|NIFC 2011 California Preliminary #Wildfire Seasonal Assessment Map|
This preliminary outlook is a product of the National Seasonal Assessment Workshop held virtually during the week of April 18th, 2011. The inter-agency workshop brought together subject matter experts from climatology, fire weather meteorology, fuels, fire behavior, and fire danger. The outlook is based on past developments, current conditions, trends, and predictions for the months May through August.
Objectives of the Executive Summary are to:
• Provide a prognosis of 2011 wild-land fire potential in California, based on fuel conditions and available climate forecasts.
• Highlight concerns and key implications for management.
• Provide supporting documentation regarding weather and fuels information.
• Provide the framework for comprehensive final North Ops and South Ops outlooks to be completed in June.
This executive summary should aid California wildland fire managers in 2011 fire season preparedness, and add preliminary insight. More detailed fire season outlooks, for both North and South Ops, will be available in June. Those documents will give increased detail regarding all aspects of the coming fire season, and will have higher confidence levels. In addition to this outlook, the GACC Predictive Service Units at Riverside and Redding will continue to issue detailed monthly assessments of fire weather and fire danger.
|California Average Precipitation / Mountain Snowpack|
2011 FIRE SEASON OVERVIEW:
Fire season for the majority of Northern California is expected to begin in typical May to June time frames. However, elevations at or above 5,500-6,000 feet had an April 1st snowpack ranging from 125-170% of normal (see Figure 2). For that higher terrain, significant activity could be delayed until the start of August.
Factors pertinent to the 2011 Northern California fire season include:
• No existing drought areas remain in California
• The height and continuity of annual grass crops ranges from generally normal, to locally above normal.
• For high terrain, significant fire activity will likely begin two to four weeks later than average dates.
• Given expected fuels conditions, it is not likely that a lightning event will produce multiple large fires prior to July 1 at low-mid elevations, or prior to August 1 at high elevations.
Temperatures and precipitation are forecast to trend from near normal in May to a little warmer and drier than normal in August.
• Above 5,500-6,000 feet, significant fire activity will likely begin two to four weeks later than average dates.
• Given fuels and weather conditions, it is not likely that lightning events will produce multiple large fires prior to July 1 at low or mid elevations, or prior to August 1 high elevations.
• Temperatures and precipitation are forecast to trend from near normal in May to a little warmer and drier than normal in August.
• Drought stress, insects, and disease affect vegetation across the GACC to some degree.
• Annual grass crop ranges from normal to locally above normal.
• Below Normal risk for large fires over the central coast and the higher elevations of the Sierra Nevada Range.
• Normal large fire potential elsewhere over the region.
• Delayed start to fire season across lower elevations with an even later start in mountain areas above 6,000 feet.
• Slightly below normal temperatures near the coast and near normal temperatures expected over the interior portions of the state.
• Near normal precipitation expected.
• No clear signal with regards to summer monsoon activity over the district.
There will be a below normal large fire potential over many high elevation sections of the district where heavier fuels are present. Large timber (as defined by 1,000 hour fuels having trunk diameter of 7 inches or greater) currently possess a large amount of moisture from the heavy precipitation of the past winter. It appears unlikely that these heavy fuels will dry to the point of receptivity during the outlook period. However, large fire potential will increase in lighter fuel types by late summer when the hottest weather arrives and fuel moisture reaches a seasonal minimum. Many long-term models indicate the current La Niña condition over the Eastern Pacific will continue to decrease this spring, reaching a near neutral sea-surface anomaly by this summer. Other models indicate a La Niña may re-emerge later this year. Either way, the affect of sea surface temperatures appears to be a non-factor in determining the weather patterns late this summer and into fall. Therefore, outside the aforementioned areas in the higher elevation regions of the Sierras and portions of the central coast, expect a near average fire season this year.
|NIFC-California Drought Monitor Map|
In the South, precipitation in South Ops during the past winter was above average in most areas. The early winter and early spring rains have brought an above normal crop of seasonal grasses to the foothills and desert areas. The December rains resulted in an early emergence of herbaceous annual and perennial fuels. NDVI departure from average greenness data showed 135-150% average greenness for Central and Southern California. Live fuel moisture values in the lower elevations are running above average across the inland areas, but across the coastal regions, especially north of Point Conception, conditions are wetter than average. The latest snow pack surveys measured 165% of April 1 snow water equivalent in the Sierras. The expected weather conditions along with the antecedent fuel conditions suggest a normal fire season with the exception the Central Coast and the central Sierras which are expected to have a below average large fire potential. A big factor will be the weather in the next six-ten weeks. This could change overall live fuel moistures and grass curing rates across the South Ops area and may result in a later or more normal start to the fire season.
In the North, Northern California is emerging from several years of drought; vegetation remains drought-stressed. Winter conditions have resulted in windthrow, broken tops, and freeze-damaged vegetation adding to the fuel load, contributing to fire behavior potential and reducing fireline production rates. Green-up has already occurred at elevations to about 2,000 feet. Curing is beginning to occur in grasses at the lower elevations. There is abundant grass and brush at the lower elevations; at higher elevations (to about 6,000 feet) where snow melt has occurred herbaceous vegetation is also abundant. Spread of insects and diseases and non-native species, changing land use, fragmentation, and urbanization all affect fuels and contribute to fire potential in Northern California. Any drought-stressed or otherwise unhealthy vegetation will succumb to fire easier than healthy vegetation. Expect "normal" curing of herbaceous fuels. An abundant grass crop at the lower elevations will provide the opportunity for large fires starting about mid-May. There is good fuel continuity. Brush has substantial leader growth and is leafing out. Greenup and flowering are currently occurring, predominantly at the lower elevations. By August 1, energy release component (ERC) and 1000-hour fuel moisture should be approaching the 80th percentile at elevations below 6,000 feet. As snow melts, we are seeing areas that are inaccessible due to blow-outs and other damage to the transportation system - this will result in additional response times for ground-based resources.
California does not intend to issue a Fuels and Fire Behavior Advisory this year.
May through August Forecast:
South: The La Niña that has been occurring since last summer peaked in strength several months ago and is now expected to dissipate by early summer. The atmosphere however will be slow to respond to these large scale oceanic temperature changes, therefore the remainder of the spring into early summer will likely still be influenced by La Niña. This means temperatures should average a little below normal across the coastal areas through at least July with near normal temperatures expected over the interior portions of the state. Precipitation is forecast to average near normal over the area this summer. It is important though to keep in mind that summer time precipitation is acquired through convective activity associated with the Southwest Monsoon. This means most of the precipitation that occurs is usually spotty and mainly confined to the mountain and desert areas. At this time it is uncertain how far the Monsoon will migrate westward which will have a significant role in the amount of thunderstorm activity the area receives. Normally the area experiences at least three to four lightning episodes a summer with each episode lasting four or five days on average. Forecast Confidence = 80%
North: Review of October 2010 to April 2011: A La Nina pattern that developed in the summer of 2010 reached peak strength in January of 2011. It has been on a gradual decline since, though its effects on California weather have been more typical since mid February. October, December, and March were the wettest months compared to long-term averages, while January was the driest, due to mid-winter high pressure dominating for over a month. A large majority of Northern California currently has season-to-date precipitation ranging from 100-150% of normal (Figure 1). Due to this abundant rain and/or mountain snowfall, drought has ended in California. Mean temperatures were mostly within + 2 degrees F of normal for most of the Area (Figure 3).
Weather/Climate Forecast for May through August of 2011:
May - Northern California is expected to see temperatures within 2 degrees of normal and near-normal precipitation. Snowpack will continue to recede, but will still be well above average over high terrain.
June - Temperature anomalies forecast to range from -1 to +2 degrees F, with precipitation most likely to favor the lower side of normal.
July - Temperature anomalies forecast to range from 0 to +3 degrees F, with precipitation at or below normal (which climatologically means very little).
August - Temperature anomalies forecast to range from +1 to +4 degrees F, with precipitation continuing near to below normal.
Lightning events are the biggest “wild card” in Northern California fire seasons. At this time, it is expected to be a near-average type of lightning year. This approximates out to 2-4 limited events on a sub-GACC to GACC-wide scale. There is a 20-30% chance of a large and/or critical dry lightning event of GACC-wide impact before year's end. It would be most likely to occur in late July or August, as fuels would probably not support reaching a siege-type event any earlier.
Drought caveat - While large-scale drought is not a factor in California as of mid-spring 2011, it could again become so by late fire season IF the weather becomes persistently hotter and drier than the modest warm anomalies contained in this forecast.
Forecast Confidence = Temperatures 65%, Precipitation and Lightning events 55%
Team Members involved in the workshop:
Tom Rolinski – Fire Weather Meteorologist, USDA Forest Service, Predictive Services in Riverside, California.
Rob Krohn – Fire Weather Meteorologist, USDA Forest Service, Predictive Services in Riverside, California.
Bruce Risher – Intelligence Coordinator, USDA Forest Service, Predictive Services in Riverside, California.
Tim Chavez – Fire Behavior Analyst, CAL FIRE, Riverside Ranger Unit.
John Snook – Fire Weather Meteorologist, USDA Forest Service, Predictive Services in Redding, California.
Basil Newmerzhycky - Fire Weather Meteorologist, USDA Forest Service, Predictive Services in Redding, California.
Marva Willey – Intelligence Coordinator, USDA Forest Service, Predictive Services in Redding, California.
Vince Cohee - Coordinator, USDA Forest Service, Predictive Services in Riverside, California.
Bryan Schieber – Battalion Chief, CAL FIRE, California Northern Region in Redding, California
Jan Rea – Fire Management Specialist, Stanislaus National Forest, California
NIFC 2011 Preliminary Seasonal Assessment Link: http://gacc.nifc.gov/oncc/predictive/outlooks/seasonal_outlook.pdf