Extreme High Pressure in the Northwest

Great info from Steve Pierce of the Portland AMS:

(Thursday, December 1st 2011) — Are you feeling the pressure today, literally? If so, you are not alone. As of 9:00AM PT the Portland International Airport has recorded a maximum barometric pressure reading (rounded to the nearest hundredth of an inch) of 30.76″ (4:53am observation) which is tied for the second highest reading since records began at the airport in 1940. This is also the single highest barometric pressure reading since December 1998. Looking even further back at downtown Portland records, the record for the month of December is 30.79″ set back in 1879. The all-time Portland highest barometric pressure reading (for anytime of the year) was set back on February 2nd, 1880 at 30.84″. At this point, neither the December or the all-time record appear to be in jeopardy. But these are worth noting none-the-less.”
A follow-up comment from Maury Roos of Sacramento:

Interesting!  The Sacramento, CA, all time high sea level pressure was also a real oldie
in Feb 17, 1883, at 30.74 inches.  Early yesterday it peaked at 30.32 inches and we had
peak wind gusts of around 40 mph from the north.  As you know from the news, it
really hit the south.  Mammoth Pass in the southern Sierra at around 9300 feet
dropped 30 degrees from 45 F at noon Wed to 16 by 6 p.m. with the winds at

Mammoth mountain shifting from SW to NE and rising to 130 mph at 5 p.m. and,
according to weatherman Steve Johnson, hit 150 mph at 7 p.m., then roaring down
the west slope to the Fresno area out of the San Joaquin River canyon by early Thur
morning with winds there at around 40 mph with a temperature of about 60 degrees.

This is a vivid example of compressional heating.  There may have been a few snow
flurries on the ridge top of the Sierra, but Valley conditions were dry.  This is an
event that will be talked about for quite a while I think.

Maury

Here are the top 10 hourly barometric pressure records from the Portland Airport (1940-2011) sorted first by pressure, then by date (most recent first) —
Date
Max Sea Level Pressure
1/28/1949
30.81
12/1/2011
30.76
12/21/1998
30.76
1/11/1963
30.76
12/20/1998
30.75
1/23/1988
30.75
1/12/1963
30.75
1/16/1957
30.75
1/11/2009
30.74
2/11/2002
30.74
Here are the top barometric pressure readings for a given month of the year in Portland. Records for this data set date from 1871-2011 and include both the airport and downtown —

Month

Highest
Year
January
30.81
1949
February
30.84
1880
March
30.70
1955
April
30.68
1936
May
30.59
1931
June
30.51
1895
July
30.41
1944
August
30.39
1876
September
30.49
1937
October
30.63
1935
November
30.74
1928
December
30.79
1879
Annual 30.84
Feb 1, 1880
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