Re: Oct 29 Portland, OR wind event (was:: Official RTMA/URMA 2.8 Evaluation All - Home - RTMA/URMA Discussion Group

Hello Jeff,

I apologize if I am interpreting your message incorrectly here - but I interpret your note to imply that we (WFO PQR) should have been blacklisting the KPDX observation on the morning of Oct. 29.  Is that correct?

The short version of summing up the meteorology of the situation is "what Mel said."   This was the beginning of a larger scale wind event that became more of a "hybrid" (gap flow + Cascades downslope) later in the day as the main upper trof/cold temps/steep lapse rates translated southward across the interior PacNW. The snapshot you show in your image from 14z (7 AM PDT) shows strong easterly gap flow through the Columbia River Gorge at the beginning of the event and before the winds increased across a larger area.  If you look closely at the URMA map that you sent, you will note locally higher wind speeds through the narrow terrain gap from Troutdale (26 kt) all the way to PDX and beyond clustered immediately along the Columbia RIver.  If you need a couple of additional data points that aren't in the obs data base - the Glenn Jackson bridge (the I-205 bridge over the Columbia just east of KPDX) gusted to over 50 mph, and when I walked out of the hotel that I am still at for temp quarters just before 7 AM last Tuesday morning, which is just to the east of the runway compex at KPDX (about 1.7 miles east of the ASOS) - I can confirm that the wind was at least 20-25, with some gusts probably close to 40.  However, by the time I got to the PQR WFO, which is only a couple miles to the east-southeast, but also is not directly at the mouth of the C.R. Gorge - the wind was considerably weaker - in line with your obs map.

Basically, what we had in this instance is a micro-scale feature that was most certainly real, both in magnitude and duration, but not sufficiently sampled by the observation network.  An example that with some things, it's very difficult to sample these types of features, even with a fairly dense observation network.

To address your other point, the KPDX observation is well maintained, and probably in about as good a place as one can get (in addition to Troutdale) to capture the mass outflow at the west mouth of the gorge in events like this.  It's also at an airfield where there are no trees and few obstructions, and therefore a very high quality sample.  Many of the other observation throughout the Portland area (away from the Columbia River) are not sighted as well, and as I'm sure you know, there are a lot of trees out here, even in the city by comparison.

It's really hard to write this without sounding defensive - but the C.R. gap flow is a well-known feature to all of the forecasters here, and has been well-documented in peer-reviewed literature in the past (Sharp and Mass, 2004 for one example), and I guess I would contend that we *are* applying our local expertise.  In this case, it seems to me that the background first-guess field isn't sufficiently capturing the spatial extent or magnitude of the feature. 

I'm all for improving the URMA, but I'm not sure what more can be done in a case like this.  If you want to discuss further - please give me a call...

 Dan

On Sat, Nov 2, 2019 at 6:22 PM Mel Nordquist - NOAA Federal <mel.nordquist@noaa.gov> wrote:

Jeff,

I am sure Portland will likely pipe in on this at some point. I am not sure what the meteorological situation was on the morning of the 29th of Oct. 

I did grow up in East Vancouver, right across the river from the airport. I do know that we would often get wind blowing down the Columbia River Gorge that would be restricted to areas of east Portland and Vancouver along the river. This may be one of those cases. Like I said I was not paying attention to what was going on up there as we were pretty busy with our own wind events down here in northern CA at that time. 

One of the concerns I have always had in general terms with respect to "neighbor checks" is exactly this sort of thing where the obs may be correct and there is a micro scale phenomena that is being represented accurately. Again, I can't say for sure but I have seen that kind of event there before. These cases usually occur in January though and October seems a bit strange to me from a climo point of view.

Just my two cents, will be interested to hear from Portland.

Mel

On Sat, Nov 2, 2019 at 8:14 AM Jeffrey Craven - NOAA Federal <jeffrey.craven@noaa.gov> wrote:

OK, one more plea about blacklisting observations, and how the local expertise from the WFOs is absolutely critical in our success with RTMA/URMA and NBM.  

I was looking at the RTMA Parallel at wind speeds and I see some areas with significant improvement.  Others haven't changed much.  I don't mean to pick on anyone in particular, but I found a good example of what EMC is up against in trying to do a good, thorough, scientific analysis.  

So here is an example from Portland OR area at 14z on Oct 29th.  The sustained wind at KPDX was 29 knots (33 mph) on the METAR.

  

The background first guess was around 5 knots, and the final URMA Parallel analysis doubled the value to about 10 knots.  

I looked at the observations available to URMA at 14z, and 21 of them in the area that were accepted were below 10 knots.    11 of those 21 observations were actually Below 5 knots.  So the fact that URMA doubled the first guess is actually impressive.

The airport is a major outlier in this case, AND it is also on outlier to the first guess from HRRR.  So the reasonable analysis was provided given the mathematics behind the situation.   

BOTTOM Line:  We need the local expertise to blacklist observations that aren't representative.   

The other issue is are METAR sites actually representative of large areas?  Are these sites below 10 knots actually bad observations?  If they are, they must be blacklisted because being able to analyze anything close to 29 knots near KPDX in this example is not very scientific given the data.  

Some things to think about.  I truly believe that we should attempt to analyze to METARs within about 3F or 3 knots if at all possible, but I really don't see how we justify that based on seeing similar examples literally all over the country day after day.   I am asking AFS if we can have a virtual workshop to discuss these matters with forecasters and modelers and come up with a compromise.  But it will be a compromise, because METARs and other observations can be outliers and do not represent the whole 2.5km grid point.  They may be representative of the airport on the scale of a couple hundred meters and that is about it.  

JPC

Jeff Craven

Chief, Statistical Modeling Division (SMD)

National Weather Service, W/STI-12

Meteorological Development Laboratory (MDL)

Room 10410, SSMC2

Silver Spring, MD 20910

(301) 427-9475 office

(816) 506-9783 cell/text

@jpcstorm

https://www.weather.gov/mdl/nbm_home

On Sat, Nov 2, 2019 at 10:29 AM Jeffrey Craven - NOAA Federal <jeffrey.craven@noaa.gov> wrote:

The upgraded RTMA/URMA is slated for about March 2020.   There is an official evaluation site which is one-stop shopping for a variety of information, forums, and ways to provide feedback.  

There is plenty of information available on evaluating and providing feedback.  Improvements in RTMA/URMA almost automatically mean improvements in NBM performance.  

https://www.emc.ncep.noaa.gov/users/meg/rtma_urma_v2p8/  

JPC

Jeff Craven

Chief, Statistical Modeling Division (SMD)

National Weather Service, W/STI-12

Meteorological Development Laboratory (MDL)

Room 10410, SSMC2

Silver Spring, MD 20910

(301) 427-9475 office

(816) 506-9783 cell/text

@jpcstorm

https://www.weather.gov/mdl/nbm_home

--

Mel K. Nordquist,

Science and Operations Officer

National Weather Service

WFO Eureka CA

(707)443-0574x224

mel.nordquist@noaa.gov

--

Dan Miller

Science and Operations Officer

National Weather Service

Portland, Oregon Forecast Office

5241 NE 122nd Avenue

Portland, OR 97230

(503) 326-2340 ext. 224

weather.gov/portland

Please note change of job and duty location: for issues pertaining to NWS Duluth, MN, please contact either WFO Duluth Meteorologist-in-Charge, Chris Gitro (christopher.gitro@noaa.gov) or Administrative Assistant, Ken Branning (kenneth.branning@noaa.gov)