Potentially Significant Heat Wave Ahead

 FastCast--Tuesday, July 2 to Sunday, July 7:

A potentially significant heat wave is ahead for the Pacific Northwest near the end of this week and potentially into next week. However, Tuesday will be a relatively cool day, with highs only in the low to mid 70s with partly cloudy skies. Wednesday will have brief morning clouds giving way to sunny conditions, with highs in the mid 70s. The heat starts to build on the Fourth (Thursday), with highs reaching the upper 70s to mid 80s. The forecast from Friday to Sunday is less certain, temperature-wise. It's likely that it will be quite hot, with potential highs anywhere from the upper 80s to upper 90s. Stay tuned for more information as we get closer. Regarding low temperatures, expect lows in the low to mid 50s from Tuesday morning to Thursday morning, with lows increasing to the upper 50s to low 60s from Friday morning to Sunday morning.

Increasing heat and slight offshore winds will combine to produce very dry conditions on the Fourth, leading to a very high risk of fireworks-related fires, which could spread quickly. Please be very mindful if you are lighting off fireworks, and consider not doing any fireworks this year due to the dry conditions.

Hurricane Beryl has just become the earliest Category 5 hurricane in history, with records going back to the 1850s. Beryl hit Grenada on Monday, and is moving toward Jamaica, the Grand Caymans, and Mexico while weakening. For information and updates about the hurricane, click here: National Hurricane Center--Hurricane Beryl

----------------------------------------------------------------------

Continue reading the full blog below!

A significant heat wave is possible for the Northwest beginning later this week. A large and strong area of high pressure will build over the region, deflecting any weather systems and allowing a heat wave to impact the region.

Let's take a look at the forecast, starting with the high pressure ridge. As seen below on the European model forecast, by Saturday, the ridge will be just off the Northwest coast.

This is a prime position to produce a "heat dome" pattern that will bring a prolonged heat wave to the region. It is important to note that this will be NOWHERE near the intensity of the June 2021 heat wave, but will still be significant.

The rest of this blog will detail the forecasts for the next few days as the heat begins building.

First, the forecast for Tuesday's highs from the NWS NBM model.

This will be the coolest day for the foreseeable future. Lowland highs will only reach the upper 60s to low 70s, with the coast remaining in the low 60s, the Willamette Valley reaching the mid to upper 70s, and Eastern Washington reaching the low 80s to low 90s.

Slight warming begins on Wednesday, as seen in the NWS NBM forecast below. This will coincide with what is likely the last cloudy morning for a bit.

On Wednesday, expect lowland highs in the mid to upper 70s, coastal highs in the mid to upper 60s, and Willamette Valley highs in the low 80s. Eastern Washington will again reach the low 80s to low 90s.

Things really begin to heat up on the Fourth (Thursday), as seen below in the NWS NBM forecast.

This forecast shows highs on the Fourth reaching the upper 70s to mid 80s for the lowlands, the low to mid 70s on the coast, and likely the low to mid 90s in the Willamette Valley. Eastern Washington will reach the upper 80s to mid 90s on the Fourth.

These hot temperatures on the Fourth, combined with subtle offshore winds, will produce low humidity and a very high risk of fire spread due to fireworks. Below is the European model forecast for relative humidity on the evening of the Fourth.

Across most of Western WA and OR, humidity will drop to 20-40%, with humidity east of the Cascades in the dangerous 10-20% range. This won't recover too well by peak fireworks time, around 10 PM-1 AM. This means that fireworks have a very high risk of starting fires. Please be extremely mindful of this if you're lighting off fireworks, or consider not doing any fireworks due to the conditions.

Back to the heat wave forecasts...we'll switch to using the European model for the forecast for Friday, seen below.

This is when the heat really starts cranking. In Western Washington, highs from Seattle north will reach the upper 70s to mid 80s, while highs from Seattle to Portland will reach the upper 80s to low 90s. The coast will reach the upper 60s at the beaches and upper 70s to mid 80s just inland. The Willamette Valley will be very hot, with highs likely in the upper 90s to low 100s. Eastern Washington will reach the low 90s to mid 100s, hottest around Yakima and the Tri-Cities.

The hottest and most dangerous conditions (both daytime highs and overnight lows) are expected over the weekend and into early next week, but the forecast for exact temperatures is less certain, so stay tuned for updates over the next few days.