California 120 Day Precipitation Outlook Issued 11-01-2008 Tom Dunklee Global Climate Center This is my second updated outlook for precipitation patterns and amounts for the next 4 s of the current rainy season for the river drainages of Northern and Central California. The outlook is restricted to the drainages which have a substantial impact on runoff into the Sacramento and San Joaquin River Basins. These are, from north to south, the Upper Sacramento, the Feather, American, Stanislaus, Merced, and the Upper San Joaquin drainages. The specific statistical forecasts/outlooks have been prepared for the period, 11-1-08 through 2-28-09 with precipitation as a percentage of long term averages for each river basin, as well as for the state of California as a whole. Temperature departure from long term averages has also been prepared for each Basin, for the same period, 11-01-08 through 2-28-09. A more general outlook for the entire Sacramento Basin and the San Joaquin drainage has been made for the late Winter through early Spring period (March and April 2009). General Summary While beneficial moisture has recently fallen over much of the state of California, overall the last 30 days have been significantly drier than average. In fact these very dry conditions have prevailed over the general Northern and Central California region over the last 180 days with most areas of the region having received less than 25% of the average precipitation for that period. The dry conditions of the past 30 days (this past of October) have generally been the result of a ridge in the upper atmosphere, having been located most of the time right along the West Coast of the US, and at times extending inland into the Great Basin. This ridge has effectively deflected moisture to the north and east of California with sunny, dry and warm weather dominating much of the. Very recently this ridge has collapsed and the Polar Jet Stream has dropped southward off the Coast and is now pushing inland with periods of moisture and slowly cooling conditions. This wet and cooler weather pattern is forecast to be a short term trend, with dry and warmer weather returning for much of the first half of November. Indicators in the Sea Surface Temperatures Anomaly pattern (SSTA's) are pointing toward increasingly changeable or volatile weather conditions later this and into early December with a trend toward only slightly lower than average moisture conditions. A shift in upper atmospheric pressure patterns around or just after mid December will "open the door" to increasing moisture and storminess off the North Pacific into Northern, and at times Central California.
SST ANOMALIES FOR 8-21-08 Above are the Sea Surface temperature anomalies from 8-21-08. Temperature departures are shown in degrees C over the North and Central Pacific. Warmer than average surface water is depicted by areas shaded in yellow. gold, orange and red. While cooler than average water is shown in shades of blue. A small, cool anomaly is seen just southwest of Central California with a much larger cool anomaly to the west, through Hawaii, and then into the Central Equatorial Pacific. A very large and intense warm anomaly is seen over the Northwest Northern Pacific with a secondary warm anomaly just west of most of the US West Coast. Below are the most recent SSTA'S, from October 31, 2008. SST ANOMALIES FOR 10-31-08
There are some notable changes in the SSTA's over the North Pacific, most evident being a trend toward cooling conditions relative to average. The warm anomaly over the Northwest Pacific has weakened slightly, with stronger cooling over the Eastern Tropical Pacific, and still stronger cooling with regard to the warm anomaly west of California and Oregon.. The weakening of this warm anomaly should have a direct impact on weather conditions over much of Northern and Central California, with less upper atmospheric ridging, more troughing, cooler and somewhat wetter weather for the region. The second main weather feature is the large warm anomaly over the Northwest Pacific. This heat source will have the tendency to build upper ridges to the north and east. This has already happened a few times this Fall, and the frequency and strength of these ridges will increase late in November and more so late in December into January. This upper atmospheric ridging will increase the tendency for downstream trough formation along and off the West Coast of the US, guiding frequent storminess into Northern and at times Central California. Slowly this pattern will shift a little to the west and California will start to dry out again by late January and more so February and March of 2009. It does appear that during the mid Winter period that most of the areas in question, such as the Sacramento and San Joaquin River Drainage regions will be wetter and cooler than average. The trend will be toward somewhat drier than average conditions by late Winter and on into early Spring. This departure from average for the late Winter period will most likely be fairly minor, with close to average conditions most likely. As mentioned earlier, the of October was drier than average and somewhat warmer than average over California as a whole. These departures from average are seen on the following two pages. The to precipitation forecasts then follow.
RECENT CONDITIONS OBSERVED THE MONTH OF OCTOBER 2008
OBSERVED AVERAGE FOR THE MONTH OF OCTOBER 2008
FORECAST THE MONTH OF NOVEMBER 2008
FORECAST THE MONTH OF DECEMBER 2008
FORECAST THE MONTH OF JANUARY 2009
FORECAST THE MONTH OF FEBRUARY 2009
120 DAY OUTLOOKS FOR THE SACRAMENTO DRAINAGE BASIN LOCATION NOVEMBER 2008 NOVEMBER 2008 DECEMBER 2008 DECEMBER 2008 JANUARY 2009 JANUARY 2009 FEBRUARY 2009 FEBRUARY 2009 UPPER SACRAMENTO DRAINAGE +0.5 F From +0.8 F From 89-99% of Average for the. -0.4 F From -0.8 F From 119-132% of. -0.5 F From -0.9 F From 114-128% of. -0.3 F From -0.7 F From 100-114% of. FEATHER RIVER +0.6 F From +1.1 F From 79-93% of Average for the -0.7 F From -1.1 F From 122-135% of -0.3 F From -0.6 F From 106-117% of -0.2 F From +0.7 F From 97-107% of AMERICAN RIVER +0.7 F From +0.9 F From 75-88% of Average for the. -0.9 F From -1.2 F From 118-133% of -0.9 F From -1.2 F From 104-115% of +0.5 F From +0.9 F From 94-108% of
120 DAY OUTLOOKS FOR THE SAN JOAQUIN RIVER DRAINAGE BASINS LOCATION STANISLAUS DRAINAGE MERCED RIVER SAN JOAQUIN RIVER NOVEMBER 2008 +0.7 F From +1.2 F From +0.9 F From +0.8 F From +1.1 F From +1.3 F From NOVEMBER 2008 70-81% of Average for the. 66-75% of Average for the 54-69% of Average for the. DECEMBER 2008-0.0 F From -0.2 F From -0.4 F From -0.7 F From -0.8 F From -1.4 F From DECEMBER 2008 116-129% of. 118-127% of 110-126% of JANUARY 2009-0.4 F From -1.1 F From -0.6 F From -1.2 F From -0.7 F From -0.9 F From JANUARY 2009 107-116% of. 102-113% of 100-115% of FEBRUARY 2009 +0.7 F From +1.2 F From +0.4 F From +0.9 F From +0.8 F From +1.4 F From FEBRUARY 2009 92-103% of. 85-101% of 72-85% of Average for the GLOBAL CLIMATE CENTER 1-800-992-6875