August 16, 2022

SuperMonsoon Hits the Southwest U.S. and the Northwest Gets a Piece of It.

 There is a good name for it:   a SuperMonsoon.

In my previous blogs, I talked about the nature of the Southwest (or North American) Monsoon, and how water vapor from the Gulf of Mexico swings around a high-pressure area into the Desert Southwest from June to August.

As a result, the southwest U.S. is usually MUCH wetter than the Pacific Northwest during mid-summer.

The Southwest Monsoon has been particularly active this summer with lots of thunderstorms and an unusual westward and northward penetration of moisture.

Take a look at the percent of normal rainfall during the past month.   

Wow.  Some areas (Nevada and southwest California) have been hit by over 800% of normal rainfall.  Folks needed an umbrella in Las Vegas!

The past week has been particularly wet, with large amounts of monsoon moisture pushing into eastern Oregon! (see below).  Much of that precipitation was associated with lightning, causing several fires.

This summer's monsoon has been associated with unusual amounts of water vapor moving northward out of the tropics.  

To demonstrate this to you, below is a plot of water vapor anomaly (difference from normal) for June 1 to August 13th.  Greens to red are above normal.  Wow...lots of oranges and reds....well above normal water vapor amounts heading northwestward out of Mexico into the Desert Southwest!   Some of it even reaches the Pacific Northwest.

With all the moisture, bringing precipitation and thunderstorms, the Las Vegas  National Weather Service have been busy putting out flash flood warnings (see one from yesterday below)

Looking at the total rainfall map since June 1, only showing values above 1.5 inches, lots of areas in the southwest have gotten over 4 inches, with a few locations getting 5-17 inches.

Interesting, last year was also a big Southwest Monsoon fact, even more impressive than this year.  

Is there a trend in  Southwest Monsoon rainfall?  To gain some insight into this question, below is a plot of July Arizona rainfall for over a century.  

This year the July rainfall across Arizona is clearly above normal (and the heaviest precipitation was during August), but last year had exceptional July rain.   Some really heavy rain about 100 years ago, and July 2020 was very dry.   But all and all, a lot of precipitation variability but with little trend.

Some climate model studies suggest that the Southwest Monsoon will get drier and others project little overall change (drier first half, wetter second half of the summer).  But considerating that thunderstorms/convection produces most monsoon rainfall and that climate models don't handle them well, I suspect the jury is still out on the topic.

One final thing.  Last year's bountiful Southwest Monsoon resulted in heavy grass growth that contributed to the terrible New Mexico fires earlier this year.    The Forest Service, BLM,  and other wildfire agencies will need to be prepared for an active wildfire season next year.

August 14, 2022

Wildfire Smoke: What a Difference a Year Makes!

This has been a particularly smoke-free summer so far over the entire West Coast, and to appreciate our clean-air bounty, let's compare satellite imagery between this afternoon and a year ago.

Yesterday's MODIS visible satellite image shows smoke-free skies over nearly the entire western U.S., with two exceptions:  a very small fire west of Lake Chelan and a modest smoke area in northern CA.   That is about it!

Compare that to the smoky miasma of exactly one year ago.  Yuck!  Smoke everywhere!

 The air quality data provided by the EPA in their AIR NOW network shows the story on the ground. This year, nearly all sensors indicate good (green) air quality.  You can breathe freely in virtually the entire West.

But last year on the same date lots of yellow and reds (poor air quality), particularly over eastern Washington and northern California.

Finally, looking forward in time, here is the  NOAA HRRR model smoke forecast for today at 5 PM.  This shows the total smoke in a vertical column..the amount at the surface would be much less. 

Not too bad for this time of the year!

August 12, 2022

The Most Threatening Wildfire Period is Ahead. But Why? And a Warm, Pleasant Forecast.

This has been a very benign wildfire season so far this year, with far fewer than normal wildfires over the western U.S., with considerably less than normal area burnt (see figures below).

Number of wildfires by year:  WA DNR area

The area burned by year:  WA DNR Area

The area burned by year, California.

But we can not become complacent!   Historically, the most threatening wildfire season in the Northwest is the end of August and early September as the atmosphere starts to cool.

But why?  What is so threatening about the cool late summer/early autumn periods?  All is revealed in the podcast.

And I also provide the forecast for the next week.  Very pleasant in the west, but a bit toasty in the east. 

To listen to my podcast, use the link below or access it through your favorite podcast service.

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August 11, 2022

Monsoon Thunderstorms Across the Region

The movement of moist, unstable Southwest Monsoon air into the Northwest did not disappoint: as shown by the 24h lightning map ending 1 AM this morning, many hundreds of lightning strokes were observed over the region.

There were several bands of thunderstorms and lightning.  One was along the coast and another moved up eastern Oregon and really hit hard around Walla Walla and far SE Washington.   A narrow band of boomers crossed Tacoma into Vashon Island.

The monsoon moisture plume...directed from the desert southwest..was evident in the water vapor satellite image from yesterday morning (5 AM Wednesday)

The dew points...a good measure of atmospheric water vapor content--were very high over eastern Washington, getting up into the mid-60s in portions of eastern WA, eastern Oregon, and Idaho (see below for noon on Wednesday).  That's unusually high for the normally dry region. 

Today the moisture plume has slowly shifted eastward (see satellite image from tonight).

As a result, the only thunderstorms this afternoon in our area were located over the far eastern side of Washington and Oregon (see radar image from tonight).   Some of them had heavy rain or hail (red colors).

According to the latest model run, the monsoon moisture and associated thunderstorms will move even farther eastward tomorrow, with the forecast for 5 PM Friday showing the thunderstorms over Idaho and eastern Monday (see below)

A dry weekend is ahead with warming temperatures!

August 09, 2022

Monsoon Moisture Reaches the Pacific Northwest

 Welcome to monsoon season in the Northwest!

Showers spread northward from Oregon this morning into Washington State (see radar at 6:30 AM this morning below).  Generally only a few sprinkles, but it was nice change in any case.

The moisture is associated with a plume of water vapor coming out of the southwest---a northwestern extension of the Southwest Monsoon (also called the North American Monsoon).

The water vapor satellite image this morning shows the moisture plume

as does the infrared satellite image.

The Southwest Monsoon occurs every summer from roughly late June through late August.    It occurs as high pressure tends to build over roughly the New Mexico area, resulting in moisture being swept up from the Gulf of Mexico, across Arizona and western New Mexico, and then up across Nevada into eastern Oregon (see schematic below, showing upper-level heights at 500 hPa (you can think of this like pressure at 18,000 ft).  The white area shows the direction of the flow at that level.
During the past day, the monsoon plume of moisture was supercharged by a strong low center that developed west of California (see map below, which shows winds and heights/pressures at 500hPa/18,000 ft).  This really revved up the moisture-laden flow from the south.

During the last 24 h (see below) the monsoon clouds/showers brought light rain into eastern Oregon, with some spreading westward to the Cascades.  Here in Seattle, only about a trace.

24h precipitation ending 10 AM Tuesday

During the next 24 hr, more light showers will occur over the region as the low off California heads northwestward into our region.  Below are the 24-h precipitation totals ending 5 PM Wednesday.  You can see the showers swirling around the low offshore and more monsoon moisture heading up into eastern Oregon.

An interesting research question my group is working on deals with the implications of global warming for regional precipitation and particularly monsoon moisture.   Our initial work suggests MORE summer monsoon precipitation over eastern Oregon as things warm up (see below).   But we have a lot more work with higher resolution climate simulations to nail this down.

Differences in summer precipitation between the end of the 20th and 21st centuries.  Green indicates more summer precipitation.  These high-resolution climate simulations assume a massive increase in CO2 (RCP 8.5 scenario)....probably way too much.

August 07, 2022

Warm For A Few Days Then Cooling with Showers

 Climatologically, we are now moving past the climatologically warmest time of the year, as the weakening sun and shorter days finally start taking their meteorological toll. 

And during the next few days, we will experience substantially warmer than normal high temperatures, but comfortable temperatures at night.  

But on Wednesday, both cooling and showers will move in, with the side benefit of helping to get control of a few local wildfires.

The visible satellite image this morning shows clear skies, but some smoke from the Vantage grass fire, and the northern extent of a lightning-caused fire in the central Oregon Cascades (the Cedar Creek Fire).  There is also a small fire in south-central BC.

The warmth today and tomorrow will be associated with the northwest extension of an upper-level ridge over the Northwest (see upper-level map for 5 AM Monday, below).  But pay attention to the deep low west of northern California.

It has our name on it.

By Wednesday at 5 PM, the low will approach our coast with the inland ridge retreated eastward.  Think cooler.  And wet.

The latest National Weather Service National Blend of Models, a statistical approach that derives information from many models and observational inputs,  suggests that in Seattle the highs will rise to the upper 80s today and tomorrow, decline modestly on Tuesday, and then plummet to 75 on Wednesday, followed by around 80F for the remained of the week.    

Lows will be around 60F each night, so evening cooling should be good.

Much warmer east of the Cascades, but not equal to last week.  At Pasco, it will be as warm as low 100s through Tuesday, followed by the upper 90s.

That approaching low will bring some showers to the area on Wednesday,  with the accumulated precipitation through Thursday at 5 AM showing light rain offshore, along the western side of Washington, and across much of eastern Oregon.

Although warm, visibility should be excellent at Seafair today, if you want to catch the new (and larger) Blue Angels.

August 05, 2022

The Northwest Weather Roller Coaster and Weather Signs in the Sky: All in My New Podcast

 My new podcast is out (see below on how to listen).

I start with the forecast, which includes our typical summer weather roller coaster.  Warming into the upper 80s in the west, followed by a sharp decline on Wednesday.

Our summer weather

But most of my time is spent on how you can gain insights into future weather by watching the sky.

I start by noting that declining visibility after a clear period is often a sign of the influx of marine air.

Then I talk about "caps" on our mountains that often indicate an approaching storm.

While contrails can often indicate a weather decline

And mid-level cumulus can suggest the upcoming potential of thunderstorms or other inclement weather.

In short, there are a lot of weather insights available to an educated observer.

To listen to my podcast, use the link below or access it through your favorite podcast service.

Some major podcast servers:

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August 04, 2022

Heatwaves in the Northwest: Are Extreme Heat Events Increasing Rapidly?

 My Friday podcast on extreme heat events in the Northwest stirred up a lot of comments and some controversy, so perhaps I need a detailed blog that puts the details in front of you.

My basic point is that the peak temperature, duration, and frequency of extreme heat events are not rapidly rising in the Northwest.

And that mean/average temperatures or minimum temperatures are rising faster than the extremes.

Let me explain.

First, you have to be careful to use reliable observing sites

The Seattle Times and some climate activists like to look at temperatures at Seattle Tacoma Airport, but SeaTac is the LAST station you want to use for climate studies.  Why?  Because of the profound growth of the airport, with the addition of a third runway, many additional buildings, and lots more concrete.  Plus, massive urbanization around the airport.  Plus, the observing record only goes back to the late 1940s and the sensor location has been moved.

SeaTac Airport.  The weather sensors are at the black dot

Based on the recommendation of Mr. Mark Albright, past Washington State Climatologist, let's consider Olympia Airport instead. No additional runways, a much less developed environment (see below) and the record goes back to 1941.

Below is a plot of the highest temperatures in July and August for the entire record at Olympia.  

Do you see much of a trend in the extreme high temperatures?  I don't.

There are more very cool years in the earliest part of the record, so if you calculate a linear trend line, you get a slight upward tilt (about 1.2F over the period).  Again this is not driven by the temperature extremes but by more unusually cool years early in the record.

Now let's look at the trend in the daily average temperatures for those months.  This is the average of the daily highs and lows.   There is more of an upward trend: about 2F over the entire period.

Next, let's examine a different this case Lind 3NE, which is found in a totally rural area in eastern Washington (see a picture of the surroundings below).  This station goes back to 1931. No urbanization here.  An area of natural conditions or dryland farming.

Here is a plot of the maximum temperatures for July and August at Lind.  Mama Mia!  The extreme highs are GOING DOWN.  Many of the warmest years are early in the record.

On the other hand, the daily average temperature is going up (by 2.4F over the entire period)

Other well-exposed, mainly rural, observing sites show similar behavior.  In contrast, highly urbanized or disturbed sites (like SeaTac), particularly those with sensor exposure issues, show much more of an upward temperature trend. Obviously, these observations are not suggesting an existential threat...just a small upward trend of mean temperatures and less upward trend in extreme warmth.

Six Day Heat Waves

A lot has been made in the press and by certain climate activists about SeaTac achieving six days above 90F for the first time.  This kind of frequency above a threshold can be very deceiving, since very small warming (say .1 F) can cause one to cross the threshold.

It is far more meaningful to look at the actual temperatures during the warmest six days for each year.

So let's do that!

For Seattle, the six warm days last week came in third for the period of record.  Note that many other years were right behind.   And remember all the recent artificial warming due to the third runway and more.  Without all that development, SeaTac temperatures last week would have been much further down the list.

For Olympia, last week falls to number five, and was over two degrees cooler than the "winner" in 1981.  1941 was also warmer.

It was mighty warm in eastern Washington last week, so what about Lind (see below)?  The heatwave last week did not even make the top ten.

Were we unusually warm for an extended period last week?  You bet.  Did global warming contribute to it?  Quite possibly by a few degrees.   Was this the record six-day warm period at any of the observing sites in the region?  No.

There are some folks that get concerned when I put our summer heat waves into historical perspective, but it is critical to do so.  Heat waves are nothing new in the Northwest.  Although our mean temperatures are slowly increasing, the extremes are rising more slowly.  And when it comes to impacts, the extremes are really what count.

Why does global warming affect the means more than the extremes?

This is a topic I will cover in a future blog in some detail, but there are many reasons why global warming influences mean temperatures much more than extreme high temperatures.  

This is not surprising.  Radiative effects are stronger for minimum than maximum temperatures, some local wind circulations supporting heat weaken under global warming, irrigation causes cooling during the day, and many reasons will be discussed.

SuperMonsoon Hits the Southwest U.S. and the Northwest Gets a Piece of It.

 There is a good name for it:   a SuperMonsoon. In my previous blogs, I talked about the nature of the Southwest (or North American) Monsoon...