The first -40º temperature of the winter in Alaska

November 24th, 2018 |

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images [click to enlarge]

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).

Suomi NPP VIIRS Infrared Window (11.45 µm) image at 2314 UTC [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) image at 2314 UTC [click to enlarge]

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.

Minimum and maximum temperatures for the 24-hour period ending at 20 UTC on 25 November [click to enlarge]

Minimum and maximum temperatures for the 24-hour period ending at 20 UTC on 25 November [click to enlarge]

Eruption of Mount Veniaminof on the Alaska Peninsula

November 21st, 2018 |
GOES-17

GOES-17 “Red” Visible (0.64 µm) and Split Window Difference (10.3-12.3 µm) images [click to play MP4 animation]

* 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.

NOAA-20 VIIRS True Color RGB images [click to enlarge]

NOAA-20 VIIRS True Color RGB images [click to enlarge]

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.

Terra/Aqua MODIS and Suomi NPP VIIRS Ash Probability, Ash Height and Ash Loading images [click to play animation | MP4]

Terra/Aqua MODIS and Suomi NPP VIIRS Ash Probability, Ash Height and Ash Loading images [click to play animation | MP4]

 

Dry air within an Atlantic subtropical ridge

November 16th, 2018 |

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a large region of very dry air within a subtropical ridge over the central North Atlantic Ocean on 16 November 2018. Infrared brightness temperatures were unusually warm (brighter yellow to red enhancement) on all 3 Water Vapor bands, especially along the western edge of the dry air.

A GOES-16 Upper-level Water Vapor image at 1700 UTC (below) showed a swath of NUCAPS sounding availability close to that time. The swath passed directly over the driest air within the subtropical ridge.

GOES-16 Upper-level (6.2 µm) Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

GOES-16 Upper-level Water Vapor image at 1700 UTC, with a swath of NUCAPS sounding availability [click to enlarge]

One of the green (high-quality) NUCAPS soundings within the arc of driest air (below) revealed a remarkably dry profile above the trade wind inversion — dewpoint values were -50ºC and colder within the 500-620 hPa layer, and dewpoint depressions were about 50ºC near the 550 hPa level.

NUCAPS sounding profile within the driest air [click to enlarge]

NUCAPS sounding profile within the driest air [click to enlarge]

Even though the middle to upper tropozphere was quite dry, note that the Total Precipitale Water (TPW) value calculated from the NUCAPS profile was 0.73 inch — there was still abundant tropical moisture within the marine boundary layer of the warm central Atlantic. The GOES-16 TPW product (below) showed minimum values of 0.6-0.8 inch in the region of driest air on the Water Vapor imagery (1800 UTC comparison). In contrast, TPW values over a large portion of the Lower 48 states were 0.6 inch or less, even in regions that appeared to be “moist” on the Water Vapor imagery.

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

GOES-16 Upper-level Water Vapor + Total Precipitable Water [click to play animation | MP4]

Atmospheric River brings precipitation to south-central Alaska

November 12th, 2018 |

Blended Total Precipitable Water product [click to play animation | MP4]

Blended Total Precipitable Water product, with Upper Air sites plotted in white [click to play animation | MP4]

The NESDIS Blended Total Precipitable Water (TPW) product (above) showed an atmospheric river that was transporting moisture northward from the tropics to south-central Alaska during 11 November – 12 November 2018. TPW values were in excess of 2.0 inches near the leading edge of the moisture plume early in the period.

The corresponding Percent of Normal Blended Total Precipitable Water product (below) indicated that these values of TPW were at or above 200 percent of normal (yellow).

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Percent of Normal Blended Total Precipitable Water product, with Upper Air sites plotted in red [click to play animation | MP4]

Using the MIMIC Multi-layer TPW site, you can see how TPW is partitioned within various layers of the atmosphere (below). This TPW product uses microwave data from POES, Metop NOAA-20 and Suomi NPP satellites (description). It’s important to keep in mind that the location and continuity of a plume of TPW (such as an atmospheric river) might not always exactly agree what is seen on geostationary satellite Water Vapor imagery, since water vapor spectral bands usually sense radiation being emitted from levels above where the bulk of TPW is normally found (as discussed here).

MIMIC Multi-layer Total Precipitable Water product [click to play animation | MP4]

MIMIC Multi-layer Total Precipitable Water product on 12 November [click to play animation | MP4]

Anchorage, Alaska rawinsonde data (below) showed that TPW values reached a maximum of 0.73 inch at 00 UTC on 12 September.

Sequence of Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

Anchorage, Alaska rawinsonde data from 00 UTC on 11 November to 00 UTC on 13 November [click to enlarge]

The arrival of this moisture produced heavy rainfall and mixed winter precipitation across the region — Portage Glacier (about 50 miles southeast of Anchorage) received 9.99 inches of rainfall in 48 hours, and Anchorage set a new daily precipitation record on 11 November with 0.89″ (which included 1.0 inch of new snow). A summary of temperature and precipitation reports can be seen here.

A comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November (below) revealed widespread layered clouds across most of south-central Alaska.

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 2157 UTC on 12 November [click to enlarge]