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Cold pool in SW WY not captured well by RTMA

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Brett McDonald, modified 2 Years ago.

Cold pool in SW WY not captured well by RTMA

Youngling Posts: 12 Join Date: 9/24/12 Recent Posts
Afternoon,

A decent wide-basin cold pool was not captured well by RTMA in southwest WY this morning.  Here's our Obs grid:



And here's the RTMA analysis:



And here's a difference grid between the two:



Stations that showed the cold pool are WACFA (-17), WY42 (-18), BSRW4 (-13), and GBFW4 (-10).  Not sure why that many obs stations were dismissed.  Looks like the Pinedale Airport (KPNA) was also quite a bit off with ab observed low of -4 F.

Thanks,

Brett McDonald
RIW WY WFO - SOO

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Darren Van Cleave, modified 2 Years ago.

RE: Cold pool in SW WY not captured well by RTMA

Youngling Posts: 37 Join Date: 1/8/14 Recent Posts

Hi, 

 

I appreciate Brett bringing this up. I wanted to tag on as one of Riverton's CWA neighbors here (SLC). Our staff have recently pointed out similar missed cold pools. In case it helps to have another case to pair with Brett's case, I would bring up the MinT analysis from 12/10 in the Bryce Canyon National Park vicinity. In the attached screenshot, KBCE observed -2°F but the background was much warmer and apparently pulled up the analysis about 10°F. The valley Bryce is in had snow cover, while a nearby valley (Panguitch) without snow cover had a background that was more similar to the obs, so perhaps handling of snow cover for the background model was the culprit in our case. These 10°F+ differences are especially noteworthy when it makes the difference between above and below 0°F readings.

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Matthew Morris, modified 2 Years ago.

RE: Cold pool in SW WY not captured well by RTMA

Youngling Posts: 169 Join Date: 12/6/17 Recent Posts
Hi Brett,

Please see the following slide deck:

 Temperature Case Study - SW Wyoming

As a general reminder, the minT analysis is derived for the period of 7P-8A LST, which corresponds to 02Z-15Z for this particular case.  The background for the minT analysis is derived by taking the min of the hourly background/analysis fields over the aforementioned time period.  This background is then used in conjunction with the observations to derive the minT analysis, which is run as part of the 20Z URMA cycle.

In this particular case, the GBFW4, WACFA, WY42, and BSRW4 minT observations were rejected due to failing the gross error check.  In addition, when considering the hourly analyses, the WACFA observation was rejected at 15Z, the GBFW4 observations were rejected from 09Z-15Z, and the BSRW4 observations were rejected from 11Z-15Z, all for failing the gross error check.  The hourly temperature observations were rejected despite the gross error check being relaxed due to complex terrain.  In general, RTMA/URMA will struggle to capture cold pools that are not present in the background fields, particularly when the innovations are as large as this particular case.  While some of the hourly temperature observations that captured this cold pool were rejected, the assimilated observations acted to cool the analysis fields and, by extension, the minT background; please see slides 6-19.

We expect to see improvements in such cases in the upcoming 3D-RTMA/URMA suite, which is expected to be implemented in FY2024.

Please let us know if you have any questions.

Thanks,
Matt

On Wed, Dec 14, 2022 at 6:16 PM VLab Notifications <VLab.Notifications@noaa.gov> wrote:
Afternoon,

A decent wide-basin cold pool was not captured well by RTMA in southwest WY this morning.  Here's our Obs grid:



And here's the RTMA analysis:



And here's a difference grid between the two:



Stations that showed the cold pool are WACFA (-17), WY42 (-18), BSRW4 (-13), and GBFW4 (-10).  Not sure why that many obs stations were dismissed.  Looks like the Pinedale Airport (KPNA) was also quite a bit off with ab observed low of -4 F.

Thanks,

Brett McDonald
RIW WY WFO - SOO
--
Brett McDonald RTMA/URMA Discussion Group Virtual Lab Forum http://vlab.noaa.gov/web/715073/home/-/message_boards/view_message/26573801VLab.Notifications@noaa.gov


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