California's "March Miracle" is Not Over

Some call it the "March Miracle"--the large amounts of precipitation and snow that fallen over California the past month.  The Sierra Nevada got hit by 2-5 feet this week alone. And this is a miracle that is not over, with a strong atmospheric river poised to occur over the next week.

Here are snow water equivalent maps (amount of water in the snowpack) from the National Snow Analysis for February 17 and March 17.   A huge increase in both depth and coverage.

The origin of the wet bounty over California was a shift in the large scale atmospheric circulation, with high pressure moving further offshore and persistent troughing (low pressure) developing over the West Coast.   To illustrate, here is mean upper level (500 hPa, about 18,000 ft) heights for March 10-16th. The left shows the heights (analogous to pressure) and the right shows the deviation (or anomaly) from normal.  A trough (low heights) is found right off the West Coast...that is culprit.

Well, this pattern is not going away...and in fact, it will amplify in a few days and our friends in California need to get prepared.  A trough will form west of California with strong southwesterly flow on its south side, which will entrain large amounts of tropical moisture (see map for 11 PM Tuesday below)

As a result, a strong atmospheric river will develop, which will bring tropical moisture into central and southern California (see plot of total moisture in the vertical for 5 PM Tuesday)

How much precipitation will those folks in California enjoy?   Here is the forecast accumulated precipitation over California for the next 7 days from the European Center Model:  up to 6-8 inches in the Sierra Nevada and coastal mountains.

And plenty around southern CA, such as the mountains that surround LA.

 Snowfall?  Up to 3- 4 feet in the Sierra Nevada (see below)

With all the recent snow, the Sierra Nevada snowpack is about 60% of normal.  It will get much closer to normal after the next few weeks.  And the reservoirs, already around 100% of normal, will get topped off for the upcoming dry summer.

The only negative of all this precipitation is that it will encourage the growth of grasses, which can enhance the potential for fire danger next fall after it has dried out.  

Here in the Northwest, our situation will be far less exciting than for California, with much of the big action going south of us.  The 7-day totals show the heaviest precipitation over western Oregon but only light precipitation over the Puget Sound area and the San Juans.

from Cliff Mass Weather and Climate Blog http://ift.tt/2FQMOXX