The Autumn Transition

Nearly every September has a transition to fall-like weather, with no going back.  We are in such a transition right now.   

For Washington State, regular rains will return, 80s and 90s will be memories, and the wildfire season will be over.

Before I show you the forecast, consider the climatology of this month. 

For temperature, September average maximum temperatures at Seattle (thin red line) goes from the summer-like mid-70s to the mid-60s (the vertical red line shows today).  No more 90s by the end of the month.  Ever.

For the probability of measurable precipitation, there is only small upward trend after the typical "moistening" of late August.

But there is an interesting quirk I have noticed: we often get a decent shower mid-month.  Take a a close-up view of the precipitation climatology below:  you can see the mid-month rain spike.  Buy why?

Enough climatology.....let's consider the forecast for the next week or so.

The temperature forecasts for Seattle and Pasco predict autumn-like conditions.

Seattle will stay with fall-like 60s for the next ten days.

Pasco, in the Tri-Cities, drops into the 70s and stay there.

And yes, there will be regional rain that will end any talk of wildfires from the crest of the Cascades westward.

The predicted rainfall total though Tuesday (below) forecasts light to moderate precipitation from the Cascades to the Pacific, with substantially higher values over the Rockies.  Importantly, fire-prone eastern Oregon shares in the moisture.

The next 96h (through Thursday morning), more of the same if not a bit wetter.

The reason for this switch to a wet-cooler situation is because a series of upper levels will develop over or move into the West Coast, something illustrated by the upper-level (500 hPa, about 18,000 ft) weather map for Sunday afternoon.

Enjoy the fall weather.  Our plants will be happy and the smoke aloft should rapidly become history.

Is Hawaii Prepared for the Next Wildfire Event? I Worry That the Answer is No.

Just over a year ago, western Maui was hit by a powerful downslope windstorm that initiated a wildfire that destroyed the historic town of Lahaina.

Lahaina after the August 8-9, 2023 fire

A terrible tragedy that cost the lives of approximately 100 people and resulted in roughly 4 billion dollars of damage.

Hawaiian Electric, local government, and others have taken some steps to prevent the tragedy from reoccurring.  Unfortunately, for the reasons outlined below, I worry there are gaps in their efforts that could lead to a repeat of the terrible disaster of August 2023.

Examining the Meteorology of the Lahaina Event

I do a lot of research on the meteorology of western U.S. wildfires, and particularly wildfires associated with downslope windstorm events, which characterize the 2023 Maui wildfire.  I received a grant from the National Science Foundation to study the meteorology and predictability of the Lahaina event, and after some intensive work with research meteorologist David Ovens, published a paper on the subject.

There were several significamt findings of the paper:

1.  The wildfire was associated with a strong downslope windstorm, which damaged powerlines starting the fire.

2.  The event was highly predictable up to approximately a week ahead using high-resolution model forecasts.

3.  The observational network on Maui and the rest of the islands was very poor.

4.  There were multiple levels of failure by Hawaiian Electric and public authorities.  Furthermore, the National Weather Service never highlighted the particular threat to Lahaina even though its high-resolution model (HRRR) clearly predicted the strong winds (see below)

The NWS HRRR Model

Hawaiian Electric's Attempt to Deal with the Threat

During the last months, Hawaiian Electric announced its response to the wildfire threat.  

First, they are adding several dozen new weather stations around the island, particularly in observation gap areas.  For example, there are now observations near Lahaina, where none had existed before (see current map below).  This is good.  But there are still major gaps in the observational network.  Furthermore, surface observations tell you what is happening NOW, not what will happen in the future.  And to save lives and property, forecasts are critical.

Finally, there is a lack of upper-air observations, which are critical for forecasting (more on this later).

Current Real-Time Surface Weather Observations on Maui

Second, Hawaiian Electric plans to harden and modernize its distribution network, much of which is outdated and below modern standards for robustness to strong winds.  Commendable and high priority, but will take years to complete.

Third, Hawaiian Electric plans to start doing Public Safety Power Shutoffs (PSPSs) when threatening conditions are expected, not unlike what has been done by California utilities.  Its a way of dealing with deficient power distribution network surrounded lots of flammable fuels.

Unfortunately, there are weaknesses in their plans for PSPSs.

According to Hawaiian Electric documents, their decision to initiate a PSPS will first depend on observations (identifying persistent drought conditions, wind gusts of 45 mph and more, relative humidity below 45%).  That is a good start, but reacting to observations is not good enough.  Winds can increase suddenly.  People, businesses, and others need more time to prepare.

Hawaiian Electric states they will use National Weather Service (NWS) public forecasts, but that is not good enough, something highlighted by the relatively poor performance of NWS predictions during the Lahaina wildfire.  During that event, the NWS failed to highlight the great threat to Lahaina.  Instead, the NWS put out a broad-brush red flag warning for the lee side of all the Hawaiian Islands.  Not good enough.

Hawaiian Electric needs to use high-resolution numerical model forecasts for their decision making including PSPS declarations.

There are a variety of ways Hawaiian Electric can secure such model predictions:

1.  Run the models themselves, which is what California utilities  (e.g. PGE) are doing.

2.  Use the NOAA/NWS HRRR-Hawaii model, which is run regularly in "experimental" mode.  This is totally silly by the way....NOAA/NWS needs a hardened, high-resolution operational model for Hawaii.

3. Hawaiian Electric should use the high-resolution regional weather prediction made by the University of Hawaii Manoa.

Hawaiian Electric also needs to have a team of meteorologists constantly monitoring both the observations and high-resolution model forecasts.  I don't thing they have any at this point.

They also should talk to the USDA Forest Service to give Hawaii critical wildfire weather diagnostics enjoyed by the rest of the U.S., such as the valuable HOT-DRY-WIND diagnostic.

Better Observations Aloft of Hawaii

To forecast and diagnose downslope windstorms.... the key driver of catastrophic wildfire on Hawaii, one has to know the structure of air approaching the islands through the depth of the lower atmosphere.   Right now Hawaii has such information only twice day at two radiosonde locations:  Hilo and Lihue, which weather balloons with instruments are launched twice a day (see stars on map).  Not good enough.

Hawaiian Electric, the State of Hawaii, and the Federal Government need more upper-air observations for the islands.  One approach is to add another radiosonde unit, with more frequent vertical soundings.  Or Hawaii could secure some vertical profilers, devices that sense the atmosphere remotely (see below).   The West Coast has many of these devices, why not Hawaii?

We Can Prevent Hawaiian Wildfire Disasters

The disaster in Lahaina last year was preventable.   Weather modeling and observational capabilities have improved so dramatically that we can foresee such events with great clarity and skill, allowing an effective response that will minimize loss of life and damage.  Hawaiian Electric and Hawaiian governmental entities must use these tools to prevent another tragedy.

Oregon Smoke over Washington. Ends Monday.

 The visible satellite image this morning shows a plume of smoke over Washington, smoke that mainly originated over eastern Oregon.

The effects of the smoke were pretty obvious over western Washington, with an attenuated, red sun rising to the east this morning:

The smoke is thick enough that the intensity of solar radiation has decreased noticeably (see measurements at Seattle below for the last three days below).   That means we will be cooler today as a result. 

Air quality is good on the coast, moderate over the western lowlands and the Columbia Basis, and poor over sections of eastern Oregon

The laser ceilometers run by the Puget Sound Clean Air Agency clearly show the smoke moving in aloft.  Here is an example from the instrument at  Beacon Hill, Seattle. The time is on the x-axis (increasing to the right) and the y-axis is height in meters (3000 meters is about 10,000 ft).  Quite a deep layer of smoke is moving through overhead.

.   

Nearly all the smoke is coming from extensive fires in grass, bushes, and scattered trees in eastern Oregon (see current fire areas below).  Numerous lightning and human-ignited fires have occurred in the rangeland of eastern Oregon, with other fires over the southern Oregon Cascades.   The extensive, lush flammable invasive grasses (like Cheatgrass) are a real problem.

For most of the summer, the smoke from the fires did not influence western Oregon or Washington because winds generally move from west to east in our region.

But during the last few days, easterly winds have prevailed, associated with a thermal trough extending into western Oregon.     To illustrate, here is the forecast weather map at 850 hPa (about 5000 ft) this morning.  The solid lines are like pressure and you can see the wind symbols.  Easterly winds over northern Oregon and southern Washington.

Below are  the air motions at the same level (5000 ft) ....something called streamlines.   You can see why the eastern Oregon smoke is approaching us.

Fortunately, the situation is going to change during the next 36-48 hours.

Here are the streamlines showing airflow at 5 PM Sunday.  The wind direction has radically changed...now out of the Northwest.  That will blow the smoke away.

To show the improved smoke situation, let me display the smoke forecast (total in a vertical column) from the highly skillful HRRR smoke prediction model.  

This morning at 8 AM. Lots of smoke.

Tomorrow morning at 7AM, still smoky.

But by 5 AM Monday morning, the switch to northwesterly flow was doing its magic, with western Washington nearly clear of smoke.   Tuesday will be even better.

Relief is on the way!

Superinversion on the Hottest Day for the Rest of the Year

 An inversion is when temperatures increase with height.  

Today a super-inversion exists, with extraordinary warmth aloft.

At 6 AM this morning, temperatures are in the lower 50s in the south Sound and upper 50s to around 60F in central Puget Sound (see map).  But looking to the western Cascade slopes, you see some warmer temperatures with some in the low 70s.

It was so chilly at local river valleys that fog and low clouds formed in some of them:

But now, let me shock you.  Right above Puget Sound, just a little over a thousand feet up, the temperatures are in the 80s!   

You heard that right.   In a few hours, that warm air will mix to the surface and high temperatures will climb into the the upper 80s to near 90F over the western lowlands.

The warmest day for the remainder of 2024 will occur today

Below is the temperature structure at 6 AM from aircraft data at SeaTac Airport.  Around 63F at the surface (452 ft ASL) and 80F at around 1600 ft.  AN INCREASE OF  17F in around 1000 ft. 

 Mama Mia...that is an inversion!

Can you imagine hiking up a local peak, such as Tiger Mountain, this morning?  You would hike from 55 to 80F within 30 minutes.

The sun will warm the surface today causing increasing vertical mixing.  Rapidly, the warm air aloft will be mixed down to the surface and lowland temperatures will surge.  

The UW high-resolution ensemble of many forecasts (below), suggests a high around 90F at SeaTac, with cooling over the next several days.

And there is one other thing. Smoke.

The wind pattern aloft will move some of the smoke from fires in central Oregon into western Washington.  In fact,  you can see the smoke on a visible satellite image earlier this morning:

As the atmosphere mixes vertically today, some of that smoky air will be mixed down, mainly over SW Washington.

Finally, let me give you some good news. The National Weather Service has a red flag warning out for the western slopes of the Cascades (see below).   

Fortunately, this is little chance of western slope wildfires today and particularly spreading wildfire.  Why?  Because strong easterly winds are not forecast today.  Major wildfire events require wind and western Washington wildfires require strong easterly winds.

The Last Heatwave of the Year

After examining a wide variety of forecast models and considering the region's climatology, it appears we will have to endure only one more warm spell for the remainder of the year.

And by a warm spell,  I mean an event where western Washington rises into the mid-80s or above and eastern Washington nears 100F.

 I will start by showing you the forecasts.  

At Seattle, the skillful NOAA/NWS National Blend of Models (NBM) prediction system forecasts warming to the mid-80s on Thursday and Friday before cooling over the weekend.  Temperatures cool to below normal (upper 60s) next week.  The average high-temperature today in Seattle is 75F for reference.

As a check, consider the highly skillful European Center model ensemble of many forecasts (the mean of these forecasts are shown below).  Quite similar to the NWS prediction.... and this forecast extends through mid-month.

 

Next moving to the Tri-Cities, the prediction for Pasco shows a torrid high above 100F from Thursday to Sunday, with cooling to the lower 80s next week

The temperature anomaly (from normal) forecast (by the European Center) for the mid-month (Sept 13-20) indicates cooler than normal temperatures over western Oregon to near-normal temperatures for the remainder of the region.

Solar radiation and the length of the day rapidly decline in September making it increasingly difficult to get into the 80s by the end of the month.  Check out the monthly solar radiation at Seattle for last year to see what I mean.  September values are WAY down from July.

So why is the heat wave followed by cooling?    

Easy to explain by looking at the upper-level height/pressure pattern at 500 hPa pressure (around 18,000 ft above sea level).  The shading shows the difference from normal, with red indicating ridging or higher pressure aloft.  Blue is roughing or lower than normal pressures.

On Thursday, a strong ridge will develop over British Columbia, with the center in an ideal location to warm Washington State. If this happened in July, we would be talking about mid to upper 90s.

But by Monday,  the ridge had moved inland and a cooling trough of lower pressure will approach. Maybe even a few showers.

The situation later in the week is similar (Thursday).  So still cool.

So enjoy the heat, wear some shorts, and get that swim in.   The heat will soon be over and we will be moving towards fall-like weather starting next week.

______________________________

Reminder UW students:  I will be teaching Atmospheric Sciences 101 this fall:

And if you are over 60, you can take the class for $5 through the UW Access Program...either online or in person.

An Impressionist's Sky

 The sky this morning was beautiful (see below).   An impressionist's dream.  

What you are seeing is mid-level convection:  shallow cumulus clouds resulting from instability in the middle troposphere (I will explain this later).

French impressionists loved such beautiful skies, as illustrated by this lovely painting by Monet (The Port at Argenteuil)

Here is another one by Monet that was even more similar to what I viewed this morning.  Monet should have been a meteorologist.....

The Seine at Vetheuil

In 2024, we could do something Monet could not have dreamed of....to observe such clouds from space.  And for your viewing pleasure, below is what NOAA's GOES-West satellite observed at almost the same time as my picture above.  

Do you see the small cloud elements over western Washington and northwest Oregon?  These are the features of interest.

We can tell the elevations of these cloud elements by using another high-tech sensor system that Monet could not have dreamed of: laser ceilometers maintained by the Puget Sound Clean Air Agency.   These surface-based units use vertically pointed laser beams that scatter off clouds and smoke (see below).  The time it takes for a scattered beam to reach and return from the cloud provides the cloud height.

The clouds in question formed 5 and 6 kilometers above the surface (roughly 16,000 to 20,000 ft above sea level ) around 1:30 AM this morning.

But our high-tech bag of tricks does not end there! We have balloon-launched weather stations called radiosondes around the region, including Quillaytue on the Washington coast and Salem, Oregon.

Here is the temperature (red line), dewpoint (blue dashed line), and winds from thelayer radiosonde launched this morning at Salem, which is positioned in the middle of the cloud field.   Temperature (°C) is on the x-axis and height in pressure (hPa) is on the y-axis.  500 hPa is about 18,000 ft.

There is a layer (indicated by the red arrow) in which the dewpoint and temperatures are the same.  Such a layer is saturated (100% relative humidity) and is associated with clouds.  Matches the ceilometer height quite well.  The red temperature line also shows that the temperature was declining rapidly with height in that area, consistent with an unstable, well-mixed layer.

So why do we have these beautiful cumulus clouds in that shallow layer?

It was associated with an approaching low-pressure center aloft (see upper level, 500 hPa, about 18,000 ft)--as shown by the forecast map for 8 AM this morning.  In front of the low (to its NE) there is both upward motion and southerly winds.   Upward motion causes air to cool (air cools by expansion when as it moves to lower pressure), which causes the relative humidity to increase (because cool air can hold less water vapor than warm air).   The southerly (from the south) winds also helped move some moist air up from the Arizona "Monsoon" region.

Another high-tech capability is to view water vapor from space! Such imagery shows the moisture plume this morning

The motion of the low into the region today is going to initiate a significant onshore push of cool marine air tonight.  Tomorrow you should expect MUCH cooler temperatures and a lots of low clouds.

Enjoy the weekend.