Rare June Atmospheric River Bringing Rain, Muggy Conditions

From late Saturday through Sunday, a rare June atmospheric river will bring subtropical moisture, heavy rain, and muggy conditions to Western Washington.

Below is the UW forecast for water vapor for 5 AM Sunday.

The current of wet & moist air from the subtropics will bring the upcoming rain. This pattern looks more like winter...when atmospheric rivers frequent our coasts.  

How much rain will this system bring? The graphic below from NWS Seattle shows the rain forecast on Sunday.

Expect 0.5 to 1 inch of rain in the Puget Sound area, most from Seattle southward. There is also the possibility of heavier showers and rain rates, which could produce ponding and standing water on area roadways. Be prepared for more water on the roads than we usually have in June.

Below is the Weather Underground forecast for Puyallup.

Expect the most rain from late Saturday through Sunday. Saturday night will be warm & muggy, with lows only reaching the upper 50s. Sunday will be muggy, with highs in the mid-upper 60s and lows in the mid-upper 50s. Monday will be drier (showers possible), with highs in the low-mid 70s. 

Tuesday will be showery, but the atmosphere will be unstable (large decrease in temperature with height), and there is a chance of thunderstorms. Remember, "when thunder roars, go indoors!" I will have more on the Tuesday thunderstorm potential in the next blog.

The most abnormal part of this upcoming weather is the high dewpoints on Sunday. Expect dewpoints of 60 to 65 degrees, near record highs for Seattle. It will feel muggy outside, and will likely be one of the muggiest days in 10+ years, along with the potential for rain records to be broken.

Subtropical Moisture To Bring Rain & Muggy Conditions This Weekend

A muggy and rainy weekend is in store…weather uncharacteristic for the Seattle area.

Let’s start with the forecast from Weather Underground for Puyallup.

Remember that these rain amounts are subject to change, and won’t be exactly what’s reflected in other forecasts below. 

One thing to note is the relatively muggy conditions expected. Temperatures in the upper 60s to low 70s combined with rain and high humidity will create a muggy environment this weekend. Dew points will reach the 60s, making for some of Seattle’s muggiest days in the last 10 years.

This type of weather is relatively unusual for Western Washington, mainly because high humidity and warm weather don't normally coincide here. Now that we've covered the muggy weather...we need to examine what is causing it.

A current of subtropical moisture is being pulled north by a low center moving in this weekend. Below is the UW forecast for precipitable water (amount of water in the atmosphere) at 2 PM Sunday. (Notice the narrow current of moisture pulled from the subtropics and up the Pacific Coast).

According to NWS Seattle, this system's amount of precipitable water is "above the 99th percentile" for Western WA in June. (Translation: this very rarely happens).

This setup is reminiscent of a winter atmospheric river, but will be more on the showery side than days of steady rain. Regardless, much of our monthly rain total (normally ~1.5") will fall this weekend. 

Below is the UW forecast for rain through 5 AM Sunday.

Expect 0.3 to 0.5 inches of rain through Sunday morning. Most of this will fall on Friday and from late Saturday onward. 

However, even more rain is likely through Sunday evening. Then, showers will continue moving through the area until Tuesday. Below is the forecast for rain through the next 7 days.

The UW model shows a whopping total of 1.75 to 2.5 inches of rain in the Lowlands, most falling by Tuesday. I doubt that we will get all of that rain, but it is a good bet that the Lowlands will get at least 1 inch of rain through Tuesday. Even better is the possibility of 2+ inches of rain over SW Washington & NW Oregon, where drought is getting worse. This rain will make a dent in the drought coverage.

It is important to note that the highest rain totals will be from Seattle southward. The same area will also be prone to heavy rain showers with rain rates of 1+ inches per hour. This increases the risk of urban & small stream flooding and ponding. Be prepared!

Additionally, there is a slight chance of thunderstorms through the weekend. This chance will likely stay in the mountains, but be prepared for a rumble of thunder in the lowlands.

The upcoming rain will likely cause the drought coverage to decrease, especially over the dry areas of SW WA & NW OR. Eastern parts of WA & OR won’t be as lucky, with the exception of NE Washington, where 0.5+ inches of rain are possible.

In conclusion…a late spring soaker is expected this weekend, fueled by subtropical moisture. Mix in some muggy weather with high dew points, and it’ll be uncomfortable (by Washington standards). 

This rain will help to keep fire danger down as we head into warmer & drier weather.

Partly Cloudy & Showery Week Ahead, Lake Mead Update

A relatively calm week of weather is ahead. Let's start with the forecast for Puyallup from Weather Underground.

Thankfully, it will be warmer (mid to upper 60s, 70s by Saturday) in the coming days. Sunday was Seattle's coldest June day since 2012. Chilly June weather is commonly called "Juneuary" by local meteorologists, and a good explanation of this weekend is found on Scott Sistek's Q13 FOX Weather Blog:

https://www.q13fox.com/weather/juneuary-seattle-has-coldest-june-day-in-several-years

Below is the UW Model extended rain forecast through 5 PM Monday (June 14th). 

Through the next week, expect 0.5 to 0.75 inches of rain. Most will fall between late Thursday and next Tuesday.

Lake Mead Update:

Recently, due to extreme drought, Lake Mead’s water level has fallen below 1,075 feet, which means a federal water shortage declaration is likely later this summer. Below is a link to a very informative video from CBS News about the Lake Mead situation.

https://www.cbsnews.com/video/lake-meads-low-water-level-prompts-feds-to-consider-declaration-of-colorado-river-water-shortage/

The graph below shows how Lake Mead’s level is taking a nosedive, with no end in sight. The red line is 1,075 feet. The current level is around 1,072 feet.

Hoover Dam will stop pumping water when the level gets to 950 feet, 122 feet away. That will not happen this summer, or in the near future.

However, it is important to note that agricultural output will be impacted by the likely upcoming shortage declaration. Stay tuned for updates, and see an updated Lake Mead water level at the link below.

http://mead.uslakes.info/level.asp

Expect more updates about the drought as it intensifies as we enter into summer.