Sunday, August 30, 2020

The Lessons of Hurricane Laura for the Northwest

Hurricane Laura, one of the strongest hurricanes to hit the central Gulf coast in years, is now history, but there are important lessons for us in the Northwest.

The death toll now stands at 16.  But it is important to note that more than half the deaths were not due to storm surge or direct hurricane damage, but due to improper use of generators, leading to carbon monoxide poisoning.

Several of the other deaths were from trees falling on homes, killing those inside.

Nearly all of these storm-related deaths did not have to happen, and the lessons of Laura are important here in the Northwest, which is often hit by Pacific cyclones rivaling the hurricanes that strike the southeast U.S.

And there is something else:  Hurricane Laura was very well forecast in the days before, as is true of most of our storms.  Thus, there is time to prepare and evacuate if people would take advantage of the improving predictions.

Hurricanes Versus Northwest Winter Storms

Hurricane Laura was a category 4 storm (130-156 mph sustained winds) as it approached the Louisiana coast and rapidly declined to category 2 (96-110 mph) after landfall.  Within a half day it was no longer a hurricane.

Northwest Pacific cyclones often approach the coast with winds equivalent to category 1 hurricanes (74-95 mph) and in the case of the Columbus Day Storm of 1962, was as strong as a category 3 hurricane (111-129 mph).

Satellite imagery of Hurricane Laura and the Chanukah Eve Storm (2006) is shown below with an arrow indicating the distance of 100 miles.  Note how much larger our storms are, which means that greater areas experience strong winds.

 

 The winds of Laura gusted as high as 132 mile per hour.  Scary, particularly since serious tree damage often start when the winds get to around 40 mph. 

But what about the 192 Columbus Day Storm?   Storm expert, Dr. Wolf Read, created a map of the peak gusts for that event, and the winds were extremely similar to Laura.  Our next tier of storms, such as the 1993 Inauguration Day Storm or the 2006 Inauguration Day Storm, often produce 80-90 mph gusts.


Weather Prediction Has Become More Skillful

The track forecast (the prediction of the path of the storm) of Laura was extremely good days in advance.  I mean stunningly good.   4-5 days before, the location of landfall was predicted correctly within a few miles and few hours (see proof below).  Such small track errors within 4-5 days of landfall has become typical of hurricane predictions and represent an extraordinary accomplishment of numerical modeling and observation.  Similarly, track errors of major storms approaching the West Coast have greatly improved (decreased).


Intensity forecasts are more difficult and the skill 4-5 days out is less.  4 days before landfall, Laura was "only" predicted to have 100 mph sustained winds.  The response should not have been any different.

Lessons

1. NEVER use a generator or barbecue inside a home when the power goes out.   

As noted above, most of the deaths from Laura were from generator use inside of buildings, leading to carbon monoxide poisoning.  Here in the Northwest there have been several deaths when folks used barbecues inside homes or garages and carbon monoxide invaded homes. Never, ever do this.

2.  If strong winds are predicted, do not sleep in bedrooms that might be hit by a falling tree.

Sleep in a lower level or in part of home/apartment that is not vulnerable.  If no trees, no worries.

3.  Never drive, bicycle or walk around outside during strong winds

During almost every major windstorm in our region, someone gets killed or seriously injured while traveling outside.  The chance of any individual being hit is very, very low, but if thousands are outside, someone is going to get hurt.

Let me admit something, I almost got killed this way.  On a windy night, I bicycled home along the Burke Gilman trail and a big branch fell about 6-7 feet behind me.   That would have been the end for me if I had been a second slower.  I am very careful about this issue now.

4.  Forecasts are much better today than even ten years ago.  Take the forecasts seriously.

Combining excellent forecasts with common sense, the death tolls from major wind storms and hurricanes can decline to near zero.
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My blog on the KNKX firing and cancel culture is found here.
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Friday, August 28, 2020

Morning Weather Discussion: Corrected

I take a look at the current smoke situation and note the chance of rain over the northern portions of Washington State  late on Sunday and Monday.  A benign, near-normal situation.  If you are concerned about smoke, avoid eastern Oregon this weekend.  Cascades should be fine.


Here is the video discussion (expand to view full screen)




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My blog on the KNKX firing is found here.
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Thursday, August 27, 2020

Hurricane Laura and the Wind Speed Dilemma

Last night, Hurricane Laura made landfall on the southwestern coast of Louisiana, bring heavy rain (6-8 inches),  strong winds (gusting to 132 mph at one location), and a coastal storm surge (roughly 10 feet at the most vulnerable locations).

The NWS Lake Charles radar image at midnight central time showed a well defined eye as the storm was making landfall.


Now the dilemma and interesting part.  Based on reconnaissance aircraft and other information, the National Weather Service's National Hurricane Center had estimated that Laura was a Category Four hurricane just prior to landfall, and according to the official Saffir-Simpson scale, that means the sustained surface (10-m) winds, averaged over a few minutes, were between 130 and 156 mph (see below).  Not gusts, sustained winds.

Saffir-Simpson Hurricane Categories

But here is the issue.  What were the maximum sustained winds that occurred last night as Laura made landfall?   Looking at all available stations, the highest sustained wind was 98 mph at Lake Charles Airport.  The map below shows the sustained winds at 1 AM, when the storm was just moving inland (wind barbs show sustained winds, with gusts in red).  The blue arrow indicates Lake Charles Airport.


Looking at the sustained winds, one would conclude that Laura was only a weak category two hurricane (96-110 mph).

And then there are gusts.  Gusts are not used as part of the Saffir-Simpson hurricane scale, but, let's face it, gusts are very important.  The big damage in most storms are done by the gusts.

Below are the maximum gusts of Laura. Two locations are extreme: Calcasieu Pass on the coast and Lake Charles, a few miles to the north (127 and 132 mph gusts, respectively)


Such strong gusts are consistent with the destruction of the NWS radar dome at Lake Charles Airport--they are rated to handle up to about 135 mph. (see the before and after below).  








So what is going on?  How strong was the storm?  Category two or four?

A key issue is friction and drag, which is much greater over land (with trees, hills, buildings, etc) that over the aerodynamically smooth water.   As a result of this surface drag, winds decrease VERY rapidly over land, even if the hurricane remains relatively intact aloft. 

Let me illustrate this visually, by showing you a forecast by the state-of-the-art NOAA/NWS HRRR model as Laura made landfall.  These plots show surface (10-m) surface wind in knots (1 knot=1.15 mph)

Before landfall (9 PM PDT), a nice hurricane structure is apparent, with some winds getting to 90 knots in the eyewall.


But then as the storm makes landfall (1 AM PDT), you can see a profound weakening of winds over land.


And by 5 AM PDT, with the storm completely over land, the fastest winds are gone.


So even if the storm had category four sustained winds near the surface while it is offshore,  the sustained winds decline precipitously when the store goes onshore.

But yet the storm can still remain very, very dangerous in the hours after landfall.
Why?

First, even the reduced sustained winds (e.g., 90-100 mph in this case) can produce great damage.

But there is more.  Gusts don't necessarily decline as rapidly as sustained winds as the storm moves over land.

To illustrate this, here is a plot of the  predicted gusts as the storm made landfall.  Not as much a decline over land as for sustained winds.  Gusts are caused by the intermittent mixing down of faster (higher momentum) air from aloft down to the surface.  So even if winds are slower down lower, sometimes air from aloft...where the winds are still blowing hard...can be mixed to the surface.  So gusts can hold out longer than sustained winds as a storm makes landfall.


The bottom line: a storm that was category four over water can still maintain a real "punch" over land, even after it nominally declines to a category two. Strong, damaging gusts can remain, even when the sustained winds decline.
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Some excellent articles on the surprisingly low wind speed over land  during hurricanes, by meteorologist and writer Bob Henson, can be found here:


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Will do a weather forecast and discussion tomorrow-Friday (video on my blog)

My blog on the KNKX firing is found here.
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Tuesday, August 25, 2020

California Wildfires and the Lightning Siege: How Unusual Is It?

California is burning and smoke has covered the northern half of the state and is spreading across the U.S.  
Most of the fires were started by a huge "lightning siege" that started on August 15th.  How unusual was this massive lightning event?  That question will be answered below.
Smoke situation this morning
The situation this morning was extraordinary.  According to CALFire, more than 14,000 firefighters are dealing with 650 fires (two dozen major ones) that have burned over 1.25 million acres.  There have been 7 fire-related deaths and 1400 structures lost.
The "lightning siege" over the past ten days has resulted in over 13,000 lightning strikes, many of which were from high-based thunderstorms that did not provide much rain to the surface (rain evaporated on the way down!).
How unusual was this large number of lightning strikes in mid-August?
The answer:  very unusual.
When I want to get information about lightning statistics, I know where to go: Professor Robert Holzworth of UW ESS and Dr. Katrina Virts, a past associate of Dr. Holzworth who is now a NASA scientist.  Dr. Holzworth runs a major lightning network (WWLLN) and a lightning expert, and Dr. Virts is the Mozart of lightning statistics.
Anyway, within of hours of inquiring about the situation, Dr. Virts sent me a graph showing 3-day lightning totals going back to late 2009 (below, click to enlarge).
The event that occurred last week was the sixth highest for that period, which is impressive by itself.  
But there is more.  It was the greatest 3-day lightning total in the entire period during the midsummer (June-August) period.   So this was quite an extreme event to occur in the warm/dry California summer.  One that followed an extreme warm period with a record-breaking upper-level ridge of high pressure centered over southern Nevada.
An important aspect of the unusual event was the ability to tap the moisture of tropical storm and move it into central California (producing the thunderstorms).  This is illustrated by the map below, which shows moisture around 10,000 ft (700 hPa pressure level) for 5 AM on August 17th.  The moisture levels getting into California were as much as 4-5 standard deviations from the normal.  Trust me...this is very, very unusual.  Like never happening before on that date.

Sometimes the atmosphere rolls the meteorological dice and gets two sixes.  
And, of course, the slow warming of the atmosphere from increasing greenhouse gases, the spread of invasive, flammable grasses, and the huge influx of people into rural areas make things that much worse.
On the other hand, there is very little smoke over Washington State and things look favorable over the next week.  I am becoming increasingly confident that Washington is going to dodge the wildfire bullet this summer.
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My blog on the KNKX firing is found here.
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Sunday, August 23, 2020

Fog UFO Spotted in the Strait of Juan De Fuca!

Folks frequently send me photos of clouds and other features for explanation.  But yesterday, I was sent the absolutely strangest picture ever.  A picture so weird that normally I would have passed it off as a Photoshop confection.

But I had to take this one seriously, since it came from one of the most well-known scientists in our state, Dr. Ronald Thom, the President of the Washington State Academy of Sciences, of which I am a member.  He had never seen anything like it...and jokingly suggested it might be some kind of UFO.

Here is one of the pictures he sent, near a beach in Sequim, looking towards the northeast in the direction of the Strait of Juan de Fuca (see map of location in the map below, which also shows the direction of the picture).  The picture was taken around 6 PM Friday.  It looks like a phantom fog ship, and in fact it was moving to right.



Dr. Thom took a video of the apparition, which you can view below.


So the question, is this real or some other-worldly vaporous ship, something reminiscent of one of the scary scenes in Pirates of the Caribbean?


Well, Matey, this is nothing better than solving a weather mystery!

Looking at the fog ship picture (repeated below), you will notice a thin veneer of fog over the Strait. Sea fog.  That probably resulted from very moist air that day passing over the cool waters of the Strait.

This is a very small scale feature, but the high-resolution satellite image taken at 5:46 PM, does suggest something (oval around it).  If you look closely, there is faint suggestion of the low clouds, with the "ship" being a bit brighter.


 Something was causing the fog layer to thicken or pile up, producing this unusual feature.

Extraterrestrial influence?  Since I am a student of Carl Sagan's, I must try to find a more scientific explanation!

As you can see on the photo and map, the Dungeness spit is nearby, with a lighthouse at the end of it.  There are weather observations there!   Let's check them out, perhaps they can offer a clue!  The game is afoot!

Below is a listing of the observations at the lighthouse that day.  Eureka!  There is a big clue in that data!  Just when that feature was moving past, there was a rapid increase in the wind speed (5.8 to 9.6 knots) and a wind shift from south to southwest.


That is a big hint.  If wind suddenly picked up, this could produce an area of low-level convergence of air that could cause a lifting of the fog layer.   A picture will help here (below).   If the wind is faster on the left (west side) than on the right (east side), that means more air is coming in than going out.  So air is accumulating where the wind speed is changing, result in upward motion that pushes the fog layer upwards.  I think that is what is happening here.

The "fog ship" is moving along at the same speed as the wind surge from the southwest/west.

Of course, there are alternative explanations possible (see below), but I doubt if Carl Sagan would have approved.


Friday, August 21, 2020

Friday Morning Weather Discussion

My weather discussion is found below....check out the video.  Today I talk about Olympic rainshows, smoke over California, high humidity, and look out at the forecast for the next week!

Thursday, August 20, 2020

Record Breaking Moisture over the Region

Tonight there is an amazing plume of moisture over us....in fact, a record for the date and one of the highest on record.

Perhaps you can tell--it is very moist and sticky out there. The air seems thick and a bit oppressive.

You can see the plume of moisture on a weather satellite image that shows moisture content in the upper troposphere (roughly 18,000 to 35, 000 ft)--see below.   See the white, light gray plume passing over western Washington from the southwest?   That's the feature of interest.


Consider a plot of the climatology (daily max, min and average amounts) of water vapor in the atmosphere shown below.  This is a plot of precipitable moisture at Quillayute on the Washington Coast.  The idea is if you took ALL the water vapor in a vertical column of air above you and condensed it out, how much liquid water would be produced?  That is precipitable moisture.

The value today is represented by the gray dot:  1.57 inches.  That is what you would get if you squeezed out every bit of water vapor in the air above.  The record for the date is shown by the red line.  Wow!  We beat that record for the date!  And there are only a handful of dates in the complete record that have been greater.  You will tell your grandchildren about this one day.

So we start with a moisture-rich atmosphere and even some light rain tonight (see the radar image at 10 PM).  The rain evaporates and adds moisture to the air at low levels.


As a result of all this moisture, our dew points have been quite high tonight, reaching into the upper 60sF in the south Sound (see map).  Dew point is a good measure of the amount of moisture in a sample of air.  Mid to upper 60SF is quite unusual for the region...more like you would expect on the East Coast (click to expand image).  Several of these dew points tied or beat the daily record.


The humid air should stick around overnight, with drying by lunchtime.   But on the positive side, the humidity is perhaps good for your complexion.


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Note:  My weekly online weather discussion will come out at 9 AM Friday.  And I am working on starting a weekly weather podcast.
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My blog on the KNKX firing is found here.


Wednesday, August 19, 2020

A lightning barrage puts the western U.S. on fire

Note:  My weekly online weather discussion will come out at 9 AM Friday.  And I am working on starting a weekly weather podcast.  On this podcast I won't be as constrained as I was on KNKX, where certain topics (e.g., climate) were discouraged by the management.
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During the last few days, hundreds of fires have been ignited by an extraordinarily unusual barrage of thousands of lightning strikes over the western U.S. Major fires are burning all over California and dense smoke has spread across the region (see below).  The city of Vacaville is being engulfed in flames and air quality is rapidly degrading.


Impressively, an amazingly dense plume of smoke extends from California hundreds of miles into the Pacific.


And several major fires have started here in the Northwest--most by lightning.  Here is a satellite image of northern Oregon, with smoke extending eastward from fires on the eastern slopes of the Cascades.


And more fires are found over north-central Washington.  This sudden wildfire blow up has its origin in two meteorological events.  First, a strong persistent ridge of high pressure that brought record-breaking temperatures and drying conditions over a vast area of the west.

And then there was the most unusual and extreme "lightning barrage" with over 10,000 lightning strokes  in 72 hr.   Keep in mind this is usually the dry season in California. Let me show you the lightning in 24 h chunks.

For the 24h ending 1 AM Saturday. there was lightning over the Sierra Nevada, but much more over New Mexico.

Lightning starting moving into southern CA during the  next 24h and extended up the Sierra Nevada into southern Oregon.

But the real barrage hit on Sunday, with over a thousand lightning strikes in CA and even lightning over western Washington, something described in my previous blog.

The onslaught over CA did not end on Monday, with thousands more lightning strikes in northern CA and southeastern Oregon.

And even more on Tuesday, mainly over the eastern side of CA and Oregon.


These lighting strikes hit fuels that have been dried by not only the normal drought of the western summer, but an extraordinarily warm, dry period the last few weeks.

A persistent ridge of high pressure over the West was the cause, illustrated by the upper level weather map at 5 AM Sunday. The orange/red area is where the heights (or pressures) were much higher than normal at this level (about 18, 000 ft).   The winds are also shown at that level.  Strong southerly (from the south) winds are on the western side of the ridge---this is very important.


Why?  Because it entrained lots of moisture from the tropics and pushed it northward, creating lots of thunderstorms (see moisture map at that time).  If you look carefully you will see tropical storms to the south, which helped supply even more moisture. And it was worst than that.  The thunderstorms were mainly high-based, with much of the rain evaporating before hitting the surface.  Lightning, without wetting the surface, on very dry surface fuels.  A recipe for disaster.

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My blog on the KNKX firing is found here.
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Monday, August 17, 2020

Extreme Beauty and Extreme Temperatures

The weather during the past 24-h has been  extreme in several ways (some of which I will explain below), but so has been the raw beauty of the atmosphere around us.

Last night, I went with my wife and a friend to cool off at Richmond Beach Park and the sunset was extraordinary (see below).  The sky around the Olympics was on fire, with rays of orange and red extending overhead.   The reason for such extreme colors?  The red/orange light of sunset playing within the clouds and rain from the approaching line of showers/thundershowers.


And this morning, I went outside and thought I had entered an impressionistic painting.


This was the remnant of some low-level instability from the previous evening.   Van Gogh would have a field day with this scene.

But then there were the weather extremes.  Yesterday's temperatures hit record levels at some locations, and I am not talking about daily records.  I am talking about ALL-TIME RECORDS.

The temperatures around Everett and the Kitsap Peninsula were very unusual.  Take a look at the high temperatures for yesterday (below).  Paine Field hit 100F...which tied the ALL TIME RECORD FOR ANY DAY at that location.  Several other locations got to the century mark, with a few (Marysville and Lake Stevens) surging to 104F.  The secondary stations are not of the same quality as Paine Field, but still, this is wild.


And crazy warm temperatures were also found over the southern Kitsap and southwest Sound area, with lots of 100F values, even at sites near water.


So what was going here, particularly around Everett?

Temperatures aloft were quite warm, with lower atmospheric temperatures at Forks, on the WA coast, pretty much tying record levels.  To show this, the climatology of temperatures at 5000 ft (850 hPa pressure) are shown, with the blue star showing yesterday's value.


But there was something else. There was a low-pressure disturbance moving up the coast and high pressure inland, which helped to force strong southerly flow, which isolated Everett and vicinity from the cooling effects of the cool water to the north.  To illustrate, here is map of the heights (think pressures) around 5000 ft at 5 PM Sunday, with winds and temperatures (shading) shown.  Strong southerly flow that pushed warm air into the region.


Although we can't say global warming is the "cause" of this warm event, we should expect the number of such situations to increase slowly during this century as CO2 concentrations rise.
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My blog on KNKX is found here.
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