May 31, 2021

Strong Atmosphere River Heads into British Columbia and Southeast Alaska

While the Northwest has been drier than normal, it has been drenching wet a few hundred miles to the north.

An unusually strong atmospheric river....a long current of moisture stretching southward to the subtropics...has been in place for days, bringing large amounts of water vapor to Alaska.   And the atmospheric river will be in place for several more days, slowly moving southward.

To illustrate, the scale and beauty of the atmospheric river, here is a water vapor satellite image for 11 AM today. The lighter areas have more water vapor.  You can see the current of moisture extending from near Hawaii into central BC.  This current is the result of low pressure over the Gulf of Alaska and high pressure offshore of California.  


A forecast of total water vapor content in the atmosphere for 11 PM tonight shows a healthy atmospheric river (white and blue colors indicate the higher amounts of moisture).

As this atmospheric river slams into the mountainous West Coast, the air is forced to rise, cool, and release its moisture, resulting in massive amounts of rain.  Looking at totals over the past week, some locations of SE Alaska have gotten as much as 6-8 inches!  


The European Center weather model is predicting lots of future precipitation from this atmospheric river through 5 AM Thursday, with some locations being hit by 6-8 inches of additional accumulation (see below).   This graphic is a great illustration of the enhancement of precipitation by the terrain.


The Northwest should stay dry during the week, but our turn for rain is coming over the upcoming weekend.  Interestingly, the extended weather forecast has shifted, with the latest European Center 1-month projection going for wetter than normal conditions from the Cascade crest westward (see below).  Good to keep the fire danger down.








May 30, 2021

The Time of Year You Can See the Air Move

 Most of the time, you can not see the air move.  You can feel it, but the complex, turbulent motions are invisible to you, except when it interacts with leaves and branches on trees and plants.

But for a few weeks of the year, the sky is full of small, cotton-like tuffs that like a natural MRI machine reveals the complex three-dimensional motions of the atmosphere.  

Cottonwood season.  And we right in the middle of it.  

Being cottonwood aware is of particular value this year.  It reveals the active dispersion and movement of air that makes the outdoors essentially COVID safe, and thus should be of some comfort for those nervous about transmission outside.


Cottonwood seeds are embedded in small cotton-like fibers.   A million seeds weigh about 3 pounds.  Yes, each seed and tuff weights about .000003 pounds.   And that fact, plus the cottonwood tuff, means that these seeds fall VERY, VERY, VERY slowly.   So slowly that they are excellent markers for the three-dimensional flow of the air on which they are taking a ride.

Yesterday, I sat back and watched the cottonwood seed show, on a day when the winds were quite light.  It was quite a show and very revealing.

Check out my video below taken Saturday afternoon


Watch the leaves on the trees....they are hardly moving, yet there is substantial air motion.

You can appreciate some of the 3-D motion from this University of Wyoming video:


Watch two seed tuffs over time and you see them separate from each other--that is a visual sign of air dispersion and dilution.

And while you are watching the cottonwood tuffs, take a look around the vicinity of the sun.

We have a high cirrostratus cloud layer over the region and I expect some impressive halos and sun dogs today.   These ice crystal clouds preferentially bend light by 22 degrees, creating a ring around the sun.


At one time, halos and their cousin, sun dogs (bright areas on both sides of the halo) were thought to presage the death of kings or some other terrible events.  

Finally, you might want to find your shorts and tee shirts.  Western Washington is predicted to warm into the lower 80s on Tuesday and Wednesday and the Columbia Basin will see highs in the 100s.    To pre-warm you up, below is the forecast high temperatures for Tuesday at 5 PM.

80s from north Seattle southward and 90s and more over the Columbia Basin.  The coast is cooler and cool it will spread over the Strait of Juan de Fuca with onshore flow.









May 28, 2021

The History of Numerical Weather Prediction and A Warm Memorial Day Weekend Forecast: All in My New Podcast.

 The key technology of weather forecasting is numerical weather prediction, using powerful computers to simulate the future evolution of the atmosphere.

The first numerical weather prediction--using a digital computer to solve the equations describing the physics of the atmosphere-- occurred in 1950 using the ENIAC computer (see below)


And numerical weather prediction was immeasurably improved with the advent of weather satellites that can provide a three-dimensional global view of atmospheric structure. TIROS-1 the first weather satellite is shown below.


My podcast describes the history and technology of numerical weather prediction and provides a very favorable Memorial Day weekend forecast.  Listen to my podcast below or through your favorite streaming service.

Here is my podcast, with more streaming information at the bottom of the blog.

Click the play button to listen or use your favorite streaming service (see below)

You can stream my podcast from your favorite services:



May 27, 2021

Dust Storms on Both Sides of the Cascades

 You start with a late spring day after fields have been plowed for a number of crops.

You add a relatively dry spring, with rainfall less than 50% of normal over most of the region.

And you throw in strong winds, gusting to 40-70 mph in some places.

The result:  blowing dust, obscured roads, and even some visibility-related accidents.

Eastern Washington

There is dust blowing right now around the Tri-Cities and around I90 from roughly Moses Lake to Spokane.   Check out this video from WA State Trooper C. Thorson (click on the link) taken in Richard (I82 and Dallas Rd).  Make sure you have the sound on!

Or check out this WSDOT cam in Davenport--pretty hazy.


The visible satellite picture at 4PM clearly shows the dust--- I put on an arrow to make it clear.  The blowing dust is a light brown color.


Now springtime dust storms are not that unusual in eastern Washington.  Unfortunately, it happens every year.

Western Washington

But less usual are dust storms in western Washington.  Dan McShane sent me some pictures around the Skagit Delta, which really got my attention. He graciously allowed me to share them with you.


Here is a recently plowed field that is blowing away.

And clearly, visibility is being seriously degraded in this shot.

The big issue is wind and there is a pretty impressive wind event going on across BOTH eastern and western WA right now.

Here are the maximum winds today for the 24h ending 4 PM (click on image to expand).  In western WA, a number of locations had gusts to 30-40 mph, and even up to 50 mph in places.  40-50 mph are common in eastern Washington this afternoon in the Columbia Basin and near the Oregon/WA border.


Zooming in to around the Tri-Cities, several observing sites got to 70 mph!  The winner gusted to 77 mph.


These strong winds are associated with a strong springtime low center that passed north of Washington, producing a large north-south pressure difference (or gradient )....see below. 

 Here is the sea level pressure forecast for 1 PM, with solid lines being isobars...lines of constant pressure.  In the mountainous west, winds tend to blow from higher to lower pressure and that is what is happening this afternoon.  The winds are from the south to southwest.


The surface wind gust forecast for 5 PM today is quite impressive, with lots of eastern Washington getting to 35 knots or more (green and blue colors).  No wonder the dust is blowing.


The winds are strong enough that thousand of customers have lost their power (see below), with fully leafed out trees contributing to the problem.


 Enjoy the wind and be prepared for a warm and dry Memorial Day weekend.  Many of you west of the Cascade crest will experience 80F by Monday, while Richland and envions will soar to over 100F.

May 25, 2021

What is atmospheric pressure? Why do we care about it? Part 1.

 A few days ago, a blog reader emailed about atmospheric pressure.  

He asked:  Since can't feel it or sense it, why should we care?

I was surprised by the question since atmospheric pressure is so important in meteorology and weather prediction.     So let me give you a lowdown on pressure--by the time I finish,  you will run out and buy a barometer!


Atmospheric pressure at the surface of our planet is not negligible.  

On average, pressure at sea level is about 14.7 pounds per square inch!   That is like a bowling ball pushing against every square inch of your body!


Since the human body has about 2600 square inches of surface area, the is equivalent to the force of several thousand bowling balls.  Or 38,000 pounds of force or 19 tons!

Why aren't we CRUSHED???     

Because the pressure inside our body balances the external force from atmospheric pressure.    But you can tell that this massive pressure is there by lowering the pressure inside an object---it is summarily crushed!

If you want proof, check out this youtube video in which the pressure was reduced inside a tanker car.  Let's say this tanker will not be used again.


Atmospheric pressure is related to the weight of the air above you.    Yes, air has weight!  

A volume of a cubic meter near the surface weighs about 2 pounds.  Now air gets less dense as one moves upwards, but there is still a LOT of weight from all the air above you.

Pressure is given in a lot of confusing units.

Pounds per square inch (typically around 14.7 as noted above).

In the metric system (preferred in science) we use hectopascals (hPa).  

And, another approach is to give pressure in terms of the height of a mercury column supported by atmospheric pressure (see illustration of a mercury barometer below).  At sea level, that height is typically about 29.92 inches.    Atmospheric pressure pushes down on a bowl of mercury and the pressure is communicated to the vertical tube of mercury.  The downward weight of the mercury is supported by the upward force resulting from atmospheric pressure.

Higher pressure results in a taller column of mercury.  And  vice versa.


What if we replaced the mercury with water, which is much less dense (and thus weighs less)?  In that case, atmospheric pressure could support a column about 30 feet high!

Finally, here is your amazing factoid for today.   How do straws work?  What is the longest possible straw in the world?  Turns out the answers have to do with atmospheric pressure.

When you sip a liquid with a straw, why does the liquid move upward towards your mouth?  Are you somehow pulling up the liquid like a pump?  

NO!


Atmospheric pressure is pushing the liquid up the straw!     When you are sucking air at the top of the straw, you are reducing pressure on the upper portion of the straw, creating a zone of lower atmospheric pressure.   The liquid in your glass or soda can is at atmospheric pressure, and thus at higher pressure than at the top of the straw.  As a result, there is a force from high to low pressure, which pushes the beverage into your mouth.

One final thing....what is the longest a straw can be to work?   

30 feet!  That is the maximum column of water that can be supported by atmospheric pressure.  So if someone tries to sell you a 40 ft straw, turn down the offer.

May 23, 2021

A Wet Week Plus Full Reservoirs Should Put the Northwest in Relatively Good Shape For This Summer

The Pacific Northwest has a Mediterranean climate, with wet winters and very dry summers.

Thus, it is important for us to approach summer with full reservoirs, ample mountain snowpack (which provides melt water during the summer and early fall), and a nice late spring dousing to wet down the vegetation and soils.

And it looks like we will have all three.

As most of you know, we have had a dry spring so far, with the eastern part of the state receiving 0-3 inches less than normal and larger deficits in the west (as much as 9-16 inches below normal)--see below.


On the other hand, there is good news.  With a relatively cool, wet, and snowy La Nina late winter the key reservoirs serving our region are looking good.   The critical Yakima River reservoir system, so important to agriculture in eastern Washington, now possesses above-normal water levels (see below, blue is this year and red is normal).


Seattle's reservoirs are near normal and the snowpack above Seattle's reservoirs are above normal.


The current snowpack for Washington State is truly excellent west of the Cascade crest (287% of normal for the northwest Cascades and 152% over the Olympics) and above normal for the northeast slopes of the Cascades and the Okanagan area.   But low snowpack is evident for the lower-elevation areas of southeast Washington.

Streamflow is near normal for rivers on the eastern slopes of the Cascades and those draining off the Olympics and northwest Cascades, but low flow is a concern over southwest Washington--the result of the dry condition during the past few months.

But good news regarding precipitation is on the horizon.

The latest UW WRF model accumulated precipitation forecast through Saturday morning shows wet conditions EXACTLY where we need it:   over southwest Washington and in the Rockies that help feed the Columbia and Snake Rivers.


The wet bounty is due to the persistent development of upper-level troughs of low pressure over the eastern Pacific and the Northwest, as illustrated by the upper level (500 hPa) map of heights (like pressures) at 5 PM Thursday.   Looks like a thunderstorm pattern to me!



Considering the skill of long-term summer forecasts is very poor, one needs to be careful about summer weather prediction.  But in some sense, summer forecasts are less critical than winter projections, because the June through September period is so dry climatological around here.  In any case, we are going into this summer in relatively good shape, even with the dry spring so far.

May 21, 2021

The First Wildfire Smoke of the Season Reaches Washington State and My New Podcast

The Cherrywood Fire of southern Nevada.  DOE image.

My New Podcast

My new podcast is out, providing the latest forecast for this weekend, and in the second part, I describe the history of weather forecasting over the past 200 years.

Here is my podcast, with more streaming information at the bottom of the blog.

Click the play button to listen or use your favorite streaming service (see below)

First Smoke of the Season

I was a bit surprised when I saw the visible satellite imagery this morning:  there was clearly significant wildfire smoke over the eastern portion of Washington State (see image below).  This smoke is aloft and not reaching the surface.


This is confirmed by air quality monitors around the region, which are all green (good air quality).

The Cherrywood fire is now about 15,000 acres in size and is burning in mainly grass, so I suspect it will be short-lived (grass fires generally burn fast and are accessible to fire-fighting).  

You can see the movement of the smoke from the simulation of the NOAA HRRR-Fire system.  Here is the predicted smoke at 11 AM.  You can see the smoke's origin and its movement northward.


And the 6 AM forecast is nearly perfect, with the dense smoke over eastern Washington. 


The smoke should spread out (diffuse) and move westward over time but will remain aloft.

You can stream my podcast from your favorite services:

May 20, 2021

The Beauty of Springtime Cumulus Over the Northwest

 This is the season of large cumulus clouds over the Pacific Northwest.  And they are often stunningly beautiful.

There is a reason why these majestic clouds are so frequent this time of year:  the atmosphere is most unstable and turbulent during the spring, for reasons I will explain below.

And with strong sun and long days, the illumination is excellent, and the potential for rainbows ever-present.

Consider an image from the Seattle PanoCam for yesterday evening as the setting sun illuminated the underside of a large cumulus cloud east of Seattle.  There is an extensive cirrus anvil-like structure aloft (with wispy edges) and downward protuberances called mammatus clouds extending downward from the anvil.  These features are associated with heavier air that is sinking.


A few hours earlier, the PanoCam caught a growing cumulus cell south of Seattle with a shaft of rain falling beneath it.


And here is an extraordinary photo of a large cumulus cell over the South Sound yesterday taken by photographer Frank Jenkins.  Beautiful cirrus anvil, made of ice.  And an impressive shaft of rain reaching the surface.


Cumulus clouds, from shallow fair-weather cumulus to miles-high cumulonimbus (thunderstorm) clouds are known as convection and result from vertical instability.    This generally occurs when a large difference with temperature with height occurs:  when the temperature cools rapidly with height.

When temperatures cool sufficiently rapidly with height, a blob of air (called an air parcel), displaced upwards, will accelerate skyward on its own for a considerable distance.    And surrounding the upward accelerating air, other air is moving downward.

You are all familiar with convection when you heat water or cereal in a saucepan (see below).  Your burner is heating the bottom of the pan, causing a large vertical change in temperatures in the water or cereal, resulting in up and down motions:  convection!

Image courtesy of Bruce Blaus

What time of the year does the temperature change most rapidly with height of the Northwest?
Spring!   

Let me tell you why.

During spring, our sun is getting strong and powerfully warming the surface.  Think of cranking up the hot plate shown above.   Below is the solar radiation received in Seattle from January 1 to today.  BIG increases over the past five months!


So we are warming the surface more intensely as we enter mid-Spring.   

But the atmosphere aloft takes time to catch up....you can think of the atmosphere as a vast flywheel...... takes time to get it spinning faster!   

Below are the temperatures at roughly 10,000 ft above Seattle from January 1st to May 18th this year.  There has been only modest warming overall, and occasionally we get pulses of colder air (like at the end of the period).  During these cool periods, the atmosphere aloft is cool, while the surface is vigorously warmed.   This leads to a big change in temperatures with height, instability and convection.


You are living in the percolating atmospheric cereal pot during much of spring!  And where the air is going up, there are clouds and precipitation.  When going down, clear areas.

The early signs of cumulus convection are easy to spot:  you will see the development of shallow cumulus like shown below.  Many days that is all we get.  But if the temperature change with height strengthens and there is a source of upward motion to get things going, more serious and taller cumulus convection may occur.  Meteorologists like myself love such days.


What Controls the Movement of Wildfire Smoke? And a Perfect Forecast for the Next Week.

 We are now in wildfire season and the resulting smoke is on everyone's mind.  And the dramatic transcontinental movement of West Coast ...