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December 2017 Implementation Summary

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Overview of upgrade scheduled for December 2017. Note that this was originally scheduled for October 2017, but has been pushed back due to technical issues.

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RE: RTMA/URMA Terrain Gradient Issue in Temperature Analysis along Wasatch Front / Great Salt Lake

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David Church, modified 7 Days ago.

RTMA/URMA Terrain Gradient Issue in Temperature Analysis along Wasatch Front / Great Salt Lake

Youngling Posts: 10 Join Date: 1/8/14 Recent Posts

Lately we've noticed some higher temperature forecasts from the NBM along the benches (transitions between the mountains and valleys), than in the valley floors. I was able to trace this back to the RTMA and URMA analysis which is impacting the bias correction in the NBM. This also seems to happen at some pixels along the boundary of the Great Salt Lake lake shore as well. The issue is fairly ubiquitous at these transition zones in elevation, and does not appear to be limited to any specific observation site issues. The other odd thing is that I actually can't explain how the RMTA and URMA are arriving at the final analysis values. Using the KML files available to see how the obs are impacting the RTMA analysis, the final analysis values for the offending pixels in the KML file are actually reasonable values, but they don't actually match what I'm seeing the gridded RTMA and URMA. Furthermore, it appears the RTMA is too warm at these locations, but the URMA is even warmer at these locations, like the error magnifies between the RTMA and URMA. I've attached some examples are specific points, but the issue is far more widespread than just these pixels. The issue also shows up any day, and seem independent of how warm/cool the day is, we just happened to notice this on the warmer days as this has downstream impacts to the NBM and thus HeatRisk forecasts as well.

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MM
Matthew Morris, modified 6 Days ago.

RE: RTMA/URMA Terrain Gradient Issue in Temperature Analysis along Wasatch Front / Great Salt Lake

Youngling Posts: 171 Join Date: 12/6/17 Recent Posts
Hi David,

Thanks for sharing this case with us.  We are looking into it and will follow-up once we know more, likely early next week.

Matt

On Tue, Jun 24, 2025 at 3:21 PM VLab Notifications <VLab.Notifications@noaa.gov> wrote:

Lately we've noticed some higher temperature forecasts from the NBM along the benches (transitions between the mountains and valleys), than in the valley floors. I was able to trace this back to the RTMA and URMA analysis which is impacting the bias correction in the NBM. This also seems to happen at some pixels along the boundary of the Great Salt Lake lake shore as well. The issue is fairly ubiquitous at these transition zones in elevation, and does not appear to be limited to any specific observation site issues. The other odd thing is that I actually can't explain how the RMTA and URMA are arriving at the final analysis values. Using the KML files available to see how the obs are impacting the RTMA analysis, the final analysis values for the offending pixels in the KML file are actually reasonable values, but they don't actually match what I'm seeing the gridded RTMA and URMA. Furthermore, it appears the RTMA is too warm at these locations, but the URMA is even warmer at these locations, like the error magnifies between the RTMA and URMA. I've attached some examples are specific points, but the issue is far more widespread than just these pixels. The issue also shows up any day, and seem independent of how warm/cool the day is, we just happened to notice this on the warmer days as this has downstream impacts to the NBM and thus HeatRisk forecasts as well.


--
David Church RTMA/URMA Discussion Group Virtual Lab Forum https://vlab.noaa.gov/web/715073/discussions-forums-/-/message_boards/view_message/45549960VLab.Notifications@noaa.gov


--
Matthew Morris
SAIC at NOAA/NWS/NCEP/EMC
5830 University Research Ct., Rm. 2038
College Park, MD 20740
301-683-3758
MM
Matthew Morris, modified 9 Hours ago.

RE: RTMA/URMA Terrain Gradient Issue in Temperature Analysis along Wasatch Front / Great Salt Lake

Youngling Posts: 171 Join Date: 12/6/17 Recent Posts
Hi David,

We are still looking into this case study, but we wanted to share our initial findings with you before the holiday weekend.  Please see the attached slide deck for the RTMA/URMA figures valid 20250619/23Z:
First, we'll consider the warmer than expected temperatures along the southern boundary of the Great Salt Lake.  There is a positive analysis increment encompassing the lake in RTMA and URMA, with the magnitude slightly greater in URMA.  This seems to be driven by a MesoWest/UPR station: UP068.  For the time in question, the observation was 92.93F, while the RTMA background was 83.03F, resulting in an innovation of almost 10F.  In URMA, an additional observation from UP472 was used, although it was withheld for cross-validation in the first two outer loops of the assimilation; the observed value was 101.93F, while the URMA background was 89.51F.  These observations appear to be non-representative, and we recommend that they be flagged via the SDM reject list.

In addition, there are some questionable observations along the southern boundary of the lake.  KCC02 reported an observation of 99.23F vs 94.55F.  A colocated CWOP station (AS768) reported for URMA, but not RTMA, with an observed value of 100.13F.  Both of these factors are likely contributing to URMA being slightly warmer than RTMA.  We could try removing the temperature observations from one or both of these stations to see if it improves the analyses.

For the Provo Canyon case, several nearby observations could be contributing to this undesired behavior.  PC034 has observed and background values of 94.73F vs. 88.43F, respectively, while C9635 has values of 98.15F vs 90.41F.  We will be further investigating this case, but suspect that the recursive filter is performing poorly given the terrain in this area.  It may also be worthwhile to explore flagging these stations.

We were unable to locate an analysis increment that corresponds with the circled bench, so it's possible this feature is originating in the background fields.  Please let us know if we are mistaken on this, so we can take another look, if needed.

Finally, for the point case studies you've included, the values that are used to generate the KML file are derived using bilinear interpolation with the 4 nearest grid points, rather than taking the value from the nearest grid point.  In your examples, the points in question are surrounded by cooler grid points, which would tend to reduce the values listed in the KML files.

Please let us know if you have any further questions or would like to proceed with flagging any of the listed stations.

Thanks,
Matt

On Tue, Jun 24, 2025 at 3:21 PM VLab Notifications <VLab.Notifications@noaa.gov> wrote:

Lately we've noticed some higher temperature forecasts from the NBM along the benches (transitions between the mountains and valleys), than in the valley floors. I was able to trace this back to the RTMA and URMA analysis which is impacting the bias correction in the NBM. This also seems to happen at some pixels along the boundary of the Great Salt Lake lake shore as well. The issue is fairly ubiquitous at these transition zones in elevation, and does not appear to be limited to any specific observation site issues. The other odd thing is that I actually can't explain how the RMTA and URMA are arriving at the final analysis values. Using the KML files available to see how the obs are impacting the RTMA analysis, the final analysis values for the offending pixels in the KML file are actually reasonable values, but they don't actually match what I'm seeing the gridded RTMA and URMA. Furthermore, it appears the RTMA is too warm at these locations, but the URMA is even warmer at these locations, like the error magnifies between the RTMA and URMA. I've attached some examples are specific points, but the issue is far more widespread than just these pixels. The issue also shows up any day, and seem independent of how warm/cool the day is, we just happened to notice this on the warmer days as this has downstream impacts to the NBM and thus HeatRisk forecasts as well.


--
David Church RTMA/URMA Discussion Group Virtual Lab Forum https://vlab.noaa.gov/web/715073/discussions-forums-/-/message_boards/view_message/45549960VLab.Notifications@noaa.gov


--
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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  • 2011 RTMA Paper (Weather and Forecasting)

    The most recent peer-reviewed paper on the RTMA. Published in Weather and Forecasting in 2011.
    7 Visits

  • Public RTMA/URMA Viewer

    Another viewer of the current RTMA/URMA, with an archive going back 24 hours. This version is open to the public, but does not contain information about the (many) restricted obs used.
    54 Visits

  • RAP downscaling conference preprint (23rd IIPS)

    This link is to a presentation from the (then) RUC group on how the downscaling process works. Although we now use the RAP, HRRR, and NAM, the logic of the downscaling code is mostly unchanged from this point.
    2 Visits