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A Lake Breeze and a Foggy Night in Chicago

Tens of thousands of baseball fans took to Chicago’s North Side on the evening of 14 May 2025 to watch a Major League Baseball game between the Miami Marlins and the Chicago Cubs. Fans of the Cubs might not remember much about the game itself (the Marlins won 3–1 with... Read More

Tens of thousands of baseball fans took to Chicago’s North Side on the evening of 14 May 2025 to watch a Major League Baseball game between the Miami Marlins and the Chicago Cubs. Fans of the Cubs might not remember much about the game itself (the Marlins won 3–1 with all runs on both teams scored via solo home runs) but it might be a while before thy forget the weather. A fog began to envelop the friendly confines of Wrigley Field early in the game, and it continued until well after the last out was recorded.

GOES-19 was well situated to capture the development and evolution of this fog event. The fog formation and propagation straddled the transition from day to night, and thus different products are necessary to best assess what happened since GOES ABI channels like Band 7 (3.9 microns) have drastically different interpretations depending on the time of day. During the day, Band 7 is largely capturing shortwave reflection from the sun which reduces its quantitative value for daytime cloud products. However, at night the same band represents thermal emission. Not only that, but the emission at that wavelength is a function of cloud phase and particle size. The embedded movie from CSPP Geosphere shows the transition from day to night and the switch from a true color RGB to the Night Microphysics RGB. (You can adjust the playback speed by clicking on the three dots in the lower right corner).

At the start of this loop, in the late afternoon, strong evidence of a lake breeze can be found. There is substantial clearing in eastern Wisconsin, northeastern Illinois, and northwestern Indiana with the boundary between the cloudy and clear regions largely paralleling the shore of Lake Michigan. The effect of the lake breeze is even more readily apparent if one looks at the evolution of the cloud field throughout the day via the GOES-19 True Color RGB.

As the wind shifts to easterly flow, it brings a shallow layer of cold air ashore. This cold air is much more stable than the air it is replacing, and is often less moist too even though it originated over a vast lake. This is because the lake air is so much cooler than the land air that the absolute humidity levels are lower (even though the relative humidity levels are higher). The combination of cold, stable, and comparatively dry air kills off any convection that was taking place, so as the lake breeze propagates outward, it can easily be followed via satellite. Eagle-eyed readers might also notice that other, much smaller lakes in the area were also inhibiting convective development, including Lake Winnebago in the far upper part of the animation as well as the four lakes that characterize Madison, Wisconsin, in the middle left.

A quick visual inspection shows that the air quality of the existing airmass was much worse than the lake air that replaced it, too. A milky white pervades the regions away from Lake Michigan due to the enhanced shortwave scattering brought on by the high aerosol content; region closer to the lake are much more clear. The GOES Aerosol Optical Depth product confirms this, with notably higher aerosol optical depths further away from the shore; note the deep blues in eastern Wisconsin and northwestern Illinois with lighter blues further inland.

This persistent easterly flow was critical for what happened next. Air temperatures over the lake continued to fall, and thus reached the point of saturation. GOES-19 captured this perfectly as a filling in of the clouds over the lake, and only over the lake. Note that this was contemporaneous with sunset, so the animation segues from the daytime true color based on visible and near-infrared channels to the nighttime product which depends on longer wavelength channels.

The easterly flow persisted, however, and pushed the low-level foggy air ashore. The Night Microphyscis product clearly shows the extent of the fogginess. While it only benetrated slightly into Illinois, much of western Wisconsin experienced notable fog.

The shallowness of the fog layer is readily apparent from aircraft soundings. Over 100 commercial aircraft in the continental United States are equipped with temperature and water vapor sensors. Southwest Airlines is a major participant in this program, and with Chicago Midway being one of their most significant airports, there are several of these soundings every day. The Skew-T from 0208 UTC (9:08 local time) shows that the saturated later is only a few tens of millibars thick; above that, the air is too dry to support broad cloud formation in the absence of daytime convection. This image was obtained from Casey Webster’s wxster.com. Profiles from all over the continental United States using this publicly-available data source can also be found at that site and can be quite useful to help fill in the spatiotemporal gaps of the operational radiosonde network.

To see just how foggy it was, check out the highlights of the bottom of the 9th inning for the Cubs/Marlins game. You can see Major League Baseball’s video here.

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Nopiming Provincial Park Wildfire in Manitoba produces multiple pyrocumulonimbus clouds

1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible (0.64 µm) with an overlay of the FDCA Fire Mask derived product (above) showed the large thermal anomaly associated with a wildfire in the Nopiming Provincial Park (located just west of the Manitoba/Ontario border) as it made a rapid northeastward run of ~20 miles on... Read More

1-minute GOES-19 Red Visible (0.64 µm) images with an overlay of the Fire Mask derived product, from 1501 UTC on 13 May to 0100 UTC on 14 May [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible (0.64 µm) with an overlay of the FDCA Fire Mask derived product (above) showed the large thermal anomaly associated with a wildfire in the Nopiming Provincial Park (located just west of the Manitoba/Ontario border) as it made a rapid northeastward run of ~20 miles on 13 May 2025 — and also displayed the periodic bursts of pyrocumulus clouds that began shortly after 1800 UTC.

The corresponding 1-minute GOES-19 Infrared images (below) indicated that many of these pyrocumulus clouds eventually exhibited cloud-top 10.3 µm brightness temperatures of -40ºC (dark blue enhancement) or colder — a necessary condition to be classified as pyrocumulonimbus (pyroCb). This large wildfire generated a series of at least 8 pyroCb clouds from 1843 UTC on 13 May to 0007 UTC on 14 May.

1-minute GOES-19 Clean Infrared Window (10.3 µm) images with an overlay of the Fire Mask derived product, from 1501 UTC on 13 May to 0100 UTC on 14 May [click to play MP4 animation]

1-minute GOES-19 GeoColor RGB images with an overlay of Next Generation Fire System (NGFS) Fire Detection polygons (below) also showed the rapid northeastward run of the Nopiming Fire during the day. In addition, to the southwest of the large Nopiming Fire a NGFS thermal signature of the smaller Lac du Bonnet Fire was apparent — that wildfire was unfortunately responsible for 2 fatalities.

1-minute GOES-19 GeoColor RGB images with an overlay of NGFS Fire Detection polygons, from 1200 UTC on 13 May to 0100 UTC on 14 May [click to play MP4 animation]

Toggles between VIIRS True Color RGB and False Color RGB images from Suomi-NPP and NOAA-20 (as visualized using RealEarth) are shown below. Brighter-white pyrocumulus and pyroCb clouds were seen rising above the  wildfire smoke in both the True Color RGB and False Color RGB images; active fires appeared as brighter shades of pink in the False Color RGB images.

Suomi-NPP VIIRS True Color RGB and False Color RGB images valid at 1825 UTC on 13 May [click to enlarge]

 

NOAA-20 VIIRS True Color RGB and False Color RGB images valid at 1847 UTC on 13 May [click to enlarge]

 

Suomi-NPP VIIRS True Color RGB and False Color RGB images valid at 2006 UTC on 13 May [click to enlarge]

A larger-scale view using 10-minute Full Disk scan GOES-19 Infrared images (below) showed several of the pyroCb clouds as they were transported eastward across Ontario — with two of the larger pyroCbs exhibiting cloud-top 10.3 µm brightness temperatures as cold as the -60s C (shades of green).

10-minute GOES-19 Clean Infrared Window (10.3 µm) images with an overlay of the Fire Mask derived product, from 1650 UTC on 13 May to 0100 UTC on 14 May [click to play MP4 animation]

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GOES-19 Clean Infrared Window image at 0050 UTC on 14 May, with cursor samples of the 10.3 µm infrared brightness temperature (white), Cloud Top Temperature derived product (green) and Cloud Top Height derived product (orange) at the coldest point of the dominant pyroCb cloud top [click to enlarge]

A cursor sample of the coldest cloud-top pixel of the large pyroCb located north of Pickle Lake, Ontario (CYPL) at 0050 UTC on 14 May (above) displayed a 10.3 µm infrared brightness temperature of -62.1ºC, along with a corresponding Cloud Top Temperature of -63.21ºC and Cloud Top Height of 41362.71 ft (12.6 km) at that pixel location.

Those values of cloud-top temperature and height appeared to be comparable to those of the tropopause on a plot of rawinsonde data from Pickle Lake at 0000 UTC on 14 May (below).

Plot of rawinsonde data from Pickle Lake, Ontario (CYPL) at 0000 UTC on 14 May [click to enlarge]

GOES-19 Infrared images with an overlay of GLM Flash Extent Density (below) revealed that there was a brief 10-minute period of lightning activity with one of the larger pyroCbs over Ontario.

10-minute GOES-19 Clean Infrared Window (10.3 µm) images with an overlay of 5-minute GOES-19 GLM Flash Extent Density (large blue pixels) from 2030-2050 UTC on 13 May

The Nopiming Fire (along with the Ken Fire, just across the Ontario border) continued to burn aggressively throughout the subsequent nighttime hours — and the elongated nocturnal glow of those 2 wildfire footprints were very apparent in VIIRS Day/Night Band imagery from NOAA-20 and NOAA-21 (below), northeast and east of Winnipeg (CYWG).

NOAA-20 and NOAA-21 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) images on 14 May [click to enlarge]

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Camp House and Jenkins Creek wildfires in northeast Minnesota

1-minute Mesoscale Domain Sector GOES-19 (GOES-East) GeoColor RGB images with an overlay of Next Generation Fire System fire detection polygons (above) displayed the thermal anomalies and dense smoke plumes associated with the Camp House Fire (near Brimson) and Jenkins Creek Fire (near Fairbanks) in northeastern Minnesota on 12 May 2025. These 2 wildfires prompted the issuance of a few... Read More

1-minute GOES-19 GeoColor RGB images with an overlay of NGFS fire detection polygons, from 1200-2200 UTC on 12 May [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-19 (GOES-East) GeoColor RGB images with an overlay of Next Generation Fire System fire detection polygons (above) displayed the thermal anomalies and dense smoke plumes associated with the Camp House Fire (near Brimson) and Jenkins Creek Fire (near Fairbanks) in northeastern Minnesota on 12 May 2025. These 2 wildfires prompted the issuance of a few evacuation orders.

Thick smoke drifted northeastward across the Boundary Waters Canoe Area Wilderness and crossed the Canadian border — GOES-19 Aerosol Optical Depth values with these smoke plumes were as high as 1.0 (below).

1-minute GOES-19 Aerosol Optical Depth derived product [click to play MP4 animation]

A NGFS probe of the Jenkins Creek Fire at 2120 UTC on 12 May (below showed various parameters of the thermal anomaly at that time.

NGFS probe of the Jenkins Creek Fire at 2120 UTC on 12 May [click to enlarge]

The Camp House Fire began on the previous day, and had continued burning through the subsequent nighttime hours — its nocturnal glow was evident in a NOAA-21 VIIRS Day/Night Band image at 0831 UTC (3:31 AM local time), just northeast of Brimson (below).

NOAA-21 (mislabeled as NPP) VIIRS Day/Night Band (0.7 µm) image valid at 0831 UTC on 12 May [click to enlarge]

1-minute GOES-19 Visible images with an overlay of the Fire Detection and Characterization Algorithm (FDCA) Fire Mask derived product (below) also showed the thermal signatures and smoke plumes of the 2 larger wildfires (along with a 3rd, smaller wildfire that began to the southwest at 1953 UTC near Shaw). South-southwest winds were gusting to 20-25 knots (23-29 mph) across the region, contributing to the extreme fire behavior.

1-minute GOES-19 Visible (0.64 µm) images with an overlay of the Fire Mask derived product, from 1301-2300 UTC on 12 May [click to play MP4 animation]

An overpass of Landsat-8 provided a 30-meter resolution image of the Jenkins Creek and Camp House wildfires at 1657 UTC (11:57 AM local time) on 12 May, as viewed using RealEarth (below). The active fires appeared as brighter shades of pink, with their hazy smoke plumes extending northward.

Landsat-8 “Natural Color” RGB image at 1657 UTC on 12 May [click to enlarge]

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Using Polar2grid and Direct Broadcast files to create imagery

It was another clear night over the Great Lakes on 12 May 2025 and NOAA-20 had a descending orbit over western lower Michigan around 0740 UTC that allowed a view of all five Great Lakes. CSPP software running at CIMSS produces both SDR (Sensor Data Record) and EDR (Environmental Data Record) files that can be... Read More

It was another clear night over the Great Lakes on 12 May 2025 and NOAA-20 had a descending orbit over western lower Michigan around 0740 UTC that allowed a view of all five Great Lakes. CSPP software running at CIMSS produces both SDR (Sensor Data Record) and EDR (Environmental Data Record) files that can be then manipulated by polar2grid to create imagery. There are sites where imagery is routinely available. The image below, for example, shows NOAA-20 ACSPO SSTs from the CIMSS DBPS website, as discussed here, but that Madison-centered image does not include Lake Ontario, and the colorbar used is a little too warm for mid-May! (Note: RealEarth also used the data)

ACSPO SSTs centered from the CIMSS DBPS website, 0733 UTC on 12 May 2025 (Click to enlarge)

The direct broadcast website (https://ftp.ssec.wisc.edu/pub/eosdb/) does include an image of the entire Great Lakes produced by NOAA-20 data (at this ephemeral url). Again, the colorbar is a little too warm.

ACSPO SSTs over the Great Lakes, 0737 UTC on 12 May 2025 (Click to enlarge)

The data to create (using polar2grid) more customized imagery is available at the CIMSS ftp site mentioned above. ACSPO SSTs can be created using an EDR file (that is, the file 20250512073000-CSPP-L2P_GHRSST-SSTsubskin-VIIRS_N20-ACSPO_V2.80-v02.0-fv01.0.nc shown in this file list at https://ftp.ssec.wisc.edu/eosdb/j01/viirs/2025_05_12_132_0733/edr/. I then followed the directions in the polar2grid documentation here to produce a Lake Surface Temperature scaled from 273.15 K – 293.15 K. The commands I used are listed below. Note that ‘p2g_sst_palette.txt’ is pre-loaded within the polar2grid directories. The ‘rescale.yaml’ file is something I created following the documentation.

../p2g_grid_helper.sh greatlakes -83.5 45.1 750 -750 1800 1200 > GreatLakes.yaml
../polar2grid.sh -r acspo -w geotiff -p sst -g greatlakes --grid-configs ./GreatLakes.yaml --extra-config-path ./rescale.yaml -f /pathToVIIRS_SSTfile/20250512073000-CSPP-L2P_GHRSST-SSTsubskin-VIIRS_N20-ACSPO_V2.80-v02.0-fv01.0.nc
../add_colormap.sh ../../colormaps/p2g_sst_palette.txt noaa20_viirs_sst_20250512_073317_greatlakes.tif
../add_coastlines.sh --add-coastlines --coastlines-resolution f --add-colorbar --colorbar-height 42 --colorbar-text-size 24  --colorbar-min 0.0 --colorbar-max 20.0 noaa20_viirs_sst_20250512_073317_greatlakes.tif

The SST image created with the commands above has no value — is transparent — where there is no water. Let’s put the SSTs on top of Day Night Band imagery, and for that I needed SDR files that can be found at https://ftp.ssec.wisc.edu/eosdb/j01/viirs/2025_05_12_132_0733/sdr/ ; I downloaded all the SVDNB files (containing the data) and the GDNB0 files (containing georeferencing) to an otherwise empty directory, and created the the DNB imagery. Of the three varieties of Day Night Band imagery created (hncc, dynamic and adaptive), I decided for this day that adaptive looked the most acceptable.

../p2g_grid_helper.sh greatlakes -83.5 45.1 750 -750 1800 1200 > GreatLakes.yaml
../polar2grid.sh -r viirs_sdr -w geotiff -p hncc_dnb dynamic_dnb adaptive_dnb -g greatlakes --grid-configs ./GreatLakes.yaml -f /pathToFiles/DNB/*
../add_coastlines.sh --add-coastlines --coastlines-resolution f *dnb*.tif

I then used ImageMagick, shown below, to combine the two images.

convert -composite -gravity center noaa20_viirs_adaptive_dnb_20250512_073317_greatlakes.png noaa20_viirs_sst_20250512_073317_greatlakes.png NOAA20_VIIRS_DNB_ACSPO_SST_20250512_0733UTC.png
NOAA-20 ACSPO SSTs over Day Night Band imagery, 0733 UTC on 12 May 2025 (Click to enlarge)

Western Lake Erie, as is typical, has the warmest waters — almost 60o F! Saginaw and Green Bays also have relatively warm water. In contrast, Lake Superior and much of Lakes Huron and Ontario remain very cold — 40o F or cooler.

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