FastCast—Thursday, June 23 to Monday, June 27:
A heat wave is in the cards to begin summer in the Pacific Northwest. After a mostly cloudy day with afternoon sunbreaks on Wednesday, the warmup will begin on Thursday. Highs will reach the upper 60s to low 70s, with clouds clearing by midday. Expect lows Thursday night in the upper 40s to low 50s. Friday will be sunnier and warmer, with highs reaching the mid to upper 70s. The heat wave begins on Saturday. Highs will reach the low to mid 80s across the Lowlands and the upper 60s to mid 70s on the coast. Eastern Washington will be in the upper 80s to mid 90s, except cooler in the NE section. Sunday and Monday will be the hottest days. Temperatures in the lowlands will soar into the upper 80s to low 90s. The coast will reach the mid 70s to low 80s on Sunday (cooling to the upper 60s to low 70s on Monday) and Eastern Washington will be quite hot, with highs in the low 90s to low 100s. Nighttime lows in Western Washington will be on the warm side, in the upper 50s to low 60s. It is very important to remember that water temperatures are frigid…in the upper 40s to upper 50s in Puget Sound, the Salish Sea, and the Pacific Ocean. It is only slightly warmer, in the upper 50s to low 60s, in area lakes. Rivers are also running higher and faster than later in summer due to snowmelt. Be safe in and around water at all times during this heat wave.
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Continue reading the full blog below!
A heat wave is ahead to begin summer in the Pacific Northwest. After a cool and wet spring, this will be quite an abrupt transition.
Expect the hottest temperatures to occur on Saturday, Sunday, and Monday. The heat wave begins on Saturday, with the forecast from the GFS (American) model’s ensemble mean (average of many model runs) below.
Expect highs in the lowlands to be in the low 80s near the water and in the mid to upper 80s away from the water, especially in the foothills. The coast will reach the mid 70s to low 80s, and Eastern Washington, the Willamette Valley, and SW WA will reach the upper 80s (except in the northern tier of E. WA).
Temperatures continue to warm on Sunday, as seen in the GFS ensemble mean below.
This forecast may be a tad on the warm side, but it is reasonable to expect lowland highs in the upper 80s to low 90s. The coast reaches the upper 70s to low 80s (up to the mid-upper 80s a few miles inland), and the Willamette Valley, SW WA, and Eastern WA reach the mid 80s to mid 90s.
The heat will then peak on Monday. The GFS forecast is below.
Expect lowland highs to reach the low 90s (cooler near the water). Marine air will be moving onto the coast, limiting highs there to the upper 60s to upper 70s. Eastern Washington will reach the low 90s to low 100s, and the Willamette Valley & SW WA will reach the low to mid 90s.
Temperatures will be hottest on Sunday and Monday due to the heat trough (low pressure created by hot temperatures) that will move north into the Pacific Northwest. It is seen below (outlined in blue) on the UW model for Sunday afternoon.
The black lines are lines of constant sea level pressure. Basically, this map is showing that the heat trough, which produces the Pacific Northwest’s hot weather, will be present during this heat wave, bringing conditions such as downslope winds, low pressure, and dominant offshore flow…all which bring hot temperatures to the region.
As always with heat waves, there will be risks. Take extra precautions if you are recreating near the water. Water temperatures are in the upper 40s to upper 50s in major waterways & rivers, and only a bit warmer, in the upper 50s to low 60s, in area lakes. Additionally, rivers are running higher and faster than normal due to snowmelt. It is very important to be aware around the water during the hot temperatures.
The NWS HeatRisk for Sunday is below.
Expect a Moderate (2/5) risk around the region. This means that anyone with sensitivity to heat or who will be unable to access cooling/hydration need to be careful. Similar conditions are expected on Monday.
Another heat wave update will be posted on Friday, when high-resolution models have forecasts for Saturday and Sunday. Stay tuned to local meteorologists (on Twitter, YouTube, and local news) and NWS Seattle for more information and updates.
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