A Near Perfect Forecast of Yesterday's Event. The Next Windstorm Comes into View

 The next time someone makes a weatherperson joke, remember the nearly perfect forecast for yesterday's wind event over Washington.

No longer appropriate

For days, the models correctly predicted the rapid development of the cyclone offshore and the high pressure inland. The combination resulted in strong easterly winds that descended the western slopes of the Washington Cascades.

You want to see how perfect the forecasts were?   Here is the wind speed forecasts provided to Seattle City Light from the UW's WindWatch website, which uses the best of the regional weather prediction models.

This graph shows the highest observed wind over Seattle (black line) and the forecasts made starting Monday afternoon.  

You don't get much better than that.  Earlier predictions were just as good.

A lot of attention was given to the strong cyclone/low-pressure system that developed offshore.   It was an impressive low that not only rapidly developed, but deepened to 943-943 hPa, slightly beating or equalling the historical record.

The 18-h forecast by the UW weather model, the GFS, was 943 hPa at 10 PM last night.  Very nice.

Not impressed?   The 72-hour forecast was almost identical.

Something has happened that has not been sufficiently understood by society.  

Weather prediction technology has improved immensely in skill and detail.

The above results are not a fluke.... I could show you a dozen more, including the predictions of devasting extreme events, such as the Lahaina wildfires or heavy precipitation from Hurricane Helene.

There is so much talk about extreme events and global warming.  

But the truth is that deaths and injuries from extreme events are declining rapidly because weather predictions are so good.  Such deaths and injuries could be greatly reduced further if governments and other institutions would better use highly skillful weather prediction.

The Upcoming Storm

Another midlatitude cyclone will be moving up the coast on Friday.   

On Friday morning at 10 AM, a 977 hPa low will be directly east of the Columbia River outlet.   Much weaker than yesterday's storm, but much closer.

By 7 PM Friday, the low will be making landfall on Vancouver Island as a 980 hPa low.

Compared to Wednesday, this storm will produce strong winds on the coast, but weaker winds over the western WA interior.

For example, at 1 PM Friday (below_, fearsome winds on the coast, but "only" gusts to around 25 kt  (roughly 30 mph) in the interior.

Here is the latest guidance for our friends at Seattle City Light or Seattle--not so bad.

The Storm Reveals Itself. The Eastside Wind Threat

The latest satellite image shows the rapid development of the offshore storm.

The visible satellite image around 9 AM was stunning, with low-level clouds swirling around the low center (the orange arrow points to the low center).

Stunning.

Here is the blow-up of the clouds around the low center.  The circulation is obvious.

Strong, rapidly developing storms not only have rising motion that produces clouds, but intense sinking motion that produces a "slot" dry air coming in from the southeast.   

We can view the "dry slot" using satellite images that reveal water vapor content in the upper and middle troposphere.  Such an image is shown below, with blue indicating very dry air.    This is a strong storm... no doubt about it.

The latest National Weather Service surface map (and I do have some issues with the quality of their analyses) shows the storm at 7 AM, with an analyzed lowest surface pressure of  974 hPa.   The storm is rapidly deepening today, so the pressure will fall considerably more.

As I mentioned in my previous blogs, although strong coastal winds are an issue, my biggest concern is for strong winds east of Puget Sound tonight.  

The models are still going for threatening winds....with the clear threat of substantial tree damage and power outages.

The latest European Center forecast predicts winds exceeding 70 mph on the east side of Puget Sound, particularly towards the western Cascade foothills.  These are all easterly and southeasterly winds....not the usual direction of strong local winds.

The NOAA/NWS HRRR model, run at high resolution, is similar but extends strong winds over Whidbey Island and the San Juans.

The UW Model is also threatening with strong winds on the eastside, gusting to 50 kts (around 57 mph) at 10 PM. 

The maximum wind over Seattle based on dozens of predictions is predicted to hit 45-60 mph...from the east (see below). 

Bottom line:  strong winds from the east, gusting to 40-70 mph, will occur east of Puget Sound and will be stronger towards the Cascades.  Expect substantial vegetation damage and many power outages.    Driving down streets with lots of trees might not be a good idea after 6-7 PM if you living in the vulnerable areas noted above.

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Addendum:

Here is the 1 PM satellite image...the circulation has become very, very obvious.

Some satellites can measure low-level winds by measuring wave action...called scatterometers.  Here are the surface winds from a scatterometer around the storm around 12:30 PM PST.    The intense circulation around the low is obvious.

The Deepest Low Pressure Center in Northwest History? Damaging Winds West of the Cascades

 We may break a significant record tomorrow, with the rapid development of the deepest low-pressure center (lowest sea level pressure) on record for the coastal waters of the Pacific Northwest.

For the period of the historical record, the lowest reliable central pressure for any Pacific low-pressure area off the West Coast occurred on October 24, 2021.  I even did several blogs about the event at that time.  As shown in the figure below, at its most intense that storm had a central pressure of 943 hPa.  

The latest model run of the U.S. GFS model predicts that tomorrow's storm will have a low center of 942 hPa

While the European Center has the center at only 943 hPa.  

The fact that multiple forecast models are coming up with the same solution provides great confidence in this forecast.

Ready to be impressed?  Such low-pressure centers are consistent with the central pressures of a category 4 hurricane as shown by the official Saffir-Simpson scale (below).  No need to head to Florida for big storms!

This offshore storm and its associated front will bring major winds to the coast, with coastal winds gusting to 50-65 mph around 6-8 PM tomorrow evening (see predicted winds at 7 PM Tuesday, kt).   Winds will be even stronger over the western portion of the Strait of Juan de Fuca, with gusts above 70 mph.

Coastal flooding will be reduced by the easterly component of the wind, which will act to push water away from the coast.  

But as noteworthy as all this is, the big weather story will be in the western Washington interior, where a ferocious easterly wind will descend the western side of the Cascades, undoubtedly resulting in the loss of power to thousands.  

I am charging my electronics and flashlights right now.

We have a very interesting...and threatening situation developing.  To the west, a record-breaking low pressure center is developing.   But to the east, just the opposite:  cold air is leading to higher pressure than normal.  

Below is the pressure pattern at 10 PM tomorrow night.  The solid lines are isobars, lines of constant sea level pressure. The colors indicated low-level temperatures, with blue being cold and yellow indicate warm.  

The combination of the low offshore and inland cold high results in a crazy intense pressure change over the Cascades.

As shown by the latest high resolution UW forecast of the winds for tomorrow evening around 7 PM, strong easterly winds gusting to 40-60 kt will hit the region from the Cascades to the Sound, and from an unusual direction (from the east).

The NOAA HRRR model does something similar (winds in mph)

These kinds of winds will take out power to thousands:  not only will they be strong, this is early season, and the direction is unusual for the powerful winds. Vegetation is not used to it.  

In Seattle, the southern part of the city is most vulnerable to such strong winds.  Whidbey and the San Juans will be hit hard.

You have been warned. 😉

Extreme Offshore Storm Could Produce Damaging Winds over the Western Cascade Foothills

 The latest model forecasts are consistent:  an unusually powerful storm with extreme low pressure will develop rapidly offshore on Monday and Tuesday.

But there is something else not yet discussed:   this extreme offshore feature may cause a downslope windstorm on the western slopes of the Cascades.

One that could easily cause extensive power failures.

The latest sea level pressure forecast for Tuesday is scary, with an intense 952 hPa low center west of the Washington coast.    The strongest storm ever to hit the Northwest during the past century, the Columbus Day Storm of 1962, had a low-pressure center of 950 hPa.

The lines show the pressure analysis. Huge pressure gradients (pressure change over distance) and intense pressure changes over the Cascades.  Remember this, it will be important.

The sustained wind speeds at the same time are shown below. 70 kts and more around the storm.  Hurricane strength.  The BC, WA, and Oregon coastal zones will get a taste of it.  Expect some coastal power outages.

 

As in any late-night commercial, there's MORE.  Much more.

The low pressure offshore will create a large pressure difference down the Strait of Juan de Fuca.  As a result, winds will accelerate westward down the Strait, producing huge winds near Tatoosh Island.  They don't call the western exit of the Strait the "Graveyard of the Pacific" for no reason.  Rocks and wind and cloud.

The lowlands of western Washington will get a piece of the windy action as well.

Here in Seattle, it appears that winds will accelerate to 30-40 mph on Tuesday evening, which will blow down some leaves but do little damage (see wind forecast from the City Light WindWatch website, which my group runs).  I will have to rake the leaves....again.

But the real wind action for the western lowlands will be on the western slopes of the Cascades, due to easterly winds driven by a huge pressure difference across the Cascades.   

Below is the latest high-resolution model prediction of wind gusts on Tuesday evening.  Easterly winds gusting to 50-60 kt (57-69 mph).

Enumclaw, Black Diamond, North Bend, and other communities near the western Cascade slopes will get bruised by strong winds.  Get your candles ready.

You want to see an ultra-high resolution forecast of the winds at 10 PM Tuesday evening.  Here it is!   Strong enough for some power outages for sure.

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A Pacific "Hurricane" Off the Northwest Coast on Tuesday

An extraordinary storm will develop a few hundred miles off our coast on Tuesday, a storm every bit as strong as a Category 1 hurricane.   But we can't call it a hurricane because of its northern origins and energy source (the energy comes from horizontal temperature differences, not warm water).

A storm with gusts to 80-90 mph, deep low pressure, and huge waves.  Northwest Coast will get a substantial taste of it.

Native Americans were quite familiar with such events and they had some colorful stories of their origins: suggesting they were the result of a giant thunderbird, which lived high in the Olympic Mountains.

The sea-level pressure forecast for Tuesday at 7 PM by the European Center model shows an intense low center with a central pressure of 944 hPa due west of the Washington Coast.  

Trust me, this is an unusually deep low, with most Pacific low centers at this latitude only deepening to 980-990 hPa.  The lines are isobars of constant sea level pressure.

This is a relatively small storm, but one with intense horizontal pressure changes (gradients) and thus very strong winds.   Winds result from differences in pressure.

The sustained wind speed forecast at the same time (below) shows winds stronger that 80 mph just south of the low center.  

Very much like a hurricane with winds going to zero in the center and a ring of strong winds around the low.  You will also note a band of strong winds extending far southeast of the low center:  such winds are associated with an occluded front that projects out of the low.

This storm developed very rapidly (or explosively) the previous 24 hr and thus is considered a "bomb" cyclone (storms that deepen by 24 hPa or more in one day).

The first thing any trained meteorologist does with such an extreme forecast is to compare the prediction to those of other modeling systems.   Most have very similar solutions.  Thus, we have some confidence in the prediction.

Consider the sea level pressure forecast from the UW modeling system (below) for 10 PM Tuesday. The low center is "only" 953 hPa.  Sustained wind speeds are shown by the color shading (knots).

The UW model predicts strong winds (50-70 mph) on the Oregon and Washington coasts. Even stronger along Vancouver Island.

The European Center wave model, shows substantial (significant) wave heights reaching the coast, as the strong winds work on the Pacific Ocean.  20-25 ft waves could reach our coast.

The only reason they aren't higher is because of the relatively small size and rapid development of this storm.

Water levels on the coast are of some concern because the astronomically forced water levels will still be fairly high on Tuesday (see forecasts below for Westport, WA).  So the waves reaching the coast will ride on astronomically high water levels for several hours of Tuesday.

Let me end with the simulated satellite image of the storm on Tuesday night (below).  You can clearly see the low center.  Magnificent.

Downslope Windstorm and Extreme Precipitation Contrasts Across the Olympics

The Olympic Mountains are a meteorological laboratory par excellence.   As shown below, the Olympics are nearly ideal as a meteorological research zone:  an isolated, near-circular barrier approached by uninterrupted flow from off the Pacific.  Plus, lots of observations around and within the barrier.  

It is a topographic island of extremes, with the wettest locations in the lower-48 states only miles away areas in which aridity and cacti flourish.

Consider this week.  Strong moist flow approached the barrier from the south, producing a stunning contrast in precipitation.  Consider the total precipitation from Sunday to today (Thursday) at 6 PM (below).

Extraordinary.  10-12.5 inches over the southeast slopes of the barrier near Lake Cushman, but less than an inch from Sequim to Port Townsend.  Only 0.28 inches on northern Whidbey Island.

The Skokomish River is found on the wet southeast side of the Olympics and according to the National Weather Service, it reached flood stage.

The Skokomish River cam confirms the wet situation!

The origin of this precipitation contrast is no mystery:  there was strong upslope flow on the windward (southern) side of the barrier, which produces heavy precipitation, while strong downslope flow on the lee (northern) side resulted in drying and lack of rain (see schematic below)

But there is more!   Strong downslope winds produced powerful warming and drying on the northeast side of the barrier that was captured by several weather stations on the lee slopes of the Olympics.

Consider the Indian Creek/Lake Crescent site shown by the red arrows.

On Tuesday evening, the winds surged across the Olympic Crest and headed down to the lower slopes where this station occurred....and things went wild.  The wind went from nearly calm to almost 60 mph in a few minutes!

As the winds descended on the NE side of the barrier, the temperature (cyan color) surged upward from about 45F to around 53F and then jumped up and down wildly.  Relative humidity dropped (green colors) as did dewpoint. (blue line).

What happened?   Air descending terrain warms rapidly since the air is being compressed as it goes from low to higher pressure during descent.  Warms like your bicycle pump as you compress the air inside it.  Warm air can hold more water vapor than colder air, so relative humidity drops at the same time.. 

Pretty dramatic changes.   There are more impacts of the Olympics that will have to wait until another blog, from the Puget Sound Convergence Zone to the intense low that can form on its NE side.

Another reason that Northwest weather is so interesting and fun to study.