Highest 500 mb height in history

602.1 dam
July 7, 1989 Grand Junction, Colorado
(Highest on record in the United States)


The 600 dam height is kind of a magical number in meteorology, because it's rare and it tends to signal that summer is in overdrive. This week I loaded up all radiosonde data that exists between 1945 and 2006 in a database and ran some queries, and after some inspection of the data I came up with the above result. I found that the 600 dam barrier was cracked about every 4 years, with by far the most instances occuring in July and early August. The more significant events are:

* July 11, 1959: ELY, LAS, and WMC make it to 601 dam.
* August 1-2, 1979: VBG and OAK touched the 600-601 dam range. Oddly enough I was in San Francisco on the 1st and I do remember a heat wave. The DWM never shows a 19700 ft contour opening up, so it appears this is one of the lesser mega-highs on record.
* July 22, 1988: SLC and ELY touch 600 and 601 dam, respectively. The 600 dam line never makes an appearance on the DWM series.
* July 7, 1989: There were at least 12 600+ instances this week. The top reading was 602.1 dam at GJT, 7/8/89 at 00Z. The DWM series shows the ultra-rare 600 dam line.
* June 28-29, 1994: ELP and MAF touch 600.9 and 600.8 dam, respectively, during the big heat wave of 1994. The DWM series shows a nice large 594 dam high, but no 600 line.

The results are actually not easy to judge due to obvious QC and observational error issues, which created "noise" in the dataset. By inspecting all the results by date, looking for consistency between stations and times, and crosschecking it with the Daily Weather Map, I'm pretty confident in the result above. The only downside is that the height maxes show a strong diurnal signal (mostly occurring at 00Z), implying a strong tie to localized heating, and appeared to occur mostly on the higher terrain of the western U.S. Too bad as I hoped Florida or the Gulf Coast would have a shot at the record.

Hey Tim, interesting statistics! I could have swore there was at least one or two days last year with a pretty good 600dam contour... I investigated and found 604.0 dam at Grand Junction CO at 00z 7/22/2005. A lot of other upper 590s around it so it's probably a legit ob.


Interestingly enough, exactly one year later, July of this year.... another 600 dam via 3 obs, coincidently enough, all of them exactly 600.0 dam -- at Salt Lake City, Riverton, and Boise. I used raob.fsl.noaa.gov to find these (the tabular FSL text format).


So that 604.0 dam last year might be the highest?
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Mike, I see a 606dam right in the center of that 600dam contour on the first image. Perhaps 606 is the highest value?

EDIT: That 606dam ob is the Grand Junction ob you mentioned, just different values - dam those numerical values! ;)
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Here's the raw data with all occurrences of 6000 m or higher:

The source for 1994 onward is FSL's database, which has undergone QC and hydrostatic checks (though IMHO not as many as it should -- there's still a lot of garbage in there). The 7/22/05 00Z obs at GJT picks up as 6040 in the FSL database rather than the raw 6090. I discarded even the 6040 that since it wasn't consistent with the 12Z obs either side or with other stations and DWM on 7/21 and 7/22 had no 600 line.

Is the 6040 valid? I'm not really sure... given the tendency towards noise in the data (and there's a lot of it in that data dump) I've erred towards consistency.

Bringing this back! I ran across this Google searching what the Highest H5 height recorded in the US was.

Since.. OAX hit 600dm today at H5 at 0OZ.