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).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. 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. 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. 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.
A closer view using Himawari-8 Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (below) revealed numerous hot spots (dark black to yellow to red pixels) around the periphery of the burn scar of the large fire, along with the brief development of small pyrocumulus clouds over some of the larger, more active fires. Note that the ABI instrument on GOES-R will provide similar imagery at high spatial (0.5 km visible, 2 km infrared) and temporal (5 minute Full Disk coverage) resolutions.A Suomi NPP VIIRS true-color Red/Green/Blue (RGB) image viewed using RealEarth (below) provided a high-resolution view of the fire region and the plume of smoke curving around the low pressure feature.
During the overnight hours, a comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images at 0801 UTC or 3:01 am local time (below) revealed cloud-top gravity waves propagating northwestward away from the core of overshooting tops (which exhibited IR brightness temperatures as cold as -84º C) located just to the west of Brenham. Due to ample illumination from the Moon — which was in the Waning Gibbous phase, at 71% of Full — the “visible image at night” capability of the VIIRS Day/Night Band (DNB) was well-demonstrated. The bright white streaks seen on the DNB image are a signature of cloud-top illumination by intense lightning activity.A time series plot of surface weather conditions at Brenham is shown below.
===== 28 May Update =====A 30-meter resolution Landsat-8 false-color Red/Green/Blue (RGB) image viewed using the RealEarth web map server (above) showed widespread areas of inundation (darker shades of blue) along the Brazos River and some of its tributaries, just to the east and north of Brenham, Texas.