Very Warm Mother’s Day Weekend Ahead

 FastCast—Friday, May 12 to Monday, May 15:

A very sunny and hot Mother’s Day Weekend is ahead for the Pacific Northwest. On Friday, expect lowland highs in the mid 70s to low 80s, warmest south of Seattle. Highs will increase on Saturday to the mid 70s to mid 80s, again warmest south of Seattle. Sunday and Monday will be the hottest days, with highs north of Seattle in the upper 70s to mid 80s, and highs south of Seattle in the mid 80s to low 90s. Temperatures will be similar on Monday, with more humidity. An upper-level low full of monsoon moisture from the Desert Southwest will move into the region on Monday and Tuesday, bringing a significant chance for thunderstorms across the region (on both sides of the Cascades). There is still a good amount of uncertainty with the thunderstorm potential, so stay tuned. Additionally, gusty east winds in Eastern Washington on Saturday and Sunday, peaking at 30-40 mph, will produce a potential for dust storms. Remember, water temperatures around the region are in the upper 30s to upper 40s in lakes and rivers and upper 40s to low 50s in Puget Sound and the ocean. This shock can quickly induce hypothermia and significantly increase the risk of drowning. Water temperatures will be 30-40 degrees colder than air temperatures. Be alert and be safe!

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Continue reading the full blog below!

A significant May heat wave is almost upon us! High temperatures will increase through Friday and Saturday, peaking on Sunday and Monday. We will also induce a widespread chance of thunderstorms by Monday (likely continuing into Tuesday) as humid air arrives from the Southwest. There is also a decent chance that warm & dry conditions will continue through next week, so stay tuned for more on that!

Let’s start with the forecast on Friday, from the GFS model.

Expect lowland highs in the upper 60s to upper 70s from Seattle north, and in the upper 70s to low 80s from Seattle south. The ocean beaches will hit the upper 60s, with inland areas reaching the upper 70s to low 80s. Eastern Washington will reach the mid 70s to low 80s, warmest from I-90 south.

Let’s compare this to the NBM (National Blend of Models) forecast run by the National Weather Service, seen below.

The NBM generally agrees, with increased highs from Seattle north (to the mid/upper 70s), more isolated 80º+ from Seattle south, and highs up to the mid 80s for the Portland metro and Columbia Basin.

Next, let’s take a look at Saturday’s highs, from the GFS model.

The GFS shows lowland highs in the mid to upper 70s from Seattle north, and in the upper 70s to mid 80s from Seattle south, including inland coastal communities. The beaches will reach the low to mid 70s. The Portland metro will reach the upper 80s to near 90º, and Eastern Washington will reach the upper 70s to mid 80s.

Let’s compare this to the NBM forecast for Saturday, seen below.

The NBM is cooler for most of Western WA, likely having a hard time with the interaction of water and land (some forecast models, especially the European model, overdo cooling related to this). The NBM shows highs in the low 90s for Portland and in the upper 80s to low 90s for the Columbia Basin.

Finally, let’s take a look at Sunday (Mother’s Day), currently expected to be the hottest day of this stretch. The GFS forecast is below.

The GFS shows highs in the upper 70s to low 80s from Seattle north and in the mid 80s to low 90s from Seattle south, including inland areas of the coast. Record highs are possible. The beaches will reach the mid to upper 70s (and will be quite crowded, I’m sure!), and Eastern Washington will reach the upper 70s to mid 80s, a bit cooler due to gusty easterly winds that will increase the dust storm threat.

Let’s compare to the NBM forecast for Sunday, seen below.

Again, the NBM is overdoing the impacts of cooling breezes, but does show a more accurate depiction of highs around Portland, likely in the upper 80s to low 90s. Highs for Eastern WA are likely overdone on this forecast too, since there will be gusty winds cooling the temperatures a bit.

Speaking of winds in Eastern Washington, take a look at the European model’s forecast below for peak winds on Saturday afternoon.

Winds over the lowlands are likely too high, but 30-40 mph gusts in Eastern Washington will bring a chance of dust storms due to the abundance of fresh (and dry) soil across the countryside. Be prepared for abrupt changes in visibility, with dangerous conditions possible in strong dust storms.

You may be wondering how far above average our upcoming temperatures will be. Let’s take a look at the GFS forecast for Sunday afternoon, showing temperature departure from average across the Northwest.

The effects of downsloping easterly winds (which compress the air and bring warming) are clear in this forecast, showing temperatures reaching an incredible 20-30º above average, from Northern California all the way to British Columbia!

Now for a brief note on the upcoming thunderstorm potential…In contrast with how our heat waves typically end (with cool ocean air bringing a marine push and abruptly cooler weather), this heat wave will “end” with an upper-level low bringing monsoon moisture in from the Desert Southwest, bringing no marine cooldown and instead humid air laden with moisture, which will produce a widespread chance of thunderstorms.

Let’s take a look at how this will play out. First, the GFS forecast for Sunday morning.

Notice the massive ridge of high pressure (that will bring the heat wave) across Canada and parts of the Northwest. Then, notice the green circle, denoting the upper-level low moving north from the Desert Southwest. On Sunday, it will be over Nevada, slowly moving north.

By Monday, the upper-level low has moved north, as seen in the GFS forecast below.

Notice that my green circle noting where the system is has moved NW to Oregon and Washington. This low will bring a widespread chance of thunderstorms. On Monday, highs will likely be in the upper 70s to low 90s, and this system will bring dewpoints in the upper 50s to mid 60s, which is quite muggy and relatively rare here. This combination will cause significant instability across the region, promoting a potential for thunderstorms. However, details aren’t too certain, so stay tuned in the next few days.

One quick note at the end of the blog. As I mentioned in the FastCast, there is a very high danger of shock and hypothermia if you are recreating in area waterways. The very helpful infographic below from NWS Seattle shows the dangers of cold water. (Click on it to zoom in)

As the graphic says, “the air may be hot, but the water is cold!” Remember, water temperatures are 30-40 degrees below air temperatures, and the rapid transition can be deadly. Be safe out there!

Stay tuned for updates on the blog and on my Twitter page (link at right side of blog)!