RE: Nighttime Wind Gusts Too High?

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Chris Geelhart, modified 8 Years ago.

Nighttime Wind Gusts Too High?

Youngling Posts: 8 Join Date: 6/22/13 Recent Posts

I've been noticing the last few nights that the Day4-7 automatically populated wind gust grids seem too high for the nighttime hours. Although the overall wind speed may remain nearly constant or fall through the night, there is a steady increase of a few knots in the gusts during the evening hours, and even continuing after midnight. The cases I've had so far have been in a lighter flow, winds only averaging about 5 knots or less, but gusts increase to 10-13 knots at night. I've attached a sample of this evening's (0530Z Sep 12) run, using the Day 5 nighttime grids, 00-12Z for Sep 17 as an example.

Chris G. @ ILX

Shane Searcy, modified 8 Years ago.

RE: Nighttime Wind Gusts Too High?

Youngling Posts: 10 Join Date: 9/26/12 Recent Posts

Hello Chris,

Thanks for the posting and including the PPT. The images should help a lot. I took a look at the Forecast Builder code; specifically that part of the ForecastBuilderUtility.py that deals with wind gusts. As near as I can tell, WindGusts should equal Wind speeds for any Wind speed less than 7.5 knots. Again -that's according to the code that I looked at. Andy J. may have more details. So, I don't have an answer for you, since obviously the WindGusts you shared in the PPT are from 7 to 12 knots - but my interpretation they shouldn't be. Other team members will see your posting and reply with more detail, but I wanted to let you know we have received your posting.

Thanks - Shane - DMX/CRGMAT

Andy Just, modified 8 Years ago.

RE: Nighttime Wind Gusts Too High?

Padawan Posts: 99 Join Date: 6/2/15 Recent Posts

Chris,

First off, want to mention the WindGusts come from SuperBlend, which is composed of both smartInit'd algorithms for the base models (NAM, GFS, etc.) and bias correction from the URMA database. In the very early renditions of ForecastBuilder we had a tool built in to create WindGust from Wind, which for your case might have made WindGust = Wind. However, over the long haul, the CRGMAT looked at WindGust verification and found SuperBlend comparable if not better than the various tools (including the one built into ForecastBuilder).

I've noticed that for light flow events, up to a 5 kt difference may exist between SuperBlend Wind and WindGust, which I think you are seeing as well from the powerpoint. This difference varies, like I have an event Wednesday night where I have high pressure in place and my Wind and WindGust are nearly identical, which it should be. So my guess for your case you might have a little more breeze "right off the deck," causing the higher gusts than you might expect. Could there be potential for some higher gusts there in central IL during the night?

Chris Geelhart, modified 8 Years ago.

RE: Nighttime Wind Gusts Too High?

Youngling Posts: 8 Join Date: 6/22/13 Recent Posts

Thanks for the feedback, Shane and Andy.

We don't have any huge terrain issues in our area, so I'm not sure we can isolate that as being the problem. Looking at the grids in ISC mode, they seem in line with the neighbors, so it wouldn't seem to be a local configuration issue, either.

Normally when I'm dealing with days 4-7, I'm working the overnight shift, so I don't have much experience with how it may come out on the daytime runs. However, the lead forecaster I'm working with (the leads would normally do days 4-7 on the day shifts) has noticed them being too high as well. I haven't had any really windy nighttime periods to deal with recently, so I'm not sure if that would be standing out too.

I do have some concerns of the gusts doubling or even tripling during a light flow event under high pressure. However, I'm glad to see the efforts to make the gusts more uniform from CWA to CWA overall.

Jerry Wiedenfeld, modified 8 Years ago.

RE: Nighttime Wind Gusts Too High? (Answer)

Youngling Posts: 4 Join Date: 11/21/12 Recent Posts

Chris,

My guess is this is related to URMA. Have you tried comparing SuperBlend WindGust to CONSAll WindGust? Is the CONSAll WindGust lower? You could also compare Obs WindGust to URMA WindGust. Feel free to include some snap shots so we can see. If the URMA analysis does not look right you may want to send something to the aor-rtma@infolist.nws.noaa.gov list with images so they can see the problems.

Thanks,

Jerry

Chris Geelhart, modified 8 Years ago.

RE: Nighttime Wind Gusts Too High?

Youngling Posts: 8 Join Date: 6/22/13 Recent Posts

Hi Jerry,

For this evening's run, I did some spot checks between the CONSAll gusts and the ForecastBuilder gusts, and CONSAll looks like it is averaging about 2-3 knots lower. I've attached a comparison for the 06Z and 12Z time steps for 9/20 based on this evening's 0530Z run. I did a little looking at the URMA wind gust, but we've had some storm contamination during the period I had available, so I'll have to take a look at it on my next shift when tonight's data is available.

Chris G. @ ILX

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