First -50ºF of the season in Alaska

January 6th, 2019 |
Suomi NPP VIIRS Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images [click to enlarge]

* GOES-17 images shown here are preliminary and non-operational *

The first official temperature of -50ºF or colder during Alaska’s 2018/2019 winter season was reported by the cooperative observer at Chicken on 06 January — the 24-hour high temperature at that site was -45ºF, with a low of -51ºF (NWS Fairbanks summary). A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed infrared brightness temperatures as cold as -46.5ªC or -51.7ºF (lighter green enhancement) in the river valleys between Tok and Eagle (Chicken is located about midway between those 2 cities).

A toggle between Infrared Window images from Suomi NPP VIIRS and GOES-17 (below) highlighted the advantage of polar-orbiting imagery at high latitudes — improved spatial resolution and a better viewing angle provides more detailed images. However, it should be noted that the Full Disk GOES-17 imagery that is displayed here using AWIPS is degraded from 2-km to 4-km resolution (at satellite sub-point).

Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 (10.3 µm) [click to enlarge]

Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 (10.3 µm) [click to enlarge]

A sequence of NOAA-20 VIIRS Infrared images displayed using RealEarth is shown below. The majority of the scene was cloud-free — except for some cyan-enhanced stratiform clouds moving eastward across parts of the Alaska Range — and although there was some slight diurnal warming seen in the higher terrain, little change was apparent with the signature of colder air (shades of green) that was trapped in the lower elevations and river valleys.

NOAA-20 VIIRS Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS Infrared Window (11.45 µm) images [click to enlarge]

Plots of Fairbanks rawinsonde data from 00 UTC on 06 and 07 January (below) displayed the strong low-level temperature inversion caused by the relatively shallow arctic air.

Plots of Fairbanks rawinsonde data from 00 UTC on 06 and 07 January [click to enlarge]

Plots of Fairbanks rawinsonde data from 00 UTC on 06 and 07 January [click to enlarge]

===== 07 January Update =====

Infrared Window images from GOES-17 ABI (10.33 µm) and Suomi NPP VIIRS (11.45 µm) [click to enlarge]

Infrared Window images from GOES-17 ABI (10.33 µm) and Suomi NPP VIIRS (11.45 µm) [click to enlarge]

Minimum temperatures of -50ºF and colder were again reported on 07 January, with lows of -56ºF at Chicken and -50ºF at North Pole (NWS Fairbanks summary). 1-minute imagery from a GOES-17 Mesoscale Domain Sector allowed for a more direct full-resolution comparison with Suomi NPP VIIRS imagery — and a toggle between 1926 UTC images (above) revealed significantly greater detail in terms of the cold air confined to river valleys on the VIIRS image. The enhancements used in this comparison have identical temperature ranges for each of the color segments (there are some color vs. temperature offsets with the GOES/VIIRS infrared comparison shown on the previous day). The coldest infrared brightness temperature values on the VIIRS image were -46.4ºC in the vicinity of Tok, Alaska and -49.4ºC across the Canadian border in Yukon — compared to -44.6ºC and -45.1ºC for those two locations on the GOES-17 image.

Partial solar eclipse shadow

January 6th, 2019 |

Himawari-8

Himawari-8 “Red” Visible (0.64 µm) images [click to play animation | MP4]

A partial solar eclipse occurred on 06 January 2019 (UTC) — and JMA Himawari-8 “Red” Visible (0.64 µm) images (above) showed the shadow moving eastward across parts of Asia and the North Pacific Ocean.

Although it was less obvious, the shadow was also evident on GOES-17 “Red” Visible (0.64 µm) images as it moved across the North Pacific Ocean toward Alaska (below).

GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

Snowfall in Texas and Oklahoma

January 4th, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly plots of surface reports [click to play animation | MP4]

A winter storm produced 6-8 inches of snowfall from the eastern Texas Panhandle to central Oklahoma on 03 January 2019 (NWS AmarilloNWS Norman). On the following day, GOES-16 “Red” Visible (0.64 µm) images (above) revealed the areal extent of the snow cover, with significant melting occurring by the late afternoon hours. The snow cover seen in the far northwestern portion of the images is from a winter storm that occurred 8 days earlier on 27 December 2018.

In a comparison between Terra and Aqua MODIS Visible (0.65 µm) images and the corresponding Land Surface Temperature product at 1757 and 1936 UTC (below), LST values in the 30s F (darker shades of blue) were 20ºF colder over the snow cover than over adjacent bare ground in Oklahoma, and 35-40ºF colder than the more sparsely-vegetated bare ground in Texas. By increasing the surface albedo, the snow cover acted to suppress daily maximum temperatures by several degrees.

Terra and Aqua MODIS Visible (0.65 µm) image and Land Surface Temperature product at 1757 an 1936 UTC [click to enlarge]

Terra and Aqua MODIS Visible (0.65 µm) image and Land Surface Temperature product at 1757 an 1936 UTC [click to enlarge]

===== 05 January Update =====

GOES-16 "Red" Visible (0.64 µm) images, 04 and 05 January [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images with hourly plots of surface reports, 04 and 05 January [click to play animation | MP4]

A sequence of GOES-16 “Red” Visible (0.64 µm) images on 04 and 05 January (above) showed the continued melting of residual snow cover.

A toggle between NOAA-20 VIIRS True Color Red-Green-Blue (RGB) images on 04 and 05 January as viewed using RealEarth (below) provided a higher-resolution view of the snow cover just after 1 PM local time on those two days.

NOAA-20 VIIRS True Color RGB images on 04 and 05 January [click to enlarge]

NOAA-20 VIIRS True Color RGB images on 04 and 05 January [click to enlarge]

Light ice accrual from freezing rain/drizzle in Texas

January 3rd, 2019 |

GOES-16

GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images [click to play animation | MP4]

Portions of West Texas received a light accumulation of ice from freezing rain/drizzle/fog during the daytime and evening hours on 02 January 2019. On the following morning prior to melting, in a comparison of GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (above) the semi-transparent glaze of ice that covered the surface was not apparent in the Visible imagery but exhibited a darker appearance in the Snow/Ice imagery (since snow and ice efficiently absorb energy at the 1.61 µm  wavelength). Some localized white patches of light snow cover could also be seen, primarily in the Big Spring (KBPG) and Snyder (KSNK) areas.