Potential for King Tide Flooding this Week?

 King Tides occur when the Earth, Sun, and Moon are aligned and can be particularly high during the winter months when the Earth is closest to the Sun. Also called spring tides, King Tides can result in localized coastal flooding.

Since water levels rise as atmospheric pressure falls, something called the reverse barometer effect, King Tides can be particularly problematic if a low-pressure system is overhead.   

So what is going to happen this week?

Let's start with the predicted tide levels based on astronomical conditions, with no consideration of atmospheric pressure.   NOAA's Tides and Currents website has all the information!

Let's consider Bush Point on the western side of Whidbey Island (see red marker on the map below).

The predicted tides are shown below.  The vertical green line shows yesterday (Monday) evening.  The diurnal range between high and low tides gets larger and larger until November 18th ( Monday), with a range from -3.26 ft to 10.65 ft above Mean Lower Low Water (MLLW), the average level of the lowest tide for each day computed over a 19-year period.

Very large range.  This level is probably not enough for significant flooding without the assistance of low pressure or wave action.

The influence of low pressure is called the reverse barometer effect (see figure).  For every  1 hPa drop in pressure, the water level tends to rise 1 cm (0.39 inches).  And high pressure can push water levels down.

So any low-pressure systems expected this week?

The latest WRF forecast for atmospheric pressure on northern Whidbey Island is shown below (time is on the x-axis in GMT/UTC).  Average sea level pressure is about 1013 hPa and there appears to be a low-pressure event (to around 1007 hPa) on the 17th.

Worth checking on further.  Below is the forecast sea level pressure for Sunday around 7 AM, when pressure will be the lowest (looks like about 1007 hPa over Whidbey).   About 8 hPa below normal pressure or about 8 cm rise in water level... so should add another 3 inches to the astronomical tides.

Not the end of the world, but there could be some minor localized flooding.   

The real threat may be on the coast, where the low pressure and high astronomical tides will add to wave action from storms over the northeast Pacific.   The NOAA ocean wave model shows modest wave heights on Sunday morning offshore (below, in meters).  Perhaps 2-3 meter wave heights in the morning, increasing during the afternoon.  2-3 meters is 6-10 ft.

Will have to watch this carefully regarding the potential for coastal flooding.

The Tale of Two Troughs

 The rain has begun in earnest tonight as shown by the radar at 10 pm (below).

It will rain much of this week and the totals will be impressive by the time it is over, with some sodden locations getting 10 inches or more.

The key features bringing the rain are two upper-level troughs of low pressure. The next figures show the upper-level maps this week (500 hPa pressure, about 18,000 ft above sea level).

The first trough is moving in right now (see map at 7AM Monday)

On Tuesday, a weak ridge of high pressure moves over us, providing a break.

And then a strong trough comes in on Wednesday (see below).  Classic November pattern.

Now let me show you the precipitation totals.

Through Monday at 4 PM, some healthy totals, with up to 3 inches in the mountains.

A bit more by Tuesday at  4 PM

But by Wednesday at 4 PM..wow.  Much more, with some locations up to 10 inches.  And it is not over.

Freezing levels will be high enough today to limit snow accumulation, but later in the week it will get cool enough to bring substantial snow totals above 4000 ft.  The snowfall total through Thursday at 4 PM is shown below, with the north Cascades getting several feet.  Snoqualmie is too low and warm to get much.

Mid-November and the atmosphere is doing what it should. Our water resources are being restored, reservoirs are refilling, and moisture is percolating down into our soils.

The Upcoming Deluge

We are about to enter a very wet period, with the potential for bankfull rivers and even some localized flooding.

Let me start by showing you the total precipitation accumulation forecast over the next ten days over the region (from the European Center model, below).

Wow.   Over ten inches in some locations in the Olympics and coastal mountains and 5-10 inches in the Cacades.  Even significant precipitation east of the Cascade crest.

The UW model for the same period provides similar large totals, with over ten inches in the Cascades and Olympics and 3-5 inches over the lowlands of Puget Sound.

Temperatures will be cold enough to bring large snow totals.  Below
is the prediction accumulated snowfall over WA State for the same period.  Over FOUR FEET over the North Cascades and snow over lower elevations across the northern Columbia Basin.

The first major hit of rain and snow (in the mountains) will occur tomorrow (Saturday) and the a stronger event on Sunday night and Monday morning.

Let's take a closer look over the next few days.

Trough 4 AM Sunday, the regional gets a nice wetting, but nothing excessive.

But with heavy rain on Sunday night, by Monday morning, the story is very different.....very heavy precipitation totals in the mountains.     A profound rain shadow northeast of the Olympics.

One day later (Tuesday at 4 AM), amazing totals over the mountains and even quite heavy south of Seattle.  Continued rain shadowing from Sequim to Whidbey Is.

Rivers will respond.   For example, the Northwest River Forecast Center is predicting that the Snoqualmie River will rise to "action levels".  

This is climatologically the wettest time of the year, so it is nice to see that the atmosphere is following the calendar. 😁

 

Update on Reservoir Levels

As we start the winter wet season, it is a good idea to check the reservoir levels in the western U.S.  How is our water supply doing before the big precipitation events?

In California, which has enormous water needs for a huge population and massive agriculture, the reservoirs are now in good shape, with water levels generally at or above normal. The substantial precipitation and great snowpack of last winter deserve the credit.

What about here in Seattle?  The statistics on November 4 indicate near-normal water storage and typical water consumption.  Recent rains have helped a lot.  Seattle has no water issues.

But all is not rosy in water land.    The Yakima reservoir system east of the central WA Cascades is very low, as it was last year (see below).  The key reason for the low water levels is probably the back-to-back El Nino years, which generally result in poor Cascade snowpack...an essential for feeding the eastside reservoirs.

With La Nina this year, we will probably see enhanced snowpack and far better reservoir levels next summer.   

Furthermore, the forecast total precipitation for the next ten days is very large, with substantial rain east of the Cascade crest.

Ff you really want to be impressed, check out the forecast snow totals for the same period.  Several feet in the Cascades and even more for the mountains of southwest BC.

I suspect talk of drought, low streamflow, and reservoirs needing refilling will be ending during the next month.

Will Weather Influence a Very Close National Election?

There is a large literature on how adverse weather can suppress voter turnout and make a difference in close elections.     

This is certainly a close presidential election. 

Although about half the U.S. electorate has already voted, could the weather today be a factor?

So let's look at the latest weather observations and find out!

The latest national radar map, which shows areas of precipitation,  indicates mainly dry conditions over many of the critical states (Pennsylvania, North Carolina, Georgia, Arizona, and Nevada).  Light rain over northern Michigan and parts of Wisconsin.

The 6-hour totals ending about 2 PM EST are consistent with the radar...nothing major that would impede voting.

What about temperatures?  The predicted high temperatures today should be mild along the eastern third of U.S.--so little impact.   

 The coldest temperatures in a swing state will be over northern Wisconsin, but those will only be in the 40s.  Really not much of concern.

The National Weather Service has a national weather warning map (below).  Really nothing of any significance for critical states.

In summary, the weather gods have decided not to get in the way of this election, so storms and severe weather will not be an excuse for the losing side.😋

There WILL be Downhill Skiing by Thanksgiving

 I may be reticent about publicly forecasting the outcome of the presidential race tomorrow, but I am increasingly confident about another issue of interest, skiing during the Thanksgiving holiday weekend at the higher elevation runs.

The last few model forecasts give me some confidence that at least Whistler, Baker, and Crystal will be able to start their season.

Let's start with Whistler/Blackcomb.  During the past week, they have gotten several inches with a current base of around 25 cm (roughly 9 inches).  The cam at the mountain lodge shows the snow cover and the fact they have even started to make snow (see the snow gun on the right).

There was some additional snow today but the big accumulation will be this weekend and beyond, when a deep trough over the northwest Pacific will really get the flakes falling.

Consider this morning's run of the uber-skillful European Center forecast model. The snowfall totals are in cm, so remember 1 cm is about 0.4 inches

The total by tomorrow morning is about 25 cm (roughly 10 inches) at Whistler.

With a wet system coming in Friday and over the weekend, by next Thursday morning there will be about 82 cm (32 inches) at Whistler.   That alone may be enough to open some runs.

The forecast model run by my group, driven by the US GFS solution, is similar (and in inches).  Our snow totals are a bit more generous:

Certainly, the folks at Whistler are optimistic:

Mt. Baker ski area will get a piece of this snowy action. Currently, there is about a foot of a decent base there, as noted by Gwyn Howat, CEO of the Baker Ski area.  Crystal, as will Mt. Baker, will get enough to open I suspect.

I am not suggesting that the lower ski areas, Snoqualmie and Steven, will open.  Too low, too warm for so early in the season.

The big question is what will happen in mid to late November.  Too far ahead for skillful forecasts....so keep tuned!

Snowy Start for the Northwest's Winter Season

A substantially above-average amount of snow has fallen in the Northwest mountains this autumn:  enough to warm the cold hearts of Northwest skiers.

Let me begin by showing you the snow-laden summit of Crystal Mountain late Saturday afternoon (see below).  A very wintry scene!

The lower-elevation Crystal Mountain "Snow Stake" confirms the white bounty.

How much above normal is the current snowfall?  Please sit down before reading further (below).

In Washington State, the snowpack ranges from 188% of normal to 1775% of normal.

Not impressed yet?  Northeast Oregon is over TWO THOUSAND PERCENT of normal.

Call the Seattle Times ClimateLab!  You know they would have done a story if it had been below normal 😈.

The truth is that early in the season, when totals are typically low,  you can get these crazy percentiles.   Still impressive, though.

The current map of the water equivalent in the current snowpack (called SWE) is shown below.  Much more than last year, by the way.

What about the forecast for the next few days?  

You guessed it:  MORE SNOW!  As shown by the UW model prediction, the North Cascades and the mountains of southwest BC will be hit hard.  Several feet at some higher elevation locations.

La Nina years are generally good for snow and we are seeing some hints of La Nina weather patterns during the past weeks.   

If you really want to get excited, check out the European Center's extended (46-day) snow-total forecasts (see below).  Yards of snow in some places.   A good early start.  I am optimistic about skiing over the Christmas holidays.

I will be waxing my skis during the next few weeks...