|
|
|
|
|
|
|
|
|
Coastal areas of California had a cool gray May while statewide rainfall for the month ranged from to zero to over 12 times normal.
A saggy trough of low pressure aloft made the marine layer a nearly permanent fixture for the month. Consequently cities near the coast were mostly 2 to nearly 6 degrees below normal, though San Diego managed to be just 0.6 below normal. Inland it was also cooler than normal in most areas, though Redding in the northern Sacramento Valley was three degrees above normal while Sacramento, only 150 miles to the south, felt the persistent marine layer and was 3.2 degrees below normal.
In San Jose, after an 84 degree max on May 1st not a single day exceeded normal. For the month San Jose's average May 2015 maxima of 68.6 degrees was 5.7 cooler than its normal of 74.3 degrees, the coolest May since 67.97 degrees in 1977. (Their record coolest May is 66.81 inches in 1915.) It was also the first month below normal in San Jose since last September.
San Francisco was similarly cool, with only May 1st topping 64 degrees all month. And it was the 1st time since September 2013 that the average monthly maxima was below normal!
The persistent trough also produced several significant rain events on the South Coast, with San Diego's 2.39" for the month was their wettest May since 2.54 in 1921, and 1292% of normal. Elsewhere rainfall was hit or miss and highly variable with generally drier amounts north.
See http://ggweather.com/calif/may2015.htm
Jan Null, CCM
Golden Gate Weather Services
Updated El Niño Climatologies
With many of the May versions of the SST ONI forecasts beginning to show El Niño strengthening well into the strong category (see below) I have updated a number of El Niño climatologies to add a "very strong" category. Each of the previous categories (Weak, Moderate, Strong) spanned a half degree anomaly on the ONI and it seemed logical to add a category for the next step of greater than or equal to an ONI of +2.0. See El Niño and La Niña Years and Intensities (ONI).
This moved two years (1982-83 and 1997-98) from the strong category to "very strong" and an examination of these two years understandably shows the most definitive signature for rainfall for California. [The 1972-73 season fell just shy of the meeting the "very strong" criteria, but certainly exhibited a similar very wet California outcome.] See El Niño and La Niña Winter Historic Precipitation and Temperatures and Climatology of El Niño Events and California Precipitation.
Important Caveat: These are climatologies of past events and are made up of a broad range of events from a small sample that are averaged together. Consequently, like all averages, this type of data should not be used as a forecast! Or as your stock broker says "Past performance is no guarantee of future result."
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Updated El Niño Forecasts
The new mid-May plume of forecasts come out from IRI/CPC on Thursday (5/21) but many of the individual elements are already available and showing significant warming in future months across the eastern equatorial Pacific.
NOAA Ensemble Mean
ECMWF Nino Plumes
Australian BOM Nino3.4 Outlook
Jan Null, CCM
Golden Gate Weather Services
http://ggweather.com