Update from Chief Meteorologist Morgan Palmer (Monday night)
A very turbulent weather week is ahead for Western Washington, with some very warm and muggy conditions Tuesday into Wednesday before strong thunderstorms herald the return of cooler air late Wednesday.
Some patchy morning fog is possible Tuesday morning but as skies partially clear through the day, warm and muggy conditions are expected. Highs will be in the 60s across the northern half of the area with highs near 70 in the Seattle area and low 70s across the South Sound and south interior. We will enjoy some sunshine.
The warm, humid conditions remain in place for Wednesday as a potent disturbance approaches the Pacific Northwest. Early in the day Wednesday through early afternoon, there will be a few spotty showers with a slight chance of a thunderstorm, but the greater instability for thunderstorms arrives late Wednesday afternoon across southern parts of the area through Wednesday evening for the rest of the area.
The ingredients for strong storms look to be there in abundance for Wednesday afternoon into Wednesday night, possibly similar to thunderstorms we experienced last August 17, when thousands of lightning strikes occurred in Western Washington!
In fact, lightning will be the greatest hazard to people during Wednesday afternoon and Wednesday night as fast-moving storms from south to north pass through the region. Outdoor activities planned for Wednesday afternoon and Wednesday evening should be reconsidered due to the threat of frequent and deadly cloud-to-ground lightning.
I’m looking at the greatest risk starting well south of the Seattle area by 3-6 p.m., spreading north through Puget Sound from 5-11 p.m., and moving north of the Canadian border after midnight. This timing will be fine-tuned as we get closer to the event, but it’s looking more probable that the evening hours will be “prime time” for storms.
There will also be a chance of hailstones growing to half-inch to one inch in diameter and isolated thunderstorm wind gusts over 55 mph. The Storm Prediction Center has placed much of Western Washington in a “marginal” risk of severe thunderstorms (hail to one inch or larger in diameter and wind gusts 58 miles per hour or greater). While this is the lowest on their scale of severe weather risk — a one out of five — a “marginal” risk means the potential is greater than five percent of these severe conditions for any given point. That is greater than we usually experience!
The tornado threat is low in the lowlands but overall a greater chance than we typically see. Storms that do begin rotating will need to be watched closely for the chance for an isolated tornado. Of particular interest will be any rotating storms nearer the Cascades, as wind currents and rotation could be “tightened up” as storms enter foothill and mountain locations.
Torrential rainfall will occur with these storms as well, posing a risk for drivers especially after dark Wednesday.
Thunderstorms will be moving northward at a rapid clip, so it will be important to keep abreast of conditions using the KIRO 7 Pinpoint Weather App. It might appear calm one minute, but then storms will quickly move in.
Storms look to clear the region by early Thursday morning as colder air moves into the area. We’ll be back in the 50s for highs with rain showers Thursday through Friday.
Rainfall from the thunderstorms Wednesday could push the Skokomish and Snoqualmie rivers back to flood stage by Thursday.
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An atmospheric river is over Western Washington Monday morning, with pockets of rain and some gusty weather.
Sunday was a really active day with some record-setting rain, windy weather and some very minor river flooding.
We do have a handful of river Flood Warnings, but most of the rivers will crest just barely above flood stage later Monday morning.
We’re mild in the low-50s Monday morning and will stay mild the next couple of days.
The front is stalled over the area, but thanks to the rain shadow, we’re not seeing much rain in Seattle or Tacoma.
The more consistent rain Monday will be around Everett north to the border and in the Olympics and North Cascades.
For example, we could see around a half inch in Bellingham, but more like a tenth of an inch or less in Seattle, Tacoma and Olympia.
Expect some light rain at times, but again, the more consistent and heavier rain will be to out north.
Wind will stay around 10 to 15 mph out of the south, which is much calmer than yesterday!
Highs will be in the upper 50s and lower 60s, and snow levels will be around 7,500-8,000′.
The rain will taper even more from south to north Monday night, with just clouds and mainly dry weather overnight.
Tuesday will be warm! We’ll have some clouds early and then increasing sunshine turning partly cloudy with warm daytime highs in the upper 60s and lower 70s!
The record for tomorrow is 64° and we will easily take care of that.
Clouds and showers will increase on Wednesday with mild weather and unstable conditions, thunderstorms with scattered showers will be possible.
There is the potential for the thunderstorms to be widespread and possibly even strong.
The Storm Prediction Center has put our severe thunderstorm chances in the marginal category for Wednesday.
Marginal is ranked the lowest in the category, ranked 1 out of 5, with 5 being High or the highest.
This is something we’ll watch closely because the showers and storms will be sporadic and there are two waves of energy coming in.
One earlier in the day and the one in the afternoon would have the higher likelihood of stronger or potentially severe storms.
We have decided to call a PinPoint Alert Day to get the messaging out now, so everyone is prepared for the storms.
We’ll go back to low to mid-50s by Thursday and Friday with more showers and even some breezy weather possible on Friday.
This weekend will have scattered showers in the mid 50s.... normal for this time of year in Spring.
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