FastCast--Monday, March 18 to Thursday, March 21:
Beautiful spring weather will continue across the region on Monday and Tuesday, with sunny conditions and lowland highs reaching the upper 60s to low 70s. Tuesday may have some partly cloudy conditions in the morning and late evening. Expect morning lows on Monday and Tuesday to be in the low to mid 40s. On Wednesday, conditions will get cloudy and there will be a large drop in temperatures, with highs plummeting to the low to mid 50s. Similar conditions will exist on Thursday. Showers are possible at times on Wednesday and Thursday as cooler and wetter weather returns.
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Continue reading the full blog below!
It was an incredible weekend across the Pacific Northwest, as a huge ridge of high pressure dominated the weather pattern, bringing record-breaking highs in the low to mid 70s for Seattle, and in the upper 60s to low 70s for most of the remainder of the area. Very nice conditions will continue on Monday and Tuesday, but changes are afoot later in the week. Let's take a look at the forecast!
First, let's take a look at the NWS NBM high-resolution forecast for highs on Monday.
Expect lowland highs in the mid to upper 60s (coolest closer to the water). There's a decent chance that areas east of I-5 and south of Tacoma will reach the low 70s. The coast will continue cooling, remaining in the mid 50s to low 60s. The Willamette Valley will be quite warm, in the mid 70s (localized upper 70s possible), while Eastern Washington will reach the upper 60s to mid 70s.
These temperatures are quite abnormal, and although Monday will be a touch cooler for Western WA than the weekend, it's still quite above normal. Below is the European model forecast showing temperature departure from average on Monday afternoon.
Across Western Washington, temperatures will be 10-15° above average, with the Willamette Valley and Eastern Washington being 15-20° above average, quite an anomaly for March! Additionally, areas in the mountains are a staggering 20-25° above average. I wouldn't be surprised to see a significant lessening of the snowpack due to this warm spell.
Next, let's take a look at Tuesday's highs, on the NWS NBM model.
Temperatures will begin cooling west of the Cascades on Tuesday, with the lowlands reaching the mid to upper 60s, Willamette Valley reaching the upper 60s to low 70s, and the coast only reaching the mid 50s. Eastern Washington will be warming as the heat moves east, with highs reaching the upper 60s near Spokane to mid to upper 70s near the Tri-Cities and Yakima.
By Wednesday, major temperature changes are expected, as seen below on the NWS NBM forecast.
Major temperature declines are expected, with highs in the lowlands only reaching the mid 50s, the low 50s on the coast, and the upper 50s in the Willamette Valley. Even Eastern Washington will cool significantly, with highs dropping to the upper 50s to upper 60s. Note that the warmer temperatures have moved further east, with the Boise area reaching the low 70s.
A great way of visualizing the temperature change from Tuesday to Wednesday is the 24-hour temperature change forecast, shown below from the European model.
This forecast, showing temperature difference between Tuesday afternoon and Wednesday afternoon, shows a decrease of 10-20° across most areas west of the Cascades, in the mountains, and on the east slopes. Most of Eastern Washington will decrease by 5-10° as well.
What's fueling this big decrease in temperatures mid-week? The overall pattern is changing significantly. We will go from ridging, bringing sunny weather and warm temperatures, to troughing, bringing cooler, cloudier, and wetter weather. Let's take a look at how this looks on forecast models. Below is the European ensemble forecast for Monday.
Notice the massive ridge over the Northwest and SW Canada. This large ridge is what is causing the beautiful, warm weather we've been having.
Now, let's take a look at this same view by Friday.
This is a complete change from earlier in the week, with the massive ridge replaced by a strong trough. This is the source of the big decline in temperatures and return to more active weather.
Stay tuned over the next few days as we determine what kind of stormier weather is ahead later this week and into the weekend...but enjoy the next 2 days of sun!
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