Wednesday, July 31, 2019

The Driest Week of the Year Brings Rain and the Summer Outlook

We are now near the halfway point of summer, and it is clear that this summer has been the best in several years-- temperate, dry with brief rain periods, and very little smoke. 

July brought above normal rainfall for much of the region, with Seattle getting 1.15 inches, .45 inches above normal.  Temperatures were cooler than normal over the Cascades and eastern WA, but warmer than normal in parts of western WA.  Cool in wildfire land.


 Thursday will be warm in western WA, with highs in the mid-80s away from the water.

But our warm, dry days are about to get another interruption, with a stronger than normal Pacific front making landfall on Friday.

The front will be approaching the coast at 11 AM Thursday (see 3-h precipitation ending that time below)


And will sweep in on Friday morning.  Not a super amount of rain on Friday in Puget Sound, but enough to cool temperatures by at least 10F and wet things down. 


The accumulated precipitation through 5 PM Saturday show an important story:  SW British Columbia will get hit hard with rain, with the NW corner of our state getting the most.  Forgot much fire activity in southern BC--- this is going to be a low-fire season there.  Which means less smoke for us.


The signature weather pattern this summer has been the persistent trough offshore--something that is very evident in the upper level map for 2 AM on Friday morning.  We started seeing this pattern consistently in late June and it has remained remarkable constant over time.  Such troughing keeps us cooler than normal.


And now it is time to look at for the rest of the summer!  Here is the predicted total precipitation through Sept 13th by the vaunted European Center model ensemble system (see below).  Wow.  BC is quite wet, as is NW Washington.  SE Alaska in nutty wet.  You have to feel sorry for folks taking cruises up there.

The next map shows the difference of that precipitation from normal.  Wetter than normal over most of the region.  Crazy wet in SW British  Columbia

The take away. This is going to be a quiet wildfire season in the Northwest, with average or fewer than normal fires.  If you are planning a vacation on Vancouver Island, take rain gear. And a tarp.  And more rain gear.


Monday, July 29, 2019

The Driest Day of the Year in Seattle, But What About Other Places?

Today is a very special day here is Seattle:  climatologically the driest day of the year.   Particularly nice because our sky is smoke free and temperatures will be temperate.   The dry nature of July 29th, is shown by a plot of the historical frequency of receiving .01 inches of precipitation at Seattle-Tacoma Airport, whose record stretches back to the last 1940s (see below).  Only about 8% of July 29ths, have received rain.  By the end of August, the climatological probabilities jump to 25%!


This is why I recommend that folks plan their big events (outdoor weddings, family barbecues, etc.) on or near this date.  So if you were planning on getting married, you better call your relatives and friends right now.

Why so dry?    Major weather systems are shunted to the north in late July and summer thunderstorms  are rare over western Washington because of the cool Pacific Ocean.

But what about other locations in the Northwest?  Is July 29th their driest day?   Let's check!

Spokane's Airport?  July 29th is quite dry, but not the driest, with virtually an equal chance of super-dry conditions (about 10% chance) from mid-July until early August.  Isolated from ocean drizzle and protected by the Cascades, their precipitation doesn't come back as quickly as in Seattle.   And of course, there is a bit of randomness to the exact driest day, depending on whether an errant shower hits a location.


What about the coast at Hoquiam?  Generally similar to Seattle, but the driest day is a few days earlier (July 25th).  And the probability of light rain comes up faster (about 30% by Sept 1).


But just when you think that all regional locations have the same driest periods, we check out Yakima, which is in the very dry lee of the Cascade mountains (see below).  July and August are all dry, but the two driest days are in early and mid-July.  These are days in which it HAS NEVER RAINED.   Yakima is a different story because they get little precipitation from incoming weather systems, with most of their summer rain from thunderstorms, which have a more random component and forced in different ways (e.g.. approaching upper trough, monsoon moisture coming up from the southwest).


Finally, to throw a few bones to readers in Oregon, here is Portland.  They get down to 6%, with July 29th not being lowest.  Their dry period is longer than Seattle, roughly from early July to early August.  Probably because they are slightly further south, with a small reduction of precipitation from weather systems passing to the north.


Eugene, Oregon is even drier than Portland, with several days in July never experiencing rain and an uber-dry period from roughly July 10th through late August.    


So enjoy our dry period and this year we are blessed with minimal smoke over the region---and I suspect that will hold for a while.  There are very few BC and California fires compared to last year and the mainly grass fires started by lighting in eastern WA will be rapidly contained.

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AnnouncementL  I will be giving a talk "The Great Storms of the Pacific Coast" in Ocean Shores at 6:30 PM on September 7th at the Shilo Inn as part of the Coastal Interpretative Center's summer lecture series.  More information is found here: https://www.interpretivecenter.org/.   Shilo Inn is offering special room  rates for those wishing to stay overnight, as well as a special buffet.   

Saturday, July 27, 2019

UFO Sky

Last night, I was walking my dog in Magnuson Park and was impressed by the sky--there was a number of beautiful, sometimes multi-level, lens-shaped lenticular clouds.   In fact, after I got home I received a picture of one of them from Andrew Weller (see below).


Some of the local web cams showed the beautiful lenticular clouds as well, such one available on the KING-5 site:


As described in my NW weatherbook, the appearance of lenticular clouds is often a sign of an approaching weather system.   Such clouds are the result of air being pushed upwards by mountains and then oscillating up and down in the lee (see figure).   These are also known as mountain waves. When the air rises, it cools, and can become saturated--producing lens-shaped clouds.  And with all our terrain and multiple mountain peaks,  our sky can become a chaotic collection of such clouds.

To get lenticular clouds, you need a decent wind approaching the mountains and a sufficiently moist atmosphere that some modest upward motion will give you a cloud..... exactly what typically occurs as a weather system approaches from off the Pacific.

Take yesterday.    The satellite image Friday afternoon showed an approaching trough and weak front (see infrared image at 2 PM Friday).


But as the system approached, the winds and moisture aloft were changing--and the lenticular clouds provided a sign of that change. 

Below are the vertical soundings produced by a balloon-borne radiosonde at Quillayute, on the Washington coast.  Temperature is on the X-axis and the Y-axis is height in pressure (700 hPa corresponds to roughly 10,000 ft).   Winds are on the right, the left-most black line is dew point temperature, the right line is temperature.  The closer the lines are together, the closer the atmosphere is to saturation.  The plots are for 5 PM Thursday and 5 PM Friday.

On Thursday, the winds were light in the lower atmosphere and from the west to north.  The atmosphere was not even close to saturation.  No clouds. 


But the situation was quite different on Friday afternoon.  The winds had greatly strengthened and were uniformly from the southwest, and the atmosphere had moistened considerably, with the dew point very close to the temperature.  A little lift from the mountain waves could produce lenticular clouds.


Lenticular clouds over Mount Rainier started the UFO craze in 1948.   But they are clearly more of a sign of approaching weather systems than some alien visitation. Native Americans in our region had a saying that when Mount Rainier wore its hat, then rain would come soon.    They had real insights into our local weather.



Thursday, July 25, 2019

Rain on Saturday

We are now entering the fabled driest period of the year here in the Northwest, with the driest day on average in Seattle being July 29th.

How dry on July 29th?  The long-term average precipitation on that date is only 4 thousandths of an inch of rain at Sea-Tac Airport. Not even enough to wet down some concrete.

Now back to the Saturday precipitation.....

The latest UW WRF model run has the rain approaching at 5 AM in the morning


And reaching the Cascades by 8 AM.



The 24h total ending 5 PM on Saturday (below) predicts up to a third of an inch on the western side of the Olympics and Cascades, but much more in southwestern BC.  Good for keeping down  BC fires.



The European Center forecasts are similar and highlights the rain in BC (see below).  Forget the threat of fires in BC for a while.


And the extended forecast has more rain next Thursday (the map shows 24h precipitation ending 11 PM Thursday).


It is good we are getting some rain and cooler/moister periods.   Substantial thunderstorm activity on Tuesday resulted in thousands of lightning strikes (see below) that caused a several small fires. 


Seasonal weather without high temperature extremes and the absence of thunderstorms or strong easterly flow should allow the current fires to be controlled and work against new initiations.

Enjoy the weather...except for Saturday morning, it should be close to perfect.



Tuesday, July 23, 2019

The Meteorology (and More) of the Grass Fires of Eastern Washington

There have been a number of grass fires in a limited area of eastern Washington, roughly between the Tri-Cities and Vantage.   Generally burning in unpopulated rangeland comprised of grasses, sage, and shrub-like vegetation, the fires have done little damage, even though they have burned tens of thousands of acres.    Strong winds play an important role in these fires, as do the nature of the "fuels."   As we shall see, climate change has play little role in such fires, but human modification of vegetation and provision of ignition sources have been critical.

The current Northwest fire map (below) shows no activity in forested areas, but three fires in grass/rangeland:   the Cold Creek fire west of Kennewick, the Juniper Wind tower fire, near the Gorge, and Round Butte Fire in eastern Oregon.  And earlier this month, the Powerline Fire started near Mattawa, just to the north of the Cold Creek blaze, and is now over.


We can use MODIS satellite imagery that considers a combination of wavelengths to show burn scar areas (see below).    You can see the Columbia River.  The bottom arrow points to the Cold Creek Fire, the top arrow to the Powerline Fire, which was started by a motorcycle.


These fires started in grasses and low shrubs--the pictures below shows examples, the first near the Powerline fire, the second by the Cold Creek blaze.


Now a big problem is that the landscapes above are full of a highly flammable, non-native species called Cheatgrass---also known as grassoline.  And flammable native species like sage.

Below is a government map of the distribution of cheatgrass.   The Columbia Basin is covered by the stuff!  During the past several decades, Cheatgrass, a non-native invader, has covered eastern WA, displacing the native (and less flammable) bunchgrass.  Cheatgrass dies and dries out early in the summer, leaving highly flammable fuel.


In any normal summer, the dead fuels of grasses and small bushes dry out very quickly--one does not need above average temperatures or below normal precipitation.   In fact, this water year  (since October 1, 2018) was one of BELOW NORMAL temperature and ABOVE NORMAL precipitation over the Columbia Basin, something shown by the two figures below from the Western Climate Center.   Clearly, there is no global warming component to this.



So we start with landscape with flammable grasses and low bushes, that are dried out without the help of any special heat or lack of moisture.   Then we add human ignition sources--such a cigarettes thrown from cars, motorcycles and off-road vehicles, fireworks, and for the case of the Juniper Fire, a wind turbine that ignited and melted down--starting a fire in the grass below (see image).


Here is a youtube video of the burning turbine and you can see the grass situation as well.


But there is on more thing:  wind.  The areas of the fires are often windy--in fact, that is why the wind turbines are there.     The region from Ellensburg to the Tri-Cities often gets strong northwesterly winds coming across the Cascades.  That is illustrated by a forecast wind speed for 5 PM yesterday (Monday, see below).  The yellow and oranges indicate stronger wind.


During the summer, strong winds descend the eastern Cascades during the late afternoon and evening hours, and the winds are strongest downstream of a weaknesses in the Cascades known as Stampede Gap.  This results in the most powerful winds in a zone from Ellensburg towards the Tri Cities.   To get a good feel for this, below is the average wind speed at 80 m above ground level for Washington.  You see the red area....the windiest place in the state? Guess what?  Most of the grass fires we have seen lately are in or near this area.
The winds in the Ellensburg/Vantage/Mattawa, Tri-Cities area are strongest in the summer, when eastern WA is warmest and when there is strong pressure difference across the mountains.

So we have a dry area with lots of flammable grasses and shrubs, loads of human activities ready to ignite fires, and plenty of wind in the summer.   Sounds like purgatory.  This is a worsening problem due to the invasive grasses and increasing human ignition sources (new one:  burning wind turbines). 
And the situation is made worse by increasing human habitation and building near the flammable rangeland.  That issue is not one for an atmospheric scientist to deal with.


Saturday, July 20, 2019

Humidity Storm Hits the Northeast While the Northwest Has the Best Weather in the Nation

For those of you living in the Northwest, this is weather payoff time.   Warm, but not too warm.  Generally dry, but with a few showers next week to keep things moist enough to keep down the fires.

But the situation back east is different:  in several places the humidity will be debilitating, with effective temperatures getting well above 100F.

As I talked about this week, the dew point temperature is a good measure of moisture in the atmosphere, and when summer dew points get into the mid-60s, it starts feeling "sticky" and unpleasant.  Dew points in the 70s start getting really irritating and upper 70s, really bad.   The National Weather Service dew point analysis at 8 AM EDT today  show the national moisture divide.  The eastern half of the nation is steamy, with dew points approaching 80F that extends into the New York area.    In contrast, low dew points over the West.


Why the difference?  The east coast air is coming off the warm Gulf of Mexico and south Atlantic, while West Coast air originates over the cool Pacific Ocean.  In addition, the high terrain of  West extends into drier layers aloft.

The latest surface dew points for the New York area are amazing, with a number in the mid to upper 70s.   Some hit 80F!


These dew point, coupled with temperatures rising into the middle 90s, is resulting in effective  or apparent temperatures as high as 110F in the New York area and some locations in the Midwest.

Apparent temperatures take in consideration the decline in effectiveness of evaporation from our skin as humidity rises, and give the "dry temperature" equivalence of the current temperature and humidity.


It is interesting to consider that human beings are exquisitely designed to function in hot temperatures--more so than almost any animal on the planet.  When we have sufficient water, sweating from our bare skin can cool effectively.   But heat coupled with high humidity can undermine our prodigious capabilities for evaporative cooling.

The dew points over the Eastern U.S. are quite unusual.  Here is a plot of the climatology of surface dew point at Islip, Long Island, with the red line being the record for each date.  The circle gives the observation this morning.  Today's value was a new record for the date and one of the highest values for any date.  I want to grab a cold drink just thinking about it.

Getting back to the Northwest,  weather should be as close to perfect as imaginable over western Washington today with highs in the upper 70s in western Washington and lower to mid 80s in the Willlamette Valley.   Not too hot in eastern WA.


Sunday will be warmer, particularly east of the Cascade crest, but nothing extreme.   But dew points will be low-- in the 40s!!!----so skin evaporation should work well.  Just drink plenty of water.  Or whatever.

___________________________________________________________

I will be giving a talk "The Great Storms of the Pacific Coast" in Ocean Shores at 6:30 PM on September 7th at the Shilo Inn as part of the Coastal Interpretative Center's summer lecture series.  More information is found here: https://www.interpretivecenter.org/.   Shilo Inn is offering special room  rates for those wishing to stay overnight, as well as a special buffet.   


Thursday, July 18, 2019

The Strongest Summer Jet Stream to Hit the Pacific Northwest EVER!

An extraordinary weather event has been occurring above our heads during the past 24-hour.   A record that was not only broken, but shattered to little pieces.

The strongest summer jet stream ever observed over the Pacific Northwest.  

The jet stream is a narrow current of strong winds in the upper troposphere (roughly 25,000 ft to 35,000 ft above sea level).   It is often the conduit for storms and is associated with a large temperature gradient (change in temperature with horizontal distance) in the middle and lower troposphere.   Winds in the jet stream are westerly (from the west) and aircraft like to fly in the jet stream going east, while avoiding it going west.   You are now Jet Steam certified!

The ECMWF 12-h forecast for 5 AM this morning for the wind speed at the 250 hPa pressure level (about 35,000 ft) clearly shows the jet stream, with the orange/red colors being the strongest winds.


This is a HUGE and very zonal (east-west oriented) jet stream...as shown by the next map at the same time.  This looks like January, not July.


But now I will really impress you. 

 The wind this morning at the radiosonde site at Quillayute (UIL) was 140 knots (161 mph) at the 250 hPa level (again around 35,000 ft).   This is amazingly fast for this time of the year.

The plot below shows the climatology of the winds at this level throughout the year at this location, with the red lines being the all-time record for each date (the black lines are average winds for the date, blue lines, the record low winds).   Vertical soundings at Quillayute go back to the late 1960s...so we are talking about a half-century of observations.   The previous record was around 110 knots...so the 140 knots observed today absolutely shattered the record.     In fact, the wind over us right now is greater then the records for any date from April 1 to mid-October.


Record, but lesser winds, are being observed at the next upper air station to the south:  Salem, Oregon (see below)


A truly unusual event.   And one that should not be pinned on global warming.  In fact, several of the global warming jet stream papers (e.g., by Jennifer Francis and others) suggest that global warming will bring a weak and wavy jet stream.  This is just the opposite.


Wednesday, July 17, 2019

JAWS2 Hits--And The Atmosphere is Not Ready to Return to Normal

JAWS2 hit today and precipitation was quite substantial for July.  (Remember JAWS stands for July Abnormally Wet System).  The total accumulation for the last 24 h is found below (click to expand).  Over an inch on the western side of the Olympics and similar values at some locations on the western slopes of the northern Cascades.  Just where we needed the rain.


And the precipitation is not over.   We are in a moist northwesterly flow and over the next 48-h the European Center model shows more rain in the Cascades and lots in British Columbia.  Closer to

Seattle, conditions are right for a Puget Sound convergence zone, that will produce a band of rain from Seattle to Everett on Thursday and Friday.  To illustrate, here is the 24 hour rainfall ending  5 PM on Friday.  Lots in the north Cascades and in the convergence zone band.


Although the worst should be over by late Friday, the atmosphere seems to be stuck in an unusual configuration, with an upper level trough in our vicinity.  To demonstrate this, let me show you the height anomaly from normal at 500 hPa, about 18,000 ft.  Blue indicates lower heights than normal (associated with troughing).  The heights are in the solid lines.

At 11 PM tonight, heights are lower than normal over us and to our north.   To our south, heights are higher than normal.  As a result of this configuration, there is a large change of height with latitude over the region, resulting in much stronger than normal winds from the west.  Not typical July!

 Now there are major changes over the weekend and by Tuesday morning a big ridge builds to our east.  But a very strong and unusual close low is to our west, resulting in strong southwesterly flow over us.  That means no heat wave and a chance for some showers.


In short, next week should bring upper 70s, relatively dry conditions, and nothing that will obviously be a wildfire issue.  British Columbia is soaked--so don't expect a fire outbreak there.   Typical temperatures and no smoke.  Don't feel guilty or worried about the weather--this is when we get pay back for December.