Snowfall across northern Alaska

September 18th, 2019 |

GOES-17

GOES-17 “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog RGB and Day Cloud Phase Distinction RGB images [click to play animation | MP4]

GOES-17 (GOES-West) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog Red-Green-Blue (RGB) and and Day Cloud Phase Distinction RGB images (above) showed portions of the Brooks Range and eastern North Slope of Alaska that had significant snow cover on 18 September 2019. Some areas received 4-6 inches of snowfall during the previous day (a Winter Storm Warning had been issued, forecasting accumulations in the 4-8 inch range).

Snow cover appeared brighter white in the Visible images, and darker shades of gray in the Snow/Ice images; in the RGB images, snow was darker shades of red in the Day Snow-Fog, vs brighter shades of green in the Day Cloud Phase Distinction. Note that the Day Cloud Phase Distinction RGB provided sharper images than the Day Snow-Fog RGB (below), since the former makes use of higher spatial resolution 0.64 µm data for its Green component.

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

GOES-17 Day Cloud Phase Distinction RGB and Day Sow-Fog RGB images at 2030 UTC [click to enlarge]

Although much of the Bettles (PABT) area was masked by cloudiness on 18 September, that site received moderate to heavy snow for a few hours on 17 September (below), and reported a snow depth of 4 inches at 17 UTC (9 am local time).

Time series of surface data from Bettles, Alaska on 17 September [click to enlarge]

Time series of surface data from Bettles, Alaska on 17 September [click to enlarge]

Record May snowfall in Duluth, Minnesota

May 9th, 2019 |


GOES-16 “Red” Visible (0.64 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to play animation | MP4]

GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the cloudiness associated with a midlatitude cyclone (surface analyses) that moved across the Upper Midwest on 08 May09 May 2019.  The system produced accumulating snowfall from extreme eastern South Dakota to central/northeastern Minnesota, northwestern Wisconsin and Upper Michigan — storm total accumulations were as high as 10.6 inches at Duluth, Minnesota (observations), 10.4 inches at Poplar, Wisconsin, 5.0 inches at Atlantic Mine, Michigan and 3.0 inches at Astoria, South Dakota (NOHRSC maps of snowfall/snowdepth). Note that the NW-SE oriented band of snowfall straddling the South Dakota/Minnesota border may have been enhanced by upslope flow as northeasterly surface winds encountered rising terrain of the Coteau des Prairies.

GOES-16 Mid-level Water Vapor (6.9 µm) images (below) showed the formation of a SW-NE oriented deformation zone across Minnesota — forcing for ascent was further aided by a stretched lobe of 500 hPa vorticity and 310 K potential vorticity that moved northeastward across the region during this period, along with a favorably-coupled 250 hPa jet streak configuration. Cloud features within the deformation zone across eastern South Dakota into southern/central Minnesota had an appearance resembling convective elements/bands in both the Visible and Water Vapor imagery.

GOES-16 Mid-level Water Vapor (6.9 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to play animation | MP4]

Although lightning was not widespread — and thunder was not explicitly reported in any first-order station observations — there were isolated small clusters of GOES-16 GLM Groups detected, first over northeastern, then central and finally over southwestern Minnesota between 2256 and 0036 UTC (below), indicating the presence of thundersnow.

GOES-16 “Red” Visible (0.64 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to enlarge]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with plots of surface weather type (yellow) and GLM Groups (red) [click to enlarge]




Through occasional breaks in the clouds later in the day on 09 May, GOES-16 Day Cloud Phase Distinction Red-Green-Blue (RGB) images (below) revealed the stationary signature of fresh snow cover (darker green) across central to northeastern Minnesota and far northwestern Wisconsin (glaciating cloud tops also appear as shades of green).

GOES-16 Day Cloud Phase Distinction RGB images [click to play animation | MP4]

===== 10 May Update =====

GOES-16 “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 Visible images (above) showed two swaths of snow cover remaining across northeastern Minnesota (where reported snow depths were 1-2 inches) and northwestern Wisconsin (where reported snow depths were 4-5 inches) on the morning of 10 May.

Comparisons of GOES-16 Land Surface Temperature (LST) and Visible images at 1401 UTC and 1501 UTC (below) indicated that LST values were as much as 10ºF colder within the areas of snow cover (brighter shades of cyan) compared to adjacent bare ground.

GOES-16 Land Surface Temperature and “Red” Visible (0.64 µm) images at 1401 UTC [click to enlarge]

GOES-16 Land Surface Temperature and “Red” Visible (0.64 µm) images at 1501 UTC [click to enlarge]

Large ice lead near Utqiagvik (Barrow), Alaska

March 28th, 2019 |

Landsat-8 False Color RGB image at 2222 UTC [click to enlarge]

Landsat-8 False Color RGB images on 21 March and 28 March [click to enlarge]

A toggle between 30-meter resolution Landsat-8 False Color Red-Green-Blue (RGB) images viewed using RealEarth (above) revealed a large ice lead that had opened up to the east of Utqiagvik (Barrow), Alaska on 28 March 2019. Snow and ice appear as darker shades of cyan in the RGB image, with open water exhibiting a dark blue to black appearance.

A sequence of True Color RGB images from NOAA-20 / Suomi NPP VIIRS and Terra MODIS (below) showed the ice lead becoming wider with time during a 5-hour period (note: the time stamps on the images do not reflect the actual time each satellite passed over the Utqiagvik area). The MODIS image appeared the sharpest, since that instrument has a 250-meter resolution in the visible spectral bands (compared to 375 meters for VIIRS).

True Color RGB images from NOAA-20 and Suomi NPP VIIRS and Terra MODIS [click to play animation]

True Color RGB images from NOAA-20 / Suomi NPP VIIRS and Terra MODIS [click to play animation]

In a 14-day series of Terra MODIS composites (below) it can be seen that the same general ice fracture line had opened and closed a few times during the 15-28 March period, depending on the influences of surface wind stress and sea currents. Days with strong and persistent southwesterly winds led to an opening of the ice lead (such as 20 March); however, the largest 1-day change — and the largest opening of the ice lead — occurred from 27-28 March (MODIS | VIIRS), when the strong southwest winds were bringing unseasonably warm air (over 30ºF above normal) across the area. The daily high temperature at Utqiagvik on 28 March was 30ºF, which set a new record high for the date (the normal high temperature for 28 March is -3ºF). Incidentally, this period of above-normal temperatures contributed to Utqiagvik having its warmest March on record.

Daily composites of Terra MODIS True Color RGB images, 15-28 March [click to play animation]

Daily composites of Terra MODIS True Color RGB images, 15-28 March [click to play animation | MP4]

Signatures of fresh snowfall in the Dakotas

March 17th, 2019 |

GOES-16 Near-Infrared

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

GOES-16 (GOES-East) Near-Infrared “Snow/Ice” (1.61 µm) images (above) depicted the signature of northwest-to-southeast oriented swaths of fresh snowfall (lighter gray shades) which had recently fallen on top of the aged snow pack across North Dakota on 17 March 2019. As discussed here, the surface of the preexisting snow cover had experienced rapid melting several days earlier, which increased its “water to ice crystal” ratio — making it appear darker, since water is a stronger absorber of radiation at the 1.61 µm wavelength.

A similar (albeit broader and more continuous) northwest-southeast swath of fresh snowfall was seen across South Dakota (below).

GOES-16 Near-Infrared "Snow/Ice" (1.61 µm) images [click to play animation | MP4]

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

The radar-derived 24 hour precipitation ending at 12 UTC on 17 March is shown below.

24-hour precipitation ending at 12 UTC on 17 March [click to enlarge]

24-hour precipitation ending at 12 UTC on 17 March [click to enlarge]