Cold temperatures in Alaska

January 19th, 2017

NOAA-18 AVHRR Infrared Window (10.8 µm) image, with surface air temperatures and corresponding station identifications [click to enlarge]

NOAA-18 AVHRR Infrared Window (10.8 µm) image, with surface air temperatures and corresponding station identifications [click to enlarge]

A NOAA-18 AVHRR Infrared Window (10.8 µm) image (above) showed the signature of cold air (violet shades) settling into river valleys and other low-elevation terrain areas across the cloud-free interior of Alaska at 1916 UTC (10:16 am local time) on 18 January 2017. Note that there was a layer of clouds (warmer cyan colors) over much of the North Slope of Alaska; these clouds were acting to limit strong surface radiational cooling, with resulting temperatures only as cold as the -20s F. This AVHRR image was about 1 hour before the low temperature at Fairbanks International Airport (PAFA) dropped to -51ºF (-46ºC) — the first low of -50ºF or colder at that location since 31 December 1999 (-53ºF). While these were certainly cold temperatures, in general they were several degrees warmer than the daily record lows for 18 January:


NOAA-18 AVHRR Infrared Window (10.8 µm) image centered on Bettles (PABT), with surface air temperatures and corresponding station identifications [click to enlarge]

NOAA-18 AVHRR Infrared Window (10.8 µm) image centered on Bettles (PABT), with surface air temperatures and corresponding station identifications [click to enlarge]

Closer views centered on Bettles (above) and on Tanana (below) further highlighted the influence of terrain on the pattern of surface infrared brightness temperatures.

NOAA-18 AVHRR Infrared Window (10.8 µm) image centered on Tanana (PATA), with surface air temperatures and corresponding station identifications [click to enlarge]

NOAA-18 AVHRR Infrared Window (10.8 µm) image centered on Tanana (PATA), with surface air temperatures and corresponding station identifications [click to enlarge]

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NOAA-19 AVHRR Infrared Window (10.8 µm) image, with surface air temperatures and corresponding station identifications [click to enlarge]

NOAA-19 AVHRR Infrared Window (10.8 µm) image, with surface air temperatures and corresponding station identifications [click to enlarge]

The cold continued across much of Alaska on 19 January, as seen on a NOAA-19 AVHRR Infrared Window (10.8 µm) image at 1519 UTC or 4:19 am local time (above). However with a lack of cloud cover over the central portion of the North Slope, surface air temperatures were much colder (in the -40s F) compared to the -20s F that were seen there on the previous day.

NOAA-19 AVHRR Infrared Window (10.8 µm) image centered on Bettles (PABT), with surface air temperatures and corresponding station identifications [click to enlarge

NOAA-19 AVHRR Infrared Window (10.8 µm) image centered on Bettles (PABT), with surface air temperatures and corresponding station identifications [click to enlarge]

As was shown on the previous day, closer views centered on Bettles (above) and on Tanana (below) further highlighted the influence of terrain on the pattern of surface infrared brightness temperatures. On this day a layer of clouds (highlighted by the warmer cyan colors) covered the far eastern portion of the Tanana image — note that surface temperatures in the Fairbanks area beneath these clouds were only as cold as the -30s F. Farther to the west which remained cloud-free, the minimum temperature at Tanana was -59ºF.

NOAA-19 AVHRR Infrared Window (10.8 µm) images centered on Tanana (PATA), with surface air temperatures and corresponding station identifications [click to enlarge]

NOAA-19 AVHRR Infrared Window (10.8 µm) images centered on Tanana (PATA), with surface air temperatures and corresponding station identifications [click to enlarge]

Time series plots of surface weather conditions at Fairbanks, Tanana and Bettles during the 18-19 January period are shown below. Note that the surface visibility was periodically restricted 1 statute mile or less, due to ice fog, at all 3 locations.

Surface weather conditions at Fairbanks [click to enlarge]

Surface weather conditions at Fairbanks [click to enlarge]

Surface weather conditions at Tanana [click to enlarge]

Surface weather conditions at Tanana [click to enlarge]

Surface weather conditions at Bettles [click to enlarge]

Surface weather conditions at Bettles [click to enlarge]

Atmospheric river events bring heavy precipitation to California

January 13th, 2017

MIMIC Total Precipatable Water product [click to play MP4 animation]

MIMIC Total Precipatable Water product [click to play MP4 animation]

A series of 3 atmospheric river events brought heavy rainfall and heavy snowfall to much of California during the first 10 days of January 2017 (NWS San Francisco/Monterey | WeatherMatrix blog). Hourly images of the MIMIC Total Precipitable Water product (above; also available as a 33 Mbyte animated GIF) showed the second and third of these atmospheric river events during the 06 January11 January 2017 period, which were responsible for the bulk of the heavy precipitation; these 2 events appear to have drawn moisture northeastward from the Intertropical Convergence Zone (ITCZ)..

Terra MODIS Visible (0.65 µm) and Near-Infrared

Terra MODIS Visible (0.65 µm) and Near-Infrared “Snow/Ice” (2.1 µm) images [click to enlarge]

A relatively cloud-free day on 13 January provided a good view of the Sacramento Valley and San Francisco Bay regions. A comparison of Terra MODIS Visible (0.65 µm) and Near-Infrared  “Snow/Ice” (2.1 µm) images (above) showed that snow cover in the higher terrain of the Coastal Ranges and the Sierra Nevada appeared darker in the Snow/Ice band image (since snow and ice are strong absorbers of radiation at the 2.1 µm wavelength) — but water is an even stronger absorber, and therefore appeared even darker (which allowed the areas of flooding along the Sacramento River and its tributaries to be easily identified). A similar type of 1.6 µm Near-Infrared “Snow/Ice” Band imagery will be available from the ABI instrument on the GOES-R series, beginning with GOES-16.

Better detail of the flooded areas of the Sacramento River and its tributaries was seen in 250-meter resolution false-color Red/Green/Blue (RGB) imagery from the MODIS Today site — water appears as darker shades of blue, while snow appears as shades of cyan (in contrast to supercooled water droplet clouds, which appear as shades of white). In the corresponding MODIS true-color image, rivers and bays with high amounts of turbidity (tan shades) were evident; the offshore flow of sediment from a few rivers could also be seen.

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

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

 

Blizzard impacts North Dakota and Minnesota

December 8th, 2016

GOES-13 Water Vapor (6.5 µm) images, with hourly surface weather symbols [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with hourly surface weather symbols [click to play animation]

A major winter storm produced widespread blizzard conditions in North Dakota and northwestern Minnesota (as well as far northern South Dakota) as low pressure deepened (3-hourly surface analyses) while moving from South Dakota across Minnesota (and eventually over Ontario and western Quebec) during the 05 December08 December 2016 period. Storm total snowfall amounts included 16.0 inches in Montana, 19.0 inches in North Dakota and 13.9 inches in Minnesota; peak wind gusts were as high as 63 knots (72 mph) in South Dakota, 56 knots (64 mph) in North Dakota and 37 knots (43 mph) in Minnesota (KBIS PNS | KFGF PNS | WPC storm summary). In North Dakota, nearly the entire portion of both Interstates 94 and 29 were closed. The large size of the storm could be seen on GOES-13 (GOES-East) Water Vapor (6.5 µm) images (above).

A closer view using GOES-13 Water Vapor imagery with overlays of hourly reports of surface winds and wind gusts (below) showed that wind speeds remained strong enough to create travel-restricting blowing snow over eastern North Dakota and western Minnesota even into the early hours of 08 December (due to the continuing strong pressure gradient between the large low in Canada and the arctic high that was moving into Montana and Wyoming.

GOES-13 Water Vapor (6.5 µm) images, with hourly surface winds (yellow) and wind gusts in knots (red) [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with hourly surface winds (yellow) and wind gusts in knots (red) [click to play animation]

In the wake of the storm on 09 December, a southeastward flow of cold arctic air (with surface air temperatures in the 0 to -15º F range) over the still-unfrozen water of Lake Sakakawea (which exhibited MODIS Sea Surface Temperature values as warm as 37.9º F) caused lake effect cloud bands to form and extend downwind of the lake — these cloud bands were very evident in a comparison of 250-meter resolution Aqua MODIS true-color and false-color Red/Green/Blue (RGB) images from the MODIS Today site (below). In the false-color image, snow/ice appears as shades of cyan, in contrast to supercooled water droplet clouds which appear as shades of white. The 1.6 µm snow/ice band used to create the MODIS false-color image will also be available with the ABI instrument on the GOES-R series (beginning with GOES-16).

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

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

With a fresh, deep snow cover and cold arctic air in place, strong nocturnal radiational cooling allowed North Dakota to experience its first -30º F low temperatures of the season on the morning of 10 December. Aqua MODIS Land Surface Temperature values at 0939 UTC or 3:39 am local time (below) were as cold as -39º F (darker violet color enhancement) near the sites that reported the -30º F low temperatures.

Aqua MODIS Land Surface Temperature product [click to enlarge]

Aqua MODIS Land Surface Temperature product [click to enlarge]

Heavy rainfall and high-elevation snowfall in Hawai’i

December 2nd, 2016

GOES-15 Water Vapor (6.5 µm) images, with overlays of GFS model 500 hPa geopotential height [click to play animation]

GOES-15 Water Vapor (6.5 µm) images, with overlays of GFS model 500 hPa geopotential height [click to play animation]

6-hour interval GOES-15 (GOES-West) Water Vapor (6.5 µm) images with overlays of GFS model 500 hPa geopotential height (above) showed middle to upper tropospheric moisture that was being drawn northwestward toward Hawai’i by the circulation of a closed low centered southwest of the state during the 01-02 December 2016 period.

A closer view using 15-minute interval GOES-15 Water Vapor images (below) showed 2 distinct pulses of moisture moving across the eastern portion of the island chain. Due to the prolonged flow of moisture and the variable terrain, Flood Warnings and Winter Storm Warnings were issued for the Big Island of Hawai’i (as shown using RealEarth).

GOES-15 Water Vapor (6.5 µm) images, with hourly surface reports [click to play MP4 animation]

GOES-15 Water Vapor (6.5 µm) images, with hourly surface reports [click to play MP4 animation]

Hourly images of the MIMIC Total Precipitable Water (TPW) product (below) showed the large plume of moisture, which had its roots within the Intertropical Convergence Zone (ITCZ). Maximum TPW values in the vicinity of Hawai’i were in the 50-55 mm (2.0-2.2 inch) range. 24-hour rainfall amounts were as high as 6.27 inches on the island of Hawai’i and 3.67 inches on the island of Kauai.

MIMIC Total Precipitable Water product, with tropical surface analyses [click to play animation]

MIMIC Total Precipitable Water product, with tropical surface analyses [click to play animation]

===== 03 December Update =====

GOES-15 Visible (0.63 µm) images (below) provided glimpses of the snow-covered peaks of Mauna Kea and Mauna Loa (circled in red) on the Big Island of Hawai’i early in the day on 03 December.

GOES-15 Visible (0.63 µm) images, with hourly surface reports [click to play animation]

GOES-15 Visible (0.63 µm) images, with hourly surface reports [click to play animation]