With the increasing threat for strong to severe convection across the western portion of Hawai’i, a Severe Thunderstorm Watch was issued for an area centered on the island of Kauai at 1522 UTC on 30th January 2025 (above).

5-minute CONUS Sector GOES-18 Clean Infrared Window (10.3 µm) images (above) showed elongated clusters of convection moving eastward and northeastward across Kauai and Oahu — with embedded thunderstorms that produced heavy rain and strong winds on those two islands (Local Storm Reports).

A corresponding animation of GOES-18 Infrared images with an overlay of GLM Flash Extent Density (below) displayed the abundant lightning activity associated with these thunderstorms.

This convection was occurring within the warm sector of a deepening Gale Force to Storm Force low pressure system (bottom left on these surface analyses) that was located NW of the island chain — and the strong SW flow in advance of this storm system (and its cold front) interacting with island terrain produced wind gusts as high as 120 mph on Maui at 0850 UTC.

The air mass within the warm sector was also unusually moist — in fact, a new daily record rainfall of 3.57 inches occurred at Honolulu. The Total Precipitable Water (PW) value of 1.98″ derived from Lihue, Kauai rawinsonde data at 1200 UTC on 30th January was a record high value for that date/time, according to the SPC Sounding Climatology site (below).

The PW value derived from Lihue rawinsonde data at 1800 UTC on 30th January (about 2.5 hours after the Severe Thunderstorm Watch was issued) was even higher, at 2.06″ (below).

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Geo2grid software accesses SatPy libraries that allow for the reading of level-1c netcdf files holding FCI (Flexible Combined Imager) data from the latest operational Meteosat satellite (Meteosat-12). So if you can access to that output, you can create beautiful images as the ones shown above. The RGB shows a storm moving into western Europe. The Red/Orange in the image is associated with the Potential Vorticity Anomaly helping to support the storm (a second Potential Vorticity Anomaly is apparent over the central Mediterranean, and there seems to be one over the Arabian Peninsula too — maybe that’s a Westerly Disturbance for India later this weekend) To create the image above, I first moved all 40 (!) image sectors holding the data valid at 0000 UTC on 30 January 2025 to my computer that holds the geo2grid software (downloadable from this link). The geo2grid documentation includes a section on readers, including the FCI Level-1c reader.

The two geo2grid commands to create the image above are shown below. One creates the .tif file, one adds coastlines to the image. In geo2grid call, those last 4 wildcards (????) refer to the 40 different sectors (that is, 0001, 0002, 0003, 0004, … , 0039, 0040) that hold the data. The 0001 in the filename refers to the 1st image of the day.

./geo2grid.sh -r fci_l1c_nc -w geotiff -p airmass -f /pathtoL1CData/W*FDHSI*_0001_????.nc
./add_coastlines.sh --add-coastlines --coastlines-resolution f MTG-I1_FCI_airmass_20250130_000000_mtg_fci_fdss_2km.tif 

As with other geo2grid commands, one can create a region into which you can subsect the data so you can focus on a particular region. This was done below to focus on parts of Europe.

/p2g_grid_helper.sh Europe4 10.0 45.0 4000 -4000 1440 1120 > Europe4.yaml
./geo2grid.sh -r fci_l1c_nc -w geotiff -p airmass -g Europe4 --grid-configs ./Europe4.yaml -f /pathtoL1CData/W*FDHSI*_0001_????.nc 
 ./add_coastlines.sh --add-coastlines --coastlines-resolution f MTG-I1_FCI_airmass_20250130_000000_Europe4.tif 

The output from that series of calls is shown below.

Thanks to EUMETSAT for sharing the data that allowed the creation of these beautiful images!

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Red Visible (0.64 µm) images (above) showed a long, narrow convective cloud band associated with a strong cold front that was moving southward and southeastward across New York and Pennsylvania on 29th January 2025. Strong winds coupled with moderate-to-heavy snow along this cloud band prompted the issuance of numerous Snow Squall Warnings across the area. The appearance of intermittent GLM Flash Extent Density and GLM Flash Point signatures suggested that thundersnow may have occurred with some of these snow squalls. Note the slight northward displacement of the Flash Extent Density pixels compared to the Flash Points (1659 UTC image) — this is because the commonly-used Gridded GLM products (such as Flash Extent Density, Minimum Flash Area and Total Optical Energy) are not corrected for parallax, as the GLM Flash Points are.

5-minute CONUS Sector GOES-19 (Preliminary/Non-operational) Day Cloud Phase Distinction RGB images created using Geo2Grid (below) helped to highlight this cold frontal cloud band — the shades of green to yellow indicated that the cloud band was either mixed phase or fully glaciated.

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For the second day in a row, residents of the southern United States have awoken to dense fog advisories. A view of the continental United States surface map shows that overall, there is very weak synoptic forcing across the south, which results in calm winds and little mixing or advection. This allows radiative cooling to dominate other processes in the overnight hours, and eventually air temperatures cool until they reach the dew point temperature at which point condensation occurs and fog forms. With little wind to disturb things, the fog persists overnight. During the day, the sun rises and heats the ground, which causes near-surface air temperatures to rise. However, the absolute moisture content of the air is relatively unaffected, so the dew points remain unchanged. The warmer air temperatures mean that the air is no longer saturated, and so the fog dissipates.

Band 13 from the GOES-16 ABI measures the atmospheric window brightness temperature and is often the first stop for observing conditions at night when no visible channels are available. Since fog has effectively the same temperature as the land, it can be challenging to discern where the fog ends and clear air begins using just that channel. This is particularly evident in the pre-dawn hours of 28 January 2025. The Band 13 loop over Alabama and Mississippi from 10:00 – 12:00 UTC (4:00 AM to 6:00 AM Central Time) shows little of note. The clouds moving in from the west indicate some elevated instability due to their convective shape, but otherwise conditions look clear and calm.

However, the Nighttime Microphysics RGB tells a very different story. Here, three different parameters are combined into one image to help users identify various features. In this case, the 12.4–10.4 micron brightness temperature difference (sensitive to optical depth) is assigned to the red channel. The 10.4–3.9 micron brightness temperature difference (sensitive to cloud particle size and cloud phase) is assigned to green, and the 10.4 micron brightness temperature (sensitive to temperature) is assigned to blue. Fog, which is a warm liquid cloud, is going to be a light blue or mint green in this combination. Looping this RGB for the same time as above shows the undeniable presence of fog over the region. Of particular note is the long, narrow Tennessee River valley stretching diagonally from northeastern Alabama into eastern Tennessee. This feature is practically invisible in the traditional IR window, yet the fog that formed in this valley is easily seen in the RGB.

It is important to note that this RGB depends on the 3.9 micron brightness temperature channel. This channel straddles the border between terrestrial emission and solar reflectivity. At night, it represents the infrared emission of the surface, but during the day, it is dominated by reflected radiance from the sun. Because of this, the interpretation of the RGB cannot be used during the day as the relationship between the 3.9 ?m brightness temperature and cloud microphysics is only valid at night.

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