Archive for January, 2017

California – The wettest start since 2010… And more on the way
January 31, 2017

I’m getting asked a lot of questions about our weather.  Why are we getting so much rain?  Why is it a year delayed from last year’s strong El Nino?  Is the drought over? What’s going on?

sofarthisyear

Four months into the water year we have the wettest start ever recorded.

To answer these questions I first have to give some perspective on climate in California and probabilities.

In case you don’t know, California is a state of extremes when it comes to precipitation.  Throughout recorded history we’ve alternated between drought and excessive rain.  Los Angeles is a good example of these extremes.  While we average 15 inches of rain a year, we are rarely near this amount.  If you look at the past 30 years, we’ve gone from extremely dry years to well above average years.  In the end, it averages 15 inches.

30yearsrain

snowpack

Next snow survey is February 2nd and we’ll near 200%.

The one question that is a little more difficult to explain is the why we’re getting the heavy rain this year instead of last year.  Last winter we were prepared for the potential of heavy rain. The reason we thought this was because in all of the significantly strong El Nino climate patterns, Southern California got soaked.  The odds were in our favor.  But the rain didn’t come.

2015_Significant El Ninos

The 2015/16 water year only recorded 6.57″ of rain.

What is fascinating this year is we are in a weak La Nina or neutral weather pattern.  Both of these patterns slant dry for the state of California and especially for Southern California.  The probability our state would be dry this year is 70%, leaving a 30% chance we’d be above average.  And, if you really study this image, there isn’t a weak La Nina pattern that is well above average for Southern California.

laninaneutralpattern

Instead what we are seeing is the wettest winter since 2010.  The storms of the past two months have recouped 37% of the state’s five-year snow/water deficits. And for the first time since January 2014, no place in California is in an exceptional drought.  Precipitation is more than 200% of average and the Sierra Snow pack is looking great!

droughtupdate2016_snowpack_update

So what gives? Why the two extremes in outcomes?  I could give the answer, “That is how the weather works sometimes.” And this reply wouldn’t be completely wrong because even with an excellent forecast for a 90% chance of rain, there are days it’s dry.

But the answer is a little more complicated.

Last year the water was so warm in the Pacific that it affected the jet stream and moved all of the heavy rain to the Pacific Northwest and Northern California.

This winter we’ve been aided by numerous atmospheric rivers or a Pineapple Express.  This type of pattern can occur at any time regardless of an El Nino, La Nina or neutral pattern.  These rivers of atmospheric moisture are responsible for much of the devastating flooding in California’s history.  And it played a big part in the flooding on Jan. 22.

longbeachflooding

Long Beach received the most rain ever recorded in a 24 hour period, 3.97″.

ar

Most people don’t know about the mega flood of 1862, which was caused by an intense atmospheric river. It has a return period of 100-200 years, meaning it will happen again.

califlooding

And this leads me to climate change.  The latest research shows that in a warming planet, droughts will become more severe and heavy rain events will occur more often.  Before we started getting the rain in December, Southern California went through the driest five-year stretch ever recorded.  And, if you look at tree ring data, it may have been the driest stretch in 1,000 years.

record-dry2016_recorddry

But if you look at the history of flooding in California, intense flooding events occurred before the industrial age and atmospheric rivers are responsible for most of these events.  Attributing climate change to future flooding events may be hard to do.  Upcoming research will need to address how a warming world affects atmospheric rivers.

Going forward, the key for our drought, especially in Southern California, is we need this kind of winter pattern for two more years so we can get out of a drought cycle.  And, of course, I’ll keep you posted.

 

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Hole Punch Clouds
January 22, 2017

holepunchcloud_2

Dan Gregoria, NWS San Diego, Huntington Beach, CA

A few years ago I went to a weather conference and one of the more fascinating talks was on Hole Punch Clouds.  Meteorologists know that these “holes” in the clouds are created by airplanes.  The speaker explained that the latest research shows they are created by the propellers of airplanes not engine combustion.

holepunchcloud

Courtesy: Sean Browning, KNBC Photographer, Burbank, CA

Here is how they form:

The first requirement is the clouds have to be vertically thin.  The temperatures beneath the wings of a C-130 (seen below) are 14 degrees warmer than the surrounding environment.  This temperature difference and propeller motion creates a dry punch of air falling from the sky evaporating the clouds beneath.  This is always the case but if the clouds are too thick or the plane is above 20,000 feet a hole will not occur.  This is why Hole Punch Clouds are fairly rare to see.  But when you do get to see them, like Saturday, it’s an incredible sight!

c130

If you have pictures to share, I’d love to see them.  Tweet or Facebook me @anthonynbcla

To see other hole punch clouds from Saturday, click here: Hole Punch Clouds