Significant Cooling Ahead, Rain on the Horizon

8 out of the first 9 days of September have had a high of 75+ degrees. However, that is about to change. A significant cooling trend is expected, and temperatures at or above 75 degrees aren't expected for at least the next 10 days.

Thursday's highs are below. Widespread readings of 80-84 degrees were observed, with temperatures up to 85-86 degrees in the Eastern Lowlands.

We are in for a major temperature change in the coming days. Below is the Weather Underground forecast for Federal Way.

Cooling of around 10 degrees is likely for Friday. Highs remain in the low 70s through next Tuesday, with lows in the upper 40s to low 50s, except a bit warmer on Saturday night.

Now...what you've been waiting for...rain!!!

Below is part of the extended Weather Underground forecast for Federal Way at the end of next week (9/16-18).

Rain probability increases Thursday night, peaks on Friday, and becomes more showery on Saturday. (Take the chance of thunderstorms on Saturday with a grain of salt). Forecast models show up to 1.1 inches of rain through around the 19th. Bottom line: increasing chances of rain are expected by the end of next week! 

Something to look forward to! Stay tuned!

Chance of Showers Overnight & Another Round of California Smoke

Tuesday was mostly sunny, but you probably noticed smoke aloft moving in throughout the day. It was most apparent as the sun sank lower in the sky, as seen around 7 PM in Federal Way.

The sun became increasingly red/orange, and the layer of smoke was evident on the horizon. We'll talk about smoke soon, but first the forecast.

Below is the Federal Way forecast from Weather Underground.

There is a chance of showers overnight due to a system moving through. Wednesday will be in the upper 70s to low 80s, with temperatures in the low to mid 70s from Thursday to Sunday. Low temperatures decrease from the upper 50s on Tuesday to the upper 40s by Sunday night.

Regarding that chance of showers overnight Tuesday into Wednesday, there is also a slight chance of thunderstorms from 2-8 AM Wednesday. Instability doesn't look great, so this chance isn't very likely.

However, some rain is possible. Below is the 24 hour rain forecast from the UW model, ending 5 AM Wednesday.

Let's just say that this will be very little rain, with a trace to 0.03 inches for Puget sound and up to 0.2 inches for parts of the mountains & coast.

I don't know about you, but I am very excited for the day when we have a real rainstorm! Hopefully within a month!

Now for the smoke forecast...this is all vertically integrated smoke (smoke aloft). 

Below is 7 PM Tuesday. Moderate concentrations of smoke over Puget Sound, with more moving north.

The thickest smoke will be overhead early Wednesday morning. The forecast for 5 AM Wednesday is below.

At 5 AM, thick smoke is present over Western Washington from Puget Sound eastward. Soon after this (by 7-8 AM), westerly winds will clear out most of the smoke.

By 1 PM, the skies are almost clear, with a slight haze remaining.

Conditions get progressively better west of the Cascades, and by 7 AM Thursday, skies are free of smoke on the west side of the mountains in Oregon and Washington.

In Eastern Washington, conditions will be largely dependent on if you are downwind of a wildfire. The Schneider Springs Fire (94,206 acres, 14% contained) will likely create a large smoke plume by Wednesday evening, impacting areas from Yakima northeast. Additional (smaller) smoke plumes will be present from other fires.

Eastern Oregon and Idaho won't be as lucky, as their location relative to massive fires in California will allow smoky skies to continue.

One Year Ago (September 7-8, 2020):

Very strong winds moved through the gaps in the Cascades in Oregon and Washington, resulting in massive wildfires in Oregon & Eastern WA and a widespread power outage event in the South Sound. These winds, some of the strongest ever observed in Western WA during September, sparked the Sumner Grade Fire early on September 8th. The fire burned over 800 acres and destroyed multiple homes before reaching 95% containment on the 16th.

The photo above was taken by Bonney Lake WX on Twitter on September 8th, as the fire grew and moved southward. The area was evacuated just hours later.

I think we are all glad to not be experiencing an extreme fire weather event this year!

Fall & Winter Outlook: La Niña Likely Again

As we begin September and fall approaches, one thing on the mind of many Pacific Northwest residents is what to expect during the storm season. Fortunately, by this time of the year, we have a good idea of the general conditions and trends to expect this fall and winter. 

The weather patterns across parts of the Northern Hemisphere are influenced by the sea surface temperatures (SST) of the equatorial Pacific Ocean. These patterns are El Niño (warmer than average SST), neutral (normal SST), and La Niña (cooler than average SST).

This winter will most likely be a La Niña winter, which generally means above average rain, above average mountain snow, and a higher potential for lowland snow.

The forecast graphic below from the NWS Climate Prediction Center shows the probability of La Niña, Neutral, or El Niño in 3-month periods.

The blue bars on the graph shows the probability of La Niña increasing by August and September. La Niña probability is over 60% from approximately fall to midwinter, which has prompted a La Niña Watch to be issued by the Climate Prediction Center earlier this summer. Current forecasts show neutral conditions increasing around March, though time will tell how this evolves.

Another way to show the La Niña forecast is through a long-range forecast run by many forecast models, showing departure from average sea surface temperatures.

This forecast plot is best described as a forecast model ensemble, like we use for snow predictions, etc. during the winter. This forecast confirms the previous one, and shows that a majority of the forecast models are predicting SSTs in the equatorial Pacific to be 0.3-1.0° Celsius below average. 

The bottom line is that it’s safe to expect a La Niña winter. We’re sure to see the effects of La Niña beginning this fall.

Now for a quick look at our upcoming forecast…below is the Weather Underground forecast for Federal Way.

From Saturday through Tuesday, temperatures will be a bit warmer than they have been, with highs in the mid 70s to low 80s, warmest on Saturday, Monday, and Tuesday. Expect lows in the low-mid 50s except in the upper 50s-low 60s on Saturday night.

Below is the rain forecast from the UW model through Monday morning.

Expect 0.01-0.05 inches of rain south of Seattle, bands of 0.1-0.2” totals between Seattle and Everett, and 0.2-0.5 inches on the coast and from Arlington northward.

Enjoy our warm & mostly dry weather while it lasts!