October snowfall on the Big Island of Hawai’i

October 14th, 2014
GOES-15 6.5 µm water vapor channel images (click to play animation)

GOES-15 6.5 µm water vapor channel images (click to play animation)

McIDAS images of GOES-15 (GOES-West) 6.5 µm water vapor channel data (above; click image to play animation) showed an upper-level low that moved from east to west over the Hawaiian Islands during the 13 October – 14 October 2014 period. This low forced the development of widespread showers and thunderstorms, especially over the Big Island of Hawai’i — and even produced some snowfall in the highest elevations around the summits of Mauna Kea and Mauna Loa. Some excerpts from Area Forecast Discussions issued by the National Weather Service at Honolulu on 13 October:

FXHW60 PHFO 131350
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
400 AM HST MON OCT 13 2014
[...]
FORECAST MODELS HAVE BEEN CONSISTENTLY CALLING FOR 500 MB TEMPERATURES BETWEEN -12 AND -13C WITHIN THE CORE OF THE COMPACT UPPER LOW. THIS IS EXCEPTIONALLY COLD FOR OCTOBER
[...]
FORECAST MODELS SHOW THAT THIS FEATURE WILL HOLD AS IT MOVES OVER THE BIG ISLAND LATER TODAY INTO TONIGHT…LIKELY PRODUCING ACCUMULATING SNOW OVER THE SUMMITS ABOVE 12000 FT. AS A RESULT…A WINTER WEATHER ADVISORY HAS BEEN ISSUED.
[...]

=====

FXHW60 PHFO 140152
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
330 PM HST MON OCT 13 2014
[...]
THE SUMMITS OF THE BIG ISLAND HAVE BEGUN TO REPORT SNOWFALL ACCUMULATION…AND THIS WILL CONTINUE WITH A COUPLE OF INCHES POSSIBLE OVERNIGHT.
[...]

While examining a nighttime (11:21 UTC or 1:21 am local time) comparison of AWIPS II images of Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) and 11.45 µm IR channel data covering Tropical Storm Ana (below), the main feature of interest was the inner core of cloud-top IR brightness temperatures as cold as -86º C (yellow color enhancement) associated with Ana — however, equally interesting was the appearance of a pair of bright white features in the middle of the Big Island on the DNB image (which highlighted the areas of snow cover that remained at the higher elevations).

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

A closer view comparing the VIIRS DNB and IR images centered over the Big Island (below) seemed to suggest that the 2 patches of bright snow cover (well-illuminated by a nearly Full Moon) were located along the western slopes of Mauna Kea and Mauna Loa. A similar comparison of the DNB image and high-resolution topography can be seen here.

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

An animation of GOES-15 0.63 µm visible channel images during the following daylight hours of 14 October (below; click image to play animation) revealed the gradual melting of the 2 patches of high-elevation snow cover as temperatures rose from around freezing into the 50s F near the summits (Cooperative observations).

GOES-15 0.63 µm visible channel images (click to play animation)

GOES-15 0.63 µm visible channel images (click to play animation)

Great Lakes ice motion and lake-effect snow bands

February 27th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

A southward to southeastward surge of arctic air across the Great Lakes in the wake of a strong cold frontal passage (18 UTC surface analysis) on 27 February 2014 produced widespread lake-effect snow bands and also contributed to a renewed growth of ice. McIDAS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) showed (1) a variety of lake-effect cloud bands streaming across Lake Superior, Lake Michigan, Lake Huron, and western Lake Erie, (2) the motion of lake ice, due to strong northerly, northwesterly, and westerly winds across the region, and (3) the rapid formation of new lake ice in the previously ice-free nearshore waters in the far northwestern portion of Lake Superior.

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data and a false-color “snow/ice vs cloud discrimination” Red/Green/Blue (RGB) product at 19:02 UTC (below) demonstrated how the RGB product could be used to highlight the various cloud features — snow and ice appeared as darker shades of red, while supercooled water droplet clouds were depicted as varying shades of white (glaciated cloud features exhibited a pink to lighter red appearance).

Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

Suomi NPP VIIRS 0.64 µm visible channel and false-color RGB images

Lake Michigan: ice motion, cloud streets, and a mesovortex

February 16th, 2014
GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

AWIPS images of GOES-13 0.63 µm visible channel data (above; click image to play animation) displayed a number of interesting Lake Michigan features on 16 February 2014: (1) the motion of lake ice in the northern and far eastern portions of the lake, (2) the formation of parallel cloud streets over the ice-free waters of the central part of lake, and (3) the development of a mesoscale vortex (or “mesovortex”) over the southern end of the lake.

Northerly winds were blowing down the long axis of Lake Michigan in the wake of a departing area of low pressure; Metop ASCAT surface scatterometer wind speeds were as high as 35 knots at 15:26 UTC (below).

GOES-13 0.63 µm visible channel image with ASCAT surface scatterometer winds

GOES-13 0.63 µm visible channel image with ASCAT surface scatterometer winds

False-color Red/Green/Blue (RGB) images created from Suomi NPP VIIRS 0.64 µm visible and 1.61 µm “snow/ice channel” data (below) helped to disctiminate between snow cover and ice fearures (which appeared as varying shades of red) and supercooled water droplet cloud features (which appeared as brighter shades of white). Even in the relatively short 1.5 hour period separating the two VIIRS RGB images, a significant amount of ice motion could be seen.

Suomi NPP VIIRS false-color "snow/ice vs cloud discrimination" RGB images

Suomi NPP VIIRS false-color “snow/ice vs cloud discrimination” RGB images

As an aside, another feature of interest seen in the GOES-13 visible images included arc-shaped aircraft dissipation trails (or “distrails”), created by air traffic that was likely circling upon approach or departure from the Chicago O’Hare or Midway airports (below; click image to play animation). Partcles in the aircraft exhaust acted as ice condensation nuclei, glaciating a trail as they penetrated the supercooled water droplet cloud deck.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

“Industrial-enhanced” snow in Texas

February 10th, 2014

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images [click to play animation]

GOES-15 (left) and GOES-13 (right) 0.63 µm visible channel images [click to play animation]

Examples of “industrial-enhanced snow” were seen in the Texas Panhandle region on 10 February 2014. In the overnight hours, areas downwind of agricultural plants near Borger (KBGD) received anywhere from 3.0 to 4.3 inches of snowfall. During the following morning and early afternoon hours, the particles contained within the hot, moist plume emanating from a factory located just northeast of Amarillo (KAMA) acted to glaciate the supercooled water droplets within the surrounding stratus deck — as the ice particles fell out of the cloud as snow, the cloud deck began to partially dissipate as seen in McIDAS images of 1-km resolution GOES-15 (GOES-West) and GOES-13 (GOES-East) 0.63 µm visible channel data (above; click image to play animation).

A similar comparison of 4-km resolution GOES-15 and GOES-13 3.9 µm shortwave IR images (below; click image to play animation) confirmed that the plume streaming southward from the Amarillo area was indeed glaciated — the plume appeared significantly colder (brighter white) compared to the surrounding supercooled water droplet stratus cloud deck, which appeared warmer (darker gray) due to the shortwave IR channel’s sensitivity to the reflection of solar radiation off the liquid droplet cloud tops.

GOES-15 (left) and GOES-13 (right) 3.9 µm shortwave IR channel images [click to play animation]

GOES-15 (left) and GOES-13 (right) 3.9 µm shortwave IR channel images [click to play animation]

A comparison of AWIPS images of 1-km resolution Terra MODIS 0.65 µm visible channel, 3.7 µm shortwave IR channel, and 11.0 µm IR window channel images (below) provided a slightly sharper view than the GOES images. Again, the glaciated plume south of Amarillo appeared colder (brighter white) than the surrounding supercooled water droplet clouds; on the IR window channel image, the slightly warmer (darker gray) signature was due to the satellite sensing radiation from the warmer ground surface through the thinner glaciated areas of the cloud plume.

Terra MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR window channel images

Terra MODIS 0.65 µm visible, 3.7 µm shortwave IR, and 11.0 µm IR window channel images

A 250-meter resolution Terrra MODIS true-color Red/Green/Blue (RGB) image from the SSEC MODIS Today site (below; visualized using Google Earth) showed that the plume was drifting southward over parts of Interstate 27; one inch of snowfall was reported as far south as Happy, in the far northern part of Swisher county.

Terra MODIS true-color Red/Green/Blue (RGB) image

Terra MODIS true-color Red/Green/Blue (RGB) image

===== 11 February Update =====

On the folllowing day, a Terra MODIS true-color image at 17:44 UTC (below; visualized using Google Earth) provided a fantastic view of the mesoscale patch of snow cover southwest of Borger, Texas.

Terra MODIS true-color image (visualized using Google Earth)

Terra MODIS true-color image (visualized using Google Earth)