Friday, December 15, 2017

Strange Holes in Clouds Explained

On Wednesday, I received nearly a dozen emails with pictures of strange circular holes in the cloud deck around Seattle.  Here are a few samples:

 Courtesy of Lawrence Wallman

  Courtesy of Lawrence Wallman

Courtesy of Justin Green

These strange features, known as hole-punch clouds...among other names, are caused by the penetration of aircraft through a cloud deck made of supercooled liquid water.  

Believe it or not, many middle-level clouds are below freezing but are still made  of liquid water.  Turns out that clean water can take its time to freeze when temperatures are below 0C.   

We had a cloud deck over Seattle around 3 PM Wednesday that was made up of such supercooled water.  A vertical sounding (vertical ascent from a weather balloon) at Quillayute on the WA coast at 4 PM suggested that the cloud was at roughly 450 hPa pressure or around 6600 m (22,000 ft) and a temperature around -22C (-8F).

We were dealing with an altocumulus or cirrocumulus clouds of liquid water.  A past colleague of mine, Peter Hobbs, and one of his past associates (Art Rangno) studied this situation and called the holes APIPS (Aircraft Produced Ice Particles).   Let me tell you why.

Look closely at the picture shown above (repeated below).  Do you see the fibrous looking material in the middle of the hole. Those are ice crystals! You can tell because they have a wispy, less distinct look to them.  

But what caused the transition between liquid water clouds (with much sharper edge  to ice clouds?   The passage of an aircraft!


When air goes across the wings of an aircraft the air is speed up and that causes pressure to fall on the upper side of the wing (that is what keeps a plane in the air!).  When air parcels experience lower pressure they expand and cool (this is called adiabatic cooling).  

Now clouds can be comprised of liquid water at -10C to around -22C, but if temperatures drop further, it is harder to remain liquid.  Also air can become saturated when it cools on the air frame and go directly to ice if the air is cold enough (-30C to -40C).


It turns out that ice and liquid water find it difficult to be in the same environment, water vapor leaves the liquid water and heads over to the ice crystals (this is often called the Bergeron process).  The ice crystals grow rapidly, become heavy, and fall out of the cloud, producing the hole.  You can see that happening in the cloud picture above.

Mystery solved....

Wednesday, December 13, 2017

Light Rain Returns to the Pacific Northwest, California Smoke Exits the Region, as the West Coast Ridge Weakens

After over a week without rain, precipitation will soon return to the Pacific Northwest.  But not much.

Morning temperatures will warm, freezing fog will lessen super temperature inversions will fade, and the hated Southern California wildfire smoke will leave our region for good.  But the ridge of high pressure is not done with us, continuing in a weakened form.

Today and Thursday should be dry, but by Friday, the probability of precipitation will increase---withe light rain Friday, Saturday, and into next week.

Let's look at the forecast upper level maps.  One valid at 4 PM today shows a ridge (high pressure) over us...and you can see the weak upper level disturbance (trough) over Idaho that brought some clouds yesterday.


The map for Friday at 10 AM shows a modest upper level disturbance passing through, depressing the ridge.  Clouds and perhaps some light showers.

But fast forward to Sunday afternoon at 1 PM.  The ridge is still there, but pushed southwards, and we are in the northern portion of it, with strong flow going into northern BC.  

Meteorologists call this a dirty ridge.  No...nothing to do with porn, but a ridge that allows some clouds and perhaps some light rain.  But no real weather.


The 72-h precipitation total ending 4 PM Friday shows unremarkable precipitation over Washington and Oregon.  Even the north Cascades only gets a few tenths of an inch.


The next 72hr?    Pretty much the same story.


Snow in the mountains?  You don't want to know about it.  Not much during the next week.  Best bet is north, up at Mt. Baker and Whistler.

Finally, the smoke issue.  Yesterday, a lot of California smoke reached the Northwest (see midday image from the NASA MODIS satellite below)


Here is a close up view centered on Oregon.   Yuk.   Look closely...do you see a lot of fine lines?  Those are aircraft contrails.  You can also see the darkening effect of the smoke over the low clouds of eastern Washington.


The forecast models are moving he smoke out and it should stay out for the rest of the season.    A California import we don't need.



Sunday, December 10, 2017

Are California Coastal Wildfires Connected With Global Warming: The Evidence Says No

California's coastal mountains have been hit by two major wildfire events, resulting in dozens of deaths and billions of dollars of damage

The first occurred on October 8-9th in the "Wine Country" north of San Francisco.  The second started on December 4th in Ventura County and now has spread south to Los Angeles and San Diego.

A number of political leaders, media outlets, and activist groups have boldly stated that these fires were caused by, enhanced by, or consistent with climate change forced by anthropogenic global warming.

Governor Jerry Brown has made it clear that the fires are a "new normal" forced by global warming.


The NY Times has made the same point:


The climate advocacy group Climate Central talks about climate change "stoking the fires"

And quite honestly, I could easily give you dozens of additional examples of the such claims.  That global warming is a key element driving California coastal fires.


The trouble is that these claims are not correct.    A reading of the peer-reviewed literature on California fires and an examination of observations and prior climate information can easily show that these claims are baseless, if not outright wrong.

Let me demonstrate this to you, with facts, peer reviewed papers, and the best science can tell us. 

First, some facts everyone should agree on:

1.  That wildfires took advantage of an environment with sufficient dry fuels (e.g., grasses and shrubs) to support fires.
2.  The initiation of the wildfires were associated with the onset of strong offshore (northeasterly) winds that developed as high pressure built into the intermountain West.

The question, of course is whether these elements had anything to do with global warming.  As we will see, the answer is clearly no.  And we will also see that there is a slew of other elements (prior fire suppression, irresponsible expansion of homes, influx of invasive grasses) that have made the situation much worse.


Did Global Warming Produce Drying That Led to the Fires?

The simple answer is no.   Coastal California has dry summers because the jet stream goes far north during the warm season and they don't have many thunderstorms because of the relatively cool Pacific.   So grasses, shrubs, and other fuels will be dry by the end of summer and during fall, no matter what.    And even if the fuels weren't dry, they would dry within hours of the initiation of strong, offshore winds--which accompany virtually every major fire event.

So even if the summer/fall temperatures rose and the conditions dried further under global warming, IT WOULD NOT MATTER.  Without any additional warming, the fuels in late summer and fall are dry enough to burn over coastal California and always have been.  There is a large number of papers in the scientific literature that state this fact (Keeley and Fotheringham 2003; Keely et al., 2004, Abatzoglou and Kolden 2013, Keely and Syphard 2016). And one might note that the recent fires were actually associated with cool air and temperatures dropping into 30sF at night.
__________________________________________________________
"climate does not appear to be a major determinant of fire activity in all landscapes. Lower elevations and lower latitudes shown little or no increase in fire activity with hotter and drier conditions" Keeley and Syphard, 2016
___________________________________________________________

So if the summer/fall precipitation and temperatures are not important, what about the quantity of fuels? 

This year there was a bountiful crop of grass in southern/central coastal California because last winter was so wet.  And there a number of studies that document that heavy precipitation the winter before results in more grasses that contribute to wildfires the next summer and fall. 

There is NO reason to expect global warming has or will provide southern California with MORE winter rain.   Here is the winter precipitation trend from the latest U.S. national assessment (last 30 years minus the first half of the century).  Very small changes, with varying sign over coastal CA.

Changes are the average for present-day (1986–2015) minus the average for the first half of the last century (1901–1960 for the contiguous United States

The trend of December to March precipitation over coastal southern California shows no obvious trend since 1950.  So during a period in which greenhouse gases have been rapidly rising, there is no hint of increasing precipitation over coastal southern CA.


Looking to the future, Deser et al., 2012 completed a large ensemble of climate simulations for the period 2005-2060.  They found drying over the California in the ensemble mean for the winter season (DFJ) (below)


Other climate simulations have provided a variety of solutions, most with drying in southern California grading to moistening over the Pacific Northwest.

Bottom line:  no reason to suggest that the excessive winter rains this year and subsequent bountiful grasses have much to do with global warming.

Ok... so the summer conditions are not relevant because the fuels are dry enough to burn in any case, and there is no indication of increasing winter rains and more grass from global warming.  Some may argue that global warming is delaying the onset of precipitation in the fall, which might contribute to a longer fire season. In fact, Governor Brown said this.

But two facts contradict such a suggestion.  First, there is no trend in late fall (October to December) precipitation over the southern CA coastal zone (see below).  Here is the proof.  And there is no downward trend in December precipitation either (see second plot).

And in any case, southern CA climatologically gets very little precipitation during the fall--and this the impacts are minor.  For example, at downtown LA (see below) Sept. and October get .5 inches or less and November only 1.25 inches.  Not enough to make much a difference when a strong Santa Anna wind is blowing.


The bottom line of all this is that observations and the best scientific reasoning do NOT suggest that global warming is enhancing CA coastal wildfires through effects on temperature and precipitation.

So what is left to consider?  

The winds. 

The two big events this year, and a deep collection of peer-reviewed research reports show that virtually every major coastal wildfire event has been been associated with strong offshore winds.  In southern California they are known as Santa Anas and in central California as Diablo Winds.  The meteorological set ups for these event are very similar:  surface high pressure builds in across the intermountain west, establishing offshore winds at crest level of the regional terrain, and an offshore pressure gradient at lower levels.  The pressure pattern at 4 PM Tuesday illustrates this pressure configuration at the surface (and the upper air map at 500 hPa--roughly 18,000 ft-- at the same time is also shown).  Note the position of the upper level ridge:  just off the Pacific  Northwest. And you can see the strong offshore flow at higher levels in the 500 hPa map.



So the question is whether this ridge pattern and the offshore flow it produces has become more frequent during the past few decades due to global warming, something that is being claimed by some folks that suggest that a Ridiculously Resilient Ridge is becoming more frequent (e.g., the work of Swain and Diffenbaugh).    I won't get into the details of these papers, but they have scientific and technical issues, and fail to provide any real evidence of a long-term trend in West Coast ridging.

Let's see if observations support their claims.  Are upper high pressure ridges becoming more frequent just west of the Pacific Northwest?  Using the reanalysis grids available from NOAA ESRL, I created a time series of the heights/pressure in this critical area for the cool season (November to March)....see below.

The major drought year (2015) had a big positive anomaly, but looking back several decades indicates little upward trend, particularly after 1975 when there was a switch in the sign of a major north Pacific mode of natural variability, the PDO.   Bottom line: there are no long-trends of ridging that would produce more offshore flow or increasing droughts.


A recent, highly publicized paper (Cvijanonic et al) has suggested that reductions of arctic sea ice results in greater ridging along the West Coast (see figure from their paper).  But there has been a large loss of sea ice the last few decades and no trend in the ridging in the exact position they talked about.  So their hypothesis does not seem well founded.


What about easterly (from the east) flow over southern California for the Santa Anna season (Sept to Nov)?  As shown below, there is no trend toward more offshore (easterly) flow (negative numbers) over the region.


There are several papers (e.g., Hughes et al. 2009Hughes et al. 2011) that have examined the issue of whether Santa Ana winds will change under global warming.  Their findings based on both historical data and climate simulations for the next century is that Santa Ana winds have not increased in magnitude/frequency and will be reduced under global warming.  Yes, reduced.  And this makes sense.  Part of the forcing of Santa Ana is the difference in temperature between the interior and the ocean.  A very robust finding of virtually all climate models is that the interior of the continent will warm more quickly than the eastern Pacific.  Thus, warming should WEAKEN a major forcing mechanism of Santa Anas. 

What about the observed trends of major wildfires over coastal California during the past decades?  Any evidence of a GW effect?   Dennision et al., 2014 published a comprehensive paper about western wildfires, finding a REDUCTION in major wildfires over the coastal region from San Diego to San Francisco.  Here is a plot from their paper.  Totally consistent with everything I have described above.  Totally inconsistent with the claims of Governor Brown, some climate activists, and a too many media outlets.


Finally, any consideration of the origin of any trends in wildfires must consider that humans are the cause of fire ignition for most California fires.   An article in the Proceedings of the National Academy of Sciences (found here)  noted that 84% of  U.S. wildfires were initiated by humans, with particularly high human ignition over southern/central California.   This is not surprising considering the population density and lack of lightning over the region.

Putting it all together

Considering the results of numerous studies of wildfires over coastal California and its relationship to prior and concurrent conditions, observed trends in key meteorological drivers, and even the number of major wildfires themselves strongly suggests there is no credible evidence that global warming is causing an increase currently or will increase in the future  of the number or intensity of wildfires over coastal California from San Diego to the SF Bay region.


Those that are claiming the global warming is having an impact are doing so either out of ignorance or their wish to use coastal wildfires for their own purposes.  For politicians, claiming that the big wildfires are the result of global warming provides a convenient excuse not to address the real problems:
  • Irresponsible development of homes and buildings in natural areas that had a long history of wildfires.
  • Many decades of fire suppression that have left some areas vulnerable to catastrophic fires.
  • Lack of planning or maintenance of electrical infrastructure, making ignition of fires more probable when strong winds blow.
  • Lack of attention to emergency management, or to providing sufficient fire fighting resources
  • Poor building codes, improper building materials (wood shake roofs), and lack of protective space around homes/buildings.
And to be extremely cynical, some politicians on the left see the fires as a convenient partisan tool.

Wildfires are not a global warming issue, but a sustainable and resilience issue that our society, on both sides of the political spectrum, must deal with.

Summing up, perhaps Mark Twain said it best:


Saturday, December 9, 2017

Los Angeles Smoke Reaches the Northwest

We just can't win at  this.  Last summer, western Washington was hit by smoke from British Columbia, then Oregon, and finally our own Cascade mountains.   The smokiest summer in a half-century.

And now the most amazing thing has happened.  Smoke from unusually late wildfires over southern California  have reached our region, producing reduced visibility and degraded air quality.  Really stunning.

The smoky haze was evident in this shot of Mt. Rainier by Peter Benda


Or in an image from Seattle's Space Needle Panocam:


The sun this afternoon had that yellow/orange cast reminiscent of last summer's wildfire season.

But what will really knock your socks off are the satellite images from the NASA MODIS imager.  Here is the visible image taken around noon.  Can you see the smoky stuff moving northward from offshore of California right into us?  That is Los Angeles smoke. 


Here is a closer view.  REALLY dense smoke from the Olympic Peninsula southward into NW Oregon.

Now if you want some proof of the origin of the fires, here is the vertically integrated smoke product from the NOAA/NWS HRRR Smoke model for 1 PM today.   From La Land straight to us.


And now the great irony.

Most of the LA pollution is aloft and can't reach the surface here because of the very strong inversion above us.  Usually inversions keep pollution emitted near the surface in the lower atmosphere and make things worse.  In this case, it is protecting us.  Very strange.

The strong inversion also made for some weird skiing.  Consider Alpental in Snoqualmie Pass (the NW Avalanche Center observations shown below). At 2 PM today (1400 PST) it was 25F at the base (3100 ft) and 22F at 4350 ft, but 50F at 5470 ft, at the top of the run.  Can you imagine?  Going from 50F to the low 20s in a run of few minutes?


Friday, December 8, 2017

Dangerous Icing and Super Inversion over Western WA This Morning

Roadway conditions are quite dangerous over much of western Washington, particularly on less traveled roads, as the combination of freezing fog and frost has put a glaze on many roadway surfaces (and pathways).

Foggy Sunrise Over Seattle

With high pressure in place, skies are relatively clear aloft allowing good radiational cooling to space from the surface.  At the same time, temperatures aloft have warmed.  The result is a super inversion, with temperature increasing rapidly with height.  Here are the latest temperatures above Seattle from the radar-wind profiler at Sand Point.  An increase of 12C (22F!) in 800 meters (2600 ft)

 Here are the 7 AM observations around the region.  Lots of fog and air temperature at and below freezing at many locations.  And remember these temperatures are taken at 2 meters above the surface--the surface is colder!


Really dangerous, so be careful.   The street in front of my house is all glazed up...I will have to be extremely careful in my bike in to work.  Fog is more extensive this AM because the offshore flow has weakened, something shown by the time-height cross section for the observations above Seattle-Tacoma Airport (red temps, blue winds, height in pressure...850 being about 5000 ft, time increasing to the left).


Why is fog and subfreezing temperatures so dangerous?  Because fog has a lot of water content and can freeze rapidly on roadway surfaces.  So, an image like this spells DANGER on a cold morning.

And in this one, you can SEE the ice on the roadway!
Some folks have reported strange sound effects with the strong temperature inversion, hearing boat horns many miles away.

Thursday, December 7, 2017

Extreme Temperature Variations Hits the Pacific Northwest

Anyway you look at it, our temperatures are showing some interesting variations during this dry period:

  • Extreme differences in temperature in the vertical
  • Extreme changes during the day
  • Large variations in the horizontal
  • Some amazingly warm temperatures in favored surface locations
  • Unusually warm temperatures aloft

The high temperatures on Wednesday ranged from the low to mid-60s on the southwest side of the Olympics to low-mid 50s over Puget Sound, and 30s east of the Cascade crest.


And today was toasty around the southern and western sides of the Olympic (up to mid-60s), with around 60F on the western slopes of the Cascades.


The key issue yesterday, today, and the immediate future is the high pressure aloft over the region.  With the typical westward tilt with height of weather  systems, the surface high pressure is to our east (see pressure map at 10 AM today--solid lines are pressure and colors give lower atmosphere temperatures, blue is cold).  

Cold, high pressure is east of the Cascade crest with a very large pressure gradient over the Cascades (around 11 hPa between Yakima and Seattle...that is large).  The result is easterly flow that is descending the eastern slopes of the Cascades and Olympics, warming by compression as it descends.


The surface temperature forecast for 1 PM yesterday (below), clearly shows the warm temperatures on the western downslope sides of the terrain.


The high pressure overhead, with its sinking and warming air has pushed the freezing level about 11,000 ft, and with warming aloft, and good radiational cooling to space under clear skies, an amazing inversion has formed.  Here is the plot of temperatures (red lines) and dew point (blue line) this morning at Quillayute, on the Washington Coast. Temperatures rise from 4C to 16C over a thousand feet.

And a strong inversion was apparent this morning (black line) and yesterday (red line) at Seattle.
Clear skies have allowed both good solar heating during the day and strong radiational cooling at night, giving us mild afternoon temperatures and frosty mornings (with lots of frost in lower locations).  The situation at Sat Tac is shown below.
Finally,  with cold air and high pressure, eastern Washington has fogged over, a major issue this time of the year (see below).



The ridge is not going anywhere..so expect dry conditions for the next week.