SF Dry Spell Ends at 43 days

With 0.01" of rain being recorded this morning between 08:00 and 09:00 am the dry spell in downtown San Francisco has ended at 43 days. The last measurable rain in SF was recorded on December 24, 2014 making this the second longest winter dry spell since records began during the Gold Rush in 1849. The record is 60 consecutive days set between November 17, 1876 and January 15, 1877.

Jan Null, CCM
Golden Gate Weather Services



National Weatherpersons' Day

February 5 commemorates the birthdate of John Jeffries (1744) as National Weatherpersons’ Day; a day that recognizes the contributions of meteorologists in the United States.  Jeffries (1744-1819) was one of America's first weather observers, having begun to take daily weather observations in Boston in 1774 and took the first balloon weather observation in 1784.

Born in America, he trained as a physician in England and was the Surgeon General for British Forces in North America during the Revolutionary War.  Historically he is best known in his era for the first balloon flight across the English Channel with Frenchman Jean Pierre Blanchard  on January 7th 1785.



Atmospheric Rivers - Background Information

Below are a number of links relating to Atmospheric Rivers (ARs). These relatively narrow (~240 miles) slow moving bands of subtropical moisture account for between 30% and 50% of the rainfall occuring along the West Coast. Many of Washington, Oregon and California's historic flooding events have been related to ARs. They are also colloquially known as the "Pineapple Express" because some of their moisture originates from the vicinity of the Hawaiian Islands.





Jan Null, CCM
Golden Gate Weather Services


California Rain and Reservoir 3-month Roller Coaster

To illustrate the roller-coaster ride of both rainfall and reservoir storage in California, see the following three graphics from the 1st day of the month for December 2014, January and February 2015.  

For example, the 8-Station Index for Northern Sierra Nevada Precipitation went from 86% of normal on December 1, to 127% on January 1 and back to 86% on Feb 1st. Most other metrics statewide saw similar swings.



Jan Null, CCM
Golden Gate Weather Services


Groundhog Day: More than a Furry Forecast and a Movie

Groundhog Day has its roots in an ancient Celtic celebration called Imbolog. This date is the midpoint between the winter solstice and the spring equinox. In an agrarian society that was very dependent on the weather, this was a time to celebrate having made it halfway through winter. The superstition arose that if the weather was fair on Imbolog, the second half of the winter would be cold and stormy, but if the weather was cold and overcast or stormy, the second half of the winter would be mild.

In Christian times, February 2nd was celebrated as Candlemas, but the earlier Imbolog superstition continued. In Scotland they said, ``If Candlemas be bright and clear, there'll be two winters in the year'' and in England, they said, ``If Candlemas be sunny and warm, ye may mend your mittens and look for a storm.''

The Romans learned of this tradition from the Celts, and eventually brought them to the area that would become Germany. Eventually German immigrants brought these beliefs to Pennsylvania. Their tradition of predicting the weather became centered on the woodchuck, or groundhog, and if he could see his shadow, there would be six more weeks of winter.

A newspaper in Punxsutawney, PA helped keep the tradition alive and in 1887 declared Phil as America’s official forecasting groundhog. As the story became embellished each year the other newspapers picked it up and the rest as they say is history. Regionally there have been a number of other furry rodent contenders such as General Beauregard Lee of Atlanta, Sir Walter Wally in Raleigh, NC and Jimmy of Sun Prairie, WI.  And in 1993 the motion picture "Groundhog Day" popularized the event even further.

NOAA's National Climatic Data Center's look at this tradition and some of the associated climatology is at http://www.ncdc.noaa.gov/customer-support/education-resources/groundhog-day  

Today it has been reported that Punxsutawney Phil did see his shadow this morning (despite a Winter Storm Warning still being in effect) and forecasted six more weeks of winter for 2015.

Jan Null, CCM
Golden Gate Weather Services


Driest January?

Across much of Northern and Central California there has been little if any rain this month and monthly totals will wind up at or near long term records.  Below are the 15 lowest January totals for each station's period of record.

Looking at San Francisco, note that three of the five driest years are in the top five.  This has brought the average for the past ten years down to 3.03, dramatically lower than the 30-year normal of 4.55 inches.  

December California Climatology

Happy New Year and Best Wishes for a healthy, happy and properous 2015.

December 2014 was a wet and warm month across the Golden State. Precipitation ranged from "only" 120% of normal at Eureka to 294% at Los Angeles and 297% at San Jose.  December maxima were well above normal, ranging from 1.6 degrees above normal at Redding to 5.9 above normal at Sacramento; with the exception of Los Angeles whose maxima were 0.2 below normal.

December California Key City Climatology

December Max Anomaly Map

December Mean Anomaly Map

December Min Anomaly Map

December Precipitation Map

December Precipitation % of Normal Map

July - December Precipitation Table

July - December % of Normal Map

Northern Sierra Nevada 8-Station Index

Southern Sierra Nevada 5-Station Index

California Snow Water Content

Jan Null, CCM


Should You Walk or Run in the Rain?

With the recent rains I have been re-asked the eternal question: "Should I Walk or Run in the Rain?" This is a classic question that meteorologists get asked and upon which we have probably spent way too much time. So, does a person make impact with more droplets as they run faster even though they are exposed for a shorter period of time? Or do more drops hit the front of a running person than on their head and shoulders when they run instead of walk?

There have even been a number of studies to "scientifically'' calculate whether it's better to run or walk to shelter. One of the simpler studies had people wear a piece of cardboard over their heads and in front of them as they walked or ran through the rain and then the number of drops that marked the cardboard were counted. A more detailed effort from the National Climatic Data Center in Asheville, North Carolina had their experimental subjects wear identical moisture absorbing clothing as they walked 100 yards at 3 mph and then ran the same course at 9 mph. Their clothing was then weighed to find out how much water was absorbed. They found that speed helps ... the person who ran the course absorbed 40 percent less water than the walker!

And of course someone, again with way too much time on their hands, has put up a website to calculate how wet you would get based upon your size, speed and the rate of rainfall. See http://www.dctech.com/physics/notes/0006.php and http://www.dctech.com/physics/notes/0005.php.

Stay dry!

Jan Null, CCM
Golden Gate Weather Services


Not Necessarily the Worst California Drought in 1200 Years!

In the past week there has been extensive media coverage and headlines about "the worst California drought in 1200 years". This was based on a paper to be published in Geophysical Research Letters by the AGU. However a thorough reading of that paper,"How unusual is the 2012-2014 California drought?", indicates that this "worst" declaration should have at least a few asterisks. The article is not inaccurate but it takes only a limited view at looking at the current California drought.

- The study defines drought using the Palmer Drought Severity Index (PDSI). This is an agricultural index, based on soil-moisture as a function of both temperatue and precipitation. While, agriculture is incredibly important in California, it is not necessarily the best metric for the state's overall water deficit and its impacts.

- The paper also does not look at all of California. Instead it only examines the PDSI for central and southern California (i.e. NCDC California Climate Divisions 4, 5, 6, 7). This methodolgy gives a skewed prespective since much of the water used throughout the entire state originates in northern California (i.e., Climate Divisions 1,2,3) and the 3-year deficit has been less there than in the sampled southern two-thirds of the state. [For additional context see the just released NOAA California Drought Assessment.]

The bottom line is that the paper really only speaks to agricultural drought in central and southern California while both the Ranked 3-year Precipitation and PDSI show that currently the drought in northern California is only on the order of the 4th or 5th driest in the past 120 years; certainly not the driest in the past 1200 years statewide.

Jan Null, CCM
Golden Gate Weather Services


Links referenced above: