First full day of Summer: snow in the Brooks Range of Alaska

June 22nd, 2016

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

GOES-15 Water Vapor (6.5 µm) images [click to play animation]

GOES-15 (GOES-West) Water Vapor (6.5 µm) images (above) showed the southeastward migration of an upper-level low across the North Slope and the eastern Brooks Range of Alaska during the 21 June – 22 June 2016 period. A potential vorticity (PV) anomaly was associated with this disturbance, which brought the dynamic tropopause — taken to be the pressure of the PV 1.5 surface — downward to below the 600 hPa pressure level over northern Alaska. Several inches of snow were forecast to fall in higher elevations of the eastern portion of the Brooks Range.

With the very large satellite viewing angle (or “zenith angle”) associated with GOES-15 imagery over Alaska  — which turns out to be 73.8 degrees for Fairbanks — the altitude of the peak of the Imager 6.5 µm water vapor weighting function (below) was shifted to higher altitudes (in this case, calculated using rawinsonde data from 12 UTC on 22 June, near the 300 hPa pressure level).

GOES-15 Imager water vapor (Band 3, 6.5 µm) weighting function [click to enlarge]

GOES-15 Imager water vapor (Band 3, 6.5 µm) weighting function [click to enlarge]

The ABI instrument on GOES-R will have 3 water vapor bands, roughly comparable to the 3 water vapor bands on the GOES-15 Sounder — the weighting functions for those 3 GOES-15 Sounder water vapor bands (calculated using the same Fairbanks rawinsonde data) are shown below. Assuming a similar spatial resolution as the Imager, the GOES-15 Sounder bands 11 (7.0 µm, green) and 12 (7.4 µm, red) would have allowed better sampling and visualization of the lower-altitude portion of this particular storm system. The 3 ABI water vapor bands are nearly identical to those on the Himawari-8 AHI instrument; an example of AHI water vapor imagery over part of Alaska can be seen here.

GOES-15 Sounder water vapor weighting function plots [click to enlarge]

GOES-15 Sounder water vapor weighting function plots [click to enlarge]

As the system departed and the clouds began to dissipate on 22 June, GOES-13 Visible (0.63 µm) images (below) did indeed show evidence of bright white snow-covered terrain on the northern slopes and highest elevations of the Brooks Range.

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

A sequence of 1-km resolution POES AVHRR Visible (0.86 µm) images (below) showed a view of the storm during the 21-22 June period, along with the resultant snow cover on 22 June. However, the snow quickly began to melt as the surface air temperature rebounded into the 50’s and 60’s F at some locations.

POES AVHRR Visible (0.86 µm) images [click to play animation]

POES AVHRR Visible (0.86 µm) images [click to play animation]

The increase in fresh snow cover along the northern slopes and the highest elevations of the central and northeastern Brooks Range — most notably from Anaktuvuk Pass to Fort Yukon to Sagwon — was evident in a comparison of Suomi NPP VIIRS true-color Red/Green/Blue (RGB) images from 17 June and 22 June, as viewed using RealEarth (below). The actual time of the satellite overpass on 22 June was 2134 UTC.

Suomi NPP VIIRS true-color RGB images, 17 June and 22 June [click to enlarge]

Suomi NPP VIIRS true-color RGB images, 17 June and 22 June [click to enlarge]

GOES-14 SRSO-R: convective outflow boundary in southern Texas

April 20th, 2016

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

1-minute interval SRSO-R GOES-14 Visible (0.63 µm) images (above; also available as a large 259 Mbyte animated GIF) showed a curved outflow boundary — produced by a strong quasi-linear convective system the preceding overnight hours in northern Texas — which continued to propagate southward across southern Texas during the day on 20 April 2016. New clusters of convection formed along and in the wake of the eastern portion of the outflow boundary (which dropped an additional 0.67 inch of rainfall in one hour across the flood-ravaged Houston area), while the western portion was marked by a low-level arc cloud.

On the corresponding GOES-14 Water Vapor (6.5 µm) images (below; also available as a large 126 Mbyte animated GIF), a very subtle signature of the western  part of the outflow boundary could be seen in the dryer atmosphere (where the water vapor weighting functions were shifted to lower altitudes). Also of interest were a few long and narrow contrails which appeared within that same dry region of the atmosphere after about 1800 UTC — these thin contrails were not evident in the GOES-14 visible or infrared imagery.

GOES-14 Water Vapor (6.5 µm) images [click to play MP4 animation]

GOES-14 Water Vapor (6.5 µm) images [click to play MP4 animation]

A comparison of the 3 Water Vapor bands (6.5 µm, 7.0 µm and 7.4 µm) available from the GOES-14 sounder instrument (below) demonstrated how each of the individual bands was detecting radiation emitted from a different layer of the troposphere; this was further shown by examining plots of the water vapor weighting functions for the 1 imager and the 3 sounder water vapor bands (calculated using 12 UTC rawinsonde data from Del Rio, Texas KDRT). The ABI instrument on GOES-R will have 3 water vapor bands similar to those on the current generation sounder instrument, but with significantly improved spatial and temporal resolution.

GOES-14 sounder Water Vapor bands 6.5 µm (top), 7.0 µm (middle) and 7.4 µm (bottom) images [click to play animation]

GOES-14 sounder Water Vapor bands 6.5 µm (top), 7.0 µm (middle) and 7.4 µm (bottom) images [click to play animation]

GOES-14 SRSO-R: heavy snow in the Upper Midwest, severe thunderstorms in the Deep South

February 2nd, 2016

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

A strong occluded mid-latitude cyclone moved from the central Plains northeastward across the Upper Midwest on 02 February 2016 (surface analyses). This storm produced a variety of precipitation, most notably heavy snow — exceeding 12 inches at some locations in Nebraska, Iowa, Minnesota, Wisconsin, and the Upper Peninsula of Michigan (map) — and blizzard conditions. One-minute interval Super Rapid Scan (SRSO-R) GOES-14 Visible (0.63 µm) images (above; also available as a large 151-Mbyte animated GIF) showed the cloud-top shadows and textured appearance that is indicative of embedded convection — in fact, many sites in Iowa and southern Wisconsin reported thundersnow which produced snowfall rates of 1-2 inches per hour.

Farther to the south, as moisture from the Gulf of Mexico was drawn northward (GOES-14 sounder Total Precipitable Water derived product images) in advance of the eastward-moving cold frontal boundary (surface analyses) associated with the aforementioned Upper Midwest storm, areas of strong to severe thunderstorms developed across the Mississippi River and Tennessee River Valley regions during the afternoon and evening hours. GOES-14 Infrared Window (10.7 µm) images (below; also available as a large 208-Mbyte animated GIF) showed the cold cloud-top IR brightness temperatures (orange to red color enhancement) exhibited by the widespread convective activity.

GOES-14 Infrared Window (10.7 µm) images [click to play MP4 animation]

GOES-14 Infrared Window (10.7 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

GOES-14 Visible (0.63 µm) images [click to play MP4 animation]

Taking a closer look at the severe thunderstorms which produced multiple tornadoes from eastern Mississippi  into far western Alabama (SPC storm reports), GOES-14 Visible (0.63 µm) images (above; also available as a large 66-Mbyte animated GIF) revealed numerous overshooting tops; the counties where tornadoes were reported are indicated by their dashed red outlines. Another visible image animation from RAMMB/CIRA is available here. NWS storm damage surveys (Jackson MS | Birmingham AL) found EF-1 to EF-2 damage in both Mississippi and Alabama.

The corresponding GOES-14 Infrared Window (10.7 µm) images (below; also available as a large 37-Mbyte animated GIF) indicated that the coldest cloud-top IR brightness temperatures were in the -50º to -60º range (darker orange to red color enhancement), which was at or above the tropopause level according the Jackson MS and Birmingham AL rawinsonde data.

GOES-14 Infrared Window (10.7 µm) images [click to play MP4 animation]

GOES-14 Infrared Window (10.7 µm) images [click to play MP4 animation]

GOES-14 Sounder Operations

January 31st, 2016

GOES-14 Sounder DPI of Total Precipitable Water (TPW) at 1800 UTC on 31 January 2016 [Click to enlarge]

GOES-14 Sounder DPI of Total Precipitable Water (TPW) at 1800 UTC on 31 January 2016 [click to enlarge]

GOES-14, over the Equator at ~105º W Longitude, has been activated in support of SRSO-R Operations in February 2016. One-minute imagery will commence on Monday 1 February. The GOES-14 Sounder has also been activated to fill in, temporarily, for the GOES-13 Sounder that has been inactive since November 2015. An animation of all 19 Sounder channels is available at this link; animations of Derived Product Images (DPI) of Total Precipitable Water from GOES-14, as shown above, are available here, with GOES-14 DPI of Lifted Index available here.