Hi David,

We shared this case study with our collaborators from CIMSS at the University of Wisconsin.  First of all, GOES-18 does not have the same cooling system as GOES-17, so the loop heat pipes were not the cause of this issue.  Instead, it was found that an old version of the cloud mask and CLAVR-X software were being used to generate the GOES Imager output that we use in URMA.  There was a diurnal signal in this outdated cloud mask, likely due to false cloud cover over cold/snow.

After updating the CLAVR-X software and cloud mask, CIMSS was able to re-run the GOES Imager files from 20250228 13-16Z.  With assistance from EMC's satingest team, we were then able to run URMA retrospective experiments using the revised output.  The results of this experiment are shown in the following slide deck on slides 7-12.  Slides 9 & 10 show that the observations and resulting analyses are much more consistent going from 15Z to 16Z.  Keep in mind that there is QC on these observations, where observations of less than 30% sky cover are rejected when the solar zenith angle is greater than 80 degrees.  As a result, many of the observations over Nevada are now rejected at 15Z.

 URMA Sky Cover Analyses over Great Basin - 20250228

This fix is now running in the real-time processing at CIMSS, so you should already be seeing improvements in the sky cover analyses over this region.  Please let us know if you have any questions or encounter any further issues.

P.S. Work is underway to transfer the processing of these observations from CIMSS to NESDIS, where it will be under 24/7 support.

Thanks,
Matt

On Mon, Mar 3, 2025 at 4:39 PM Matthew Morris - NOAA Affiliate <matthew.t.morris@noaa.gov> wrote:

Hi David,

Thanks for bringing this issue to our attention.  We see the issue on our end (see attached slide deck), and we will reach out to our contacts at CIMSS to see if they have any insight on this issue.

 URMA Sky Cover Analyses over Great Basin - 20250228

-Matt

On Fri, Feb 28, 2025 at 2:10 PM VLab Notifications <VLab.Notifications@noaa.gov> wrote:

Bad sky analyses are back over the Great Basin from approximately 13-15Z. This appears to be during the night/day transition. Sky cover spikes to high values by around 15Z, then rapidly drops back to clear skies by 16Z. This analysis is impacting the National Blend of Models forecast, and resulting in operational meteorologists concerns and additional forecast edits to compensate for this affect. This issue had come up previously, and was largely attributed to the GOES-17 heat loop pipe issue at the time, so I'm concerned as to why this is cropping back up again with GOES-18 in place now for the west.  In the attached images, the RMTA/URMA analysis is in the inset map, while the NBM forecast is in the main background map.

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David Church RTMA/URMA Discussion Group Virtual Lab Forum https://vlab.noaa.gov/web/715073/discussions-forums-/-/message_boards/view_message/43330955VLab.Notifications@noaa.gov

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Matthew Morris

SAIC at NOAA/NWS/NCEP/EMC

5830 University Research Ct., Rm. 2038

College Park, MD 20740

301-683-3758

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Matthew Morris

SAIC at NOAA/NWS/NCEP/EMC

5830 University Research Ct., Rm. 2038

College Park, MD 20740

301-683-3758

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Matthew Morris RTMA/URMA Discussion Group Virtual Lab Forum http://vlab.noaa.gov/web/715073/home/-/message_boards/view_message/43682424VLab.Notifications@noaa.gov