Part of assessing geologic risk is understanding weather and climate. This past month has had some extreme weather. Not the kind that gets a lot of attention, but we did have some landscape altering weather this past month.
First, Felton at the Seattle National Weather Service noted this:
CLIMATE NOTE...WITH 0.05 INCHES AT SEA-TAC TODAY AS OF 9 PM THIS WAS
THE 27TH DAY WITH MEASURABLE PRECIPITATION THIS MONTH. THIS IS THE
MOST DAYS WITH MEASURABLE RAIN FOR THE MONTH OF DECEMBER ON RECORD.
THE OLD RECORD WAS 26 DAYS IN 1971. THERE HAVE ONLY BEEN TWO MONTHS
WITH MORE DAYS OF MEASURABLE PRECIPITATION SINCE RECORDS STARTED IN
SEATTLE IN 1891. JANUARY 1953 AND JANUARY 2006 HAD 28 DAYS. THERE
WAS MEASURABLE PRECIPITATION THE LAST 26 DAYS OF THE MONTH IN
JANUARY 1953 WHICH IS PART OF THE RECORD 33 STRAIGHT DAYS OF
MEASURABLE PRECIPITATION FOR SEATTLE. FELTON
While we have not had any huge rain events or flooding, it really has been wet and cloudy even for western Washington. The constant dribble of rain has led to numerous episodes of slope failures on very steep slopes subject to saturation along the railroad between Everett and Seattle as well as a few other places that don't make the news so often.
This steady wet weather brought about another subtle but extreme event at least where it took place. The extreme event was not the amount of snow, but the amount of a certain kind of snow. Cool and wet with days of chilly rain in the low lands led to days of steady snow in the mountains. Cliff Mass proposed that the steady right-around-freezing temperatures at discrete elevations mixed with lots of wet snow took out hundreds of trees in areas that experienced that sort of weather why-are-so-many-trees-falling. A follow up on his proposal would be to assess the kinds of trees that were susceptible to being taken down by days of wet snow and see if this kind of event took place in other Cascade valleys that do not have highways. The tree collapses closed the Mount Bake Highway for a few days and closed Highway 2 over Stevens Pass for several days. It was a fascinating phenomenon given that the locations where the trees collapsed typically get lots of snow. The extreme even was not the snow but the kind of snow - days of wet sticky snow.
One other extreme event this past month was the combination of very high winter tides coinciding with a low pressure system and winds that were just right causing the highest tide level ever in Seattle. Some minor flooding was associated with event not only in Seattle but elsewhere as well. And erosion and deposition along shorelines from the event may have lasting impacts that will manifest later. For example the erosion of the toes of slopes will cause slopes to become over steep setting up future shoreline bluff failures.
First, Felton at the Seattle National Weather Service noted this:
CLIMATE NOTE...WITH 0.05 INCHES AT SEA-TAC TODAY AS OF 9 PM THIS WAS
THE 27TH DAY WITH MEASURABLE PRECIPITATION THIS MONTH. THIS IS THE
MOST DAYS WITH MEASURABLE RAIN FOR THE MONTH OF DECEMBER ON RECORD.
THE OLD RECORD WAS 26 DAYS IN 1971. THERE HAVE ONLY BEEN TWO MONTHS
WITH MORE DAYS OF MEASURABLE PRECIPITATION SINCE RECORDS STARTED IN
SEATTLE IN 1891. JANUARY 1953 AND JANUARY 2006 HAD 28 DAYS. THERE
WAS MEASURABLE PRECIPITATION THE LAST 26 DAYS OF THE MONTH IN
JANUARY 1953 WHICH IS PART OF THE RECORD 33 STRAIGHT DAYS OF
MEASURABLE PRECIPITATION FOR SEATTLE. FELTON
While we have not had any huge rain events or flooding, it really has been wet and cloudy even for western Washington. The constant dribble of rain has led to numerous episodes of slope failures on very steep slopes subject to saturation along the railroad between Everett and Seattle as well as a few other places that don't make the news so often.
This steady wet weather brought about another subtle but extreme event at least where it took place. The extreme event was not the amount of snow, but the amount of a certain kind of snow. Cool and wet with days of chilly rain in the low lands led to days of steady snow in the mountains. Cliff Mass proposed that the steady right-around-freezing temperatures at discrete elevations mixed with lots of wet snow took out hundreds of trees in areas that experienced that sort of weather why-are-so-many-trees-falling. A follow up on his proposal would be to assess the kinds of trees that were susceptible to being taken down by days of wet snow and see if this kind of event took place in other Cascade valleys that do not have highways. The tree collapses closed the Mount Bake Highway for a few days and closed Highway 2 over Stevens Pass for several days. It was a fascinating phenomenon given that the locations where the trees collapsed typically get lots of snow. The extreme even was not the snow but the kind of snow - days of wet sticky snow.
One other extreme event this past month was the combination of very high winter tides coinciding with a low pressure system and winds that were just right causing the highest tide level ever in Seattle. Some minor flooding was associated with event not only in Seattle but elsewhere as well. And erosion and deposition along shorelines from the event may have lasting impacts that will manifest later. For example the erosion of the toes of slopes will cause slopes to become over steep setting up future shoreline bluff failures.
Bluff slope at Birch Bay
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