Warm weather and threat of lightning increases wildfire danger

Warm weather and threat of lightning increases wildfire danger
A sun-kissed Seattle skyline with Mt. Rainier in the background on July 15, 2013 -- the 18th day in a row with no measurable rain in Seattle. (Photo: Puget Sound Clean Air Agency Visibility camera)

SEATTLE -- A warm-to-hot stretch of weather is on tap around the Northwest this week and now with a threat of thunderstorms, wildfire danger risk is on the rise.

Monday's weather will remain pleasant and tranquil, with sunny skies and an afternoon seabreeze keeping highs in the upper 70s to low 80s and no pesky thunderstorms.

However, the weather pattern gets quite complex for Tuesday as changes in both the lower and upper levels of the atmosphere will conspire to make for a hotter day and then a potentially stormy night.

During the day, a thermal trough is expected to move into the region from Eastern Washington, which will provide an east-northeast wind along the ground. Those are the winds that warm when they sink down the Cascades and as a result, highs are expected to push into the upper 80s around the Puget Sound region -- perhaps even a few spots to break 90 in the usual warm spots south and east of Seattle. Even the coast should warm into the low 80s.

But high above, a weak upper level low pressure system will push in some high-level moisture in from the south that will destabilize the atmosphere and create a chance for widespread thunderstorms. The storms are expected to develop in Oregon early Tuesday then move into Washington from the south as the day progresses, potentially reaching the Puget Sound area as early as the afternoon or evening. The bulk of the storms will be in the Cascades and Olympics but all areas have a chance of getting storms, with the peak of the storms during the overnight hours Tuesday into about late morning Wednesday before they taper off as the low moves away.

With dry air on the ground at first, some of the storms may not have any rain as it evaporates before it reaches the ground, but the lower air mass will gradually moisten, giving the air a increasingly muggy feel and allowing a little rain to reach down here. While the storms aren't expected to bring any extended rain, they could have frequent lightning.

The lightning is of the main concern as it has been well over two weeks since any significant rain has fallen around the Puget Sound region (18 days to be exact for Seattle, counting Monday) and lightning-sparked wildfires are a concern.

It's an even greater concern for parts of Eastern Washington and northeastern Oregon where a Fire Weather Watch is in effect for much of the Columbia Basin due to heat, dry weather, and the threat of thunderstorms. Fire weather forecasters with the National Weather Service say the Cascades are in a little better shape since it hasn't been as dry for as long, but still a risk of wildfires under the right conditions.

The thunderstorms should taper off by midday Wednesday, which will also be a little cooler in Western Washington thanks to a light push of marine air. Highs should drop into the lower 80s.

The extended forecast computer models keep it very warm and very dry across the region through the weekend and into next week. There is still some variability in their opinions for high temperatures but the general theme is that 80s are a good bet for several days (it'll just be whether it's low, mid, or upper 80s that are still a bit uncertain.)

As for rain, there are no significant threats of rain foreseen for at least the next two weeks, leaving the possibility that if measurable rain does not fall at Sea-Tac Airport Tuesday night or Wednesday morning with the passing thunderstorms, 2013 might be the eighth time in Seattle's history that no measurable rain fell in July.