The California Winter of 1997-98
Kelly Redmond
Regional Climatologist
Western Regional Climate Center
Reno NV
Status Report for
Federal Emergency Management Agency
March 3, 1998
(Figures and captions are at the end)
The winter of 1997-98 has become the latest in a succession of
memorable winters for the state of California extending over the past
15 years. This period began with the snowiest and wettest winter on
record in 1982-83 for much of the state. After the February 1986
flood, the state entered an extended period of six consecutive dry
winters from 1986-87 through 1991-92, ending with the very wet
1992-93, one more dry winter in 1993-94, and then four consecutive wet
winters from 1994-95 through 1997-98. The previous winter of 1996-97
featured one of California's largest and costliest floods ever, in
early January, followed by a record dry period into summer. A
four-year stretch of wet winters has not occurred for a half-century
or more. Overall, this has been a period of highly variable climate
for the state of California.
In March of 1997 another El Nino developed (by most counts, the 9th El
Nino year since 1976, an item of great interest globally), then grew
rapidly. From late summer through approximately January 1998 this
event exceeded (by most criteria) the previous record El Nino of
1982-83. After January 1998, the 1982-83 El Nino, which peaked later
in the winter, was the "stronger" of the two. Historical studies show
that El Nino usually (not always) brings wetter winters to central and
especially southern California. Large El Ninos (a very limited
sample) appear to extend wet conditions further north. A second
forecasting tool, namely the recently improved physically based
numerical simulations of seasonal climate, being put to their first
important test, indicated a similar outcome. Much of what the winter
could bring was understood, and widely publicized, by early autumn,
well before the rainy season, when there was little to do but talk,
and wait. This situation, of predicted potential major impacts of a
natural event months in advance of their actual occurrence, and an
almost palpable region-side sense of apprehension and expectation, is
unprecedented in the history of the United States.
The 1997 portion of the winter was relatively uneventful, although
November was somewhat wetter than usual in the northern Sierra. One
very powerful and significant storm affected southern California
around December 6th, bringing 8-11" in one day to the mountains north
of Los Angeles. This storm later affected desert regions to the east.
As occurs more often during El Nino conditions, storms tended to split
and direct their energy and effects southward and northward along the
coast. The Sierra snowpack accumulated more slowly than average in
December, then sped up and only reached to near average by the end of
January. Along the coast, precipitation accumulated steadily, and the
northern California 8-station index (representing the upper Sacramento
River, an important water supply region) totaled 18.7" during January,
209% of its 30-year average. Farther north, Honeydew reported 35.5".
An extremely strong jet stream, characteristic of El Nino years,
formed early in the winter, blowing across the Pacific to the north of
Hawaii (which became very dry, an expected El Nino result), then
dipped southward on a southerly track across central Mexico, southern
Texas and Florida. Another extension split off and approached the
U.S. near the California/Oregon border, and brought a very wet month
to the northern half of the state. Then, in early February, the
Pacific jet stream strengthened to over 200 mph and moved very close
to California. Research aircraft near San Francisco measured some of
the highest speeds ever recorded in Earth's atmosphere, about 285 mph
near 40,000 feet.
On February 2nd and 3rd, just as doubt was beginning to surface in
southern California about the reality of El Nino's consequences, the
first of a month-long succession of dramatic and impressive storms
paid a visit, with high winds, intense rain, heavy mountain snows, and
high surf. Embedded in the fast flow, storms followed closely and
quickly on each other's heels, for most of the remainder of the month,
leaving little time for recovery. Almost no part of the state escaped
unaffected. Although storms cannot be individually ascribed to its
presence, El Nino certainly played a prominent role in setting the
stage as an "enabling factor" for the unfolding sequence of events.
Many locations from the San Francisco Bay area southward set February
and/or any-month precipitation records, including: UCLA (20.51",
wettest month ever), Bakersfield (5.36" wettest Feb), Mojave (6.70",
wettest Feb, 615 percent of average), Edwards Air Force Base (5.88",
wettest month, 42 years), UC Riverside (9.49", wettest month), Santa
Maria 11.59" (wettest month), Los Angeles Civic Center (13.79",
wettest Feb), Oxnard 17.80" (wettest month), Ventura Downtown (18.91",
wettest month, 132 years), Santa Barbara (21.74", wettest month, 132
years), Lompoc (12.86", wettest month), San Francisco (14.88", wettest
Feb, 148 years of records, 508 % of average, old record 12.52" in
1878), and Lake Lagunitas (second to 1891, record starts 1879).
Monthly totals reached 36.37" at Cazadero in Sonoma County, with
automated mountain gages north of Los Angeles reporting February
totals up to 43 inches (likely to be slightly underestimates). In
Santa Clara County, Ben Lomond recorded 19.7" in the first 8 days of
the month, and by February 20, many locations had already set monthly
records. Major episodes included the 3rd-6th, 8th-11th, 17th-19th,
and 23rd-24th.
North of about Hopland on the Russian River, the constant rains of
January and February were spread out well enough that no serious
flooding ensued. Eureka reported 13.95", (295%, its third wettest
February), with February totals in Crescent City of 19.85" (238%),
Orleans 15.26" (223%), and Hayfork 15.36" (312%). The Eight-Station
Index for February totaled 20.9" (284%), and the total from Oct 1
through Mar 2 stood at 57.2" (163% for the season-to-date, and 115% of
the long-term average for the entire year).
The rains were not only heavy but persistent. Eureka recorded 26 days
with measureable rain in January, and another 26 days in February.
San Francisco counted 24 in January and 22 in February. Blue Canyon
had 21 and then 25, with 12 and 10 days respectively exceeding one
inch. The lack of any significant letup in rains allowed almost no
days for drying. Each period of heavy rain sent more earth sliding to
lower elevations at a number of locations in the central and south
part of the state. Wet soils above and wave action below eroded
oceanfront property the length of the state, with many homes
endangered and some lost.
Heavy snows brought the snowpack from near (and even below) average in
late January to well above in late February, with snowpack as percent
of average for the date in the Tahoe / Carson / Walker area increasing
from 82-108% of average at month start to 140-152% at month end for
February. Overall on March 1 in the Sierra Nevada, snowpack stood at
185 percent of average (north) to 140 percent (central) to 165 percent
(south), for a statewide average of 165 percent. Alpine Meadows Ski
Area (Tahoe Basin) recorded its snowiest February with 186", just 2
inches shy of the snowiest month on record, and a seasonal
accumulation of 396" (annual average is 350"). By late in the month,
Mount Shasta Ski Area reported over 200" of snow on the ground.
The vigorous storms caused high winds throughout the month up and down
the state. On the 2nd gusts to 92 and 100 mph were measured at two
oil platforms near Santa Barbara, to 86 at Lompoc and 90 at Hearst
Castle, and to 81 in southern Oregon at Cape Blanco. Again on the
7th, winds reached 81 at Cape Blanco, to 62 near Ashland OR, 65 at The
Presidio, and to 125 mph at Mt Diablo at 11:20 am on the 7th. Gusts
reached 74 north of Weed and 83 at Cape Blanco on the 10th, to 79
there on the 18th, and to 98 numerous times, on the 20th. Sierra
winds were relatively quiet all month, reaching 100 mph only once all
month on the crest in the Tahoe area.
The combination of high winds, heavy surf, intense rains, eroding
beaches, sliding earth, washed out roads and bridges, swift current,
hail, lightning, and even tornadoes led to a great many
inconveniences, considerable property damage, many injuries, and a
number of deaths.
It should be emphasized that El Nino driven storms do not in general
have the "pineapple" connection to the tropics that characterized the
New Years Flood of 1997. Although such moisture taps to tropical
latitudes sometimes did develop to some degree, the jet stream in
February sped straight across the Pacific, seemingly directly from the
Nagano Olympics, blowing more than twice as strong as usual from the
central Pacific north of Hawaii toward central and southern
California. This promotes considerable mid-latitude evaporation over
the cool open ocean.
El Nino storms tend to be colder storms, with average or somewhat
lower than usual snow levels, and access to colder air from south of
the Aleutians. For this reason, the El Nino floods that occur in
California are generally at lower elevations and nearer the coast,
with intense rains in cool unstable air, rather than the large scale
warm, wet, tropically influenced rain-on-snow events with high
freezing levels that produce the largest floods on the largest
mountain-fed rivers. On the main Sierra rivers, none of the
historical top-ranked flood flows have occurred in El Nino
years.
Figure 1. Long-term average (climatology) of February speeds (colors) and directions (arrows) at 40,000 feet. (data, CDC)
Figure 2. February 1998 monthly average speeds (colors) and directions (arrows) at 40,000 feet. (data, CDC)
Figure 3. February 1998 monthly mean, expressed as departure from long-term average climatology, (positive values are faster than usual) at 40,000 feet. Speeds (colors) and directions (arrows). (data, CDC)
Prior Months. 40,000 foot Jet Stream.
Figure 4. November Climatology,1997,1997 Departure from Average
Figure 5. December Climatology,1997,1997 Departure from Average
Figure 6. January Climatology,1998,1998 Departure from Average
Figures 7a, 7b, 7c February 1-10 (climatology, 7a), (1998, 7b), (1998 departure, 7c)
Figures 8b, 8b, 8c February 11-20 (climatology, 8a), (1998, 8b), (1998 departure, 8c)
Figures 9a, 9b, 9c February 21-28 (climatology, 9a), (1998, 9b), (1998 departure, 9c)
Further contact information:
Dr. Kelly T. Redmond
Regional Climatologist/Deputy Director
Western Regional Climate Center
Desert Research Institute
PO Box 60220
Reno Nevada 89506-0220
702-677-3139 voice
702-677-3243 fax
krwrcc@dri.edu
http://www.wrcc.dri.edu