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