Strong cold front moves through the Hawaiian Islands

January 23rd, 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 4-km resolution GOES-15 6.5 µm water vapor channel data (above; click images to play animation) showed the dramatic signature of rapid intensification of a very large mid-latitude cyclone over the eastern Pacific Ocean during the 20 January – 23 January 2014 time period.

A comparison of AWIPS images of 1-km resolution Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data (below) revealed the tightly-wrapped center of circulation at 13:01 UTC on 20 January. Intricate mesoscale banding structures could also be seen within portions of the warm conveyor belt southeast and east of the storm center (which was analyzed to have a central pressure of 956 hPa).

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 Suomi NPP VIIRS 0.64 µm visible channel image (below) showed a small but well-defined comma-shaped cloud feature marking the center of the storm at 00:13 UTC on 21 January (which was analyzed to have a central pressure of 952 hPa).

Suomi NPP VIIRS 0.64 µm visible channel image

Suomi NPP VIIRS 0.64 µm visible channel image

A Suomi NPP VIIRS 0.64 µm visible channel image at 23:54 UTC on 21 January (below) depicted the band of clouds associated with the 950 hPa cyclone’s cold front as it approached the northwestern portion of the Hawaiian Island chain. A narrow “rope cloud” marked the leading edge of the cold frontal boundary.

Suomi NPP VIIRS 0.64 µm visible channel image

Suomi NPP VIIRS 0.64 µm visible channel image

In a closer view centered over the Hawaiian Islands at 23:54 UTC on 21 January (below), a hazy “vog” plume (from the active Kilauea volcano on the Big Island) could be seen blowing northeastward ahead of the approaching cold front. Note how the areal coverage of the vog plume shows up better in the broadband 0.7 µm Day/Night Band image compared to the 0.64 µm visible channel image with its more narrow spectral width.

Suomi NPP VIIRS 0.64 µm visible channel and 0.7 µm Day/Night Band images

Suomi NPP VIIRS 0.64 µm visible channel and 0.7 µm Day/Night Band images

Finally, a Suomi NPP VIIRS 0.64 µm visible channel image at 23:35 UTC on 22 January (below) showed the cold frontal band as the leading edge was about to move southeast of the Big Island of Hawaii. Note that Honolulu (PHNL) had a temperature/dewpoint of 78ºF/45ºF, with northwesterly winds gusting to 34 knots at 00 UTC. Wind speeds on the summits of the Big Island of Hawaii were sustained hurricane force, with gusts to near 100 mph. The strong winds also caused a giant northwesterly ocean swell, with significant wave heights as high as 31 feet at Buoy 51101 (located 91 miles northwest of Kauai). There was also a notable air temperature drop at Buoy 51101 as the cold front passed, with a peak wind gust of 39 knots.

Suomi NPP VIIRS 0.64 µm visible channel image

Suomi NPP VIIRS 0.64 µm visible channel image

GOES-15 0.63 µm visible channel images (below; click image to play animation) showed the cold front as it was passing through the Hawaiian Island chain on 22 January. A few areas of orographic wave clouds could be seen as the strong northwesterly winds in the wake of the cold front interacted with the topography of the islands.

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

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

Monsoon low over northwestern Australia

January 21st, 2014 |
MTSAT-2 0.675 µm visible channel and 10.8 µm IR channel images (click to play animation)

MTSAT-2 0.675 µm visible channel and 10.8 µm IR channel images (click to play animation)

McIDAS images of MTSAT-2 daytime 0.675 µm visible channel data and night-time 10.8 µm IR channel data (above; click image to play animation; also available as an MP4 animation) showed a monsoon low which exhibited a well-defined circulation for several days as it slowly tracked southwestward across the northwestern portion of Australia during the 15-21 January 2014 time period.

The mean seal level pressure analyses from the Australian Bureau of Meteorology (below; click image to play animation) indicated that the monsoon low deepened to a pressure of 988 hPa at 12 UTC on 19 January.

Mean sea level pressure analyses (click image to play animation)

Mean sea level pressure analyses (click image to play animation)

MTSAT-2 visible images and surface observations during the 17-18 January period are shown below (click image to play animation), visualized using the SSEC RealEarth web map server.

MTSAT-2 0.675 µm visible channel images (click to play animation)

MTSAT-2 0.675 µm visible channel images (click to play animation)

Mesoscale streaks of snow cover across Iowa and Missouri

January 17th, 2014 |
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

A comparison of AWIPS images of Suomi NPP VIIRS 0.64 µm visible channel data with the corresponding false-color “snow-vs-cloud discrimination” Red/Green/Blue (RGB) product (above) revealed numerous northwest-to-southeast oriented mesoscale bands of snow on the ground (varying shades of red on the RGB image) across much of Iowa extending into northern Missouri at 18:30 UTC or 12:30 PM local time on 17 January 2014. Some of these bands of snow cover appeared to be only about 10 miles wide!

The disturbance that created these snow bands moved across the region on the previous day (16 January) — GOES-13 0.63 µm visible channel images (below; click image to play animation) showed the development of a feature that resembled a “mesoscale squall line” which propagated southeastward across Iowa during the daylight hours. Surface METAR observations showed the strong winds (gusting to over 50 mph at a few sites) which created blizzard conditions as the fresh snowfall was easily lofted from the ground. Note that there was even one negative cloud-to-ground lightning strike noted just west of Des Moines (station identifier KDSM) at 21:45 UTC or 3:45 PM local time, indicating the presence of convective elements within the squall line which led to enhanced snowfall rates — in fact, the maximum snowfall reported from this fast-moving system was 3.1 inches at Des Moines (where surface visibility was reduced to 1/16 mile with thundersnow).

GOES-13 0.63 µm visible channel images, with surface reports and cloud-to-ground lightning strikes [click to play animation]

GOES-13 0.63 µm visible channel images, with surface reports and cloud-to-ground lightning strikes [click to play animation]

For a radar animation of the feature, see this NWS Des Moines event summary.

Severe turbulence over the Mid-Atlantic and Northeast regions of the US

January 16th, 2014 |

GOES-13 6.5 µm water vapor channel images [click to play animation]

GOES-13 6.5 µm water vapor channel images [click to play animation]

United Airlines Flight 89 enroute from Newark, New Jersey to Beijing, China encountered severe turbulence at an altitude of 33,000 feet over Vermont (pilot report) around 18:31 UTC on 16 January 2014, which injured 5 flight attendants and forced the flight to return to Newark where the injured crew members were taken to local hospitals for evaluation. AWIPS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above; click image to play animation) showed that a large baroclinic leaf signature was rapidly developing over the northeastern US and southeastern Canada during the day.

Suomi NPP VIIRS 0.64 µm visible channel images, with pilot reports of turbulence

Suomi NPP VIIRS 0.64 µm visible channel images, with pilot reports of turbulence

17:12 UTC images of 1-km resolution Suomi NPP VIIRS 0.64 µm visible channel data (above) and 11.45 µm IR channel data (below) displayed evidence of “transverse banding” structures along portions of the cloud top of the baroclinic leaf feature — such transverse banding is often associated with turbulence. Pilot reports of turbulence for the hours ending at 17, 18, and 19 UTC are also plotted on the VIIRS images; over this region there were 5 reports of severe turbulence within this 3 hour period.

Suomi NPP VIIRS 11.45 µm IR channel image, with pilot reports of turbulence

Suomi NPP VIIRS 11.45 µm IR channel image, with pilot reports of turbulence

GOES-13 water vapor images with overlays of CRAS model 250 hPa wind speed isotachs (below) showed that there was a strong (150-160 knot) upper level jet streak along the back (western) edge of the baroclinic leaf during the 12 UTC to 21 UTC period. At 18 UTC, the 2 pilot reports of severe turbulence were located in the vicinity of the left entrance region of the jet streak — an area generally expected to have strong downward vertical velocities forced by ageostrophic circulations near the altitude of the jet streak.

GOES-13 water vapor images, CRAS 250 hPa isotachs, and pilot reports of turbulence

GOES-13 water vapor images, CRAS 250 hPa isotachs, and pilot reports of turbulence

GOES-13 water vapor images with overlays of CRAS model pressure of the PV1.5 surface (below) — generally thought of as representing the dynamic tropopause — indicated that the tropopause was as low as 500-600 hPa within the narrow warm/dry band just west of the back edge of the baroclinic leaf during the 12 UTC – 21 UTC time period.

GOES-13 water vapor images, CRAS PV1.5 pressure, and pilot reports of turbulence

GOES-13 water vapor images, CRAS PV1.5 pressure, and pilot reports of turbulence

An automated Turbulence Risk product (below) also indicated that tropopause folding (blue) was occurring along the western edge of the baroclinic leaf, bringing the tropopause as low as 22,500 feet. The yellow ‘+’ symbols represent a portion of the flight track of United Airlines Flight 89.

Turbulence risk product

Turbulence risk product