A prescribed burn in Montana, as viewed from GOES-15, GOES-16 and GOES-13

GOES-15 (left), GOES-16 (center) and GOES-13 (right) Shortwave Infrared (3.9 µm) images, with plots of hourly surface reports [click to play MP4 animation]

GOES-15 (left), GOES-16 (center) and GOES-13 (right) Shortwave Infrared (3.9 µm) images, with plots of hourly surface reports [click to play MP4 animation]

A prescribed burn the SureEnough fire — in central Montana was viewed by GOES-15 (GOES-West), GOES-16 (GOES-East) and GOES-13 Shortwave Infrared (3.9 µm) imagery on 02 January 2018. The images are shown in the native projection for each of the 3 satellites.

Due to the improved spatial resolution of the GOES-16 3.9 µm Shortwave Infrared band (2 km at satellite sub-point, vs 4 km for GOES-15 and GOES-13) and the more frequent image scans (routinely every 5 minutes over CONUS for GOES-16), an unambiguous thermal anomaly or fire “hot spot” was first evident on GOES-16 at 1707 UTC, just southeast of Lewistown (station identifier KLWT). The GOES-16 fire thermal signature was also hotter (black pixels) compared to either GOES-15 or GOES-13.

GOES-13 will cease transmission on 3 January 2018 [Update: 8 January]

GOES-13 Visible (0.63 µm) Image, 1745 UTC on 2 January 2018 (Click to enlarge)

The GOES-13 Satellite, operational as GOES-East from April 2010 through December 2017 (with a notable interruption) will be turned off sometime after 1500 UTC on Wednesday 3 January 2018. (Update: due to an impending East Coast winter storm, GOES-13 deactivation was postponed to 8 January)

The visible Full Disk image above, from 1745 UTC on 2 January 2018, is one of the last fully illuminated visible image the satellite will process.  (The first processed full disk visible image, from 22 June 2006, can be viewed here.)

On 28 December 2017, GOES-13 imagery included a view of the Moon, as shown here (and zoomed in here).  Future GOES-East imagery from GOES-16 will not include images of the Moon.  GOES-16 will scan the moon when it is near the horizon (and there are occasional GOES-16 mesoscale sectors placed over the Moon for calibration purposes).  However, GOES-16 imagery is remapped to Earth points before being broadcast to the public.  The Moon (happily) is not on the Earth and its points will not be remapped.

Thank you GOES-13 for your long years of service.  A full-resolution version of the image above is available here.

When Water Vapor Channels are Window Channels

GOES-16 Low-Level Water Vapor Imagery (7.3 µm), 1322 UTC on 2 January 2017 (Click to enlarge)

The very cold and dry airmass over the eastern half of the United States during early January 2018 is mostly devoid of water vapor, a gas that, when present, absorbs certain wavelengths of radiation that is emitted from the surface (or low clouds). That absorbed energy is then re-emitted from higher (colder) levels. Typically, surface features over the eastern United States are therefore not apparent. When water vapor amounts in the atmosphere are small, however, surface information can escape directly to space, much in the same way as occurs with (for example) the Clean Window channel (10.3 µm) on GOES-16 (water vapor does not absorb energy with a wavelength of 10.3 µm). The low-level water vapor (7.3 µm) image above, from near sunrise on 2 January 2018, shows many surface features over North and South Carolina, Kentucky, Tennessee and southern Illinois. The features are mostly lakes and rivers that are markedly warmer than adjacent land. (In fact, Kentucky Lake and Lake Barkely in southwest Kentucky are also visible in the 6.9 µm imagery!)

Weighting Functions from 1200 UTC on 2 January for Davenport IA (left), Lincoln IL (center) and Greensboro NC (right) for 6.2 µm (Green), 6.95 µm (blue) and 7.3 µm (magenta), that is, the upper-, mid- and lower-level water vapor channels, respectively, on ABI. Peak pressures for the individual weighting functions are noted, as are Total Precipitable Water values at the station (Click to enlarge)

GOES-16 Weighting Functions (Click here ) describe the location in the atmosphere from which the GOES-16 Channel is detecting energy.  The upper-level (6.2 µm) and mid-level (6.95 µm) weighting functions show information originating from above the surface.  Much surface information is available at Greensboro, with smaller proportional amounts at Davenport and Lincoln.

The “Cirrus” Channel on GOES-16’s ABI (Band 4, 1.38 µm) also occupies a spot in the electromagnetic spectrum where water vapor absorption is strong.  Thus, reflected solar radiation from the surface is rarely viewed at this wavelength.  The toggle below, between the ‘Veggie’ Channel (0.86 µm) and the Cirrus Channel (1.38 µm) shows that some surface features — for example, lakes in North Carolina — are present in the Cirrus Channel.

ABI Band 3 (0.86 µm) and ABI Band 4 (1.38 µm) (That is, Veggie and Cirrus channels) at 1502 UTC on 2 January 2018 (Click to enlarge)

Whenever the atmosphere is exceptionally dry, and skies are clear, check the water vapor channels on ABI to see if surface features can be viewed. A few examples of sensing surface features using water vapor imagery from the previous generation of GOES can be seen here.

Cage Match: Nov-Dec 1976 vs. Nov-Dec 2017


By popular demand, we now compare Nov-Dec 2017 with the comparable start period of the "season that shalt not be named", the "drought year," or simply, 1976/1977.

The 1976/1977 season is the worst on record in the modern era (i.e., since WWII) in the Wasatch Range.  Records for Alta-Guard show a total seasonal snowfall (November through April of only 314.5 inches.  This is the second lowest on record next to 2014/15, when only 267.5" was recorded.

If 1976/77 was only the 2nd worst snow year at Alta, what makes it the worst ski season?  The lack of early season snowfall.  Nov-Dec 1976 produced only 30.5 inches of snow, 17.5 inches less than the second lowest comparable period on record, Nov-Dec 1962, and 102.5 inches less than Nov-Dec 2014.  In my book, a lack of early season snow is far worse than a lack of late season snow, mainly because you can't ski on dirt and the backcountry powder skiing is far less vulnerable to the sun during November and December than March and April. 

This season, Alta-Guard reported only 15 inches of snow in November.  I haven't seen their numbers for December, but Drew Hardesty of the Utah Avalanche Center notes in today's Salt Lake Tribune that Alta-Guard hasn't yet hit 50 inches for the season, and currently sits with the second leanest snowfall behind the 1976/77 season.  I think it will come in a shade under 50 inches.  Thus, in terms of snowfall, this season is bad, but not as bad as Nov-Dec 1976.

What about temperatures?  Nov-Dec 1976 had a mean temperature at Alta 28.8ºF, making it the 10th warmest such period on record.  This Nov-Dec it was 31.2ºF, good for fourth warmest.  One might be able to make an argument that this difference in warmth may have had some impact on melt and snowmaking.  In the case of the former, the loss of snow to melt on high-elevation north aspects is very small (or non-existent) this time of year when the sun angle is low.  Perhaps the difference in temperature has had some impact on snow losses down low during warmer periods (rain on snow, for example).  I'm going to guess that the impact is small, but stand to be corrected if someone can further than analysis with more data than I can look at in the short amount of time this morning.  I suspect that the situation on south aspects between the two seasons is a draw.  Near to nothing in both instances.  In the case of the latter, perhaps snowmaking conditions were a bit worse this Nov-Dec, but the argument is irrelevant since I don't think any resorts had snowmaking in 1976.  It would be interesting to go back and read some news reports from the 1976 holidays about what was happening at the resorts (alternatively, share your perspectives in the comments).  This Nov-Dec, we clearly have benefited from snowmaking in ways that were not possible in 1976 and, for resort skiers, that's probably a trump card surely making the start of this season better.

Now, getting to the meteorology.  If you are into El Niño and La Niña, you might be interested to know that weak El Niño conditions prevailed during Nov-Dec 1976, whereas weak La Niña conditions prevailed this Nov-Dec.  That's all I'll say about that.

The upper-level pattern during Nov and Dec 1976 was very high amplitude (i.e., wavy) across the Northern Hemisphere with a high amplitude ridge parked along the Pacific coast of North America and a deep trough over eastern North America.  This pattern kept much of the western US dry, but the eastern U.S. cold and snowy.
Source: ESRL

Source: ESRL

I was 9 years old at the time and living in upstate NY, and I still remember that as a very cold winter.  The extreme nature of the winter across the US sparked a good deal of research on climate and climate variability.  In what would have been a "rapid response" paper at the time, Henry Diaz and Robert Quayle published a paper in the October 1978 Monthly Weather Review arguing that January 1977 was probably the coldest month experienced in the eastern half of the U.S. in the last 200 years and that the 1976–77 winter set a new record for fuel demand due to the extreme cold in high population areas.

Source: Diaz and Quayle (1978)
This Nov-Dec was also characterized by a very high-amplitude pattern across the Northern Hemisphere.  However, the pattern over North America in November featured a ridge centered over the west-central U.S., rather than along the Pacific coast.

Source: ESRL
 This enabled storm activity in the Pacific Northwest, but kept the Southwest dry.  For northern Utah, the snowfall numbers for November 1976 and 2017 are nonetheless quite similar at Alta Guard, with 13.5 and 15 inches, respectively.   I haven't had a chance to dig into the water equivalent numbers to see how those compare and if there were any differences in the fraction of precipitation that fell as snow in the two years.

By December, the west coast ridge was dominant.  This is a pattern somewhat reminiscent of November and December 1976.  Alta-Guard, however, did a bit better for snow this December than in December 1976. 

Source: ESRL
It's not surprising that we see some similarities (and differences) between the two Nov-Dec periods.  Droughts in the west are frequently associated with ridging along the Pacific coast and that is a preferred area for ridge development.   Whether or not the remainder of this season evolves in a manner similar to the 1976/77 season remains to be seen, but my personal view is that analog forecasting based solely on local precipitation characteristics is not bound to be reliable over many cases.  My take is we just have to see how this will play out and hope that things shift for the better soon.

A few other thoughts:

1. The 1976/77 season was unbelievably bad in the southern Sierra Nevada.  Mammoth Mountains snowfall history (available here) shows a total seasonal snowfall of only 94" and no snowfall at all from October through December.  Four inches of that 94 fell before October.

2. Alta Ski Area's web site shows 74" in this Nov-Dec, but their observing site is higher up on the mountain.

3. I have not addressed the issue of observational representativeness and uncertainty in this post.  The Alta-Guard measurement site has changed over the years and this does affect snowfall measurements.  Similarly, I've never dug into the Alta site information to see if the location of the temperature measurements have changed, and that could affect the temperature comparison (there's a big difference depending on sun exposure, especially in December).

4. SNOTEL observations in the central Wasatch do not extend back to 1976.  It would be very interesting to utilize the manually collected snow course data to do a comparison.