CIMSS Satellite Blog

NOAA-18 AVHRR 10.8 µm IR image

October 2008 turned out to be the 4th coldest October on record at Fairbanks, Alaska. About 150 miles (240 km) to the north of Fairbanks, a minimum surface temperature of -40º F (-40º C)  was reported at Chandalar Lake, Alaska on 25 October, followed by a low of -42º F (-41º C) on 26 October 2008:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1124 AM AKDT SUN OCT 26 2008

…VERY COLD TEMPERATURES OVERNIGHT IN THE NORTH EASTERN INTERIOR…

FOR THE SECOND NIGHT IN A ROW CHANDALAR LAKES OVERNIGHT TEMPERATURE WAS BELOW 40 DEGREES BELOW ZERO.

SATELLITE IMAGERY THIS MORNING INDICATED THAT SOME VALLEYS IN THE NORTH EASTERN BROOKS RANGE WERE APPROACHING 50 BELOW ZERO OVERNIGHT…BUT WITH NO OBSERVERS IN THE AREA WE HAVE NO OFFICIAL TEMPERATURE REPORTS FROM THERE.

THE PLACES THAT WERE 20 BELOW ZERO OR COLDER:

CHANDALAR LAKE…………………….-42
NORUTAK LAKE………………………..-30
BEAVER…………………………………..-29
COLDFOOT……………………………..-26
CHALKYITSIK……………………………-25
BETTLES AIRPORT……………………..-20

NOAA-18 AVHRR 10.8 µm IR imagery (above) showed numerous narrow fingers of very cold air draining into the valleys of the Brooks Range in northern and northeastern Alaska — many valleys exhibited IR brightness temperatures as cold as -40º C (darker blue color enhancement).

A magnified version of that same NOAA-18 AVHRR 10.8 µm IR image (below) revealed that some of the valleys located to the northeast of Chandalar Lake (station identifier PALR) were even colder, with IR brightness temperatures as low as -45º C or -49º F (violet color enhancement) — however, Eric Stevens (Science and Operations Officer at the Fairbanks AK NWS forecast office) informed us that the ASOS instruments at Arctic Village (station identifier PARC) were out of service at that time, so no surface temperature data was available to verify the cold values seen on satellite IR data. The coldest IR brightness temperature in the immediate PALR region was -44º C  (-47º F) at 12:38 UTC — a surface air temperature of of -39º C (-38º F) was reported at PALR about 2 hours after the time of the NOAA-18 IR image.

NOAA-18 AVHRR 10.8 µm IR image

While the corresponding GOES-11 10.7 µm IR images (below) did show a similar area of cold IR brightness temperatures near -40º C (darker blue color enhancement) from Chandalar Lake (PALR) to Arctic Center (PARC), the fine detail of the cold air drainage into the valleys was lost (the effective resolution of the “4 km” GOES IR pixels increase in size to about about 20 km over northern Alaska, due to the large satellite viewing angle). The coldest IR brightness temperatures seen on GOES data in that region at 12:30 UTC was -39º C (-38º F), compared to -45º C (-49º F) indicated by the AVHRR data at 12:38 UTC.

GOES-11 10.7 µm IR images

According to the USA Today tabulation of daily national temperature extremes, this is the earliest -40º F temperature reported in the US during the 1995-2008 period (the earliest -40º date was 05 November in 1999, with the latest -40º date being 31 December in 2002). While this was also the earliest recorded -40º temperature for Chandalar Lake, it did not threaten the monthly October record low temperature for the state of Alaska (which was -48º F or -44º C at Clear Water, set in 1975).

GOES-11 + GOES-12 water vapor channel images

AWIPS images of the GOES-11 + GOES-12 water vapor channels (above) showed the large size of a major snowstorm that impacted much of the western US during the 10 October - 12 October 2008 time frame. This storm dropped as much as 48.8 inches of snow at Cole Creek, Montana and 29.7 inches at Lander, Wyoming (their greatest October snowfall on record), and Glasgow, Montana received 12.8 inches of snow on 12 October (their heaviest snowfall for any calendar day during the month of October). At Billings, Montana the snow depth of 9 inches on 13 October was the earliest date on record for a 9-inch snow depth.

AWIPS images of the MODIS visible channel and the 1.6 µm near-IR “snow/ice” channel (below) displayed the areal coverage of snow on the ground across much of Wyoming, eastern Montana, far northwestern South Dakota (including the higher elevations of the Black Hills) and western North Dakota, stretching northeastward into portions of Saskatchewan and Manitoba on 13 October. Snow cover exhibits a darker signal on snow/ice channel imagery (in contrast to supercooled water droplet clouds, which appear as lighter shades of gray).

MODIS visible and snow/ice channel images

An AWIPS image of the MODIS Land Surface Temperature (LST) product (below) showed the effect of the deep snow cover on surface temperatures across much of Wyoming and Montana on 13 October — LST values within the snow swath were only in the upper 20s to low 30s F (green colors), compared to the 60s and 70s F (orange colors) north of the deep snow cover. The daily maximum temperature on 13 October at Glasgow, Montana was only 37º F (which tied the record for coldest maximum temperature for that date), while the daily high temperature of 28º F at Wisdom, Montana was the earliest date for such a cold maximum temperature.

MODIS Land Surface Temperature product

A 250-meter resolution MODIS true color image (below, viewed using Google Earth) displayed the extent of the snow cover across parts of Wyoming and Montana. Note that there were a few snow-free patches located within the broad swath of snow cover (a result of the complex terrain across the region).

MODIS true color image (viewed using Google Earth)