•Precipitation since October 2011 has been mostly between 55-90% of normal. Drought conditions diminished in March-April, but continue in the East and South.
•As of early April, snowpack ranged from near normal in the northwest to only near 50% of normal in the southeast.
•The temperature and precipitation forecasts in this Preliminary Outlook are based on staying in an ENSO neutral condition, but this is far from certain (see details within the report).
•A mild late winter period helped fuels in some lower elevation sites green up earlier than usual.
•Tall residual dead grass from last year is still standing in eastern areas of Northern California.
•Although most PSAs recorded seasonal record high ERC and low Fuel Moisture values, most of the Geographic Area has recovered to seasonal averages.
•Winter rains throughout the Geographic Area were 50-70% of normal and snow pack in the Sierra is half of normal
•Most fuels are drier than normal and should be fully cured by June.
•Expect a normal start to fire season.
•Drought conditions are developing and expanding over the region.
•Large fire potential will be above normal over most of the mountain and foothill areas.
•This year’s fire season will largely be driven by the fuel conditions. Tall residual dead grass from last year is locally still standing in eastern portions areas of the Geographic Area.
Review of October 2011 to mid-April 2012
The fall of 2011 was characterized by a high frequency of offshore winds, mainly across southern California. Some of the strongest Santa Ana winds of the season occurred in early November and again in December, however none of these events resulted in large fires. Winter precipitation arrived a few weeks earlier than normal with wetting rains having fallen over most of the region by mid-to-late October. Most areas received above normal amounts of precipitation by early December but an extended period of warm and dry weather set in from mid-December through early February. Late season rains in March and April helped bolster fuel moistures over much of the region with a secondary grass crop returning to many lower elevation locations.
A La Nina pattern peaked by the end of 2011, but was significantly weaker than the La Nina of late 2010. It produced varied weather effects in the first four months of 2012, though its influences were winding down quickly as we approach the end of April. Much of North Ops was very dry through early March, and by that point the seasonal precipitation POAs (percent-of-average) had dipped to a 35-65% range. The winter dryness was especially seen in December and to a lesser extent in February, with persistent high pressure ridges governing both months. Many locations had their 1st or 2nd -driest Decembers on record, or at least their driest in 20 years. A few sites reported no precipitation at all! There was finally a shift in the large-scale governing pattern about 10 days into March, and many areas have had at or above normal precipitation in the 5-6 weeks since. Still, this has only helped season-to-date POAs to climb back to a 55-90% range (see Figure 3). The minor wetter exception is near to slightly above normal seasonal rain totals along and near the far north CA coast. Figure 4 shows that mean temperatures since October have roughly averaged below normal west of the I-5 corridor, and above normal to the east. April snowpack ranged from near normal in the far north, to closer to 50% south of the Feather River drainage in the Sierra Nevada. As usual, there have been some wind events associated with Pacific storms over the winter, but only a couple had very strong S to SW pre-frontal winds. However, there was an extremely strong N to E (Foehn type) wind event of 3-4 days duration centered at the start of December 2011. Biggest effects were in the Sierra, especially south of I-80 with widespread areas of tree damage.