Biggest storm in decade bears down on San Francisco

San Francisco, California had a rainstorm last week that was called the biggest rainfall event since 2008. Over the next 24 hours, what the National Weather Service is calling the biggest storm in a decade bears down on San Francisco and northern California.

I hope you are not scheduled to fly on Thursday in or out of northern California. Any rain in San Francisco slows the airport down and there were numerous delays and cancelled flights last week. I expect travel in or out of SJC and SFO on Thursday, December 11 to be a washout.

Locally, we have already been warned that electricity will likely be out tomorrow when the Monterey pines start falling in the 50mph winds.

Yesterday, I hiked Point Lobos State Reserve and signs of big swells preceding the big storm were evident.

This is the latest National Weather Service Forecast from 4:21am Wednesday, December 10, 2014:

MAIN PACIFIC LOW AROUND 550 MILES WEST OF SEATTLE CONTINUES TO
STRENGTHEN THIS HOUR WITH A CENTRAL PRESSURE NOW DOWN TO 968 MB (COMPARED TO AROUND 975 MB JUST THREE HOURS AGO). ALONG AN
ASSOCIATED COLD FRONT AN INTENSE AREA OF LOW PRESSURE — POSSIBLY DOWN TO 973 MB — WILL FORM AND HEAD TOWARD THE NORCAL/OREGON COASTAL AREA BY THURSDAY. THIS SECOND LOW WILL PRODUCE A VERY TIGHT PRESSURE GRADIENT (UP TO 15 MB FROM SFO TO ACV) HELPING TO INCREASE SOUTHERLY WINDS THROUGH THE DAY. AT THE SAME TIME VERY MOIST (PW VALUES POSSIBLY IN EXCESS OF 1.50 INCHES) WILL BECOME ENTRAINED IN THE FLOW AND TAKE DIRECT AIM ALONG THE COAST. STEPPING BACK AND LOOKING AT THE BIG PICTURE JUST AT THE PW IS IMPRESSIVE AS IT CAN BE TRACED FAR TO THE WEST OF HAWAII WITH ITS DIRECT AIM RIGHT THROUGH OUR CWA. IN ADDITION…IT SHOWS NO SIGN OF DISSIPATING AS IT FOLLOWS THE FRONT TO THE SOUTH. KEEP IN MIND THAT PW VALUES THIS HIGH ARE AT THE 99TH PERCENTILE FOR DECEMBER AROUND HERE. OTHER PARAMETERS ARE JUST AS IMPRESSIVE INCLUDING THE ISENTROPIC FLOW AN AMAZING 60 TO 80 KTS FROM THE SW. ALL SIGNS POINT TO A BIG 1 DAY RAIN EVENT FOR OUR ENTIRE CWA. RAINFALL TOTALS FOR THURSDAY SHOULD BE GENERALLY 1.5 TO 3 INCHES FOR URBAN SPOTS SOUTH OF THE NORTH BAY WITH LOCALLY 4 INCHES POSSIBLE. FOR THE NORTH BAY PLUS OTHER COASTAL RANGES 4 TO 6 INCHES ARE FORECAST WITH LOCAL AMOUNTS TO 8 INCHES. THE BIG THING TO REMEMBER IS MUCH OF THE RAIN WILL FALL AS THE FRONT GOES THROUGH SO RAIN RATES WILL BE VERY HIGH FOR AN HOUR OR TWO. THIS WILL CREATE ADDITIONAL HYDRO CONCERNS.
FOR THE WINDS ALL OF THE GUIDANCE CONTINUES TO REMAIN VERY BULLISH WITH 925 MB SPEEDS 50 TO 70 KTS IN MOST LOCATIONS AS THE FRONT GOES THROUGH. JUST GOING OFF THE RAW ARW SURFACE SPEEDS SHOWS 30 TO 40 KT FOR MOST SPOTS. WOULD EXPECT URBAN LOCATIONS ON THURSDAY TO SEE WINDS OF 20 TO 35 MPH WITH GUSTS UP TO 50 MPH. HIGHER ELEVATION LOCATIONS COULD EASILY SEE GUSTS WELL OVER 70 MPH DURING THE FRONTAL PASSAGE.

BOTTOM LINE...NOW IS THE TIME TO PREPARE BEFORE 

THE STORM ON THURSDAY. THIS WILL LIKELY BE ONE OF THE 

STRONGEST THAT WE HAVE HAD IN THE PAST TEN YEARS. 

PREPARATIONS SHOULD BE MADE ASAP.

National Weather Service 

San Francisco Bay Area/Monterey