An upper level disturbance off the Northern CA coast will combine with subtropical moisture to produce showers and thunderstorms over the higher terrain of the North Ops region today and Thursday.  Most activity will be over the high country of the Cascade-Sierra range and eastward, but isolated activity is possible from the mountains north of Clear Lake northward to the OR border.  Light rainfall is expected with any thunderstorm, but isolated dry lightning strikes are possible.  Beginning late Thursday low pressure will gradually deepen offshore and produce an increasing SW flow over the region.  This should push most of the moisture east of the area by Friday, leaving only a slight risk of afternoon thunderstorms in the far northeastern area.  As the low deepens and moves closer to the coast lower temperatures can be expected, but also with gusty S-SW winds in the higher elevations from the Cascade-Sierra crest east.  The low will be over or near Northern CA through early next week, producing below normal temperatures, gusty winds, and a chance of showers and thunderstorms each day.

A moderately strong ridge of high pressure aloft bridges across north-central CA today, connecting high centers near 4-corners in the desert southwest, and a high about 200 miles west of Cape Mendocino.   Moisture to the south of this ridge is drifting northward but, at least for today, only the Tahoe NF and southward into the Sierra Nevada is expected to see a slight chance of afternoon thunderstorms.   Moisture and instability will further combine and spread north by Wednesday, allowing a larger area to see a chance of convective activity, mainly in the p.m. hours.   Lower level pressure gradients around a thermal trough have relaxed somewhat since Sunday, with fairly light  winds across much of the Area this morning.  The strongest afternoon winds will likely be the sea breeze into the Sacramento Delta, and some SW to West winds in eastern Lassen Co. southward to Lake Tahoe.  The high will weaken and allow a low pressure trough to bring stronger winds and cooling Sunday, and perhaps scattered showers or thunderstorms by Monday.

 High pressure aloft became pretty strong over the weekend, leading to max temps in a 100-109 range over low elevations.  There were plenty of 100+ readings in and west of the coast range, including the Bay Area.   The high will weaken only very slightly through midweek...with more heat as  temperatures remain 10-15 deg above normal.  As for thunderstorms...none are expected today.  However, there may be just enough moisture and instability for a chance of isolated thunderstorms in the Tahoe area Tuesday...possibly  spreading a little further north  toward the Lassen region on  Wednesday.  Overall winds are expected to be light to moderate from the SW to W over the next few days. 

One year ago the Lightning Siege of 2008 was making headlines and keeping fire suppression resources busy in Northern California. Activity is somewhat slower for the summer solstice of 2009.

Weather models show the possibility of mild North wind events early and late next week. The later episode winds look like they will exceed 15 MPH, both events will have significant effect toward curing fuels.  Initial attack activity continues to increase as weather and fuel conditions become more favorable for fire growth.

Wetting rain across the region has delayed or slowed the drying of the fuels in the Geographic Area.  Wetting rains have been sporadic across the area, resulting in a broad range of fuel moistures across the PSA’s.  Areas least affected by the showers will demonstrate fire behavior that match expectations for this time of year.  Continued warming and drying trends in forecasts will work to dry fuels, at what may seem to be surprisingly fast rates.  This is reflected by an increase in initial attack activity at lower elevations, as warming and drying continue, increasingly higher elevations will become active for IA.

Lightning struck the NOPS area again yesterday and throughout the night. About 15 fires were reported as a result of yesterday's lightning. From May 25 through May 31 144 fires were reported in the NOPS area. 86 of these were caused by lightning and burned less than 40 acres.

While the number of lightning strikes recorded is very high for this past week, we must remember fuel conditions are different than they were for last June's Lightning Event. This lightning is coming with much more precipitation and fuels at higher elevations and on northern aspects are not quite ready to burn real actively. This doesn't mean we won't see active fire behavior, it merely means we must maintain our situational awareness at all times and be heads up!

Keep an eye on our seven day fire potential product: http://gacc.nifc.gov/oncc/predictive/weather/Fire_Potential.html

Several small fires have been reported as a result of recent lighting. In the past few days lightning has returned to Northern California, bringing with it some precipitation. The Eldorado, Tahoe, Plumas, Lassen, Modoc, Klamath, and Shasta-Trinity National Forests have each had a few lightning fires.

Activity is not limited to lightning caused fires, though, as the Santa Clara Unit of CAL FIRE has recently had two incidents totaling over 800 acres. Yesterday the Lake Napa Unit had a 155 acre fire near Danville.

Please continue to check our weather page for updates on conditions. And, look for our June monthly forecast to be posted on Monday on the outlooks page.