Diurnal Intricacies of the Inversion

PM2.5 concentrations during our current inversion event have shown remarkable variations from day to night.

Below is a time series of PM2.5 measured at our mountain meteorology lab at the University of Utah showing a clear long-term upward trend, but also a tendency for PM2.5 concentrations to spike just before noon, remain elevated until mid to late afternoon, and then decline.

Source: MesoWest
What are the causes of this diurnal behavior.  There are several possible contributors.

First, there is the possibility that photochemistry - chemical reactions occurring in the presence of sunlight, are contributing.  Comparison of the above plot with the incoming solar radiation below shows some relationship, with the PM2.5 exhibiting a bit of a lag relative to the solar radiation.

Source: MesoWest

Another possibility is that temperature is playing a role since it also affects the PM2.5 chemistry.  Again, there is some correlation.  

Source: MesoWest
Finally, there is the transport possibility as the winds are also changing diurnally, with a good correlation between wind direction and PM2.5 concentrations.  

Source: MesoWest
Another perspective is provided by the someone hacked-up graphs below, based on data collected at the University of Utah by our MesoWest team over the 24-hour period ending this morning at 10 AM (the hacking reflects my splicing of their multiple graphs together).  The top figure is derived using a laser that is shot vertically through the pollution.  The color fill is backscatter, a measure of how much of the laser light is reflected back to the ground, with higher values roughly correlated with greater PM2.5 concentrations (brown-white being the dirtiest air).

The plot begins on the left at 10 AM on Sunday when the local flow just shifted to predominantly westerly (some variability from SW-NW).  Surface PM2.5 concentrations during this period are quite high and, in addition, the pollution is quite deep.  At just after 1700 MST (5 PM), the flow shifts abruptly to ENE, which reflects the onset of down valley flow from Red Butte Canyon.  This marks the beginning of a gradual decline of surface PM2.5 concentrations, as well as a decrease in PM2.5 concentrations aloft.

Source: MesoWest
There is a brief lull in the wind that occurs just before 2300 MST (11 PM MDT), with the flow becoming somewhat erratic.  Without the inflow of cleaner air from Red Butte Canyon during this period, the surface PM2.5 values climb, although things don't change too much aloft.  Finally, after midnight, the ENE flow returns and PM2.5 values drop again, although there are a few spikes during the night that may correlate with declines in wind speed (I haven't bothered to check yet...so take this comment for what it is worth).

At the end of the time period, the PM2.5 values climb again, abruptly, when the flow shifts to westerly.

All of this illustrates some of the intricacies of these inversion events.  Pollution concentrations vary in the vertical (yes, there is clean air up there), although if you look carefully at the plot above, you can see that it's not as simple as polluted air near the ground and non-polluted air aloft.  There are layers.  In addition, pollutant concentrations vary horizontally and at the University of Utah one can clearly see the migration of pollutant-laden air onto campus when the wind shifts to westerly in the morning.

What role photochemistry and temperature play in all of this is unclear to me.  I suspect it plays a secondary role compared to meteorological factors, but I am not an atmospheric chemist and over the years I've learned that when all you have is a hammer, everything looks like a nail.  In other words, as a meteorologist, I might be guilty of placing too much weight on meteorological factors.

One thing to keep in mind is that not all inversions look or behave like this and even this one might behave differently in the days to come.  As a scientist, I think what we see over the next few days will be "interesting."  As a citizen, I wish the damn thing would just blow away.

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 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:


Day 7 of the Thomas Fire in Southern California

GOES-15 Shortwave Infrared (3.9 µm) images, with hourly surface reports plotted in yellow [click to play MP4 animation]

GOES-15 Shortwave Infrared (3.9 µm) images, with hourly surface reports plotted in yellow [click to play MP4 animation]

The Thomas fire began burning in Southern California around 6:30 PM local time on 04 December (blog post) — and on 10 December 2017, GOES-15 (GOES-West) Shortwave Infrared (3.9 µm) images (above) revealed that the fire showed little signs of diminishing during the nighttime hours, and in fact began to exhibit a trend of intensification around 05 UTC or 9 PM local time. However, toward the end of the day on 10 December, bands of  thick cirrus clouds moving over the fire region acted to dramatically attenuate the satellite-detected thermal signature of the fire complex. Although the Santa Ana winds were not as intense as they had been during the previous week, some strong wind gusts were still observed.

A sequence of 4 Shortwave Infrared images from Terra MODIS and Suomi NPP VIIRS (below) showed the westward and northwestward expansion of the fire during the 0637 to 2032 UTC period. The Thomas fire has now burned 230,000 acres, making it the fifth largest wildfire on record in California.

Terra MODIS and Suomi NPP VIIRS Shortwave Infrared images, with corresponding surface reports plotted in cyan [click to enlarge]

Terra MODIS and Suomi NPP VIIRS Shortwave Infrared images, with corresponding surface reports plotted in cyan [click to enlarge]

In a toggle between Terra MODIS true-color and false-color Red-Green-Blue (RGB) images at 1846 UTC (below; source) the true-color image revealed a broad plume of thick smoke being transported westward and northwestward from the fire source region, while the false-color image showed the areal coverage of the burn scar (which appeared as reddish-brown hues beneath the clouds) as well as locations of the larger and more intense active fires (brighter pink to white) that were burning along the northern to western perimeter of the burn scar.

Terra MODIS true-color and false-color images [click to enlarge]

Terra MODIS true-color and false-color images [click to enlarge]

A comparison of Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images at 2032 UTC or 12:32 PM  local time (below) showed a well-defined thermal signature before the thicker cirrus clouds moved overhead from the south. A small cloud cluster (located just northwest of the fire thermal signature) exhibited a minimum infrared brightness temperature of -43ºC — if this cloud feature was indeed generated by the fire complex, it meets the -40ºC criteria of a pyrocumulonimbus cloud.

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images, with surface reports plotted in cyan [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images, with surface reports plotted in cyan [click to enlarge]

The fire was producing very thick smoke, in addition to deep pyrocumulus clouds (top photo taken around 1945 UTC or 11:45 AM local time):

 


===== 11 December Update =====

Suomi NPP VIIRS Day/Night Band (0.7 µm), Near-Infrared (1.61 and 2.25 µm), Shortwave Infrared (3.75 and 4.05 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm), Near-Infrared (1.61 and 2.25 µm), Shortwave Infrared (3.75 and 4.05 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A toggle between Suomi NPP VIIRS Day/Night Band (0.7 µm), Near-Infrared (1.61 and 2.25 µm), Shortwave Infrared (3.75 and 4.05 µm) and Infrared Window (11.45 µm) images at 1035 UTC or 2:35 AM local time (above; courtesy of William Straka, CIMSS) demonstrated how different spectral bands can be used to detect nighttime fire signatures. The recently-launched JPSS-1/NOAA-20 satellite also carries a VIIRS instrument.

GOES-15 Shortwave Infrared (3.9 µm) images (below) showed that once the thicker bands of cirrus clouds moved northwestward away from the region, a more well-defined thermal signature became apparent.

GOES-15 Shortwave Infrared (3.9 µm) images, with hourly surface reports plotted in yellow [click to play animation]

GOES-15 Shortwave Infrared (3.9 µm) images, with hourly surface reports plotted in yellow [click to play animation]

A 7-day sequence Nighttime and Daytime composites of Suomi NPP VIIRS Shortwave Infrared (3.74 µm) images (source: RealEarth) is shown below — it illustrates the spread of the Thomas Fire from 05 December to 11 December. Hot infrared pixels are black, with saturated pixels appearing bright white.

7-day sequence Nighttime and Daytime composites of Suomi NPP VIIRS Shortwave Infrared (3.74 µm) images [click to play animation]

7-day sequence Nighttime and Daytime composites of Suomi NPP VIIRS Shortwave Infrared (3.74 µm) images [click to play animation]

Snowfall across the Deep South

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 Visible (0.63 µm) images [click to play animation]

GOES-13 (GOES-East) Visible (0.63 µm) images (above) showed a broad swath of snow cover from Louisiana to Virginia on 09 December 2017. Some notable storm total accumulations included 6.5 inches at Kentwood, Louisiana, 7.0 inches at Bay Springs, Mississippi, 12.0 inches at Jacksonville, Alabama, 2.0 inches at Century, Florida, 18.0 inches at Mountain City, Georgia, 7.0 inches near Roan Mountain, Tennessee, and 25 inches at Mt. Mitchell State Park, North Carolina. Daily record snowfall accumulations included a Trace at New Orleans, Louisiana, 5.1 inches at Jackson, Mississippi and 1 inch at Mobile, Alabama.

A closer view of GOES-13 visible images (below) showed the band of snow cover across Louisiana, Mississippi and Alabama. Much of the the snow melted quickly, due to warm ground temperatures and a full day of sun.

GOES-13 Visible (0.63 µm) images, with station identifiers plotted in yellow [click to play animation]

GOES-13 Visible (0.63 µm) images, with hourly surface reports plotted in yellow [click to play animation]

A more detailed view of the snow cover was provided by 250-meter resolution Terra and Aqua MODIS true-color Red-Green-Blue (RGB) images from the SSEC MODIS Direct Broadcast site (below). Note that snow cover was evident all the way to the Gulf Coast at Atchafalaya Bay, Louisiana early in the day.

Terra and Aqua MODIS true-color RGB images of the central Gulf Coast region [click to enlarge]

Terra and Aqua MODIS true-color images of the central Gulf Coast region [click to enlarge]

Terra and Aqua MODIS true-color RGB images, centered over Atchafalaya Bay, Louisiana [click to enlarge]

Terra and Aqua MODIS true-color RGB images, centered over Atchafalaya Bay, Louisiana [click to enlarge]

Terra and Aqua MODIS true-color images, centered over New Orleans, Louisiana [click to enlarge]

Terra and Aqua MODIS true-color images, centered over New Orleans, Louisiana [click to enlarge]

Terra MODIS true-color image, centered over Atlanta, Georgia [click to enlarge]

Terra MODIS true-color image, centered over Atlanta, Georgia [click to enlarge]

It is interesting to note that with the aid of reflected moonlight — the Moon was in the Waning Gibbous phase, at 59% of Full — the Suomi NPP VIIRS Day/Night Band (0.7 µm) was able to detect the area of deeper snow cover across southeastern Louisiana and southern Mississippi at 0741 UTC or 1:41 AM local time; this snow cover was then seen during the following morning on GOES-13 Visible (0.63 µm) imagery at 1440 UTC or 8:40 AM local time (below). A VIIRS instrument is part of the payload on the recently-launched JPSS-1/NOAA-20 satellite.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and GOES-13 Visible (0.63 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and GOES-13 Visible (0.63 µm) images [click to enlarge]

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?


Scenes from the Inversion

Classic inversion conditions are now apparent over northern Utah.  Here are a few photos.

First, the view of the valley smoke that befuddled me, and is discussed in the previous post.  It sure looked like clouds this morning, but as soon as I descended down into it, I smelled campfire and knew I was in error.  Turns out it was smoke from a major arson fire near 500 South and 200 East. 


In contrast to the cesspool in Salt Lake, morning at Alta was splendid and whiter than expected.


A bit later.  A good example that no matter where you are in the Salt Lake Valley today, you're only a few hundred meters (vertically) from clean, pristine air. 


Valley cold pools can be found just about everywhere over northern Utah right now.  If there's emissions, there's pollution.  The smog below is in the Heber Valley. 


Just about anyone who has skied in Little Cottonwood knows this view.  Unfortunately, it is common in the wintertime.


And, this afternoon back in the Avenues.  Ick. 


On the positive side, air quality remains in the moderate category so far. 
Source: DAQ
On the negative side, we have at least 5 days left of this, and air quality is going to worsen.

Overnight Stratus Formation?

I woke up this morning and was surprised to see a shallow layer of stratus already beginning to form over the northeast portion of the Salt Lake Valley.


I thought it might be smoke in the early morning light, but after watching it for a little while, I think it's cloud.  It's a bit unusual for the first stratus in an inversion to form in this part of the valley.  Typically it happens at lower elevations and near the airport, but perhaps the distribution of cloud cover is having an effect.

As one might surmise from the photo, the atmosphere is now quite stable over the Salt Lake Valley.  The morning sounding shows temperatures increasing from -4.7ºC at the surface to 3.4ºC at 763 mb (8200 feet).

Source: RAL
We're stuck with this now for several days.

You're going to hear a lot of talk about a possible trough passage toward next weekend, but the strength, structure, timing, and implications for northern Utah vary quite a bit across the various GEFS ensemble members.  

Source: GEFS
Keep the faith.

Snowfall in southern Texas

GOES-13 Visible (0.63 µm, left) and Shortwave Infrared (3.9 µm, right) images, with hourly plots of surface reports [click to play animation]

GOES-13 Visible (0.63 µm, left) and Shortwave Infrared (3.9 µm, right) images, with hourly plots of surface reports [click to play animation]

The combination of lift from an upper-level trough and cold air behind the passage of a surface cold front  set the stage for accumulating snow across far southern Texas on 08 December 2017. As the clouds cleared, GOES-13 (GOES-East) Visible (0.63 µm) and Shortwave Infrared (3.9 µm) images (above) revealed a narrow swath of snow cover running northeastward from the Rio Grande River toward Corpus Christi — the highest snowfall total associated with this feature was 7.0 inches near Corpus Christi. Daily snowfall records included 0.3 inch at Brownsville and 1.0 inch at Corpus Christi.

A toggle between Terra MODIS true-color and false-color Red-Green-Blue (RGB) images from RealEarth (below) showed the southwestern portion of this band of snow cover (which appeared as darker shades of cyan in the false-color image).

Suomi NPP VIIRS true-color and false-color RGB images [click to enlarge]

Suomi NPP VIIRS true-color and false-color RGB images [click to enlarge]

Farther to the north, another southwest-to-northeast oriented band of snow cover was seen on Terra MODIS true-color and false-color RGB images (below), stretching from San Antonio to Austin to College Station. The highest snowfall total there was 5.0 inches (NWS Austin/San Antonio summary),

Terra MODIS true-color and false-color images [click to enlarge]

Terra MODIS true-color and false-color images [click to enlarge]

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.

Heartbreak Ridge Tightening the Inversion Noose

Noontime smog yesterday, looking southwest from the Natural History Museum of Utah, University of Utah
Given that our last storm was winding down on Monday, I'll call today Day 4 of Heartbreak Ridge.

So far, the pollution buildup has been modest.  Because the center of the ridge has been along the Pacific Coast, we've been on the downstream side, temperatures aloft have been cool, and the inversion relatively weak and elevated.  This has enabled some vertical mixing of pollutants through a decent portion of the valley atmosphere.  As a result, the increase in pollution has been gradual and we've been fluctuating between good and moderate air quality.  

Source: Utah Division of Air Quality
However, Heartbreak Ridge is sliding eastward and the inversion is strengthening, as can be seen in the soundings from yesterday afternoon (top panel below) and this morning (bottom panel below).  


Source: University of Wyoming
Note in particular the warming in the layer between about 800 and 700 mb (6500–10000 feet), which equates to a strengthening of the "lid" over the valley atmosphere.  This morning, temperatures near the base of that layer increase about 5ºC through a depth of around 50 mb (1500 feet). 

The NAM sounding loop below (note: this is a skew-t diagram, not directly comparable to the diagrams above) shows further warming aloft over next two days, with temperatures aloft warming an additional 5ºC.  
Thus, the inversion will be strengthening and lowering through the weekend.  It appears we will be in the grips of the inversion at least through the next work week, unless a system stronger than presently advertised slides down the back side of the ridge and gives it a stir. 

Model Products Information

We have been having some problems with the server that hosts weather.utah.edu and it has been down intermittently the past two days.  Behind the scenes (and unrelated to the outages), I've been updating some of our products.  Options for the GFS now include global and regional plots from the 0.25 degree latitude-longitude grid (we've been using the old 0.5 degree grids), higher frequency (every 3-h to 240 hours), more regional sectors (e.g.,  Intermountain, Northwest, Southwest), and time-height section options that match the time period of the NAM for comparison.  Some little used plots are gone, such as the Indian Ocean sector.