Historic El Nino Analyses

With a "possible" El Niño event forecast for next winter it is important to examine the very broad range of past events that make up an "average" El Niño.

Since 1950 there have been a total of 22 El Niños, eight which have been weak, nine in the moderate range and five which have been  categorized as strong. [see Oceanic Niño Index (ONI)].  Even within each of these categories there are huge variations.  See El Niño and La Niña Winter Historic Precipitation & Temperatures, a catalog of events.  

For example, 1977-78 and 1978-79 were weak El Niño events but the winter precipitation patterns and amounts were dramatically different.  The first year, 1976-77, was a drought season in the West (

) while the next year, 1977-78, saw above normal rain in California and much of the West ( ).

The bottom line is that first, any climatology is simply an average over a broad range of previous events.  And second, a climatological analysis is NOT a forecasting tool. 

This and other El Niño data and analyses can be found on the El Niño/La Niña Resource Page.

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Myths and Realities of El Nino

Let the hype begin.  CPC has issued an El Nino Watch for the 50% possibility of a weak El Niño next fall from the IRI/CPC forecast ensemble.   A similar Watch was issued in 2012 but El Niño never materialized.

Already there are headlines about El Niño being the answer to California's drought which only perpetuates the myth that El Niño definitely means lot of rain for California.  To put aside this and some of the more prevalent misconceptions see The Myths and Realities of El Niño

Also see:
El Niño and La Niña Winter Historic Precipitation &Temperatures

Comprehensive Climatology of ENSO Events and California Precipitation

The bottom line is that climatology should NOT be used as a forecast tool.  An "average" El Nino is made up of a very broad range of past events!

 

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The Busted Winter Forecasts in Review

If I were grading this past winter's CPC precipitation and temperature forecasts they would not receive a passing mark.   Except for Arizona, New Mexico and the northern Rockies, the forecast bore little resemblance to what was ultimately observed and in some locations was 180 degrees out of phase!

A graphical comparison of both the Winter 2013-14 (i.e., December-February) seasonal and monthly forecasts and actual conditions can be found at http://ggweather.com/cpc/2014/

Comments welcome.

 

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February 2014 California Weather Summary

Despite several recent significant rainstorms, most of Northern and Central California ended up with February rainfall totals only near normal.  The exceptions were wetter than normal across the northern tier of counties and near the Tahoe Basin. In Southern California it was mostly below normal.   See 
http://www.wrcc.dri.edu/cgi-bin/anomimage.pl?wrc30dPpct.gif

Likewise temperatures were near normal with the exception of the southern half of the Central Valley where Sacramento and Fresno average maxima were 3.2 and 5.1 degrees above normal respectively.   See http://ggweather.com/calif/feb2014.htm

Jan Null, CCM
http://ggweather.com
jnull@ggweather.com

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Not the Driest on Record - San Francisco

The overnight rainfall (through 7 am Friday, Feb 28)  has pushed San Francisco's seasonal rainfall to 7.57".  While still a paltry amount, this means that the 2013-2014 rainfall season (July 1-Jun 30) will NOT be the driest in the 165 years since rainfall records began in SF in 1849.  And given the expected rainfall through the rest of the day, this season may jump into 3rd place.   The Ten Driest Seasons were:
1850    7.42"
1975    7.95"
1897    9.38"
1863   10.08"
1958   10.46"
1919   10.46"
1876   11.04"
1976   11.06"
1971   11.06"
1917   11.47"
(See http://ggweather.com/sf/season.html)

And it should be noted that the normal San Francisco rainfall for the remaining four months (Mar-Jun) is still another 5.60".

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High Pressure Blues

Back during the California drought of 1975-77 I was an Intern at the National Weather Service and decided to be "clever" and write the California Weather Summary on Valentine's Day 1977 in poetic verse titled "High Pressure Blues".  (NWS management was not amused)  I'm sure all will agree that it's a good thing that I can make my living as a meteorologist and not as a poet. 

However,  the meteorology is certainly just as apropos  for the current drought.   An image of the original teletype message can be seen

and is replicated below.


High Pressure Blues

Strong High Pressure
Remains firmly entrenched...
Blocking all storm
That might leave us drenched.

Light offshore breezes
Are warming the air...
To unseasonable readings
Under skies fair and warm.

Temps in the 70s
Were found all around...
And marks over 80
In the south state were found.

Some rain would be nice
With snow in the mountains...
Enough to fill up the dams
Or even some ountains.

But the new forecast says
It's more sunny days...
With patches of fog
And afternoon haze.

E Jan Null
Feb 14, 1977

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California Storm Rainfall Summaries

The rainfall totals across northern California were very impressive, but 4-day totals dropped off rapidly into central California.  Many locales in the north more than doubled their season to-date totals, jumping from percent of normal (PON) values in the teens to PON's in the 30% to 40% range.  See http://ggweather.com/feb2014rain.htm

But the important takeaway is that while this is a great start, the north half of the state would still need on the order of 4 more equivalent storm systems to get close normal.


The very important Northern Sierra 8-Station Index also jumped significantly; doubling with over 5 inches to 9.58" to-date.  This is approximately 35% of normal, up from 18% on Wednesday.  See http://cdec.water.ca.gov/cgi-progs/queryDaily?s=8si&d=today


There have been some rain totals of over 20 inches being reported for Mt. Tamalpias.  However In light of surrounding locations this seems to be a bogus.  Kentfield's big-time 96-hour total of 11.83" would appear to be more representative.  See https://marin.onerain.com/sensor.php?site_id=1555&device_id=1&view_id=3

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Atmospheric Rivers

There has been considerable information disseminated in recent days in regards to Atmospheric Rivers; some of it factual and some so much so.  Here are a couple pretty good resources:

NOAA ESRL Atmospheric River (AR) Info page
http://www.esrl.noaa.gov/psd/atmrivers/

ESRL Real-time AR Modeling
http://www.esrl.noaa.gov/psd/psd2/coastal/satres/data/html/ar_detect_gfs.php

Dettinger - Scripps Presentation on Atmospheric Rivers in California
http://www.scwa.ca.gov/files/docs/outreach/calendar/extreme-events/Atmosperic%20Rivers%20Dettinger%20EE%203-14-12.pdf

 

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Numbers Don't Add Up

While I like the visual, the numbers don't add up. The normal accumulated rainfall for the 8-Station Index (8SI) from Oct 2011 through January 2014 is 126.5 inches, and actual accumulated amount has been 92.0 inches. That's a deficit of 34.5 inches. Given http://www.cnrfc.noaa.gov/precipForecast.php?cwa=RSA... a conservative forecast precipitation amount for the 8SI would be about 5 inches or about 14% of the deficit. Given a 5-gallon bucket (640 ounces), 14% would be 90 ounces or 9 of the displayed 10-oz mugs.

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No Drought Buster

The approaching weather system has the potential to be the wettest storm since before December of 2012; but is a very long way from being a "drought buster".  To put it in context, I have looked at both San Francisco rainfall and the rainfall for the 8-Station Index (8SI, which averages rainfall in the Northern Sierra Nevada from about Interstate 80 to Mount Shasta).

So far in the 2013-2014 rainfall season San Francisco has had just over 3 inches of rain since July 1st, or about 22% of the 13.59 inches normal to date amount.  Forecasts are that over the weekend San Francisco may see about 2 more inches of rain; but it would take four more of these 2-inch storms to erase the over 10 inch rainfall deficit.

Likewise the 8-Station Index has had about 20 percent (4.9") of their normal 27" to date.  The forecast of the weekend is for as much as 5 inches falling in the 8SI area, But again it would take the equivalent of at least four more 5" storms to get the Index to near in this watershed.

The bottom line is that even though the "storm door is open" it will need to remain open for there to be a significant easing of the drought.

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