Snow cover in the Brooks Range and North Slope of Alaska

September 2nd, 2018 |

Suomi NPP VIIRS Infrared Window (11.45 µm) images on 01 and 02 September [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) images on 01 and 02 September [click to enlarge]

A low moved eastward across the Beaufort Sea on 01 September 2018, bringing a cold front southward across the North Slope and Brooks Range in far northern Alaska (surface analyses). A sequence of Suomi NPP VIIRS Infrared Window (11.45 µm) images (above) showed the clearing of high/cold clouds in the wake of the frontal passage.

The upslope flow of cold air helped to generate accumulating snowfall across that region — prompting a Winter Storm Warning to be issued for the eastern Brooks Range, where 4-8 inches was expected at higher elevations — and some of the resulting snow cover was seen on a Suomi NPP VIIRS Day/Night Band (0.7 µm) image at 1415 UTC or 6:15 am local time on 02 September (below). A comparison with the corresponding VIIRS Infrared Window (11.45 µm) image and Topography is also shown. The darker shades of brown on the topography image correspond to elevations of 6000-8000 feet in the Brooks Range.

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

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

Later in the day on 02 September, additional clearing of patchy low clouds revealed more of the snow cover, as seen in a toggle between VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images (below). Supercooled water cloud droplets are efficient reflectors of incoming solar radiation, making patches of low cloud appear darker shades of gray on the Shortwave Infrared image (helping to identify low clouds over snow cover).

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Topography images [click to enlarge]

At 2124 UTC (or 1:24 pm local time), a 30-meter resolution Landsat-8 False Color Red-Green-Blue (RGB) image viewed using RealEarth (below) provided a more detailed view of a portion of the snow cover. Snow and ice appear as shades of cyan in this type of RGB image — which is created by combining Landsat bands 6 (1.61 µm), 5 (0.865 µm), and 4 (0.655 µm) as Red, Green, and Blue — and numerous small ice floes can also be seen off the coast.

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

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

On a side note, farther to the west an interesting pattern of contrails was seen in VIIRS Visible and Infrared Window images at 2046 UTC (below). On the Visible image, note that the darker contrail shadows cast onto the surface are displaced about 15 miles to the north (due to the low sun angle); the contrail features exhibited Infrared brightness temperatures of -10 to -15ºC. These contrail patterns were generated by military aircraft performing training exercises: similar features have been noted over California and North Dakota.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A curved portion of one of these contrails was seen on web camera images looking south from Atqasuk (below).

 

Valley fog and mountain snow in the Catskills of New York

May 1st, 2018 |

As pointed out by NWS Binghamton, valley fog and higher-elevation snow cover was apparent on GOES-16 (GOES-East) Visible imagery in the Catskills of southeastern New York on the morning of 01 May 2018. A closer view comparing GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images (below) showed the dissipation of the valley fog, followed by the melting of the snow cover in higher terrain (snowfall amounts of up to 3-4 inches fell in the area on 29 April). The Snow/Ice imagery was helpful in discriminating between the brighter valley fog features and the darker snow cover.

GOES-16

GOES-16 “Red” Visible (0.64 µm, left) and Near-Infrared “Snow/Ice” (1.61 µm, right) images, with hourly plots of surface reports [click to play animation | MP4]

A 250-meter resolution Terra MODIS True-color Red-Green-Blue (RGB) image acquired from the SSEC Direct Broadcast ground station (below) showed the remaining snow cover over the Catskills (near the center of the image) at 1539 UTC.

Terra MODIS True-color image [click to enlarge]

Terra MODIS True-color image [click to enlarge]

Heavy snow across southern Minnesota, northern Iowa and southern Wisconsin

April 18th, 2018 |

24-hour snowfall ending at 12 UTC on 19 April [click to enlarge]

24-hour snowfall ending at 12 UTC on 19 April [click to enlarge]

The map above shows a band of heavy snow that fell across southern Minnesota (as much as 11.0 inches), northern Iowa (as much as 12.0 inches) and southern Wisconsin (as much as 9.4 inches) on 18 April 2018.

Animations of 1-minute Mesoscale Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm), “Clean” Infrared Window (10.3 µm) and “Low-level” Water Vapor (7.3 µm) images (below) showed the formation of convective elements and banding along the southern edge of the colder cloud shield — snowfall rates were enhanced when these convective features moved overhead, and thundersnow was noted at some locations in northern Iowa and southern Wisconsin.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with hourly surface weather type plotted in cyan [click to play MP4 animation]

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images, with hourly surface weather type plotted in yellow [click to play MP4 animation]

GOES-16

GOES-16 “Low=level” Water Vapor (7.3 µm) images, with hourly surface weather type plotted in cyan [click to play MP4 animation]

In south-central Wisconsin, Madison (KMSN) received 7.2 inches of snowfall, which set a new record for daily snowfall (and helped to make April the snowiest month of the 2017/2018 winter seeason). In addition, the daily maximum temperature was only 33 ºF, which was a record low maximum for the date. Over the southwestern part of the city, a cluster of GOES-16 Geostationary Lightning Mapper (GLM) Groups was detected from 1918 to 1919 UTC (below; courtesy of Dave Santek, SSEC) — the GOES-16 Visible image at that time did display a textured cloud top appearance characteristic of embedded convection across southern Wisconsin.

GOES-16 GLM Groups [click to enlarge]

GOES-16 GLM Groups [click to enlarge]

===== 20 April Update =====

GOES-16 true-color (daytime) and Infrared Window (10.3 µm, nighttime) images [click to play MP4 animation]

GOES-16 natural-color RGB (daytime) and Infrared Window (10.3 µm, nighttime) images [click to play MP4 animation]

A fast animation of GOES-16 natural-color Red-Green-Blue (RGB) images (above) revealed the rapid rate of snow melt — especially on 19 April — along the southern edge of the snow cover (where lighter amounts of snow fell). The effect of the high late-April sun angle also played a role in the rapid snow melt.

Some satellite signatures of Winter remaining on 01 April

April 1st, 2018 |

GOES-16

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

Some remnant signatures of Winter could be seen on 01 April 2018 — the first were seen  on GOES-16 (GOES-East) GOES-16 “Red” Visible (0.64 µm) and Near-Infrared “Snow/Ice (1.61 µm) over North Dakota and South Dakota, in the form of snow cover and snow/ice on parts of the Missouri River (above). With the high April sun angle, the lesser snow cover over northern South Dakota melted rather quickly, and the southern edge of the deeper snow cover in southern North Dakota also receded during the day.

Farther to the east, the motion and breakup of ice in Green Bay was evident on GOES-16 “Red” Visible (0.64 µm)  images (below).

GOES-16

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