast and mountains will receive 1-2" of rain, most in the Olympic Mountains. Parts of Eastern Washington, mainly mountainous areas, will get 0.1-0.3" of rain.

Let's compare this forecast to the high-resolution NWS NBM forecast, also showing total rain through midday Friday.

This forecast largely agrees with the European model, except it shows a lesser rain shadow, which is mainly confined to areas west of Whidbey Island. This forecast shows 0.5-0.9" of rain in the lowlands, with 1-2" on the coast, and up to 3.75" in the mountains, most in the Olympics and Southern Cascades.

What about mountain snow? Below is the European model forecast for total snow through midday Friday.

As we get later in spring, it gets harder to get significant snowfall. The winners for snow will be the volcanic peaks, with Paradise and Mount Baker being the only recreation areas to get some snow, as the snow level remains around 5,000 feet.

You'll definitely notice that temperatures will be on the cooler side, as seen below in the NWS NBM forecast for Thursday's highs.

This forecast shows highs on Thursday only reaching the low to mid 50s west of the Cascades. Eastern Washington will reach the low to mid 60s. Expect temperatures across the state to warm a few degrees on Friday.

We'll end this blog by taking a look at the extended outlooks for the end of April and first few days of May. These outlooks are from the NWS Climate Prediction Center (CPC). 

First, the CPC temperature outlook.

For April 30-May 4, this outlook shows a 50-70% probability of below-average temperatures in Washington, highest for Western Washington.

Next, let's see how the temperature and precipitation outlooks correlate.

This outlook shows a 40-50% probability of above-average precipitation for Washington through the first week of May. 

Stay tuned for more information, and enjoy the rainy weather while we have it! All the rain counts toward more water for the summer!

Warm Tuesday, Wetter & Cooler Pattern Ahead

FastCast--Tuesday, April 23 to Friday, April 26:

A warm day is ahead on Tuesday, with highs in the lowlands reaching the upper 60s to low 70s, under partly to mostly sunny skies. However, a major pattern change is ahead, with a shift to cooler and wetter conditions. Highs will drop to the upper 50s to low 60s by Wednesday, with overcast skies. Rain will move in on Thursday, continuing at times through Friday. Through late Friday, most of the lowlands will receive 0.4-0.8" of rain. High temperatures will also be on the cool side, only in the low to mid 50s. Expect lows in the low to mid 40s. (Check the bottom of the blog for a list of peak winds from the stronger-than-expected Saturday storm).

To see some video of the gusty winds and a timelapse of the Saturday storm, check out my YouTube channel by clicking the YouTube logo to the right!

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For the last time in awhile, the lowlands will have a warm and pleasant day, with highs likely reaching into the 70s. However, big changes are ahead, with a pattern change likely. Let's take a look at the forecast!

Let's start with the NWS NBM high-resolution forecast for high temperatures on Tuesday.

Tuesday will be warm and pleasant across Washington. Expect lowland highs to reach the upper 60s to low 70s, except in the mid 60s from Everett northward. The coast will reach the upper 50s to low 60s, the Willamette Valley will warm into the low to mid 70s, and Eastern Washington will reach the mid 60s to low 70s.

Temperatures will begin to cool down on Wednesday. Below is the NWS NBM forecast for highs on Wednesday.

Lowland highs will drop to the upper 50s to low 60s on Wednesday, with the coast dropping to the mid 50s and the Willamette Valley dropping to the mid 60s. Eastern Washington will warm into the mid 60s to mid 70s, getting warmer instead of cooling down as the high pressure ridge moves eastward.

Temperatures will cool further by Thursday, as seen in the NWS NBM forecast.

Highs across Western Washington and Oregon will drop to the low to mid 50s. Eastern Washington will drop to the low to mid 60s, except the upper 60s around the Tri-Cities. 

As the temperatures cool across the region, weather systems will begin to move in. A system will spread rain across Western Washington on Thursday, with showers continuing on Friday, and likely into the weekend. The European model forecast below shows total rain through Friday night.

This forecast shows the lowlands getting 0.5-0.8" of rain, except some areas north and east of the Olympics will get less rain in a rain shadow. Areas from Olympia south will receive 0.8-1.3", and the coast will get 1.3-1.6". Even Eastern Washington will get in on the rain, with 0.1-0.3" for most of the region. The mountains of NE Washington will get up to 1" of rain.

So...what's the cause of this pattern change? Take a look at the European model forecast below, showing the high and low pressure systems at around 18,000 feet late Thursday.

This shows a broad area of troughing over the Pacific Northwest by Thursday. Troughing will likely continue across the Northwest through the end of April...so stay tuned!

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Saturday Peak Winds:

NAS Whidbey: 49 mph

Shelton: 46 mph

Port of Tacoma: 44 mph

Bremerton: 43 mph

Camano Island: 42 mph

Lake Stevens: 40 mph

Tacoma Narrows: 39 mph

Boeing Field: 38 mph

Sea-Tac Airport: 37 mph

These winds caused over 22,000 PSE customers to lose power, with over 10,000 customers losing power in the Seattle City Light and Snohomish PUD service areas as well.

Rapid Saturday Evening Cooldown to End Warm Stretch

FastCast--Friday, April 19 to Tuesday, April 23:

Friday will be a warm and beautiful day across Western Washington. Highs will likely reach the upper 60s to low 70s, with easterly gap winds bringing warming and gusts of 30-40 mph for the foothills. High clouds will move in on Saturday, with highs reaching the upper 60s to low 70s by mid-afternoon. Then, a strong marine push combined with an incoming cold front will bring a rapid cooldown, with temperatures dropping 15-20° within 3 hours by early evening. Winds will briefly gust 30-40 mph across the region, and showers will move through. A Convergence Zone setting up between Northern King and Skagit Counties will bring a chance of thunderstorms north of Everett on Saturday night. By Sunday, conditions will be partly cloudy, with highs in the mid 50s to low 60s. Monday will be partly cloudy, with highs increasing to the upper 50s to low 60s, followed by mostly cloudy skies and highs increasing further to the mid to upper 60s on Tuesday. Overnight lows through Tuesday will be in the low to mid 40s. By the middle of next week, we'll likely start to cool down again.

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A warm and pleasant day is expected on Friday, followed by another warm day on Saturday, with a marine push/cold front combination on Saturday evening bringing a major cooldown, gusty winds, and showers. Let's take a look at the forecast!

We'll start with the NWS NBM model high-resolution forecast for highs on Friday.

Expect highs in the lowlands to reach the upper 60s to low 70s, with some areas in the North Sound remaining in the mid 60s. The coast will reach the mid to upper 60s, the Willamette Valley will reach the low to mid 70s, and Eastern Washington will reach the mid 50s to low 60s in the north and mid to upper 60s in the south.

Part of the reason that the lowlands will be much warmer than Thursday will be the presence of easterly gap winds (known as "Cascadia" winds). The NAM high-resolution forecast below shows the expected wind gusts through early Saturday.

Notice gap winds gusting 30-35 mph for parts of the lowlands, roughly from Federal Way to Seattle, with areas such as North Bend and Enumclaw reaching 35-40 mph. Also notice that the Portland metro area will have easterly gusts of 35-45 mph, strongest near the Gorge.

Now, let's take a look at Saturday's highs, also from the NWS NBM model.

Saturday will be warmer for most of the region, despite there being near 100% cloud cover due to high clouds. Expect the lowlands to reach the mid 60s to low 70s, with the coast only reaching the low 60s, the Willamette Valley also reaching the mid 60s to low 70s, and Eastern Washington reaching the mid 60s to low 70s.

However, this forecast is somewhat deceptive. Saturday's highs will occur around 2-3 PM, earlier than typical highs. Below is the NAM forecast for temperatures at 2 PM Saturday.

At 2 PM, the lowlands are in the upper 60s to low 70s. However, notice that the coast has dropped to the low 50s. Highs on the coast will occur around midday.

Around 2 PM, a marine push/cold front will be located between the coast and the lowlands, moving quickly eastward. To see this, let's take a look at temperatures by 5 PM Saturday.

By 5 PM, the marine push/cold front will have hit the lowlands, with temperatures dropping rapidly, all the way down to the low 50s in Olympia, the mid 50s to low 60s along the I-5 corridor. Notice how the foothills are still in the mid 60s at 5 PM.

However, by 8 PM (seen below), the marine push/cold front will have advanced through the entirety of Western Washington, bringing much cooler temperatures in its wake.

By 8 PM, all of Western Washington has dropped to the mid 40s to low 50s, with Eastern Washington cooling rapidly into the low 50s to low 60s.

A great visualization of the rapid temperature decrease is found on this map below, showing the NAM model forecast for temperature change from 3 PM to 6 PM Saturday.

This shows that as the marine push/cold front moves across Western Washington, temperatures will drop 15-20° within 3 hours. This temperature drop will occur across the entire region as this feature moves through.

Another impact of this feature will be a brief shot of wind through the region. In addition to strong westerly winds through the Kittitas Valley and some gusty winds across parts of Eastern Washington, gusty southwest winds will move through the lowlands on Saturday evening. Below is the NAM high-resolution forecast showing gusts at 6 PM.

Around 6 PM Saturday, as the marine push/cold front moves through the lowlands, expect winds to increase, with brief gusts of 30-35 mph, with some areas gusting up to 40 mph, especially near the water and in the San Juan Islands.

One final weather impact to be aware of with this feature is that in addition to bringing a brief round of showers from late Saturday afternoon through the evening, a Convergence Zone band between Northern King and Skagit Counties will bring a slight chance of thunderstorms late Saturday night. Below is the European model lightning forecast for Saturday night.

This forecast shows lightning potential over Island, Skagit, and Snohomish Counties. This outlines the potential for thunderstorms in this Convergence Zone band. There is also a very low, but non-zero chance for isolated thunderstorms along the main marine push/cold front as it moves across the lowlands on Saturday evening.

Stay tuned for more information via Twitter and Pacific Northwest Weather Watch YouTube (link on right side of blog) about this dynamic feature on Saturday, and enjoy the sun & warmth while it lasts!