Cold temperatures across the North Slope of Alaska

February 4th, 2021 |

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

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

Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) revealed a large area of cold surface infrared brightness temperatures across much of the North Slope of Alaska on 04 February 2021 — with the coldest IR temperature being -56ºC (darker shades of violet) about 30 miles south-southeast of Umiat (PAUM) on the 1221 UTC image. The surface air temperature at the nearby Umiat RAWS site around that time was -55ºF (-48.3ºC). Narrow fingers of cold air drainage into some of the river valleys along the northern slopes of the Brooks Range (topography) were also apparent.

The corresponding GOES-17 “Clean” Infrared Window (10.35 µm) images (below) also showed the large area of cold surface IR brightness temperatures, but the temperatures were not as cold (in the -40 to -50ºC range), and the small-scale signatures of various topographical features were not depicted.

GOES-17 "Clean" Infrared Window (10.35 µm) images [click to enlarge]

GOES-17 “Clean” Infrared Window (10.35 µm) images [click to enlarge]

A toggle between Infrared Window images from Suomi NPP VIIRS and GOES-17 (10.35 µm) at 1223 UTC is shown below.

Infrared Window images from Suomi NPP VIIRS and GOES-17 (10.35 µm) at 1223 UTC [click to enlarge]

Infrared Window images from Suomi NPP VIIRS (11.45 µm) and GOES-17 (10.35 µm) at 1223 UTC [click to enlarge]

Ice leads in the Beaufort Sea

December 20th, 2020 |
Suomi NPP VIIRS Infrared Window (11.45 µm) images [click to play animation]

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


Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed widespread ice leads in the Beaufort Sea during the 18 December – 20 December 2020 period. Some existing leads increased in width and/or length as they migrated westward, while some new leads were seen to form as land-fast ice fractured off the coasts of Alaska and larger islands of the Canadian Arctic Archipelago.

Suomi NPP VIIRS Infrared images with plots of NAM12 model surface winds on 20 December (below) indicated that the ice lead motion was influenced by surface wind stress — which also played a role in the clockwise flow of the Beaufort Gyre (the primary influence of ice lead motion in that part of the Arctic Ocean).

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of NM12 model surface winds [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images, with plots of NAM12 model surface winds [click to enlarge]


CIMSS Scientists are working on a Machine-learning Ice Lead detection method, as described here.  The toggle below compares the MODIS and VIIRS computations of Ice Leads on 18 December 2020. Leads in this toggle are white; greys are suspected leads, but the detection algorithm ultimately could not confirm their presence. At present, the algorithm is challenged when leads are moving, as in this example. Note that Banks Island, on the right edge of the animation above, is in the lower left corner in the toggle below.

MODIS and VIIRS-derived ice lead information, 18 December 2020 (Click to enlarge)

GOES-17 IFR Probability fields are now being created for Alaska

October 15th, 2020 |

GOES-17 IFR Probability fields over Anchorage AK and surroundings, 0200 – 1300 UTC on 15 October 2020 (Click to animate)

CIMSS is now producing IFR Probability fields (and Low IFR Probability, Marginal VFR Probability, and Cloud Thickness fields) using GOES-17 data.  (Recall that GOES-16 IFR Probability fields  are now produced by NOAA/NESDIS and are distributed via the Satellite Broadcast Network (SBN) to National Weather Service Forecast Offices.  GOES-16, however, does not view Alaska).  GOES-17 fields will presently be available via an LDM pull.  NOAA/NESDIS will likely start processing the fields in 2021.

The animation above shows IFR Probability fields today over the Anchorage region.  The animation is preceded by a view of the topographic features, and IFR conditions on 15 October seem centered on topographic features.

GOES-17 can view the North Slope of Alaska.  This location is quite far from the GOES-17 sub-satellite point, so resolution is degraded from the nadir 2-km views. However, regions of likely IFR conditions are easily tracked (Again, the animation is preceded by topography), with a large region between the Arctic Ocean and the high terrain of the Brooks Range.

GOES-17 IFR Probability fields over northern Alaska, 0200 -1300 UTC, 15 October 2020 (Click to animate)

 

GOES-17 views of Alaska southeast, below show probabilities of low clouds and reduced visibility. As over other regions of Alaska today, highest probabilities are over high terrain. GOES-17 IFR Probability for the PACUS domain is available at this website. Work is ongoing to insert IFR Probability (from GOES-16 and GOES-17) into Real Earth.

GOES-17 IFR Probability fields over Alaska Southeast, 0200 -1400 UTC, 15 October 2020 (Click to animate)

GOES-17 fields contain artifacts in the form of horizontal stripes that can be traced to the poorly-functioning Loop Heat Pipe on GOES-17.  GOES-17 is now in a reduced-scanning mode between 0600 and 1200 UTC to enhance the ability of the satellite to shed excess heat:  fewer Mesoscale sectors are scanned, full disk sectors are not as frequent (every 15 minutes instead of every 10), and the ‘PACUS’ sector is not scanned.  This scanning strategy will continue through the end of October.


The Forecast Decision Training Division has a Quick Guide on IFR Probability fields here.  A 20-minute YouTube video explaining the product is here.

Cutoff low over northern Alaska

June 12th, 2020 |

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red [click to play animation | MP4]

GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm) images (above) showed the circulation of an anomalous middle-tropospheric cutoff low over the northwestern portion of Alaska on 12 June 2020. A Potential Vorticity (PV) anomaly associated with this low was causing the dynamic tropopause — represented by the pressure of the PV1.5 surface — to descend as low as the 500 hPa pressure level.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red and available NUCAPS sounding profiles denoted by green/yellow points [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red and available NUCAPS sounding profiles denoted by green/yellow points [click to enlarge]

Just after 21 UTC, an overpass of the Suomi NPP satellite provided NUCAPS soundings (above) within much of the core of the cutoff low — the green NUCAPS sounding profile about 40 miles east/southeast of the 500 hPa PV1.5 pressure contour (below) displayed an apparent tropopause near the 400 hPa pressure level.

NUCAPS sounding profile [click to enlarge]

NUCAPS sounding profile [click to enlarge]

GOES-17 “Red” Visible (0.64 µm) images (below) revealed the development of numerous showers and thunderstorms across the Brooks Range and North Slope of Alaska, aided by instability beneath the cutoff low.

GOES-17 "Red" Visible (0.64 µm) images, with hourly surface reports plotted in red [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images, with hourly surface reports plotted in red [click to play animation | MP4]

A higher spatial resolution view of these showers and thunderstorms was provided by a sequence of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP, as viewed using RealEarth (below). A few of these thunderstorms moved toward the Arctic Coast, with one fairly impressive storm just southwest of Katovik which exhibited cloud-top infrared brightness temperatures near -60ºC (red enhancement) around 23 UTC.

VIIRS True Color (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS True Color (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]