GOES-16 IFR Probability fields, shown above, (click here for a slower animation) combine satellite information about low clouds with Rapid Refresh model estimates of low-level saturation. On this day, regions of observed IFR conditions (that is, ceiling less than 1000 feet and/or visibilities less than 3 statute miles) are apparent over south-central Lower Michigan, northeast Indiana and northwest Ohio. IFR probability fields overlap those regions nicely. The flat IFR Probability field over central Ohio (where dense fog is also observed) is consistent with IFR Probability being computed solely with model data — because high clouds prevent the satellite from viewing low clouds.

Night Fog Brightness Temperature Difference fields, below, and Night Microphysics RGB, at bottom, can sometimes be used to detect low clouds and fog. But not on 2 November 2022! On this day, neither field showed a strong signal of fog. (Note that the high clouds over the fog in Ohio are readily apparent). If you incorporate all satellite-based fog detection products into procedures, then all products can be viewed when needed.

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GOES-R Cloud Thickness (from just before sunrise) can be used to help predict how long it will take for burn-off. Magenta values shown below are in the 600-700 foot range, that is, very thin fog that will burn off quickly. Note the region over northwestern Ohio where the cloud thickness values are bluer; cloud thickness values there are closer to 850-900 feet, and you might expect fog to linger there a bit longer. Indeed, an mp4 True-Color animation from CSPP Geosphere, shown below, shows fog after sunrise in the region over northwestern Ohio where Cloud Thickness is greatest.

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Thanks to TJ Turnage, SOO in Grand Rapids, Michigan for alerting us to this case.

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An anomalously-deep Hurricane Force low (surface analyses) moved eastward across the southern Bering Sea and eastern Aleutian Islands on 28 October 2022. GOES-18 (GOES-West) Air Mass RGB images (above) included plots of hourly surface reports — which showed some of the strong winds produced by this storm. Peak wind gusts included 75 knots / 86 mph at Dutch Harbor (PADU, at 0309 UTC on 29 October), 68 knots / 78 mph at Akutan (PAUT, at 0455 UTC on 29 October), 61 knots / 70 mph at St. George (PAPB, at 2140 UTC on 28 October, as heavy snow was being reported), 59  knots / 68 mph at Atka (PAAK, at 1645 UTC on 28 October) and 58 knots / 67 mph at Buoy 46073 (at 2200 UTC on 28 October). The 75 knot / 86 mph gust at Dutch Harbor and the 68 knot / 78 mph gust at Akutan occurred around the time that anomalously-strong 925 hPa winds were moving south-southeastward across the eastern Aleutian Islands (along the western and southwestern edge of the low pressure center).

The orange-to-red hues seen in the Air Mass RGB imagery indicated the presence of dry, ozone-rich stratospheric air within the upper portion of the atmospheric column (due to a lowering tropopause) — and AK-NAM40 model fields (below) suggested that the “dynamic tropopause” (taken to be the pressure of the PV1.5 surface) descended to the 600-675 hPa pressure level just south of the low pressure center.

Gridded NUCAPS Tropopause Height (derived using Metop-B and Metop-C CrIS/ATMS data) from the NASA SPoRT site (below) showed a narrow corridor of tropopause pressures near 600 hPa (brighter red enhancement) over and just north of the eastern Aleutians at 2108 and 2200 UTC — in general agreement with the AK-NAM40 model fields.

On the 1800 UTC Air Mass RGB image, a northwest-to-southeast oriented cross section line (Baseline B-B’) was positioned through the area of highest PV1.5 pressure values (above). The Baseline B-B’ cross section of model wind speed, potential vorticity and specific humidity (below) displayed a tropopause fold, as the dry air and high potential vorticity characteristic of stratospheric air descended southeastward around the upper-tropospheric 140-knot jet streak axis.

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A sequence of GOES-16 (GOES-East) Nighttime Microphysics RGB and Day Snow-Fog RGB images (above) showed the nocturnal development of lake effect fog/stratus plumes (lighter shades of yellow), which drifted northward from Lake Sakakawea in northwestern North Dakota on 26 October 2022. Two of the fog/stratus features moved across the Tioga and Stanley areas, where surface reports briefly indicated a drop in surface visibility to zero along with freezing fog. After sunrise, Day Snow-Fog RGB images revealed the dissipation of these lake effect fog/stratus features — and also displayed the areal coverage of early-season snow cover (shades of red) across the Montana/North Dakota border region.

The GOES-16 Nighttime Microphysics RGB image at 1001 UTC (below) includes an overlay of NOAA-20 VIIRS Sea Surface Temperature (SST) — the southerly flow of cold air (in the 20s F) across Lake Sakakawea’s SST values of 50-54ºF (shades of cyan) helped to create the lake effect fog/stratus features.

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Himawari-9 is slated to become operational (replacing Himawari-8, which has been operational at 140.7^o E Longitude since 2015!) on 13 December 2022 (Link). One change that users might observe arises from the slightly shorter central wavelength in the shortwave infrared band (Band 7). On Himawari-8, the central wavelength is 3.885 µm; on Himawari-9, the central wavelength is closer to 3.829 µm (see this link from JMA, or this one). The effect of the shorter wavelength on Himawari-9 is more noticeable during the daytime, when solar reflectance will lead to warmer observed brightness temperatures, especially over highly reflective convective updrafts (This presentation — see slide 19 — given at the CIRA RGB Workshop in October 2022, suggests daytime differences of up to 5 C.), and especially when compared to longwave infrared imagery as a brightness temperature difference.

The toggle above compares Himawari-8 visible imagery and Day Convection RGB imagery from Himawari-8 and -9 at 0200 UTC on 26 October 2022. in a region near Guam, without much intense convection. Subtle differences in the yellow shading over some convection are apparent (here’s a toggle just between Himawari-8 and -9 Day Convection RGB over Guam). It’s very hard to discern a difference in regions of no convection.

For strong convection, however, as shown below for a case over the south-central Equatorial Pacific, differences in yellow coloring over very strong convection are noteable; users might need to adjust the range of the RGB to draw out details in cloud tops, where, for Himawari-9 imagery, contrast is lost. (Here’s a toggle, over the strong convection, between Day Convection RGBs from Himawari-8 and Himawari-9).

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Spectral Response Functions for the infrared channels are available from Himawari-8 (here) and Himawari-9 (here). You will note that most infrared channels have similar functions; the outlier is band 7, shown below (and in this animated gif).

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Thanks to JMA for providing simultaneous image files for the different bands on Himawari-8 and Himawari-9!

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