August 25,2014
NWS-SF is now saying precipitation in less likely in latest model runs……
BIGGEST FORECAST CHALLENGE AS OF LATE HAS BEEN THE POSSIBILITY OFMOISTURE FROM HURRICANE MARIE MOVING TOWARD OUR AREA. MODELS HAD GENERALLY BEEN PORTRAYING TWO GENERAL SOLUTIONS. THE FIRST HAD MARIE HEADING TO THE NW BEFORE EVENTUALLY TAKING A SHARP TURN TO THE RIGHT WITH ITS ASSOCIATED MOISTURE INTERACTING WITH A LONGWAVE TROF DIVING DOWN FROM CANADA ND GOING INTO NORCAL BY THE WEEKEND. THE OTHER CAMP INDICATED LESS OF A SHARP TURN WITH THE MOISTURE AND HAD THE RIDGE ACTING MORE LIKE A BLOCK WHICH WOULD PREVENT THE ENTRAINMENT. RUN AFTER RUN OF THE NAEFS HAD BEEN INDICATING A 1 OUT OF 3 SHOT OF MOISTURE MAKING IT GENERALLY FROM SF NORTHWARD FOR SATURDAY AND/OR SUNDAY WHILE THE OPERATIONAL ECMWF CONTINUED TO DEPICT A DRY SOLUTION. FOR THIS MORNING THERE IS NOTED TREND IN THE GUIDANCE TOWARD THE DRIER SOLUTION AS LESS THAN 10% OF THE NAEFS BRING EVEN 1/10" OF RAIN FOR A 6 HOUR PERIOD INTO THE NORTH BAY WHILE THE OPERATIONAL GFS HAS GONE COMPLETELY DRY. IT NOW APPEARS THAT IT IS ALSO SHOWING LESS OF A SHARP EASTERLY TURN DUE TO THE RIDGE ACTING MORE AS A BLOCK. THEREFORE...DECIDED TO DROP POPS BELOW 15% WHICH TAKES OUT ANY MENTION OF RAIN IN THE EXTENDED. WE WILL STILL KEEP AN EYE ON IT, BUT AT THIS TIME IT LOOKS VERY UNLIKELY TO BE A RAIN RODUCER.
Oh Well…
August 24,2014
Today the NWS San Francisco said in their forecast discussion that the Bay Area and northern California could see something unusual next weekend – rain – up to two thirds of an inch! Here is what they say adding that this uses one model and is “uncertain” but provocative.
THE MOST INTERESTING…AND UNCERTAIN…PART OF THE FORECAST CONCERNS MOISTURE FROM HURRICANE MARIE. THIS HURRICANE IS
RAPIDLY INTENSIFYING OFF THE WEST COAST OF MEXICO THIS MORNING. MARIEIS FORECAST TO MOVE TO THE WEST-NORTHWEST OVER THE NEXT FEW DAYS AND RAPIDLY WEAKEN ON WEDNESDAY…ONCE IT ENCOUNTERS COLDER WATERS NORTH OF 20N. HOWEVER…MOISTURE FROM MARIE MAY BECOME IMPORTANTTO OUR FORECAST BY NEXT WEEKEND. THE GFS HAS BEEN RELATIVELY CONSISTENT IN STEERING SUBTROPICAL MOISTURE FROM HURRICANE MARIE NORTHWARD ALONG 130W AND THEN PHASING THAT MOISTURE WITH A LONGWAVE UPPER TROUGH APPROACHING THE WEST COAST LATE IN THE WEEK. THE RESULT IS THAT THE GFS FORECASTS WIDESPREAD RAIN ACROSS OUR AREA NEXT WEEKEND. IN FACT…IF THE 00Z GFS WERE TO VERIFY SAN FRANCISCO WOULD PICK UP TWO-THIRDS OF AN INCH OF RAIN FROM SATURDAY MORNING THROUGH SUNDAY AFTERNOON. THAT MUCH RAIN IN SAN FRANCISCO IN AUGUST WOULD BE UNUSUAL TO SAY THE LEAST…ESPECIALLY CONSIDERING THAT THE RECORD RAINFALL IN DOWNTOWN SAN FRANCISCO FOR THE ENTIRE MONTH OF AUGUST IS ONLY 0.80 INCHES (IN 1976).
Here is the GFS model for next Sunday with yellow indicating higher rainfall.
