Diagnosing Snow Depth over Montana using GOES-16

October 3rd, 2017 |

GOES-16 Visible Imagery (0.64 µm), Snow Ice Near Infrared Imagery (1.61 µm) and Shortwave Infrared Imagery (3.9 µm) all at 2157 UTC on 3 October 2017 (Click to enlarge)

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

A modest early-season storm has produced a snowfall over north-central Montana and southern Alberta. This image (source) shows total precipitation, with a minimum axis over northern Montana that has an echo in the Visible Imagery above: Whereas most of the snow cover is bright, a region west of Cut Bank MT shows a greyer view, suggestive of less snow on the ground.

GOES-16 includes a channel that senses reflected solar radiation at 1.61 µm and this is a wavelength at which snow strongly absorbs radiation. Thus, snow-covered grounds (and cirrus clouds) appear dark in the 1.61 µm Channel, but very bright in the Visible (0.64 µm). Clouds made up of water droplets are bright in both channels during the day. A Toggle between just the Visible and the Snow/Ice Channel is shown below to highlight regions of snow where clouds are not present over northern Montana and southern Alberta. Note that snow can be inferred in these regions using only the Visible Imagery because rivers — still ice-free in early October — stand out very well in the Visible.  Snow is also apparent in the Mountains of northeastern Wyoming:  Bright in the visible, Dark in the Snow/Ice channel.

Note that the localized minimum in precipitation, that shows up somewhat dark in the visible, is comparatively bright in the Snow/Ice Channel.  In addition, the 3.9 µm Infrared Imagery at the same time shows a region of relative warmth:  above freezing surrounded to the north and south by sub-freezing brightness temperatures.  All three channels — the visible, snow/ice and shortwave IR suggest a relative minimum in snow from Cut Bank westward to the Rocky Mountains.

GOES-16 Visible Imagery (0.64 µm), Snow Ice Near Infrared Imagery (1.61 µm) at 2157 UTC on 3 October 2017 (Click to enlarge)

GOES-16 Baseline Products include a Land Surface Temperature Product that is shown below from 2247 UTC. Temperature warmer than Freezing are diagnosed in/around Cutbank and to th west, with subfreezing temperatures to the north and south. Previous to that time, the Cloud Mask diagnosed clouds over the snowcover and the Land Surface Temperature did not produce a value. This toggle shows the Cloud Mask at 2227 and 2237 UTC — clear skies (black) expand over the snow cover in those ten minutes.

GOES-16 derived Land Surface Temperature, 2247 UTC on 3 October 2017 (Click to enlarge)


================= Added 4 October 2017 ====================
The snow on the ground and clear skies allowed for cold temperatures. The Land Surface Temperature Baseline Product from 1047 UTC, below, shows isolated sub-zero values between Cut Bank and Havre. The morning low in Havre, which had a record snowfall from this storm, was 8.

GOES-16 derived Land Surface Temperature, 1147 UTC on 3 October 2017 (Click to enlarge)

Lightning at a Football Game

September 29th, 2017 |

GOES-16 ABI Channel 13 (“Clean Window”, 10.3 µm) Infrared Imagery, 2202 UTC 28 September to 0302 UTC 29 September 2017 (Click to animate)

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

The National Football League football game between the destined-to-win Green Bay Packers and the woeful Chicago Bears was interrupted by lightning at the end of the First Quarter on Thursday 29 September 2017. The animation of GOES-16 “Clean Window” 10.3 µm infrared imagery, above, shows a cold front passing easily through the area (in much the same way that Aaron Rodgers passed through the Bears Defense). The slow (slow, but not as slow as the Bears’ Offense) animation, below, shows the coldest cloud top moving over Green Bay at around 0130 UTC. Note that there is a parallax shift in this image: the storm top is displayed north of its actual ground location.

GOES-16 ABI Channel 13 (“Clean Window”, 10.3 µm) Infrared Imagery, 2202 UTC 28 September to 0302 UTC 29 September 2017 (Click to animate)

The UW CIMSS ProbSevere product (from here, Click here for an updated version that includes ProbTor/ProbWind/ProbHail) includes Total Lightning (from the ground network) as one of its predictors, and the stepped animation below, showing 0100, 0115 and 0130 UTC, highlights the lightning-producing cell that delayed the game. The Probability of Severe weather (Severe being defined as a Tornado, Hail exceeding 1″ in Diameter, and/or winds exceeding 50 knots) was very small (though not as small as the Bears’ chances), but note that lightning flashes, 2-3 flashes per minute, are consistently observed.

NOAA/CIMSS ProbSevere, 0100, 0115 and 0130 UTC on 29 September 2017 (Click to enlarge)

A new-to-operations instrument that is on board GOES-16 is the Geostationary Lightning Mapper (GLM). Preliminary observations from this instrument, below, show that it too detected the lightning as it approached the stadium. The GLM pixel size is 8 kilometers at the sub-satellite point, a pixel size that is significantly larger than the GOES-16 ABI Pixel size (10.3 µm, with a pixel size of 2 km at the sub-satellite point, is shown below). Whereas ground-based lightning detection systems detect only cloud-to-ground lightning, the optical detectors on GLM detect both cloud-to-ground and in-cloud lightning. Typically, a cloud will produce in-cloud lightning before cloud-to-ground, so the GLM can alert a forecaster to potentially dangerous lightning with more lead-time than is possible with ground-based systems. The animation below starts with the first detection at 0030 UTC on 29 September, about 45 minutes before Lambeau Field was evacuated, and 10 minutes before ground-based sensors detected cloud-to-ground strokes. (the evacuation occurred at about 0115 UTC) Group Density is plotted on top of the GOES-16 10.3 µm ABI (the ABI has a grey-scale enhancement). Note the relatively large pixel size of the GLM, and the obvious parallax shift between the two fields. The strengths of the GLM for lightning safety at large outdoor events is obvious in this case.

GOES-16 ABI “Clean Window” (10.3 µm) Imagery and GLM Group Density, every 5 minutes from 0030-0130 UTC on 29 September 2017 (Click to animate)

Go Pack!!

Mostly Clear Skies over Puerto Rico

September 25th, 2017 |

Suomi NPP Day Night Band Visible (0.7 µm) Imagery, 0619 UTC on 25 September 2017 (Click to enlarge)

Mostly clear skies over Puerto Rico early on 25 September 2017 allowed the Day Night Band on Suomi NPP to observe man-made sources of light on that island as shown in the image above (Courtesy of William Straka, CIMSS).  (A previous example on this blog showed lights through clouds).  A similar view is available at NASA’s Worldview site, or at Real Earth. The Lunar Phase on 25 September 2017 is Waxing Crescent with 26% illumination; similar illumination occurred on 24 August, and a link to the Day Night Band imagery at NASA Worldview on that day is here. The differences are stark.

A RealEarth examination of two Suomi NPP VIIRS Day/Night Band (0.7 µm) images — an archived “clear sky” view from 31 December 2015, and an “after-Maria” image from 26 September 2017 (below) — provides a good before/after comparison showing a reduction in the amount of city light illumination following the passage of the hurricane.

Suomi NPP VIIRS Day/Night Band (0.7 µm) images: an  archived

Suomi NPP VIIRS Day/Night Band (0.7 µm) images: an archived “clear sky’ view from 31 December 2015, and a “after-Maria” image from 26 September 2017 [click to enlarge]

The Infrared Imagery, below, suggests a few clouds over northwest Puerto Rico. Such clouds could alter the perception of light sources in that region.

Suomi NPP VIIRS Infrared (11.45 µm) Imagery, 0619 UTC on 25 September 2017 (Click to enlarge)

The Eye of Maria north of Hispaniola

September 21st, 2017 |

GOES-16 data posted on this page are preliminary, non-operational and are undergoing testing

Hurricane Maria presented a very interesting eye structure during the course of the day on 21 September 2017, as shown in the mp4 animation above (also available as a YouTube video).  The animation shows 10.3 µm imagery every 2 minutes from 0849 UTC through 2122 UTC on 21 September 2017.

Pete Pokrandt, at the University of Wisconsin Atmospheric and Oceanic Sciences Department, created a similar animation using the 0.64 µm Visible channel on GOES-16.

30-second interval (using overlapping 1-minute interval Mesoscale Sector) GOES-16 Visible (0.64 µm) and Infrared Window (10.3 µm) images covering the 6-hour period from 1031-1631 UTC are shown below. During this time, Maria re-intensified to a Category 3 hurricane, with the eye centered just off the northeastern coast of the Dominican Republic.

GOES-16 Visible (0.64 µm, left) and Infrared Window (10.3 µm, right) images at 30-second intervals (Click to animate)

GOES-16 Visible (0.64 µm, left) and Infrared Window (10.3 µm, right) images at 30-second intervals (Click to animate)

For more information on Maria, visit the National Hurricane Center website.  The CIMSS Tropical Weather Website has information as well.