The storm began as a large , but not particularly strong, mid-latitude storm in the mid-Pacific. Moisture from several decaying typhoons moved eastward and were absorbed by the storm, causing rapid enhancement. The storm deepened and grew in size, eventually reaching a diameter of several thousand miles; at one point, it stretched from western Idaho to the International Date Line, or about the size of the continental United States.

The moisture-enhanced deepening is what led to the very strong winds. The sheer size of the storm allowed it to reach well down into the tropics and tap abundant tropical moisture, which formed an “atmospheric river” – warm, moist air from the southwest, the kind of situation that brings our biggest winter flood events. And that’s exactly what occurred.

An animation showing enhanced infrared satellite images (courtesy Mauna Kea Weather Center) appears here. In analyzing the images we were impressed with the sheer size of the storm, which was approximately the size of the continental U.S. — and, in fact, comparable to the diameter of the Moon! Here is a link to a series of pictures compiled and created by Steve Pierce, as well!

Wind Storm Reports (preliminary), from National Weather Service:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE PORTLAND OR
1245 PM PST MON DEC 3 2007

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

A VERY STRONG STORM OVER THE NORTHEAST PACIFIC CONTINUES TO HOLD A TIGHT PRESSURE GRADIENT ALONG THE PACIFIC NORTHWEST COAST. THIS IS RESULTING IN VERY STRONG WINDS. THE STORM PEAKED EARLY THIS MORNING ON THE COAST THOUGH STRONG WINDS WILL CONTINUE TODAY AND MAY SEE SOME PEAKS IN THE VALLEY THROUGH EARLY TUESDAY MORNING AS THE COLD FRONT PUSHES ONSHORE.

MUCH DAMAGE HAS BEEN REPORTED. COASTAL COMMUNITIES HAVE REPORTED MANY TREES THAT HAVE BEEN BLOWN DOWN...BLOCKING HIGHWAYS AND TAKING OUT POWER LINES. DAMAGE HAS ALSO BEEN REPORTED TO HOMES. MAJOR POWER OUTAGES ARE REPORTED ALONG THE COAST FROM LINCOLN COUNTY TO THE LONG BEACH PENINSULA. IN ADDITION TO THE WIND...HEAVY RAINS HAVE SATURATED MOST OF NORTHWEST OREGON RESULTING IN FLOODING AND LANDSLIDES. STAY
TUNED FOR FUTURE STATEMENTS REGARDING FLOODING AND DAMAGE REPORTS.

LISTED ARE SOME OF THE HIGHEST WINDS AS OF 12 PM MONDAY AFTERNOON...
                                   
LOCATION                                 PEAK WIND GUST
==================================================================  

...PACIFIC BUOYS...
BUOY 50 (OFF NEWPORT)...................  76 MPH  (SUST. 50 MPH)
                                          SEAS....  40 FEET      
   BUOY BROKE FROM MOORING AND IS NOW ADRIFT

BUOY 89 (50 MI W OF TILLAMOOK)..........  67 MPH  (SUST. 50 MPH)
                                          SEAS....  48 FEET

BUOY 29 (COLUMBIA RIVER BAR)............  67 MPH  (SUST. 45-50 MPH)
                                          SEAS....  44 FEET
   BUOY BROKE FROM MOORING AND IS NOW  ADRIFT

80 MI WEST OF WALDPORT SHIP REPORT........69 MPH  (SUST.)
                                          SEAS...39 FEET
90 MI WEST OF TILLAMOOK SHIP REPORT.......69 MPH  (SUST.)
                                          SEAS...33 FEET

...WASHINGTON COAST...
CAPE DISAPPOINTMENT....................  104 MPH
KLIPSAN (Long Beach....................  102 MPH
DESTRUCTION ISLAND.....................   93 MPH
TOKE POINT (NORTH END OF WILLAPA BAY)..   75 MPH
BAY CENTER.............................   72 MPH
OYSTERVILLE............................   67 MPH
OCEAN PARK.............................   67 MPH
LONG BEACH.............................   60 MPH

...NORTH OREGON COAST...
BAY CITY (NEAR TILLAMOOK)..............  129 MPH
CAPE MEARES (ELEV. 1500 FT)............  114 MPH BEFORE POWER LOSS
ROCKAWAY BEACH.........................  104 MPH
TILLAMOOK BAY TIDE GAGE................  100 MPH
ASTORIA (WEST SLOPE)...................   86 MPH (SUST. 45-50 MPH)
CLATSOP SPIT...........................   86 MPH (SUST.70 MPH) NOT
REPORTING ASTORIA AIRPORT..............   85 MPH (LOST
POWER 4 AM) GARIBALDI..................   81 MPH (LOST
POWER 5 PM SUN) YOUNGS BAY.............   80 MPH
CANNON BEACH...........................   80 MPH
TILLAMOOK (DOWNTOWN)...................   75 MPH
TILLAMOOK AIRPORT......................   74 MPH

...CENTRAL OREGON COAST...
LINCOLN CITY...........................  125 MPH
YAQUINA HWY 101 BRIDGE (NEWPORT) ......   88 MPH (SUST. 45-50 MPH)
LINCOLN CITY (OTHER REPORT)............   85 MPH
NEWPORT AIRPORT........................   83 MPH (SUST. 58 MPH)
NEWPORT JETTY..........................   82 MPH
SEA LION CAVES.........................   81 MPH (SUST. 40-45 MPH)
AGATE BEACH............................   78 MPH (LOST POWER)
HATFIELD SCIENCE CENTER................   75 MPH
ROSE LODGE (JUST NE OF LINCOLN CITY)...   64 MPH
SOUTH BEACH (NEAR NEWPORT).............   64 MPH
FLORENCE SIUSLAW JETTY.................   63 MPH
YACHATS................................   61 MPH

...WILLAPA HILLS...
ABERNATHY MTN..........................   62 MPH

...OREGON COAST RANGE...
MT. HEBO...............................   91 MPH
CEDAR RAWS.............................   74 MPH
ROCKHOUSE RAWS.........................   72 MPH
SOUTH FORK RAWS........................   48 MPH

...SOUTHWEST WASHINGTON INTERIOR...
KALAMA.................................   45 MPH
KELSO AIRPORT..........................   43 MPH
LONGVIEW TIDE GAGE.....................   41 MPH
INTERSTATE 5 BRIDGE IN VANCOUVER.......   36 MPH
FREMONT BRIDGE.........................   36 MPH
CHEHALIS AIRPORT.......................   35 MPH

...WILLAMETTE VALLEY...
HILLSBORO AIRPORT......................   51 MPH
HARRISBURG.............................   50 MPH
MCMINNVILLE AIRPORT....................   48 MPH
SALEM AIRPORT..........................   46 MPH
ALOHA..................................   44 MPH
AURORA AIRPORT.........................   40 MPH
EUGENE AIRPORT.........................   38 MPH
BEAVERTON..............................   36 MPH
PORTLAND AIRPORT.......................   33 MPH

...CASCADE FOOTHILLS...
SUGARLOAF MTN (SW OF OAKRIDGE).........   81 MPH (SUST. 35-40 MPH)
CANYON CREEK (WASHINGTON)..............   67 MPH
WANDERERS PEAK.........................   67 MPH
BRUSH CREEK RAWS.......................   65 MPH (SUST. 30 MPH)
FIELDS (NEAR OAKRIDGE).................   55 MPH
HORSE CREEK RAWS.......................   51 MPH
YELLOWSTONE MTN........................   43 MPH

...CASCADES...
TIMBERLINE (ELEV. 7001 FT).............   99 MPH (SUST. 60 MPH)
GOVT CAMP SKI BOWL.....................   90 MPH
MT HOOD MEADOWS........................   66 MPH
BLUE RIDGE RAWS........................   51 MPH
MT ST HELENS (COLDWATER RIDGE).........   46 MPH

ROCKEY/SCHNEIDER/WOLFE

According to the weather service, the powerful weekend storm caused water levels at several rivers to exceed the levels reached during the major flood of 1996.

Floods follow storms in Tillamook County
Posted by The Oregonian December 03, 2007 10:16AM

TILLAMOOK — About 90 people have been evacuated from their homes in Tillamook County as flooding follows two days of high winds and heavy rains.

The Wilson, Trask and Nehalem rivers are expected to crest in the next few hours. All three are expected to rise above flood stage.

Storm damage has knocked out two-thirds of the power supply to the county, leaving only the city of Tillamook with electricity. Two transformers were damaged in the violent overnight storm; a transformer that supplies power to the city remains in use.

About 11,000 people are without power in the county.

At least 75 trees that caused significant damage or are blocking roads are reported down in the county.

— Kimberly Wilson; kimberlywilson@news.oregonian.com

 

Rainfall Totals (preliminary), from National Weather Service:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE PORTLAND OR
1200 PM TUE DEC 4 2007

...STORM TOTAL RAINFALL AMOUNTS DEC 1 THRU DEC 3...

FOLLOWING ARE RAINFALL TOTALS FROM VARIOUS STATIONS IN SOUTHWEST
WASHINGTON AND NORTHWEST OREGON COVERING THE TIME PERIOD FROM 6 AM SAT THROUGH MIDNIGHT MONDAY. 

SOME LOCATIONS ARE INCOMPLETE DUE TO POWER OUTAGE OR EQUIPMENT FAILURE.

LOCATION/STATION           STORM TOTAL     REMARKS
==================================================
SOUTH WASHINGTON/NORTH OREGON COAST         
  ASTORIA............      3.94 INCHES     THROUGH 4 AM MONDAY
  TILLAMOOK RAWS.....      3.76 INCHESCENTRAL OREGON COAST
  LINCOLN CITY.......      3.50 INCHES     THROUGH 6 AM MONDAY
  DUNES..............      3.10 INCHESNORTH OREGON COAST RANGE AND WILLIPA HILLS
  SOUTH FORK RAWS...      12.71 INCHES
  CEDAR MTN RAWS....      12.19 INCHES
  MILLER RAWS.......       8.65 INCHES
  LEES CAMP.........      14.50 INCHES
  VERNONIA..........      11.00 INCHES
  ABERNATHY MTN.....       1.84 INCHES
  RYE MOUNTAIN......       9.51 INCHESCENTRAL OREGON COAST RANGE
  GOODWIN PEAK RAWS.       5.59 INCHES
  ROCKHOUSE MTN.....       9.12 INCHES
  VILLAGE CREEK.....       7.60 INCHES
  HIGH POINT........       4.91 INCHESSOUTHWEST WASHINGTON INTERIOR LOWLANDS
  KELSO..............      5.16 INCHESCOLUMBIA GORGE/HOOD RIVER VALLEY
  BONNEVILLE.........      5.50 INCHES
  MIDDLE MTN.........      5.17 INCHES
  PARKDALE...........      3.57 INCHES
  HOOD RIVER.........      4.50 INCHES
  
NORTH WILLAMETTE VALLEY/CLARK COUNTY
  GRESHAM............      3.70 INCHES
  FOREST GROVE.......      6.37 INCHES
  VANCOUVER..........      3.73 INCHES
  TROUTDALE..........      3.38 INCHES
  PORTLAND AIRPORT...      3.35 INCHES
  SCAPPOOSE..........      5.97 INCHES
  HILLSBORO..........      4.48 INCHES
  GASTON.............      7.65 INCHES
  
CENTRAL WILLAMETTE VALLEY
  SALEM..............      2.44 INCHES
  AURORA.............      2.36 INCHES
  JEFFERSON..........      4.58 INCHES
  MCMINNVILLE........      3.50 INCHES
  STAYTON............      1.40 INCHES
  FALL CITY..........     10.70 INCHESSOUTH WILLAMETTE VALLEY
  EUGENE (AIRPORT)...      2.19 INCHES
  CORVALLIS..........      1.51 INCHESSOUTH WASHINGTON CASCADES/FOOTHILLS
  CANYON CREEK.......      5.76 INCHES
  COLDWATER RIDGE VISITOR  6.42 INCHES
  TROUT CREEK........      1.43 INCHESNORTH OREGON CASCADES/FOOTHILLS
  DETROIT LAKE (AG STN)    6.39 INCHES
  DEE FLAT...........      4.96 INCHES
  EAGLE CREEK RAWS...      3.17 INCHES
  HORSE CREEK RAWS...      8.37 INCHES
  LOG CREEK RAWS.....     11.23 INCHES
  SCOTTS MILLS.......      5.40 INCHES
 
CENTRAL OREGON CASCADES/FOOTHILLS
  UPPER SODA WEATHER.      3.73 INCHES  PEBBLE RAWS........      3.34 INCHES

Flood Reports (preliminary), from National Weather Service:

PUBLIC INFORMATION STATEMENT...UPDATE
NATIONAL WEATHER SERVICE PORTLAND OR
330 PM PST MON DEC 10 2007

UPDATE TO ADD FINAL CREST FOR TUALATIN AT FARMINGTON

...FINAL SUMMARY OF FLOOD CRESTS FOR DECEMBER 2-4 FLOODING...

A POWERFUL STORM SYSTEM OVER THE NORTH PACIFIC BROUGHT MUCH WARMER AIR AND HEAVY RAIN INTO THE REGION THIS WEEKEND.

SEVERAL RIVERS ALONG THE SOUTH WASHINGTON AND NORTH OREGON COAST
REACHED LEVELS HIGHER THAN THOSE OF THE FEBRUARY 1996 FLOODS. THESE
RIVERS ARE THE WILSON NEAR TILLAMOOK (18.4 FT IN 1996)...THE TUALATIN AT DILLEY (19.0 FT IN 1996)...AND WILLAPA NEAR WILLAPA (23.2 IN 1996).

NOTE THAT THIS IS PRELIMINARY STREAMFLOW DATA SUBJECT TO REVISION.
RIVER CRESTS FOR SELECT RIVERS IN SOUTHWEST WASHINGTON AND NORTHWEST OREGON FOLLOW... 

-----------------------------------------------------------------
NOTES:  CFS IS CUBIC FEET PER SECOND
        ** DENOTES RIVER REACHED MAJOR FLOOD LEVELS
-----------------------------------------------------------------

RIVER/                FLOOD     RIVER     PEAK      DATE/TIME  
GAUGE NAME            STAGE     CREST   FLOW (CFS)   OF CREST
=================================================================

...COASTAL RIVERS...
WILLAPA NR WILLAPA   21.0 FT    26.6 FT   15,000    5 PM DEC 3 **
NASELLE NR NASELLE   15.5 FT    14.7 FT    7,200    8 AM DEC 3
GRAYS NR ROSBURG     12.0 FT    16.5 FT   20,100    1 PM DEC 3 **
NEHALEM NR FOSS      14.0 FT    24.4 FT   52,200   12 PM DEC 3 **
WILSON NR TILLAMOOK  12.0 FT    20.5 FT   33,300   11 AM DEC 3 **
TRASK NR TILLAMOOK   16.5 FT    20.8 FT   20,400   10 AM DEC 3
SILETZ AT SILETZ     16.0 FT    19.0 FT   25,800    2 PM DEC 3
ALSEA NR TIDEWATER   18.0 FT    21.8 FT   27,500   10 PM DEC 3
SIUSLAW NR MAPLETON  18.0 FT    21.5 FT   30,200    9 PM DEC 3

...SOUTHWEST WASHINGTON INTERIOR...
COWLITZ AT CASTLE RK 48.0 FT    47.4 FT   64,600    6 PM DEC 3
COWLITZ AT KELSO     21.7 FT    22.8 FT    N/A      1 AM DEC 4

...WILLAMETTE VALLEY...
JOHNSON CK IN PORTLAND 11.0 FT  11.9 FT    1,300   10 AM DEC 3
CLACKAMAS NR ESTACADA  20.0 FT  20.3 FT   24,200   11 PM DEC 3
TUALATIN AT DILLEY     17.5 FT  19.0 FT    9,700    9 PM DEC 3
TUALATIN NR FARMINGTON 32.0 FT  32.6 FT   11,100    7 PM DEC 5
MARYS NR PHILOMATH   20.0 FT    21.0 FT   13,000    9 PM DEC 3 **
LUCKIAMUTE AT SUVER  27.0 FT    29.0 FT   11,000    4 PM DEC 3
S YAMHILL AT MCMINN. 50.0 FT    55.9 FT   31,000    4 PM DEC 4

===================================================================

December starts off with a bang, as the National Weather Service in Portland issued its first-ever hurricane force wind warning today for coastal waters from Cape Shoalwater, Wash., south to Florence.

COASTAL WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR OUT 20 NM-WATERS FROM CAPE SHOALWATER WA TO CASCADE HEAD OR FROM 20 TO 60 NM-248 PM PST SAT DEC 1 2007 ...GALE WARNING NOW IN EFFECT THROUGH LATE TONIGHT... ...STORM WARNING NOW IN EFFECT FROM LATE TONIGHT THROUGH SUNDAY EVENING... ...HURRICANE FORCE WIND WARNING IN EFFECT FROM SUNDAY EVENING THROUGH MONDAY MORNING...

 

Bill Schneider, science and operations, NWS explains:

 The directive that gave offices the authority to issue a "Hurricane Force Wind Warning" in the marine forecast was issued May 21, 2002. In the five years since then, none has been issued along the West Coast of the lower 48 United States. The purpose here is to highlight the extreme nature of rare storms that may only occur once every 5 to 10 years.

These storms are "extra tropical cyclones", meaning they don't have the structure of a hurricane, and should not be confused with an actual hurricane (we won't give them names or anything like that). Storms like this approaching the West Coast are normally much larger in areal extent than a typical hurricane and have much broader impact zone where damaging winds can occur.

The current threat appears to be mostly to the water and the immediate coastline. We noticed Thursday that moisture from three separate tropical cyclones will likely be drawn into this one large storm over the next several days. This is storm has the potential to damage ships or cargo and will be difficult to avoid due to the huge area it will cover.

The damage exceeded anything I've seen from a significant windstorm, especially among the northern communities. But even in the southern part of my tour, the damage stood out: At least 48 trees fell across Hwy 20, most of those in the last 15 miles. That started things off. Once at Newport, toppled trees became a common sight, and the further north I traveled, the worse the destruction became. Just when I thought things couldn't get any worse, I'd roll into a region with even heavier damage. After many miles, I ceased to be surprised. Damaged structures, not just toppled trees, eventually became commonplace. Based on what I could glean during my travels through fog and periodic rain showers, the storm's impact breaks into four fuzzy sections:

1) The southern stretch through Depoe Bay and into Lincoln City. Characterized by numerous treefalls, both due to root-failure and stem-breaks. Many tree-downed powerlines, including some large transmission lines. The breakage of some highway signs, typically those with 4' x 4' posts.

2) Lincoln City north to about Cloverdale. Characterized by local swathing of coastal forest with many trees across the road in places, some quite large. Downed large branches as numerous as twigs in a more normal storm. Light damage to house roofs, usually shingle loss. Some window breakage. Plastic store signs punched out. Some wooden fences downed. Obvious loss of electrical service.

3) Cloverdale north to about Tillamook. Characterized by: Trees as in 2). Many outbuildings and some houses with sheet-metal roofs and walls peeled off. Structures thrown out-of-kilter. Fences down. Structural debris strewn across farm fields. Frequency of broken highway signs is high enough that the sight of such damage seems as commonplace as snapped boles.

4) Tillmook north to Rockaway, and especially Bay City. Characterized by: As in 3). Broken windows more numerous, both on store fronts and houses, and usually boarded up by the time I arrived. Large percentage of houses had at least some shingle loss, with some down to the bare boards. Siding peeled off of homes and businesses. Fences of all types frequently laid flat. Many signs, especially Stop signs, broken. Especially around Bay City: Some structures, such as a wood-frame garage, and a large metal-framed public storage building, blown apart. Some houses lightly damaged, especially eave elements. Church steeple broken off and crashed in street. Masonry chimneys broken. Tree damage in nearby forestland incredible, with perhaps 20% to 40% trees lost or damaged.

After seeing the extent of damage, I have to agree that the hurricane-force wind warning was justified. Though, technically speaking, the warning didn't verify in many areas, save for a few exposed headlands.

"Historic" is a good descriptor of the coastal gale of December 1-3, 2007, especially for the counties of Lincoln, Tillamook and Columbia. At two key official weather stations, one located at the Newport Municipal Airport and the other at the Astoria Regional Airport, wind gusts were the strongest in 45 years. A gust to 83 mph occurred at the Newport station, and a burst to 85 mph at Astoria. While these values fall short of the Columbus Day Storm's 138 mph and 96 mph (respectively), it is good to keep in mind that the terrible tempest in 1962 was truly an overachiever in raw wind velocity. A look at the accompanying table of Astoria peak gusts reveals that most big windstorms produce maximums of 65 to 80 mph at Astoria. Anything above 80 mph is quite unusual. Roughly speaking, speeds of 85 mph and above appear to belong to the 50-year storm.

Peak gusts at some unofficial weather stations during the December 1-3, 2007 gale resemble accounts of the Columbus Day Storm. Speeds of 125 mph were clocked on a well-exposed anemometer located at 70-feet above ground level in southern Lincoln City. With a sensor located at the Bay City Fire Station, a blast to 111 mph was observed at 1:10 AM on December 3rd, closely followed by a gust to 114. Then, at 1:30 AM, a 129 mph surge was observed. Nearby, a church steeple toppled, crashed through a powerpole and then demolished itself on the street below. A wood-frame garage lifted from its foundation and flew to pieces, and a modern metal-framed storage building had its roof peeled off and walls disrupted. Two houses had wooden portions of their roofs yanked off, while many lost a flurry of shingles. Some windows shattered, siding peeled off and stop signs with metal poles were bent strongly toward the north. Trees at all points from the fire station toppled, some tearing through powerlines and blocking roads. Clearly winds reached extreme levels at Bay City. This kind of damage appeared in many areas of the coast, with the heaviest destruction occurring from about Lincoln City northward.

Sometimes big Northwest windstorms are responsible for a phenomenon known as windthrow, or blowdown. Windthrow describes a group of trees that have been toppled by a storm's winds. A large area of blowdown occurred along the west end of Highway 26 during the 2007 coastal gale. From the roadside, snapped trees are visible all the way to the most distant hillsides. The swath of broken timber reached the road in places, and many boles blocked the Sunset Highway. Sometimes the trees were piled on top of each other. The scene, reminiscent of the forests flattened by the Mt. St. Helens eruption of May 18, 1980, has been termed the "Blast Zone" by some witnesses. The accompanying photo shows a section of this Highway 26 blowdown. Dr. Steve Mitchell, of the University of British Columbia Faculty of Forestry, estimates that the minimum sustained wind speed required to do the damage visible in the photo, provided that recent clearcutting opend this stand to direct broadside attack (a harvest operation was underway at the site), is around 40 mph, which implies gusts of 55 to 60. Given the extreme gale measured on the coast, only a few miles away, maximum winds could easily have been above this minimum threshold. These trees didn't have a chance.

The peak gust map shows the narrow focus of the December 1-3, 2007 windstorm.The Pacific shoreline of Oregon and Washington bore thebrunt of the winds, and a heavy gale tore through the Coast Range northward, producing an extreme gust of 147 mph on Naselle Ridge, a place subject to local wind enhancement where gusts of 160 mph occurred during the Columbus Day Storm. Eastward, beyond the rainforest-draped coastal hills, the ferocity of the December 2007 gale quickly waned. Wind gusts in the Willamette Valley ranged from 35 mph at Troutdale to 54 mph at Salem: A forceful storm, but nothing like the more memorable Valley windstorms.

Peak gust is one of a number of important ways to measure wind. The Columbus Day Storm may outclass all windstorms in terms of maximum wind speed; however, the great December 1-3, 2007 gale is perhaps the longest-lasting high-wind event on record. The Columbus Day Storm sprinted through the Northwest, typically delivering its lively gale over a period of about two to three hours at most locations. The great coastal gale of 2007 proved to be a marathon runner. Allowing for a few brief lulls, high-wind criteria gusts of 58 mph (50-knots) and higher lasted nearly two days!

The accompanying table lists the duration of four categories of wind speed as measured at the Yaquina Bridge in Newport. The duration counts the hours between the first and last gust in each category. As indicated by the complete Yaquina Bridge record depicted in the graph, wind speed is highly variable, and the actual time the wind spent in specific categories of speed was considerably less. Nevertheless, with such an unrelenting series of pounding gusts, maybe the windstorm should be called the Marathon Gale of 2007.

The persistence of high winds is perhaps the most significant aspect of the December 1-3, 2007 windstorm. Duration can contribute significantly to a windstorm's damage. By the constant loading of structures, nails and other holds can gradually pull loose. Trees under heavy wind stress may build up an accumulation of microfractures in the trunk, or undergo a series of small root breaks, that could lead to catastrophic failure given enough time. Though it's tempting to think of windthrow like that in the Highway 26 "blast zone" as happening all in a matter of minutes, such swathing of forests usually takes time. A given opening in a stand gradually widens as each surge of wind topples trees freshly exposed by the loss of their neighbors. The duration of the coastal gale likely explains the extent of the blast-zone windthrow more than the maximum wind speeds.

December 1-3, 2007: The Meteorological Setup

The great coastal gale resulted from a complex arrangement of Pacific storm systems. Indeed, two storms generated the gale. Some people might even suggest three. The accompanying storm track map outlines some details.

The map outlines the tracks of the three key dramatis personae involved with the great coastal gale of 2007: Two cyclones, or low pressure areas, and an open wave. A wave is essentially a cyclone trying to develop, and they commonly show up along the long frontal systems associated with big Pacific lows. To better illustrate the three components in the gargantuan windstorm, here's a satellite photo taken at 07:00 AM on December 2nd, Image 1. This image is enhanced to show the amount of water vapor in the atmosphere. The aquamarine colors indicate lots of available moisture, whereas the grays and oranges depict dry zones. Cyclones and waves often show up as a sharp "dry slot" next to an region with plenty of moisture, often in a classic comman, or spiral shape. The three key players are pointed out in the photo. At the time the satellite image was taken, the first low has crossed 130ºW as it follows a northeastward track. The second, much stronger low, is still outside of 150ºW, and the wave along the cyclone's associated cold front is visible as a curl to the northeast of the big low's center.

On December 2nd, the first actor,urged along by a very fast jet stream, raced into the Olympic Peninsula at about 50 mph. This storm brought the initial surge of high winds, and, for places south of about Lincoln City, generated the highest wind gusts of the entire event. Included is a satellite photo that catches the first cyclone at 10:00 AM on the 2nd day of the month, Image 2. This storm quickly fell apart as it moved into the rough terrain of Washington and Canada, and winds briefly diminished on the coast. As the next system raced toward the Northwest, winds didn't relax for very long.

The second actor, the developing wave, also appears in the lower left corner of Image 2. The center of the wave, also moving about 50 mph, will end up over Vancouver Island in about 24 hours from the time of the above satellite image. The frontal system leading from the center of the wave has a deep tropical link. This "pineapple connection" is strongly visible on the next satellite photo, which was taken at 10:00 AM on December 3rd, Image 3.

The third satellite photo also depicts the wave moving into southwest British Columbia.The front reaches all the way from Canada to the Hawaiian Islands, which are just visible in the lower left corner of the image. This strong front dumped copious rain in the Northwest, especially in the coastal ranges and in parts of the Cascades. Major floods occurred on some rivers. Behind the wave, the third actor had now moved east of 140ºW and showed many signs of maturity, including a tightly wound spiral at the center. As the big low, with its leading open wave and associated frontal system, approached the coast, wind speeds escalated for a second time, especially during the night of December 2nd, and early morning hours of December 3rd. Low number two may have been degrading, but the system still hadn't lost all its punch. As the cyclone moved into British Columbia, winds on the Oregon and Washington coasts would continue to howl at gale force into the early morning hours of December 4th. And, as the strong pineapple front crossed the Pacific coastline in the early afternoon of the 3rd, winds surged with renewed energy, a third and final heavy blow to a region already thrown into chaos by record wind gusts and rainfall totals.

The Yaquina Bridge wind record shows how the three big Pacific actors played out on-the-ground. The notes on the graph detail the sequence of events. The three actors worked in close sequence to deliver the persistent and punishing gale to the coast. One key element not visible in the satellite photos also contributed to the historic storm: A very strong jet stream. At the middle levels of the atmosphere, at the 850 mb height (approximately 5,000 feet), average wind speeds over the coastal waters and western Oregon and Washington reached at least 100 knots as the series of weather systems moved through. When the mid-level airflow is 65 to 80 knots, it's considered very strong. One-hundred knots is off the charts. A very rare event. This extreme mid-level airflow was out of the south-southwest to southwest, and likely contributed to the wind speeds that occurred at the surface. When weather systems like the first low on December 2nd and the following tropically-tapped front on December 3rd moved through the region, they brought with them enhanced vertical instability (by convective processes). Such vertical mixing likely brought some of the mid-level momentum down to the surface and enhanced coastal winds.

Going back through the records, it's difficult to find a storm that behaved in a similar fashion to the great coastal gale. For the period of modern weather record, which begins around 1948, there apparently hasn't been a similar event of the magnitude witnessed on December 1-3, 2007. A series of three storms during January 5-9, 1990 share some of the characteristics of the 2007 storm, including a protracted wind event from January 8th to 9th, but the winds were not as strong on the coast, with gusts to 64 mph at Astoria. Interestingly, the 2nd storm in that series, on January 7th to 8th, produced strong wind gusts of 63 mph at Portland. George Taylor has described the December 1-3, 2007 storm as a kind of "hybrid", a sort of mix between the powerful cyclone of December 12, 1995 and the major flood-producing storm in November 1996. Indeed, much larger second cyclone in the December 2007 series had a minimum central pressure of 952 mb (28.11"), very similar to the December 1995 storm's 953 mb (28.14"). Combine a storm of such depth with the long, tropically-tapped frontal system that brought a downpour to the Pacific Northwest, and the recent December storms do have the combined flavor of the two mid-1990s events.

Moisture from the remains of two typhoons, Hagibis and Mitag, were entrained in the monster-sized second low of the series. This moisture brought in abundant latent heat energy which contributed to the storm's great depth an intensity. With that tropical connection, and the very fast mid-level (850 mb) airflow sweeping the moisture-filled air into the coastal mountains, a significant rainstorm arrived with the powerful, hurricane-force winds. In this way, the typhoons that fed the new storm were echoed along the temperate shores of the Oregon and Washington.