Cold night in Labrador, Canada

January 22nd, 2015
Suomi NPP VIIRS 11.45 um IR channel image, with METAR surface reports

Suomi NPP VIIRS 11.45 um IR channel image, with METAR surface reports

With a cloud-free sky and light winds under a dome of high pressure, strong radiational cooling over a deep snowpack allowed the overnight low temperature to drop to -47º F (-43.9º C) at Wabush Lake (station identifier CYWK) in far western Labrador — this was quite possibly the coldest site in North America on 22 January 2015 (the coldest overnight low temperature in Alaska that morning was -39º F or -39.4º C at Galena). AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel data (above) and MODIS 11.0 µm IR channel data (below) showed minimum surface IR brightness temperatures of -47º C or -52.6º F (darker blue color enhancement) in the western Labrador.

MODIS 11.0 um IR channel image, with METAR surface reports

MODIS 11.0 um IR channel image, with METAR surface reports

A comparison of 1-km resolution Soumi NPP VIIRS 11.45 µm and 4-km resolution GOES-13 10.7 µm IR images (below) showed the advantage of higher spatial resolution for more accurately locating the coldest regions.

Suomi NPP VIIRS 11.45 um and GOES-13 10.7 um IR channel images

Suomi NPP VIIRS 11.45 um and GOES-13 10.7 um IR channel images

Lake effect snow band from Lake Huron brings heavy snow to Pennsylvania

January 7th, 2015
GOES-13 0.63 µm visible channel images (click to play animation)

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

McIDAS images of GOES-13 0.63 µm visible channel data with overlays of surface weather type (above; click image to play animation) showed a large lake effect cloud band that had formed over Lake Huron, moved inland across southern Ontario, and then became further lake-enhanced as it moved over Lake Erie and across northwestern Pennsylvania on 07 January 2015. The report of heavy (4-star) snow in far northwestern Pennsylvania was at Meadville — it reduced surface visibility there to 1.25 miles at times, and produced at least 6 inches of snowfall at that location. To the north of Meadville, 8.5 inches of snow were reported at Edinboro.

Suomi NPP VIIRS 0.64 µm visible image, with surface METARs, RTMA winds, and frontal boundaries

Suomi NPP VIIRS 0.64 µm visible image, with surface METARs, RTMA winds, and frontal boundaries

AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data are shown with overlays of surface METARs, RTMA winds, and frontal boundaries at 17:39 UTC (above) and 19:19 UTC (below). The RTMA surface winds showed that there was low-level convergence in the vicinity of the weakening cold frontal boundary/surface trough that was sagging southward and southwestward across the region (animation) — this convergence may have helped to maintain the cloud band as it continued to move southeastward across Lake Erie during the afternoon hours. Meadeville PA is station identifier KGKJ.

Suomi NPP VIIRS 0.64 µm visible image, with surface METARs, RTMA winds, and frontal boundaries

Suomi NPP VIIRS 0.64 µm visible image, with surface METARs, RTMA winds, and frontal boundaries

Suomi NPP VIIRS 11.45 µm IR channel images (below) showed that the coldest cloud-top IR brightness temperatures over both the Ontario and Pennsylvania portions of the band were -36º C (lighter green color enhancement) — at London, Ontario (CYXU), embedded towering cumulus (coded TCU EMBD) were reported at both 18 UTC and 19 UTC.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

The Terra MODIS Sea Surface Temperature product around 18:11 UTC (below) showed that Lake Erie water temperatures were still as warm as the middle 30s F (blue) on either side of the blacked-out lake effect/lake enhanced cloud band — so moving an arctic air mass with 850 hPa temperatures colder than -20º C or -4º F over that water yielded a sufficient “delta-T” value to promote further enhancement/growth of the snow-producing cloud band which originated over Lake Huron.

MODIS Sea Surface Temperature product

MODIS Sea Surface Temperature product

Rare low-elevation snowfall in the eastern Mojave Desert

January 1st, 2015
Aqua MODIS 0.65 µm visible channel image and False-color Red/Green/Blue (RGB) images

Aqua MODIS 0.65 µm visible channel image and False-color Red/Green/Blue (RGB) images

A cold storm system moving through the Southwest US on 31 December 2014 produced significant snowfall in many of the higher-elevation mountain ranges of California, Baja California, Nevada, and Arizona (up to 20 inches at Mountainaire AZ), but also left lighter amounts of snowfall at some low-elevation locations of the eastern Mojave Desert where snowfall is considered to be quite rare (NWS Las Vegas Public Information Statement) | Event  Summary). This event marked the first time that snowfall had been recorded during the month of December at Needles, California.

As clouds began to clear over the region on the following day (01 January 2015), areas which still had snow on the ground could be seen using satellite imagery. On a comparison of Aqua MODIS 0.65 µm visible channel and false-color Red/Green/Blue (RGB) images at 20:33 UTC or 1:33 PM local time (above), snow cover that appeared as shades of white on the visible image also appeared as darker shades of red on the RGB image.

As the day progressed, the sun had the effect of melting the lighter amounts of snow cover, as seen on GOES-15 (GOES-West) 0.63 µm visible channel images (below; click image to play animation). However, due to the presence of the unusually cold air mass, new records for coldest 01 January daily maximum temperature were set for Phoenix (46ºF) and Tucson (41ºF).

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

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

Mountain wave clouds over southern California

December 21st, 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)

AWIPS images of 4-km resolution resolution GOES-15 (GOES-West) 6.5 µm water vapor channel data (above; click image to play animation) showed the development of a patch of mountain wave or “lee wave” clouds immediately downwind of the higher elevations of the western Transverse Ranges in southern California on 21 December 2014.  These clouds developed in response to strong northerly winds interacting with the west-to-east oriented topography (12 UTC NAM 700 hPa wind and height). As seen on the plotted surface reports, at Sandberg (station identifier KSDB) the highest wind gust was 52 knots or 59 mph  at 17:42 UTC — and later in the day there also a peak wind gust of 87 mph at Whitaker Peak and 86 mph at Montcito Hills. In addition, there were isolated pilot reports of moderate turbulence in the vicinity of the mountain wave cloud at 20:21 UTC and 23:06 UTC;  farther to the east there was a pilot report of moderate to severe turbulence at 01:27 UTC.

A comparison of 1-km resolution MODIS 6.7 µm and 4-km resolution GOES-15 6.5 µm water vapor channel images around 21:00 UTC (below) demonstrated the advantage of higher spatial resolution (and the minimal parallax offset) of the polar-orbiter MODIS imagery for more accurate location of the mountain wave cloud.

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

MODIS 6.7 µm and GOES-15 6.5 µm water vapor channel images

At 20:42 UTC (below), the coldest 1-km resolution POES AVHRR Cloud Top Temperature value associated with the mountain wave cloud feature was -69º C (darker red color enhancement), with the highest Cloud Top Height value being 14 km or 45,900 ft (cyan color enhancement)., which is actually colder and higher than the tropopause on  the 12 UTC rawinsonde report at Vandenberg AFB. The highest elevation in the western portion of the Transverse Ranges where the mountain wave cloud formed is Mount Pinos at 8847 feet or 2697 meters, so it appears that a vertically-propagating wave developed which helped the cloud reach such a high altitude.

POES AVHRR Cloud Top Temperature and Cloud Top Height products

POES AVHRR Cloud Top Temperature and Cloud Top Height products

At 21;20 UTC, a comparison of 375-meter resolution (projected onto a 1-km resolution AWIPS grid) Suomi NPP VIIRS 0.64 µm visible channel, 3.74 µm shortwave IR channel, and 11.45 µm IR channel images (below) showed that while the coldest cloud-top 11.45 µm IR brightness temperatures were around -60º C, the 3.74 µm shortwave IR temperatures were in the +5 to +10º C range — this indicates that the mountain wave cloud was composed of very small ice particles, which were efficient reflectors of solar radiation contributing to much the warmer shortwave IR brightness temperatures.

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible, 3.74 µm shortwave IR, and 11 45 µm IR channel images

A 375-meter resolution Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image from the SSEC RealEarth web map server is shown below.

Suomi NPP VIIRS true-color image

Suomi NPP VIIRS true-color image