Active Tuesday, Major Change & Extended Warmth Ahead

 FastCast--Tuesday, June 4 to Sunday, June 9:

After a significant atmospheric river brought 1-2" of rain to the lowlands and 2-4" to the mountains & coast from Sunday to Monday, we have one more storm system before conditions dry out and warm up for the remainder of the extended forecast. Overnight Monday into Tuesday, expect rain at times with winds potentially gusting 30-40 mph, locally stronger, mainly on the coast and Everett northward. Gusty winds will slowly diminish through the day Tuesday, with showers remaining but decreasing in coverage all day. Most of the lowlands will receive an additional 0.15-0.3" of rain on Tuesday. Expect highs on Tuesday to reach the low 60s, with lows in the mid 40s to low 50s. Conditions will change dramatically from Wednesday onward, as a strong ridge builds over the Western United States. This ridge will bring a dangerous heat wave to much of the Southwest, while providing pleasantly warm conditions to Western Washington. Expect Wednesday to Sunday to be mostly sunny, with highs increasing from the mid to upper 60s on Wednesday to the upper 70s to low 80s on Saturday and Sunday. Some high clouds could bring filtered sunshine at times over the weekend. Lows will range from the mid to upper 40s on Wednesday morning to the mid 50s on Sunday morning, thanks to high clouds. Sunny & calm weather is expected to continue into next week, as of now.

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An interesting beginning to June continues overnight Monday into Tuesday, with another round of wind and rain expected.

Winds gusted 35-45 mph across the region early Monday morning, causing over 40,000 customers to lose power across Western Washington. Winds later caused two cruise ships to be unable to dock in Elliott Bay on Monday afternoon.

More wind will impact the state on Tuesday, peaking in the morning west of the Cascades and in the afternoon east of the Cascades. Below is the NAM high-resolution forecast, showing the higher end of potential winds.

This forecast shows another round of 35-40 mph gusts across the lowlands, with gusts of 40-45 mph for Island, San Juan, and Whatcom Counties. The coast gusts 40-50 mph in this forecast. Eastern Washington gusts 40-45 mph, with backcountry areas of the Cascades and Olympics gusting 45-55 mph.

Let's compare this to the European model's forecast, also showing peak winds on Tuesday.

This forecast shows gusts of 35-40 mph for most of the lowlands and the coast, except 40-45 mph around Whidbey and Camano Islands. Eastern Washington gusts 35-45 mph in this forecast, with gusts over 50 mph in some backcountry areas of the Cascades.

Regarding rain, expect rain at times overnight Monday into Tuesday, turning showery through the day, with showers gradually diminishing in coverage. Below is the European model forecast for rain through Tuesday night.

This forecast shows 0.2-0.3" for the lowlands, 0.5-0.8" on the coast, and 0.4-0.6" for Whatcom & Skagit Counties. The Cascades and Olympics will get an additional 1-1.8" with this system.

However, major changes are afoot as this system clears the region. A great way to see these changes is to look at our upper-level pattern of low pressure troughs and high pressure ridges.

Below is the upper-level forecast (at around 18,000 feet) from the European model, for late Monday night.

Notice the large area of troughing across the Northwest and over the Gulf of Alaska. This is what has given us cooler and wetter conditions over the past few days.

Now, let's compare to the forecasted pattern on Friday, seen below.

This is a huge change! All troughing is gone, replaced by a massive ridge that covers the entirety of the Western US. This will bring a mostly sunny pattern for at least a week. 

Let's take a look at how temperatures across the region will change through this week. We'll use the high-resolution NWS NBM model, looking at highs from Tuesday to Friday.

First, the NWS NBM forecast for Tuesday's highs.

Expect lowland and coastal highs in the upper 50s to low 60s, with some areas reaching the mid 60s. This is definitely on the chillier side for June. The Willamette Valley will reach the mid 60s, and Eastern Washington will reach the mid 60s to mid 70s.

Next, the forecast for Wednesday's highs.

Wednesday will be the first of a long stretch of pleasant days across the region. Expect lowland highs in the mid 60s to low 70s, coastal highs in the low to mid 60s, and Willamette Valley highs in the mid 70s. Eastern Washington will reach the upper 60s to upper 70s.

Conditions continue to warm up on Thursday, especially in Eastern Washington, as seen below.

On Thursday, expect lowland highs to increase to the upper 60s to mid 70s, with the coast reaching the mid to upper 60s, and the Willamette Valley reaching the low 80s. Eastern Washington will skyrocket to the upper 70s to upper 80s, hottest around the Tri Cities.

Finally, let's take a look at the forecast for Friday. It'll be an early June scorcher for some parts of the region.

Expect highs reaching the mid 70s to low 80s in the lowlands, the low to mid 70s on the coast, and the mid to upper 80s in the Willamette Valley. Eastern Washington will reach the mid 80s to mid 90s, with the Tri Cities likely reaching the mid 90s (upper 90s aren't out of the question either).

Conditions will remain somewhat similar on Saturday, although a significant chance of thunderstorms over SE Oregon and Idaho could change temperature forecasts due to cloud cover. Stay tuned!

Atmospheric River, Potential Flooding, and Gusty Winds to Begin June

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A strong atmospheric river, potential flooding, and even gusty winds are ahead as we begin June. This is an odd combination of weather conditions for June, and there will be some impacts across the region, so let's take a look at the forecast!

We'll start with the precipitable water forecast (amount of water vapor in the atmosphere), from the European model, for Sunday evening.

Notice the large area of high moisture content aimed at the Pacific Northwest. That's the atmospheric river that will impact the region from Sunday to Monday. An additional, faster-moving atmospheric river will move through from late Monday through Tuesday, before rain ends by Wednesday.

Next, let's look at how much rain is expected through late Tuesday night. We'll start with the European model forecast.

This forecast shows 1.2-1.75" of rain for the lowlands, with a rain-shadowed area from the Northern Kitsap Peninsula to Victoria BC getting 0.6-0.9". The coast will get 2-2.5", with the Cascade foothills and areas from Skagit County northward getting 1.5-2". The Cascades and Olympics will receive 2-4", with Eastern Washington getting 0.1-0.2" in the basin to 0.5-1" along the Cascades and along the Idaho border.

Let's compare this to a higher-resolution forecast, the NWS NBM model, also showing total rain through Tuesday night.

This forecast shows 1.3-1.7" for the lowlands, with a rain shadow from Seattle to Victoria (0.4-0.9"). The coast gets 2-3" in this forecast, with a substantial 3-7" in the mountains. In Eastern WA, significant rain (0.5-1") is limited to counties bordering Idaho, except in the Blue Mountains, where up to 2" is possible.

With significant amounts of rain (especially for June) expected, many rivers will rise, and some will reach bankfull. Below is the NWS forecast for river flooding.

Yellow squares mean a river reaches bankfull. This is possible on the Snoqualmie, Snohomish, Skykomish, White, Nisqually, Naches, Stehekin, and Skokomish Rivers, with most cresting on Monday.

There is one additional aspect to this incoming storm, and that is region-wide gusty winds. Winds will likely be strongest across the state on Monday, potentially remaining gusty for some areas through Tuesday. 

Below is the high-resolution NAM forecast for peak winds through Tuesday.

This forecast is definitely on the higher end of possibilities, showing gusts across the lowlands of 35-45 mph, with the Seattle metro area having gusts on Monday morning up to 40-45 mph, which would be very significant for June. This forecast also shows gusts of 40-45 mph across Eastern WA and 45-50 mph along the WA & OR coasts.

For a forecast showing somewhat lesser winds (at least for Western WA), check out the European model forecast below.

This forecast shows gusts of 35-40 mph from Tacoma northward, 35-40 mph along the coast, and potentially 40-45 mph for Island, San Juan, and Whatcom Counties. Notably, this forecast also has stronger winds for Eastern WA, with gusts of 40-50 mph, including 45-50 mph in Spokane.

This blog sure feels like it belongs somewhere in our storm season, but this is all happening in June! Be sure to treat this like a typical storm, with potential impacts being standing water, ponding, low visibility, and downed tree limbs. Stay safe!

Significant Atmospheric River Possible to Begin June

 FastCast--Thursday, May 30 to Tuesday, June 4:

A couple dry days are expected across the region to end the work week, after region-wide showers on Tuesday and Wednesday. On Thursday and Friday, expect partly sunny skies, with highs reaching the mid to upper 60s on Thursday and upper 60s to low 70s on Friday. Mostly cloudy conditions will return on Saturday, with highs in the mid 60s. There is also a chance of showers on Saturday, although no more than 0.2" of rain is likely (most from Everett northward). Lows from Thursday to Saturday will be in the mid 40s to low 50s. Then, on Sunday, a significant atmospheric river will move into the region. This will likely bring moderate to heavy rain at times from Sunday morning through Monday morning, heaviest later on Sunday. Precipitation totals across the lowlands will be quite heavy, likely between 1.25 and 1.75", with some areas getting upwards of 2" by Monday. However, some uncertainty remains as to precipitation totals, so stay tuned. A second potential atmospheric river looms for Tuesday, although this forecast is far less certain. With a strong atmospheric river bringing an influx of moist air, temperatures will remain steady from Sunday through Tuesday, with highs in the upper 50s to low 60s, and lows in the low to mid 50s. The impacts of this atmospheric river will likely include standing water, reduced visibility, and potential rises on area rivers.

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June will begin in abnormal fashion, with a significant atmospheric river likely to impact the region from Sunday to Monday. Let's take a look at the forecast!

We'll start with the forecast for precipitable water (amount of water vapor in the atmosphere) for Sunday afternoon, from the European model.

This forecast clearly shows that an atmospheric river is likely for the Northwest. Notice the large area of moisture moving directly into the region.

Let's compare this to the GFS forecast, showing the same thing, also for Sunday afternoon.

This forecast is nearly identical, with a large atmospheric river moving into the region, stretching across the Pacific Ocean.

The European and GFS forecasts being in such good agreement about this atmospheric river is a good indication of confidence in the forecast. With that in mind, let's take a look at possible rain totals, through Monday night.

We'll start with the European model, shown below.

The European model shows the lowlands receiving 0.9-1.75" of rain, with 1.5-2" on the coast, and 2-4" in the mountains. Eastern Washington gets 0.15-0.5", except up to 1.25" along the Idaho border. The high amount of rain in the Cascades and Olympics will bring the potential for rises on area rivers, so stay tuned for more on this possibility.

Next, let's take a look at the GFS forecast, also showing total rain through Monday night.

This forecast shows a couple different things. First off, it has higher precipitation amounts. Secondly, it has much more pronounced rain shadows, both NE of the Olympics and across Eastern Washington. The GFS shows 1.5-2" of rain across the lowlands, with a significant rain shadow from Seattle to the San Juans. In this forecast, the coast gets walloped with 2.5-3.5" of rain in 2 days, while the mountains receive 2.5-5". Eastern Washington is a whole different story, with a significant rain shadow for the western half, and 0.4-1.2" for the eastern half.

As you can see, there is some disagreement between the European and GFS forecasts. A good go-between is the NWS National Blend of Models (NWS NBM) high-resolution forecast, showing total rain through Monday night.

This forecast shows 1-1.5" for the lowlands, 2-3" for the coast, and 2-4" for the mountains. Eastern Washington gets 0.1-0.8", depending on location (least in the Columbia Basin, most along the Idaho border and in the Blue Mountains).

Regardless, this is likely to be a significant event, especially for early June, so stay tuned for updates as we get closer to the atmospheric river's arrival!