2012 Weather: Year in Review

Uploaded by NWSSacramento on 01.01.2013

Now that we have begun a new year, we can take a look at the highlights from 2012. So
here is the Year in Review of weather information presented by the NWS – Sacramento.
We saw quite the spectrum of weather in northern California last year. This includes very dry
conditions during the early months, lightning episodes and a very active fire season during
the summer, and much wetter conditions with tornadoes during the fall. In this video,
we will summarize each of these events, and at the end we’ll look at what may be in
store for early 2013. We started the calendar year in the midst
of a very dry stretch. This graphic shows the percentage of normal precipitation during
the month of January across northern California. As you can see, much of the region saw only
25-75% of normal last January. We can look closer at the statistics by focusing on Sacramento’s
precipitation numbers. Between December of 2011 and February 2012, only 3.10 inches of
rain fell. Normally in this timeframe we would expect 11.14 inches. This made the Dec 2011
through Feb 2012 period the 6th driest such stretch on record!
At this point it may seem like a distant memory, but interior northern California did see two
tornadoes last Spring. Interestingly enough, they occurred only two days apart. The first
of these tornadoes occurred in French Camp, just south of Stockton, on April 11th. This
tornado was rated as an EF1. Just two days later, an EF0 tornado struck Yuba City. Little
did we know at the time, more tornadoes would strike around Yuba City later in the year.
If we were to look exclusively at temperatures, summer 2012 would have gone down as uneventful.
Sacramento saw twenty 100 degree days in 2012, which is pretty close to the 30-year average
of twenty-three triple-digit days a year. However, summer 2012 will be marked by three
separate thunderstorm events within the span of a month. Many northern California residents
were treated to quite a spectacle, with the most impressive of these events recording
over 2000 lightning strikes. Of course, the biggest concern during and
after these summertime thunderstorm events is the possibility of wildfire startups. Unfortunately,
the combination of very dry antecedent conditions and thousands of lightning strikes led to
the most active fire season since 2008. Ultimately, hundreds of thousands of acres were burned
with multiple high-impact incidents. This map shows the burn scars left behind from
the many fires. Perhaps the most memorable event of 2012 was
the tornadic outbreak that occurred on October 22nd. Ultimately, 5 tornado touchdowns were
confirmed, this tied the record of most tornadoes in a day from northern California history.
4 of these tornadoes were rated as EF1 tornadoes, a California record for a single day. On the
right is a radar graphic with the Browns Valley tornado highlighted. As you can see, there
were many supercells lined up that day! After a month with relatively quiet weather,
things picked up in a big way once again. A series of warm, very wet storm systems took
aim at northern California in late November and early December. All told, within a 5-day
timespan, between 15-20 inches of rain fell in parts of the Shasta drainage and Feather
River Basin. Most of the Sacramento Valley saw between 3-5 inches of rain fall. The last
storm in the series was the most potent, and overwhelmed many of the area creeks and streams.
Just a few weeks later, another series of storm systems brought significant precipitation
to the region. This time, however, the storms were notably colder and brought significant
snow accumulations as well as low elevation snow. The city of Redding, at around 500 ft
elevation, saw snow not once but twice in the matter of a week. Storm total accumulations
were impressive with 4 to 6 ft of new snow being measured along the Sierra. The low elevation
snow greatly impacted pre-Christmas travel, with Interstate-5 being closed multiple times,
and long duration chain-controls across trans-Sierra highways. Shown here is an interesting graphic
comparing the amount of year-end snow at the end of 2012 vs practically no snow at the
end of 2011. And now we’ve caught up to the current time
so that we can see how the wet season is doing thus far. At Downtown Sacramento, 12.07”
of rain has been observed since the water year began. This is much greater than the
normal of 7.34” through December, or 164% of normal. Another way to analyze precipitation
totals is to look at the 8-Station Index, as shown in this graphic. This index measures
precipitation at stations across the northern Sierra and southern Cascades. At this juncture,
the mountains have also seen well above normal precipitation, running at 187% of normal.
Interestingly enough, as of December 31st, we are on pace to break the wettest year on
record, the water year of 1982-1983. So what’s in store for the upcoming year?
Unfortunately, at this point, it’s hard to say for sure. The official forecast is
for us to remain in ENSO neutral conditions through the spring with ENSO being the El
Nino-Southern Oscillation. There is no correlation between ENSO-neutral conditions and northern
California precipitation. Some years we’ve been very wet, other years we’ve been very
dry, and an equal number of years we’ve been near normal. This graphic reflects just
that…there’s an Equal Chance of each scenario playing out. However, keeping in mind that
we’ve had a very wet fall and winter so far, this means that we are in decent shape
in terms of water storage, even if we suffer through a dry winter month.
As always, you can get our latest forecasts at www.weather.gov/sacramento. We also regularly
post to Facebook and Twitter. Thanks for listening to this video, and have a great day!