Snow Squall Warnings over Duluth Minnesota and northwestern Wisconsin

February 18th, 2022 |
GOES-16 Day Cloud Phase Distinction 1731 – 2046 UTC on 18 February 2022 (Click to enlarge)

The animation above, of the Day Cloud Phase Distinction RGB, shows bands of snow showers/squalls rotating cyclonically through northern Minnesota and northwestern Wisconsin, to the south of a strong cyclone over northern Minnesota and northwestern Ontario (link to map from 1800 UTC on 18 February). The tops of these clouds are fairly low — in the RGB they have a periwinkle color in contrast to the orange/red color of the higher cirrus to the south. The RGB also allows for good contrast between the clouds and the clear snow-covered grounds (with greenish tones) to the west.

A potency of the upper air system supporting the surface cyclone is highlighted in the Ozone Anomaly fields from gridded NUCAPS data, shown below. Anomalies of 120-140 dobson Units are present.

NUCAPS estimates of Ozone Anomaly at 1730 and 1930 UTC on 18 February 2022 (Click to enlarge)

The National Weather Service in Duluth MN issued a series of Snow Squall Warnings; the first one, valid until 1945 UTC, is shown below (taken from this tweet); sequential tweeted Warnings are here (valid until 2015 UTC), here (valid until 2100 UTC), here (valid until 2145 UTC) and here (valid until 2215 UTC). (Note, WFO ARX — in Lacrosse, WI, is issuing Snow Squall warnings for this system as well!)

NWS Duluth Graphic of snow squall warning for 18 February 2022, for the time period ending 1945 UTC (Click to enlarge)

Three radars for this event are shown below: 1907, 1937 and 2007 UTC.

Radar Reflectivity at 1907, 1937 and 2007 UTC on 18 February 2022 (Click to enlarge)

VIIRS imagery (available from the CIMSS LDM feed) over the Duluth Area afforded a high-resolution view of this event. The toggles below show True and False Color imagery at 1838 UTC (from Suomi NPP) and at 1929 UTC (from NOAA-20) At 1838 UTC, the clouds producing the snow — between Moose Lake and Floodwood — do not stand out. They are much more noticeable in the 1929 UTC image, southeast of Duluth and northwest of Solon Springs.

True and False Color imagery, Suomi-NPP VIIRS, 1838 UTC on 18 February 2022 (Click to enlarge)
True and False Color imagery, NOAA-20 VIIRS, 1929 UTC on 18 February 2022 (Click to enlarge)

What was the effect on visibility? That is shown in the animation below with a 10-minute time step. Note how Duluth goes from southwesterly winds with light snow and 5- to 10- mile visibility to strong northwest winds (gusts to 45 knots) and reduced visibilities as the squall moves through.

GOES-16 Day Cloud Phase Distinction 1731 – 2041 UTC on 18 February 2022 along with surface observations (Click to enlarge)

As this front moved through southern Wisconsin, it generated lightning, as shown in the animation below (from this website).

GLM Flash Extent Density overlain on top of nighttime GeoColor, 2236 18 February – 0126 UTC 19 February 2022 (Click to enlarge)

LightningCast in cold air

December 11th, 2021 |
RealEarth presentation of GOES-16 Clean Window infrared along with contours of LightningCast Probability (10 (blue), 25 (cyan), 50 (green) and 75 (purple) %). GLM Flash Extent Density is also shown. Data are every 5 minutes from 0700 – 1000 UTC on 11 December 2021 (Click to enlarge)

LightningCast probabilities are part of the ProbSevere portfolio, and they are available in RealEarth (link). This machine-learning product relates Band 13 and Band 15 observations to the probability of lightning occurrence (in daytime, Band 2 and Band 5 are also used). When your blogger was awakened by thunder (at 0826 UTC), as cold rain fell on the roof, he naturally thought: “I wonder what LightningCast is doing?” The animation above shows probabilities increasing as lightning developed over southern Wisconsin. Initial lead time for lightning from the probabilities is not big — but probabilities do expand and encompass the region that is experiencing lightning. The time of the lightning did match the closest approach of the surface low, as shown in this 0900 UTC surface analysis.

That lightning was produced in near-freezing surface temperatures reflects the vigor of this extratropical system that spawned a deadly tornado outbreak over the mid-Mississippi River Valley and lower Ohio River Valley (SPC Storm Reports).

GLM observations of a long-track tornado

December 11th, 2021 |
GOES-16 GLM Total Optical Energy, 2101 UTC on 10 December through 0600 UTC on 11 December 2021 (Click to enlarge)

Gridded GLM observations of Total Optical Energy, above, capture the tornado-producing long-lived storm that hit Mayfield KY (and others) on 10 December. This storm had its genesis in eastern Arkansas, and it moved northeastward through the bootheel of Missouri, then into western Kentucky. It was mostly isolated from a line of convection to its west until it approached Louisville at around 0600 UTC, when the cells began to join together.

GLM observations of Average Flash Area for the same time period are shown below.

GOES-16 GLM Average Flash Area, 2101 UTC on 10 December through 0600 UTC on 11 December 2

Viewing Fall lightning with RealEarth

October 21st, 2021 |

Cooler temperatures across the Midwest are often heralded by thunderstorms. Yesterday evening and last night, a system brought rain and lightning to parts of Iowa, Minnesota, Wisconsin, Illinois, and Michigan, moving over Ohio by Thursday morning. RealEarth, a web-based visualization platform developed at UW-Madison, can display data from GOES-16 to monitor such events. RealEarth’s data archives usually go back at least 24-hours which provides temporal context to weather events.

RealEarth is a free data discovery and visualization platform developed at SSEC/CIMSS at the University of Wisconsin-Madison. It is available at

A 24-hour animation every hour from RealEarth (time in UTC) showing GOES-16 ABI Band 13 with the purple areas representing lightning. More specifically, the purple areas depict Flash Extent Density from the Geostationary Lightning Mapper (GLM) also aboard GOES-16.