And to think as July turned to August, we wondered if summer was ever coming this year...
Oh, summer is coming, and it's getting ready to make up for lost time.
While this Labor Day Weekend has been fairly warm, all signs are pointing to it just being the appetizer to an even hotter stretch of weather as we head into later this week and into the weekend.
After a brief break Monday when we just nudged over the 80 mark, a ridge of high pressure is starting to intensify again as we wade through Tuesday and Wednesday. In addition, a strong thermal trough will be building up from the south along the coast that will generate additional warming via an east wind for the end of the week.
The east wind does two things: One, it holds back the cool, ocean breezes from its usual march inland. Second, the sinking process will warm the air even further as it comes down the western slopes of the Cascade Mountains. In addition, it will also dry out the air, causing very low humidity -- good for comfort levels, bad for wildfire danger. More on that in a moment.
High temperatures are forecast to increase as the week progresses, with highs in the low 80s on Tuesday, then mid-upper 80s on Wednesday, followed by a three-to-four day streak of highs in the upper 80s or low 90s as the thermal trough reaches its peak and the air mass warms further. Right now, we have expected highs in Seattle proper just under 90 Thursday through Saturday and possibly even into Sunday, and the foothills and southwestern Washington should easily cross into the 90s.
In July or August, while not exactly routine, a stretch of hot weather like this would be notable, but not unheard of. (Then again, had this been July or August, the forecasted high temperatures would probably be even higher. We are deducting a few degrees in deference to the calendar and that there is about 2 1/2 hours less daylight than in mid July.)
But in September, while a hot day here and there has happened, getting a stretch of heat this high for this long is exceedingly rare.
The longest stretch of consecutive days at 80 or above in September is eight, set Sept. 7-14 in 1989, but the warmest day of that stretch was 85 with six of those days between 80-83 -- not exactly a roaring heat wave. After about a week of cooler weather, a second warm event occurred with four days over 80 with a high of 91 on Sept. 22 -- tied for the latest 90 degree date on record.
But the record really in danger is that the current longest stretch of 85 degree or warmer temperatures is two, set six times before, (but not in 1989). This current warm stretch has potential to go anywhere from 3-5 days above 85.
And if we should hit 90 in Seattle, which is certainly not out of the question, it would only be the 11th time Seattle at Sea-Tac Airport has hit 90 degrees in September. And only twice before has it hit 90 on back-to-back dates in September -- in 1967 and 1988. And the warmest temperature ever recorded after Sept. 7 is 93 degrees, to give a gauge of how it's ever been this late in the season.
Wildfire Danger Extremely High
While the heat can make for some sweaty days and uncomfortable nights, one of the more dangerous aspects will be the risk for wildfires.
It's already been bone dry out there -- Seattle has only had three days with measurable rain since July 18th, and it's accumulated to a whopping 0.26 inches. Put another way, it's been dry 42 of the past 45 days.
Meanwhile, the sinking process from the east winds also dries out the air, which when combined with the lack of rain over the past six weeks and intense heat, is making fire conditions critical in the mountains -- and even in the urban areas. So while it makes the heat a desert heat with no mugginess to worry about, and this pattern is so dry that lightning is not any concern, any kind of man-made spark could create a raging fire in very little time.
Thus, the National Weather Service has issued a Red Flag Warning -- the higest fire danger warning in their arsenal -- for much of the Cascades and Olympic Mountains, including Mount Baker-Snoqualmie National Forest, North Cascades National Park, Mount Rainier National Park, Olympic National Park and Olympic National Forest.
The watch as of now is in effect from Wednesday morning through Thursday afternoon but I'll bet it eventually gets extended through the weekend.
Forecasters warn of humidity levels that will be in the 15-25 percent range in the Cascades with record high temperatures in the 70s and 80s at high elevations.
The Weather Service warns that "weather conditions will support large fire growth and erratic fire behavior on fires above... roughly 2,000 feet elevation."
When does this end?
Long range models as of Tuesday ease off the heat just a little as we get into next Monday, then finally push in our cooler marine air for next Tuesday and beyond. However, the trend of the models has been to keep delaying the onset of the cooler air, so we'll see how long this goes.
Records we are aiming for:
Daily record highs for Seattle:
* Sept. 8: 85 (1993). Forecast: 87
* Sept. 9: 89 (1963). Forecast: 88
* Sept. 10: 85 (1946). Forecast: 89
* Sept. 11: 83 (1975). Forecast: 85
* Sept. 12: 85 (1975). Forecast: 82
Consecutive warm days in Seattle in September:
* Number of consecutive days at 80 or warmer: 8. Forecast: 10
* Number of consecutive days at 85 or warmer: 2. Forecast: 5
* Number of consecutive days at 90 or warmer: 2. Forecast: 0 (for now)
* Number of days to reach 90 or warmer in Seattle since 1948: 10
Hottest September days in Seattle (Sea-Tac) history:
1) 98 Sept. 2, 1988
2) 94 Sept. 7, 1981
3) 93(t) Sept. 15, 1967 & Sept. 14, 1979
5) 92(t) Sept. 3, 1988 & Sept. 22, 1990
7) 91(t) Sept. 16, 1967, Sept. 2, 1974, Sept. 22, 1989.