Saturday’s rain was refreshing, wasn’t it? Some spots saw far more rain than forecast as a weak upper-level low slowly drifted southeastward from the Olympic Peninsula through the Willamette Valley and into Central Oregon, while other spots saw hardly any rain at all. This was particularly true for the Puget Sound region, where a local area of dynamic uplift associated with the upper-level low created a band of showers that encircled the downtown Seattle, bringing over 0.30 inches to Tacoma and North Seattle/South Everett while giving as little as 0.01 inches to Renton equidistant from the two.
Credit: NWS
Paine Field (Everett) was the region-wide winner with 0.60 inches on Saturday. Amounts were more uniform over the Portland metro area and NW Oregon/SW Washington, where 0.10 – 0.20 inches were common.
Credit: NWS
The normally-dependable UW WRF model completely missed the Puget Sound precipitation but did a decent job with the precipitation over the Portland metro area and NW Oregon/SW Washington. On a side note, one of my pet peeves is the saying ‘weather forecasting is sometimes as much of an art as science,’ which is oft repeated during blown forecasts. Weather forecasting is 100% science, through and through, so sometimes our existing scientific knowledge fails us. But communicating the forecast- ah! That’s where art comes in.
Credit: University of Washington
Current Conditions and Monday’s Forecast:
The atmosphere is currently in a very “congested” configuration, with a large ridge of high pressure off the West Coast causing the jet stream to split into a southern branch over Southern California and the Baja Peninsula and a northern branch all the way to the Gulf of Alaska and Anchorage. Though we are not in an El Nino, this type of pattern – a split jet stream off the West Coast with the Pacific Northwest between the two branches – commonly occurs during El Ninos.
GOES-17 loops are always remarkable, but today’s was especially cool for the Pacific Northwest. Low clouds over the Western Washington lowlands burnt off this morning as the sun mixed out a low-level inversion, but clouds filled back in again from the mountains inward towards (but not over) Puget Sound and the Strait of Juan de Fuca. The same daytime heating that mixed out low clouds helps create convection and over the mountains and, to a lesser extent, the lowlands, but the cool ocean waters keep the surface over the water cool enough to prevent convection and daytime cloud formation. The morning clearing and afternoon clouds filling back in gives the appearance of the atmosphere “breathing,” at least to my eyes.
This ridge will move slightly further east on Monday and will be centered over Western WA/OR instead of the I-5 corridor, resulting in stronger large-scale subsidence and slightly less afternoon convection than today. Patchy low stratus is likely across Western Washington and the Willamette Valley, but this should burn off a few hours after sunrise on Monday, resulting in mostly sunny skies in the afternoon.
Transition Tuesday, Wet Wednesday
This split flow regime will begin to buckle on Tuesday, and by Wednesday, we’ll have a strong, consolidated, singular jet pointed directly at the Pacific Northwest. A fast-moving open wave will ride along this jet Wednesday and slam right into NW Oregon/SW Washington, giving us 0.25 – 0.50 inches of rain. It doesn’t sound like much, but after how dry we’ve been (Portland has only seen 0.27″ of rain this April) it will feel like a deluge.
Showers will continue Thursday and we’ll finish the work week on a dry note, but models show another system dropping a long, somewhat juicy front through the Pacific Northwest for the weekend. Nothing that would give us a ton of rain or add to our now rapidly-declining mountain snowpack in any fashion, but definitely better than nothing!
Drought Concerns:
Finally, we are unfortunately getting to the point of the year where I am a bit concerned about our drought prospects for this summer. The US Drought Monitor has us in a “moderate” or even “severe” drought, and with us quickly approaching “dry season” and no super-wet patterns in sight, our chance of making up this drought before summer is fast decreasing. To make matters worse, long-range forecasts are calling for warmer and drier-than-average weather this summer. Just in case you needed some other stuff to worry about. :/
But in the meantime, let’s not worry about what we can’t control, and rejoice at the rain we’ll see this week. 🙂
Take care,
Charlie
