Western US weather
A few more opportunities for rain coming to the dry Northwest through mid-month
By Brian Thompson , AccuWeather meteorologist
7/05/2019, 11:42:18 AM
Despite July typically being a very dry month in the Northwest, there are a few chances for rain on the horizon in the next week or two, especially across western Washington and northwestern Oregon.
While it certainly doesn’t look like this will be drought-busting rain in Washington, where it has been very dry for the past several months, the rain will be a welcome sight.
Rainfall amounts are solidly running above the month-to-date average in Seattle and Portland. In fact, Portland received 0.54 of an inch of rain on July 1, which is just shy of the 0.65 of an inch they average for the entire month of July. That was also the day that an EF-0 tornado touched down in Portland.
Seattle had a similar day on July 2, picking up 0.43 of an inch of rain, a good chunk of the monthly average of 0.70 of an inch.
This wetter-than-average pattern appears poised to continue over the next 10 to 14 days, with several different impulses set to move through.
In the upper levels of the atmosphere, there is currently a huge ridge over Alaska which is causing phenomenal warmth over the state. This anomalous ridge is blocking the pattern up over the North Pacific, really preventing things from moving.
Because of this, an upper-level low straddling the British Columbia/Washington border will hang around through the weekend, bringing unsettled weather to some areas. The highest risk area for showers and even some thunderstorms through the weekend will be from the Northern Cascades eastward through the Methow Valley, far northern Idaho and eastward into Montana.
Eventually, the large ridge over Alaska will separate itself from the main flow later this weekend, and upper lows will start to move underneath this ridge across the North Pacific. As things start to move again, the upper low in the Northwest will move and could help to spark locally severe storms across Montana on Sunday.
As that low moves out, another one will be right on its heels heading into Tuesday and Wednesday. This will bring a renewed threat of showers and even a few downpours and thunderstorms over western Washington and Oregon.
There may be another disturbance swinging through heading into next weekend around the middle of the month, but there is far more uncertainty that far out.
The stormy pattern will likely yield the most rain across the Olympic Peninsula and across far northern Washington, where some places could get more than a half inch of rain through next weekend, especially in areas that get thunderstorms.
These are areas that need the rain. Below is the Drought Monitor from Thursday:
The severe drought has been fairly consistent from the Seattle area back through the Olympic Peninsula. Another area of severe drought has been quietly showing up over the past few weeks across far northern Idaho and the northeastern corner of Washington. Relief from these drought conditions will likely be minimal in this pattern, but it may help prevent things from getting worse in the short term.
With these impulses being aimed mostly into British Columbia, that will limit rain opportunities east of the Cascades, so it may be difficult to squeeze much rain out in places like Spokane, Yakima and the Tri-Cities. However, any spoke of energy that breaks off one of these lows could be enough to spark some spotty thunderstorms.
The main downside with the threat of thunderstorms will be the concern for lightning sparking wildfires in the dry brush, especially at times when the wind is blowing harder. Lightning has been the main trigger of fires across Alaska in the past month or so and is typically the primary trigger for fires in the Northwest.
Thanks to the dry conditions, soil moisture levels are running below normal and the brush has been drying out over the past month or two. This will increase the risk of lightning starting fires (in addition to human-caused fires) over the next several weeks and even into August.
The most recent fire potential outlook issued by the National Interagency Fire Center continues to highlight western and northern Washington as well as western Oregon as concern areas for wildfires from July through September. The red areas below are the places of most concern in July.
You can view the full report on their website, which contains the fire potential outlooks for each month from July to October as well as a lot of other good information. They show a growing concern in California as we head into autumn, which is pretty typical.
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