June 12, 2024

More Rain for the Northwest is Good News for Wildfires

After a very pleasant dry spell, another rainy period is ahead for the western side of the region and the Cascades on Friday and Saturday.   And there is no hint of heat waves in our future.

Today and Thursday will be partly sunny, with highs in the upper 60s to low 70s in the west, with the Columbia Basin being about 10F warmer.   Typical June weather.

But on Friday, an upper-level low-pressure area (or trough) will be moving in (see below for 8 PM Friday), bringing clouds, showers, and cooler temperatures.

Such features have been persistent this spring.

The forecast 24-h precipitation total ending 5 PM Friday shows showers in the west, with the heaviest precipitation along the coast.  Eastside dry.

The next 24-h (ending 5 PM Saturday) is quite wet in the West, particularly over the western slopes and crest of the Cascades.  

Perhaps not the best day for a Cascade hike.


As the system passes through, the region will dry out on Father's Day (Sunday), except for a band of Puget Sound from the Puget Sound convergence zone and over northeast Washington.


The predicted temperatures for Seattle (below), show a substantial cool-down over the weekend (about 10F below normal on Saturday), but warming to near-normal conditions (low 70s) next week.   Again, add about 10F for the Columbia Basin.


All the gnashing of teeth and predictions about summer drought and wildfire by certain media outlets does not appear to be well-founded.  

Below is the latest one-week predicted significant fire potential by the Northwest Interagency Coordination Center, which is responsible for region wildfire prediction.  Green indicates below-normal potential.   Looks favorable.


The most skillful extended forecast is by the European Center and their latest guidance predicts COOLER than normal conditions for the next month over most of the region (see below)


Of course, we have the challenge of July 4th, where crazy people shooting fireworks start many fires. often in dry grass.  Hopefully, the grass will be moist this year.


June 09, 2024

Lightning Returns to the Pacific Northwest

 Lots of thunderstorms, some approaching severe levels, have hit eastern Oregon and Washington during the past day.....and there are severe thunderstorm warnings out between Wenatchee and Spokane as I write this blog (see below).


The latest radar image over eastern Washington shows strong storm cells, with the red colors indicating substantial radar reflectivity.   Such high levels are either very heavy rain or hail. 


Earlier today (around 3:30 PM) similarly strong storms were moving eastward across southeast Oregon (see below)


Precipitation during the past day has been substantial over southeastern Oregon (up to 1.23 inches) and northeast Washington has also experienced some of the thunderstorm showers (see below).


This is the first major lighting event of the year for our region.    Yesterday (Saturday), there was a substantial number of lightning strikes over eastern Oregon ( see below).


The latest lightning strike map (at 7:50 PM Sunday) shows plenty of lightning, with thunderstorm cells over eastern Washington and others over southeast Oregon.


And here is the total lightning strike picture for Sunday.  Southeast Oregon and downstream are well covered by lightning, with quite a few over NE Washington.



So why so much lightning?

Today an upper-level trough moved through, as shown by the weather map at roughly 18,000 ft (500 hPa) this morning at 8 AM (the red dashed line shows the trough line).   In front (east) of the trough, there is both upward motion and the movement of warm, moist air from the south, both very favorable for generating thunderstorms.   


The atmosphere over eastern Washington and Oregon had lots of CAPE (Convective Available Potential Energy)... think of this as fuel for thunderstorms.  

To illustrate,  here is the CAPE prediction for 8 PM tonight (Sunday).  Some values getting as high at 600 (J/kg).  Decent for around here, a big yawn for those in the Midwest.


All our local thunderstorm action will be over over night as the trough moves inland and cooler marine air moves into the region.



June 07, 2024

New Podcast: Perfect Saturday Followed by June Gloom

It is a phrase that puts fear into the hearts of all true Northwesterners:  June Gloom.

You thought we escaped it?   Think again.

But first, we have an even warmer day than today in store for Saturday, with Puget Sound Country hitting 80F and another ten degrees over the Columbia Basin.

During June Gloom periods the northeastern Pacific fills with low clouds, which push into western Washington and Oregon (see below).  In fact, the whole West Coast can suffer from this affliction.

The cloud coverage this morning shows why today was so warm:

But Sunday morning is a different (and cloudier) story.

As is Tuesday (below)...and Wednesday and Thursday.... is the same.  That is June Gloom!


Anyway, check out my podcast for more details:

You can listen to the podcast below or through your favorite podcast server.


Some major podcast servers:

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June 05, 2024

A Very Wavy Atmosphere

The high-resolution MODIS satellite image taken mid-day yesterday was remarkable, with extensive wave-like cloud features east of the Cascade crest in Washington and Oregon (see below).    More waves over Montana as well.


Here is a closer look at the waves over eastern Oregon.  Very regular features with north-south cloud lines and clear zones between them.


Over southern Washington, there were still waves of clouds but they were distorted east of Mt. Rainier into more of a "v" shape.


What is going on here?

You are looking at mountain lee-wave clouds or, more precisely, trapped lee-wave clouds.  You will learn about the "trapped" business in a second.

When air approaches a mountain barrier with sufficient wind speed and under stable conditions, air is pushed up by the mountains and then oscillates up and down downwind of the terrain (on the lee side).  Think of a swing--you give a push and the swing goes back and forth for a while.

When the air goes up it cools (moving to lower pressure causes air to expand and cool), which can result in air becoming saturated (cool air can hold less water vapor than warm air). leading to withcloud formation.  So one can get a series of clouds with clear zones in between (where air is sinking) downwind of a mountain barrier.


The mountain waves are stronger in the lower atmosphere and weaken with height.  Thus, they are "trapped" in the lower atmosphere downwind of the mountain barrier.

If the mountain barrier is an elongated linear feature that is oriented north-south  (like the Cascades), one ends up with north-south lines of clouds and clear zones downstream of the barrier.  Exactly, what we see downstream of the north-south Cascades.

If the barrier is more isolated, the mountain wave clouds appear more like the wake of a ship (see below).  The mountain wave clouds downstream of Mt. Rainier looked like the  "ship wake" clouds.

Can high-resolution weather prediction models correctly simulate and forecast such waves?

I am proud to say that the answer is definitively yes.  Below is a nine-hour prediction of the cloud field from the UW ultra-high resolution WRF prediction model (the kind of thing I work on in my real job) for 2 PM yesterday.

Wow.   Near perfection.


Trapped mountain lee wave clouds are popular destinations for glider pilots, who try to stay in the upward motion associated with clouds.  Free vertical lift courtesy of Mother Nature!


June 03, 2024

A Winter Storm in June

A combination of heavy rain and wind, more reminiscent of November than June, came through yesterday and this morning, and the effects were substantial.

Winds gusting to 35-50 mph, acting on fully leafed out trees, led to massive loss of branches and trees.   My bicycle commute to the UW along the tree-lines Burke-Gilman trail was interrupted by several major treefalls (see picture below).

Tens of thousands of Seattle City Light customers lost power this morning.   Same for Puget Sound Energy.



Below is a plot of maximum winds overnight. Some mountain locations gusted over 60 mph, with over 45 mph near Puget Sound, the Strait, and the Washington coast.


Why were the winds so strong?   

The figure below shows the sea level pressure (solid lines) at 8 AM this morning.  A Pacific low-pressure system passed north of western Washington, creating a large north-south pressure difference that accelerated the winds northward.


Precipitation totals?   Over the past 36 h (see below), the western slopes of the Cascades and Coastal Mountain received 2-4.5 inches.... a lot for June.


Puget Sound was rainshadowed by the Olympics and Seattle "only" received about 1 inch.  

If you really want world-class mountain rainshadowing, head to a station just south of Port Townsend, which only received 0.11 inches over the same period (see red arrow).  No wonder folks retire there.


Forecasts were excellent for this event.  

Western Washington and Oregon rivers are running very high now, some at record levels (see below, blue and black dots are much, much higher than normal).


I hope the Drought Monitor folks will consider dropping the "moderate drought" designation for the western Cascades slopes.

More showers are occurring today across the region, as shown by the latest radar image (see below)


And the precipitation is not over!  Another plume of water vapor (a.k.a. an atmospheric river) is rapidly approaching (see water vapor satellite image below)


Rain will rev up tomorrow morning. By the time precipitation ends Wednesday AM, substantial rainfall will have occurred, particularly over the north Cascades and mountain of SW British Columbia (see 48 h total ending 5 AM Wednesday below).


Enjoy this wet interlude.  Drier conditions and a slow warm-up are expected Wednesday through Saturday, as our highs climb into the mid-70s.

June 01, 2024

New Podcast: The Heavy Rain Event, Heat Wave, and Perhaps Thunderstorms!

 Mother Nature is keeping the meteorological plate full for us.

My new podcast describes the latest on heavy rain events occurring on Sunday through Tuesday.   But we are now close enough in time to see what's next:  a minor heatwave peaking over next weekend, with the potential for thunderstorms from the Cascade crest eastward.

Friday afternoon, the European Center model has thunderstorms over eastern Washington

The simulated radar imagery from 11 PM next Saturday from the UW WRF model shows an area of thunderstorms moving into western Washington. 


You can listen to the podcast below or through your favorite podcast server.


Some major podcast servers:

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More Rain for the Northwest is Good News for Wildfires

After a very pleasant dry spell, another rainy period is ahead for the western side of the region and the Cascades on Friday and Saturday.  ...