Wednesday, August 25, 2021

July Climate Anomalies

Regrettably I've been hard-pressed to find time for posts lately, but I couldn't help noticing that July saw another discrepancy between competing estimates of the month's North Slope temperatures.  Last month I pointed out that the NOAA/NCEI climate division data showed below-normal temperatures in the North Slope division for June, whereas the ERA5 gridded reanalysis was distinctly warmer than normal.  The same thing happened for July - click to enlarge:

According to NCEI, the North Slope division saw the 6th coolest July among the prior 30 years, but most of the area was warmer than normal in the ERA5 data.  Rick Thoman's excellent summary of station data again supports the warmer view:

Judging from the published documentation of NCEI's methods, the only inland stations contributing to the North Slope climate division are the RAWS sites at Umiat and Noatak - the latter being in the broad upland Noatak River valley in the western Brooks Range.

Here's another way of looking at the rank of the July temperatures for these two sites, as well as Utqiaġvik and the ERA5 and NCEI regional averages.  The Umiat RAWS period of record only extends back to 2008, but even so it's clear that July was significantly warmer than normal there.  Utqiaġvik was near-normal.  However, the Noatak site was definitely cool: 8th coolest out of 28 complete July values since 1991.

The long-term trends in the NCEI data also look a bit suspect: the North Slope division shows no warming in July since about the mid-1980s, whereas Utqiaġvik has a considerable warming trend, and ERA5 also shows warming for the regional area average.  Interestingly Noatak has not warmed in July over the last 30 years, but we wouldn't expect that one site to dominate the NCEI divisional values.

In short, there seems to be something awry with the NCEI data, and it would be nice to diagnose and help fix the problem.

Below are the ERA5 July climate ranks for other variables, with NCEI's estimate thrown in for precipitation.  It was extremely wet, cloudy, and windy for the time of year in most of the west, but sunny and dry weather in the eastern interior led to significant soil moisture deficits.  It's a bit of a surprise that wildfire activity wasn't worse; I'll put together a seasonal summary on that in the coming days.

No comments:

Post a Comment