April 3, 2017 – The winter season was quite wet for the North Ops region with periods of very moist weather systems delivering well above average precipitation. Moisture plumes from off the Pacific, or so called atmospheric rivers, brought regular periods of heavy precipitation ashore across the region. The bulk of precipitation since the beginning of the water year (October 1) has occurred since Jan 1, resulting in total precipitation for January through March commonly 150% or more of average for the 3 month period.
Unlike January and February, March 2017 precipitation amounts were not particularly above normal for the month as a whole, and outside of the very wet NW tip of California, most locations had totals near to below normal.
Average temperatures during the winter months were mostly within a degree or two of normal across the North Ops region.
This helped develop a deep mountain snow pack at elevations that typically have that and at much more widespread locations than last year. The winter of 2015- 2016 had rather mild temperatures, and the lower elevations of the typical snow pack zone mostly received rain, leaving last year’s snow pack to occur at just the highest elevations.
At the end of March, water content of the snow pack was well above normal in all the mountain areas. During January and February for the central and southern Sierra, it rivaled the record winter of 1982-1983.
Since March precipitation amounts were mostly near to below normal for the month, additions to the water content of the snow pack slowed down and leveled off to quite a bit below the record values from winter 1982-1983.
Also due to the rather wet winter, drought conditions were mitigated significantly across all of California. By the end of February and continuing through March, the North Ops region was no longer in designated drought conditions, a significant change from conditions since early October 2016.
North Ops Fuels
Fuels are directly reflecting the effects of the wet winter conditions. Green-up is well underway in the lower elevations across the region and will begin in the mid elevation areas during April.
Moist soil conditions will linger through April and a robust crop of annual grass is already in place and beginning to bloom and head-out in some of the warmer southern valley areas of the North Ops region.
By the end of April, those areas will probably see some stages of curing in the grass.
Other annual and perennial vegetation are seeing rapid leaf growth and that will continue in the lower elevations in April and start in the mid elevations. Live fuel moisture will remain high through the month.
North Ops Outlook
Predictive Services’ weather outlooks for April through July indicate April will be cooler and moister than normal overall. We anticipate at least the first half of April will continue this year’s wet trend, although most of the first week of the month will be rather dry. Snow levels will generally be average for the time of year over the next few weeks, so more snow accumulation is likely at higher elevations. Rain elsewhere will continue the moist soil conditions and encourage plant growth. Precipitation amounts are expected to be relatively heavy again over all the northwest areas and eastern mountains in particular. Temperatures and precipitation are expected to be closer to normal values for May though July.
Fine fuels will likely be a little slower to cure this year. With a deep snow pack this year, snow melt will continue for some time this summer at mid and high elevations keeping live fuel moistures high there fairly late into summer. We expect this to delay the onset of the active period of fire season at higher elevations until late July or August.
Additional moisture expected in April and possibly near normal amounts during May combined with the fact that significant fires are rare in spring strongly suggests nothing outside of normal large fire potential for April and May.
As is typical, fire potential will increase in June, especially in the Sacramento Valley and surrounding foothills. Moist conditions in the Far Eastside PSA are likely to linger over the next few months and keep live fuel moisture above normal there in June. So while there will be a good grass crop as well, higher live fuel moistures are expected to keep significant fire potential below normal in June for our far Eastside PSA.
All other areas will remain near normal for June. Large fire potential/occurrence will increase seasonably during July starting the peak summer fire season in late July as typical drying of soils and fuels takes place. At this time, all areas are expected to have normal large fire potential for July. However, lower elevation areas such as the Sacramento Valley and surrounding foothills that have had a heavy annual grass crop may develop a trend toward above normal fire potential in late July.