Preliminary 2005
Seasonal Fire Weather / Fire Danger Outlook
for the Northwest Geographic Area
<Pot
Peak Column image>
The 2004 Pot Peak Fire encounters heavy fuels and pushes a smoke column to
30,000 ft.
OkanoganWenatchee NF, Washington
Issued April 1, 2005
Paul Werth
Mike Fitzpatrick
Predictive Services
Northwest Interagency Coordination Center
Portland, Oregon
Executive Summary
The following report is a preliminary 2005 fire season severity assessment based
upon seasonal precipitation patterns, drought, current snowpack data and
long-range weather forecasts for the remainder of the spring and summer. The
assessment will be updated in late May and a final version will be issued in
late June when additional weather, fuel moisture and fire danger information
becomes available.
Many weather factors can affect fire season severity in the Northwest Geographic
Area. Known factors include winter precipitation, mountain snowpack, drought,
snowmelt date, June rainfall, live and dead fuel moisture, and the amount of
summer dry lightning. Because the preliminary assessment only considers a few of
these factors (snowpack and drought), confidence in the analysis is moderate. If
April through June are much wetter than usual (best case scenario), the threat
of an above-average fire season will diminish significantly.
Winter 2004 - 2005 experienced a return of El Nino conditions in the tropical
Pacific Ocean. This El Nino event was classified as weak, with sea surface
temperature anomalies (SSTs) of around + 1°C. The last time an El Nino of this
magnitude occurred was in 1994.
This year’s winter weather pattern was typical of weak El Nino conditions. The
jet stream split well off the west coast, directing storms toward California and
northern British Columbia. High pressure aloft persisted over the Pacific
Northwest and western Canada throughout the winter. Except for southern Oregon
(which received heavy December snowfall) snowpacks throughout Washington and
most of Oregon started late and at a slower-than-usual pace. Dry, mild weather
in January and February plunged the snowpack percentages to near or record low
values by March 1, challenging the previous low drought years of 1977 and 2001.
The Oregon March 1 snowpack was 46% of normal and ranged from 79% in Lake County
(south central Oregon) to only 21% of average on the Lower Columbia drainage
(includes the Mt. Hood area). Washington’s snowpack was even worse than
Oregon’s. Statewide it was only 30% of normal and ranged from 44% of average in
the Spokane River Basin to a dismal 17% on the Cedar / Snoqualmie Basin. Most
Washington river basins were in the 20-30% range. Preliminary April 1 snowpack
snow water equivalent (SWE) indicated that Oregon snowpack remained at 44% while
Washington’s increased slightly to 36% of average. Every snowpack reporting
station in Washington reported record low values.
Long-range weather forecasts are based on indications that El Niño will either
remain at the same strength or weaken slightly during the next few months. The
outlook for April through June slightly favors warmer-than-normal conditions
throughout the geographic area and equal chances of above, normal, or
below-normal rainfall. Statistics indicate that spring has to be much wetter
than normal to significantly lower the threat of large summer wildfires.
The outlook for July through September favors a normal warm, dry summer across
the Pacific Northwest. Although lightning outlooks for the summer are not
available, the Northwest historically receives two or three episodes of problem
lightning every summer, with the first event around the middle of July.
Three possible scenarios for the 2005 fire season were developed based upon
current conditions and combinations of spring and summer weather.
Best Case Scenario – A major change in the weather pattern occurs, resulting in
wet, cool weather throughout April, May and June. High pressure that has been
over the Pacific Northwest during the winter gives way to a series of spring
storms as the jet stream consolidates over the area. To mitigate the effects of
drought and a historic low snowpack, rainfall would have to exceed 150% of
normal over the next three months to significantly diminish the threat of an
above-average fire season. A wet, warm spring could actually increase the threat
of large rangeland fires due to increased grass growth. Cool, wet weather would
also delay snowmelt at the mid and higher elevation into May and June. This
delay would prevent dead and live fuel moistures from dropping below critical
values until mid or late July. The threat of large, higher-elevation timber
fires would only extend from late July through early September. The best chance
for large fires would occur in the low and mid-elevation timberlands from the
west slope of the Cascades into eastern Washington and eastern Oregon. If summer
thunderstorms produce wet rather than dry lightning, the risk of large fires
could drop into the average or below-average categories. This scenario has a low
probability of occurrence given current conditions and long-range weather
forecasts. Climatology (1970-2004 rainfall data) indicates there is less than a
15% chance that April through June would be wet enough to significantly diminish
the threat of a severe fire season.
<PNW Snowpack image>
Worst Case Scenario – High pressure continues to dominate Washington and Oregon
through early June, with unseasonably warm and dry weather. Storms are either
deflected north into Canada, or are too weak to produce much rain over the area.
Hot, dry weather develops after mid-June and continues into mid-September as
high pressure becomes even stronger over the Pacific Northwest. Summer
thunderstorms would have limited moisture and three or four episodes of dry
lightning could be expected. Mountain snowpack in this scenario would melt
rapidly, with little or no snow remaining by mid-May, even at the higher
elevations. Snowmelt would occur four to six weeks earlier than usual. Large
dead fuels (1,000 hr) would be unusually low, reaching critical values by late
June. The threat of large fires would extend from late June through September,
and likely into October west of the Cascades. Drought conditions would continue
to worsen with severe to extreme drought in areas both east and west of the
Cascades. Large timber fires would be likely, even at higher elevations.
Washington and Oregon would likely have a severe fire season, similar to 1994
and 2001. Resource demands would be heavy. This scenario has a low to moderate
probability of occurrence. Climatology (1970-2004 rainfall data) indicates that
after a dry winter, there is a 67% chance that the spring will be dry, but only
a 30% chance that the summer will also be dry. However, during severe drought,
above-average fire seasons in timber can even occur during wetter-than-usual
summers.
<PNW Fire
Potential image>
Most Likely Scenario – Near-normal temperatures and rainfall will occur from
April through June. July and August will be typically hot and dry. The record
low mountain snowpack would melt a month earlier than usual. The only snow
remaining in May would be in the higher elevations. Large dead (1,000 hr) fuels
would be unusually low, reaching critical values in late June or early July.
Spring moisture would result in increased rangeland grass growth. Severe drought
conditions would extend across most of Oregon and Washington. Large timber fires
would be possible, even at higher elevations. One to three episodes of dry
lightning would be possible, with the first episode around July 18. Washington
and Oregon would experience a very active fire season, both east and west of the
Cascades. This scenario has a moderate to high probability of occurrence.
The table below lists the projected 2005 acres burned by agency and the
probability of an above-average fire season based upon winter precipitation,
Palmer drought indices and April 1 snowpack water equivalent (SWE).
2005 Probability of Projected Threshold Acres Burned
Agency Fire an Above Average 2005 for an Above Average
Season Fire Season* Acres Burned Fire Season*
USFS Above Avg 70% 120,000 acres 80,000 acres
BLM Above Avg 50% 123,000 acres 90,000 acres
BIA Above Avg 70% 33,000 acres 20,000 acres
ODF Above Avg 75% 27,000 acres 11,000 acres
WADNR Above Avg 55% 24,000 acres 10,500 acres
* Threshold for upper third of fire season acres burned 1970 - 2004
Summary and Management Implications:
The Pacific Northwest is primed for an above-average fire season due to a dry
winter and record low or near record low snowpack. Long-range weather forecasts
favor warmer temperatures and near to below normal precipitation through spring
and summer. To counteract the low snowpack and long-term drought, April through
June would have to be exceptionally wet (best case scenario) to significantly
diminish the threat of large fires. Moderate amounts of spring rain are
essential for large range fires; however, if the spring is dry, fire problems
would be concentrated in timber. Listed below are the fire management
implications for the most likely scenario in an above-average 2005 fire season: