A sequence of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images centered over the North Slope of Alaska (above) showed a few patches of thin stratus cloud drifting westward on 24 November 2018. Ample illumination from the Moon — which was in the Waning Gibbous phase, at 98% of Full — maximized the “visible image at night” capability of the Day/Night Band. A faster animation of Infrared images helped to emphasize the westward motion of multi-year drift ice in the Beaufort Sea as it collided with the growing wedge of first-year land-fast ice off the northeast coast of Alaska.

In areas with deeper snow cover that remained generally cloud-free for long periods of time, temperatures at first-order stations dropped into the -20s and -30s F; a low of -35ºF was recorded at Nuiqsut (PAQT). A closer look at the 2314 UTC Infrared image (below) revealed surface brightness temperatures as cold as -47ºC or -53ºF (lighter shades of yellow) in the valleys near Galbraith Lake (PAGB).

The RAWS site at Umiat Airfield (PAUM) registered a minimum temperature of -40ºF (hourly summary) at 2123 UTC on 24 November (below) — this was the first reliable -40º temperature of the 2018/2019 Winter season in Alaska. Farther to the east, the HADS site at Sagavanirktok recorded a low of -44F, but that max/min temperature data was flagged as being suspect (red) by Mesowest quality control.

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

Following an eruption of Mount Veniaminof on 21 November 2018, 1-minute Mesoscale Domain Sector GOES-17 “Red” Visible (0.64 µm) and Split Window Difference (10.3-12.3 µm) images (above) showed the volcanic ash plume drifting southeastward over the Gulf of Alaska. During the period 1947-2323 UTC the plume was seen to grow to a length of 200 miles from the volcano summit. Note in the Visible imagery that the 2625 ft (800 m) volcano acted as a barrier to the northwesterly boundary layer winds to create a cloud-free “notch” immediately downwind of Veniaminof.

NOAA-20 VIIRS True Color RGB images viewed using RealEarth (below) highlighted the light brown color of the ash plume.

A sequence of retrieved Ash Probability, Ash Height and Ash Loading (source) derived from Terra/Aqua MODIS and Suomi NPP VIIRS data (below) indicated high probabilities of ash content, height values primarily in the 4-6 km range and ash loading exceeding 4 g/m3 at times.

 

Spectacular @planetlabs imaging of ash emissions from #Veniaminof #volcano (AK, USA) on November 21. @alaska_avo @CIMSS_Satellite @SanGasso @NWSAnchorage

Images Copyright 2018 Planet Labs Inc. pic.twitter.com/jEziZMgrmu

— Simon Carn (@simoncarn) November 22, 2018

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

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed the diurnal cycle of warming and cooling of the summits of Mauna Kea and Mauna Loa on the Big Island of Hawai’i on 21 November 2018. There was even a subtle warming signature of the higher terrain of Maui on 7.3 µm and 6.9 µm imagery. This example helps to underscore the fact that Water Vapor bands are Infrared bands, which — in the absence of clouds — essentially sense the mean temperature of a layer (or layers) of moisture within the troposphere.

The presence of very dry air within the middle/upper troposphere over Hawai’i on 21 November had the effect of shifting the water vapor weighting functions to lower altitudes, as seen on plots for the 3 ABI Water Vapor bands calculated using 00 UTC rawinsonde data from Hilo PHTO (below). This allowed thermal radiation from the higher terrain to pass upward (un-attenuated) through what little high-altitude moisture was present and reach the 7.3 µm / 6.9 µm / 6.2 µm detectors on GOES-17.

Compare the altitudes and depths of Hilo water vapor weighting function plots on 19 November vs. 22 November (below). Increased moisture within the middle troposphere on 19 November shifted the water vapor weighting function plots for the 7.3 µm and 6.9 µm bands to higher altitudes (and increased the magnitude of the high-altitude contributions for the 6.9 µm and 6.2 µm bands).

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After increasingly colder air began moving from eastern Nunavut across Hudson Bay beginning on 06 November (surface analyses), the daily sea ice concentration as derived from GCOM-W1 AMSR2 data (source) began to increase in the northern half of Hudson Bay (above) — especially after 15 November once mid-day (18 UTC) temperatures colder than -20ºF were seen at reporting stations along the northwest coast.

A sequence of daily Terra/Aqua MODIS True Color Red-Green-Blue (RGB) images (source) showed signatures of the increasing of ice coverage.

A toggle between Terra MODIS True Color and False Color RGB images on 21 November (below) confirmed that much of the northern half of Hudson Bay contained ice — snow/ice (as well as ice crystal clouds) appear as darker shades of red in the False Color image (in contrast to the cyan shades of supercooled water droplet clouds).

19 November maps of Ice Concentration, Ice Stage and Departure from Normal via the Canadian Ice Service (below) further characterized this ice formation, which was ahead of normal for the central portion of Hudson Bay.

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