The Strong Sou'wester of March 25-26, 1971

compiled by

Wolf Read

The big sou'wester of March 26, 1971 followed a path similar to the powerful storms of October 26, 1950, October 12, 1962, November 14, 1981 and December 12, 1995. The closest track match appears to be December 1995, yet the 1971 storm was a cut below the 1995 event in peak wind speeds, and singificantly short of the incredible pressure minimums achieved in December of 1995. For comparison of wind strength, if one averages the peak gusts at the 11 key stations listed in the pressure minimum table far below (Table 1), these figures are produced: 80.5 mph for the 1962 "Big Blow", 65.9 for the November 14, 1981 storm, 60.5 for December 12, 1995, 55.4 for October 26, 1950, and 53.9 for March 26, 1971. Of these five big storms, the 1971 event comes in last. But it isn't the weakest example of a windstorm following this path--events like April 14, 1957 have produced lower overall readings (48.8 average). Thus, the strength of this storm shouldn't be underestimated. Wind gusts still reached 71 mph at Portland, and 70 at Astoria, levels that can be quite damaging.

With a central pressure of 978 mb as the storm moved northward along the Washington Coast, this event was not as deep as the other four mentioned above. The 1950 event had a minimum central pressure of 970 mb, the Columbus Day Storm of 1962 had a minimum of 960 mb, the November 14, 1981 cyclone reached 958 mb and the incredibly deep December 12, 1995 storm dropped to at least 954 mb. Through the period of record, the lower the intensity of the cyclone, the more commonly it tends to show up along the Pacific Coast. At least two major storms with a central pressure similar to the March 26, 1971 event have occurred in the 1950-to-present period: the October 2, 1967 windstorm that slammed into Western Oregon, and the Inauguration Day storm of 1993 that hammered Western Washington. The reader is encouraged to visit the web pages on these two storms to compare the results of events with similar intensities, but different tracks.

Figure 1, below, shows the surface weather conditions over the Northeast Pacific at the time the March 26, 1971 cyclone was nearing landfall on Washington's Olympic Peninsula. This path spared the northwest tip of Washington the high winds dealt out elsewhere in the region. At the time of the surface map, 04:00 PST, tightly packed south-to-north stacked isobars were moving into Oregon, with corresponding elevation in wind speeds. The small secondary low in Eastern Washington is a fature that has shown up in other events, including the Columbus Day Storm. These secondary features typically develop at the point of occlusion along a cyclone's leading frontal boundary. Source: The original map was obtained from the Oregon Climate Service.

General Storm Data

Minimum Pressures and Peak Gradients

Table 1, below, lists the lowet barometric pressures achieved during the March 26, 1971 storm for 11 Pacific Northwest locations. The readings tell the tale of a cyclone moving in out of the southwest and pouncing upon the region during the night and early morning hours. Some of these pressures are fairly low, with places like Olympia and Astoria showing the lowest readings for any of the March windstorms examined on this website.

Source: all pressure data is from the National Climatic Data Center, Unedited Surface Observation Forms.

Location

Lowest
Pressure

Approx Time
of Lowest Pressure

California:    
Arcata

29.43"

19:00 HRS, 25th

Oregon:    
North Bend

29.21"

22:00 HRS, 25th

Astoria

29.00"

03:00 HRS, 26th

Medford

29.37"

21:00 HRS, 25th

Eugene

29.18"

00:00 HRS, 26th

Salem

29.15"

00:00 HRS, 26th

Portland

29.14"

01:00 HRS, 26th

Washington:    
Quillayute

28.97"

05:00 HRS, 26th

Olympia

29.06"

04:00 HRS, 26th

Seattle (Sea-Tac)

29.09"

04:00 HRS, 26th

Bellingham

29.11"

06:00 HRS, 26th

     
AVERAGE

29.16"

 

Table 2, below, lists the maximum pressure gradients achieved during the March 26, 1971 storm for 10 Pacific Northwest measures. These gradients are fairly strong, but none are records.

Source: all pressure gradient data is calculated from hourly readings obtained from the National Climatic Data Center, Unedited Surface Observation Forms.

Location

Max Gradient, mb

Approx Time
of Max Gradient

Coast:    
ACV-OTH

14.2

00:00 HRS, 26th

OTH-AST

17.1

04:00 HRS, 26th

AST-UIL

9.7

11:00 HRS, 26th

ACV-AST

27.3

04:00 HRS, 26th

OTH-UIL

23.3

09:00 HRS, 26th

Interior:    
MFR-EUG

8.6

00:00 HRS, 26th

EUG-PDX

8.0

05:00 HRS, 26th

PDX-SEA

11.1

11:00 HRS, 26th

SEA-BLI

7.2

13:00 HRS, 26th

AST-DLS

-11.4

01:00 HRS, 26th

Pressure Tendencies

Table 3, below, lists the maximum hourly pressure falls and rises achieved during the March 26, 1971 storm for 11 Pacific Northwest stations. Peak hourly falls of -2.4 to -3.3 mb (-0.07" to -0.10") and climbs of +1.8 to +4.5 mb (+0.05" to +0.13") are fairly standard for big storms in the Pacific Northwest. In fact, this storm's pressure trends were a bit tame compared to many windstorms in history.

Source: all pressure gradient data is calculated from hourly readings obtained from the National Climatic Data Center, Unedited Surface Observation Forms.

Maximum Pressure Tendencies for the March 26, 1971 Storm

Location

Max
Hrly
Fall
mb

Time of
Max Fall
PST

Max
Hrly
Rise
mb

Time of
Max Rise
PST

California:        
Arcata

-3.3

19:00 HRS, 25th

+2.4

21:00 HRS, 25th

Oregon:        
North Bend

-2.4

16:00 HRS, 25th

+2.7

02:00 HRS, 26th

Astoria [1]

-2.9

20:00 HRS, 25th

+4.5

11:00 HRS, 26th

Medford

-2.4

20:00 HRS, 25th

+1.8

06:00 HRS, 26th

Eugene

-2.4

19:00 HRS, 25th

+2.5

05:00 HRS, 26th

Salem [2]

-2.4

18:00 HRS, 25th

+2.6

05:00 HRS, 26th

Portland

-2.8

00:00 HRS, 26th

+3.3

07:00 HRS, 26th

Washington:        
Quillayute

-2.4

21:00 HRS, 25th

+3.9

11:00 HRS, 26th

Olympia

-2.4

17:00 HRS, 25th

+3.4

12:00 HRS, 26th

Seattle (Sea-Tac)

-2.6

22:00 HRS, 25th

+3.6

13:00 HRS, 26th

Bellingham

-2.4

02:00 HRS, 26th

+4.0

14:00 HRS, 26th

         
AVERAGE

-2.6

 

+3.2

 

Table 3 Notes:

[1] The -2.9 mb hourly fall is the last of two occurrences.

[2] The -2.4 mb hourly fall is the last of two occurrences.

Peak Wind and Gust

Table 4, below, lists the peak wind and gust for eleven key stations in the Pacific Northwest, their direction, and their time of occurrence. "Peak Wind" is a 1-minute average, and "Peak Gust" is an instant (approximately 1-second) average. By my own personal methodology, a wind event rates the term "windstorm" when the average peak gust of these eleven stations reaches 39.0 mph (gale force) or higher. The March 26, 1971 storm ranked as a high-end moderate windstorm, and came very close to being a major event. Moderate windstorms have an average of 45.0 to 54.9, and major windstorms are those that reach or exceed 55.0. Only a handfull of storms have made the majors, including December 12, 1995, November 14, 1981 and October 12, 1962. This ranking favors those storms that follow a northward path close to the U.S. Pacific Coast, and for good reason--such storms affect the largest land area, and therefore are potentially the most destructive. The March 26, 1971 cyclone followed such a path, with damaging winds striking many points along the way.

The March 26, 1971 windstorm struck the Portland area particularly hard, with sustained winds reaching above the peak gusts of lesser storms. The trend toward higher gusts northward in the Willamette Valley is a fairly typical one for the big sou'westers, and is a characteristics used in this study for singling out offshore-trending sou'westers from the Washington-landfall group of storms.

Sources: National Climatic Data Center, undedited surface observation forms.

Location

Peak
Wind
mph

Direction
Pk Wnd
degrees

Obs Time of
Peak Wind
PST

Peak
Gust
mph

Direction
Pk Gst
degrees

Obs Time of
Peak Gust
PST

California:            
Arcata

23

190º

00:56 HRS, 26th

55

200º

22:57 HRS, 25th

Oregon:            
North Bend

29

200º

23:58 HRS, 25th

61

190º

01:03 HRS, 26th

Astoria

39

170º

05:58 HRS, 26th

70

160º

07:10 HRS, 26th

Medford

29

160º

20:58 HRS, 25th

40

160º

20:56 HRS, 25th

Eugene

35

180º

01:37 HRS, 26th

49

190º

01:56 HRS, 26th

Salem

40

190º

06:55 HRS, 26th

58

190º

03:15 HRS, 26th

Portland

46

200º

04:55 HRS, 26th

71

200º

04:17 HRS, 26th

Washington:            
Quillayute [1]

 21

250º

14:57 HRS, 26th

27

250º

14:57 HRS, 26th

Olympia

35

200º

11:05 HRS, 26th

48

180º

09:56 HRS, 26th

Sea-Tac

37

200º

11:55 HRS, 26th

60

210º

11:45 HRS, 26th

Bellingham

29

160º

12:54 HRS, 26th

54

160º

11:38 HRS, 26th

             
AVERAGE

33.0

191º

 

53.9

190º

 

Table 4 Notes:

[1] Wind speeds were too low for gusts to be noted at Quillayute, and a peak of 27 mph was estimated from the highest 1-minute reading using a standard 1.3 gust factor.

Footnotes

1971

References

1971

Last Modified: March 2, 2003
Page Created: December 7, 2002

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