An aerial view of the flooded I-5 overpass looking south Flooding in Chehalis. (Associated Press )

A Synopsis of the December 1-4, 2007 Storm Events

Maryanne Reiter, Hydrologist Weyerhaeuser Co.

Photo from Kiro News

The

Win

dTh

e R

ain

The

Snow The Three Storms of

Early December 2007

Photo by Stephen Pierce from OCS link

Storm 1: The SnowSnowfallThe first storm produced heavy snow in the mountains and lighter low elevation snow throughout the region due to the artic air over the area. While only up to 1" of snow fell around Seattle, several higher elevation areas of the Cascades received over a foot of snow. This heavy snow resulted in deadly avalanches in the Washington Cascade Mountains.

Snowmelt The warm temperatures early in the storm caused much of the new snow to melt. However, because the new snow did not contain high amounts of water (low snow water equivalent) and because there was not a significant low elevation snowpack, snowmelt amounts were minimal (1-3“) for areas below 4,000 ft compared to the high rainfall.

Snotel sites used to estimate snowmelt in flood area

Storm 2: The Wind

On December 2, a low pressure system moved over the area resulting in extremely high winds along the Coast from Newport to Hoquiam. It is the first time the NWS issued a warning for hurricane-forces winds. Wind gusts of over 80 mph were observed along much of the coast with record set at Naselle Ridge with a peak wind gust of 147 mph.

PUBLIC INFORMATION STATEMENTNATIONAL WEATHER SERVICE PORTLAND OR

1245 PM PST MON DEC 3 2007

..A STRONG PACIFIC SYSTEM CONTINUES TO ROCK THE COASTAL REGION THIS AFTERNOON...

Figure 1. Clatsop Spit Station Wind Speed (mph)

0

10

20

30

40

50

60

70

80

11/30/20070:00

12/1/20070:00

12/2/20070:00

12/3/20070:00

12/4/20070:00

12/5/20070:00

12/6/20070:00

Win

d sp

eed

(mph

)

The wind storm had not only high wind gusts, but also had a long duration, increasing the potential for damage. This chart shows high wind speeds for Clatsop Spit in Oregon that lasted from Dec 2nd through the 4th.

LOCATION PEAK WIND GUST ...WASHINGTON COAST...CAPE DISAPPOINTMENT................104 MPHKLIPSAN (Long Beach.................... 102 MPHDESTRUCTION ISLAND...................93 MPH...OREGON COAST...BAY CITY (NEAR TILLAMOOK)........129 MPHCAPE MEARES (ELEV. 1500 FT).....114 MPHROCKAWAY BEACH.........................104 MPHTILLAMOOK BAY TIDE GAGE..........100 MPHASTORIA (WEST SLOPE).................86 MPH CLATSOP SPIT ..........................86 MPH REPORTING ASTORIA AIRPORT.... 85 MPH LINCOLN CITY ...........................125 MPHYAQUINA HWY 101 BR ...... 88 MPHLINCOLN CITY (OTHER REPORT).. 85 MPHNEWPORT AIRPORT........................83 MPH

Storm 3: The Rain

This image shows rainfall totals as recorded by theMulti-satellite Precipitation Analysis (MPA) at NASA Goddard Space Flight Center.

The most significant of the three storms arrived December 3rd with near record high temperatures and a moist tropical air which led to record rainfall in many areas of southwestern Washington and northwestern Oregon (Wolf Read, OWSC).

Total storm rainfall (observed)

Total storm rainfall: satellite Wildwood 12.53

In some areas, 24-hour maximum storm intensities exceeded 100 year 24-hr amounts as estimated by NOAA. For example, the Chehalis maximum 24-hour storm precipitation of 5.38” exceeded the 100-year 24-hour amount of 3.74”. In Vernonia, OR the 24-hour rainfall intensity was 8.31”, exceeding the 100-year intensity by almost 2.5”.

24 hr amounts from http://www.nws.noaa.gov/oh/hdsc/noaaatlas2.htm

The Rain: Maximum 24 hour precipitation

6.103.80WA203Olympia Airport15

6.393.83WA151Rochester14

8.624.71WA140Humptulips salmon hatchery13

6.254.77WA70Elma12

3.745.38WA262Chehalis (RAWS)11

6.006.40OR1031Miller (RAWS)10

8.506.42WA269Shelton9

10.077.29OR2000Rye Mountain8

4.928.31OR755Vernonia7

11.219.18OR2220Cedar6

6.759.29WA370Wildwood5

9.869.49OR2257South Fork4

7.849.70WA230Frances3

7.5913.85WA1086Raccoon Weyerhaeuser2

7.5014.35WA1424Rock CrWeyerhaeuser

1

NOAA 100-year 24

hr precip. amount

(in)

Dec. 2007 storm 24-

hour max.

precip. (in)

StateElevation (ft)Site_NameRank

6.103.80WA203Olympia Airport15

6.393.83WA151Rochester14

8.624.71WA140Humptulips salmon hatchery13

6.254.77WA70Elma12

3.745.38WA262Chehalis (RAWS)11

6.006.40OR1031Miller (RAWS)10

8.506.42WA269Shelton9

10.077.29OR2000Rye Mountain8

4.928.31OR755Vernonia7

11.219.18OR2220Cedar6

6.759.29WA370Wildwood5

9.869.49OR2257South Fork4

7.849.70WA230Frances3

7.5913.85WA1086Raccoon Weyerhaeuser2

7.5014.35WA1424Rock CrWeyerhaeuser

1

NOAA 100-year 24

hr precip. amount

(in)

Dec. 2007 storm 24-

hour max.

precip. (in)

StateElevation (ft)Site_NameRank

Storm 3 continued: The FloodsDECEMBER 2007 FLOOD HYDROGRAPH FOR THE

CHEHALIS RIVER NR DOTY

0

10000

20000

30000

40000

50000

60000

12/1/0712:00 PM

12/2/0712:00 AM

12/2/0712:00 PM

12/3/0712:00 AM

12/3/0712:00 PM

12/4/0712:00 AM

Dis

char

ge (c

fs)

100 year event

Equipm ent m alfunction

NOTE: This is all provisional data and should be used with caution until approved by the USGS

0100002000030000400005000060000700008000090000

12/1/0712:00 AM

12/2/0712:00 AM

12/3/0712:00 AM

12/4/0712:00 AM

12/5/0712:00 AM

12/6/0712:00 AM

12/7/0712:00 AM

Dis

char

ge (c

fs)

USGS 12027500 CHEHALIS RIVER NEAR GRAND MOUND

100 year event

USGS 12013500 WILLAPA RIVER NEAR WILLAPA

0

2500

5000

7500

10000

12500

15000

17500

12/1/0712:00 AM

12/2/0712:00 AM

12/3/0712:00 AM

12/4/0712:00 AM

12/5/0712:00 AM

12/6/0712:00 AM

12/7/0712:00 AM

Dis

char

ge (c

fs)

100 year event

USGS 12025500 CHEHALIS RIVER AT CENTRALIA, WA Gage height, feet

50

55

60

65

70

75

80

12/1/20070:00

12/2/20070:00

12/3/20070:00

12/4/20070:00

12/5/20070:00

12/6/20070:00

12/7/20070:00

12/8/20070:00

Stag

e ht

(ft)

Storm 3: Flood surge in Centralia

The Chehalis River at Centralia had an extreme rise in stage beginning around 7 PM on the 3rd indicating the potential effect of the flood wave from the upper Chehalis in the Doty area according to Larry Schick of the ACOE.

NOTE: This is all provisional data and should be used with caution until approved by the USGS

These charts show the December 2007 peak flows compared to historic flows for selected gages where the recent event appears to be the flood of record. The Chehalis River basin had 5 new records set as a result of the storm.

Storm 3: The Floods

NOTE: Dec 2007 is provisional data and should be used with caution until approved by the USGS

PEAK FLOW HISTORY of the SOUTH FORK CHEHALIS RIVER NEAR WILDWOOD

0

5000

10000

15000

20000

25000

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

Ann

ual p

eak

disc

harg

e (c

fs)

Dec 3rd, 2007 event

PEAK FLOW HISTORY for the CHEHALIS RIVER NEAR DOTY

0

10000

20000

30000

40000

50000

60000

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

Water year

Ann

ual p

eak

disc

harg

e (c

fs)

100 year event

Dec 3rd, 2007 event

PEAK FLOW HISTORY for the WILLAPA RIVER NEAR WILLAPA

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

1949

1953

1957

1961

1965

1969

1973

1977

1981

1985

1989

1993

1997

2001

2005

Water year

Dis

char

ge (c

fs)

Mis

sing

100 year eventDec 3rd, 2007

event

Summary

A series of extreme magnitude events:

•The first ever hurricane-force wind warning issued by NWS. Maximum recorded wind gust of 147 mph. It was also a long-duration wind event.

•Record rainfall: climate stations in the north Oregon coast and in SW Washington had high rainfall with several stations breaking records. The highest storm totals were recorded in SW WA. In addition, several stations there had 24 hour rainfall well in excess of the 100 year 24 hr amount.

•Ten rivers exceeded their flood of records. In the Chehalis River basin 5 all-time high records were broken. As Larry Schick meteorologist with the Army Corps of Engineers said referring to the Chehalis River at Doty, "This is an extraordinarily rare event. A huge event. Double the previous record.“