Wildfire in California, September 9 to 15, 2013

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
928 AM PDT MON SEP 9 2013

.SYNOPSIS...
VERY WARM TEMPERATURES TODAY & TOMORROW AS HIGH PRESSURE IMPACTS
THE WEST COAST. TODAY SHOULD BE THE PEAK HEAT DAY BEFORE A SLOW
COOLING TREND STARTS TUESDAY. THERE IS A THREAT OF THUNDERSTORMS
NEAR THE SIERRA CREST MID WEEK.

.DISCUSSION...

NORCAL IS BETWEEN UPPER HIGH OVER THE EASTERN PACIFIC AND LOW
PRESSURE OVER THE LOWER COLORADO RIVER VALLEY. THIS IS KEEPING THE
AREA IN A NORTHERLY FLOW PATTERN WHICH IS PROVIDING MUCH ABOVE
NORMAL HIGH TEMPERATURES. HIGH'S WILL BE NEAR OR JUST ABOVE 100
DEGREES AT MOST VALLEY LOCATIONS THIS AFTERNOON. A RATHER DRY
ATMOSPHERE IS IN PLACE OVER NORCAL WITH PRECIPTABLE WATER VALUES
BELOW 0.70 INCHES. A FEW CLOUD BUILD-UPS WILL BE POSSIBLE OVER THE
SOUTHERN SIERRA THIS AFTERNOON...BUT NOT EXPECTING ANY THUNDERSTORMS
WITH THE DRY ATMOSPHERE IN PLACE. HOWEVER...INCREASING MID-LEVEL
MOISTURE TUE AND WED WILL LEAD TO ISOLATED STORM CHANCES SOUTH OF
INTERSTATE 80. HAZY SKIES WILL BE LIKELY THE NEXT FEW DAYS DO TO
THE RIM FIRE AND THE MORGAN FIRE WHICH IS OVER MT. DIABLO IN
CONTRA COSTA COUNTY.

.PREVIOUS DISCUSSION...

ANOTHER HOT DAY FOR THE VALLEY. THE AIRMASS ALOFT IS QUITE WARM
MEASURING ABOUT 24 TO 27 DEGREES C OVER OUR CWA. THAT WILL
TRANSLATE TO DAYTIME HIGHS PEAKING IN THE UPPER 90S TO LOW 100S
JUST LIKE YESTERDAY. HOTTEST PART OF THE VALLEY WILL BE IN THE
REDDING/RED BLUFF VICINITY WHERE MAX TEMPS TODAY WILL BE AROUND 103.

LIGHT NORTHERLY FLOW WILL CONTINUE IN THE VALLEY TODAY. THE DELTA
BREEZE IS EXPCTED TO RE-DEVELOP LATE TONIGHT/EARLY TUESDAY BUT IT
WON'T HAVE MUCH ABILITY TO COOL US THIS AFTERNOON. THE MARINE
LAYER IS STILL SHALLOW AT 1000 FT DEEP PLUS THE ONSHORE GRADIENT
IS NOT QUITE STRONG ENOUGH TO OVERTAKE THE NORTHELRY GRADIENT TODAY.

FOR TOMORROW, WE WILL START A SUBTLE COOLING TREND. THE DELTA
BREEZE BEGINS TO RE-DEVELOP AS THE HIGH PRESSURE CELL WEAKENS AND
MOVES OFFSHORE. HOWEVER, TUESDAY WILL STILL BE A VERY WARM DAY IN
THE VALLEY WITH HIGHS MID 90S UP TO AROUND 101 DEGREES. MOUNTAINS
AND FOOTHILLS WILL STILL BE IN THE 70S TO LOW 90S. LOW CLOUDS
THROUGH THE DELTA MAY ALSO NUDGE INTO THE DELTA REGION WITH THE
RETURN OF WEAK ONSHORE FLOW.

BY WEDNESDAY, A FEW MORE DEGREES OF COOLING WILL KEEP THE VALLEY
HIGHS IN THE LOW TO UPPER 90S AS WE SAY GOODBYE TO THE TRIPLE
DIGIT TEMPERATURES.

AFTER THE HEAT STARTS TO COOL, THE NEXT CONCERN IS THE POSSIBILITY OF
SIERRA THUNDERSTORMS FOR TUESDAY AND WEDNESDAY.  THERE WILL BE
ENOUGH INSTABILITY ALONG THE CREST AND SOME MOISTURE THAT WE COULD
SEE SOME CONVECTION...ALTHOUGH IT SHOULD BE LIMITED TO AREAS
CLOSER TO THE CREST AND SOUTH OF LAKE TAHOE.  JBB

.EXTENDED DISCUSSION (FRIDAY THROUGH MONDAY)

DRY WEATHER WITH NEAR TO SLIGHTLY ABOVE NORMAL MAX TEMPERATURES
EXPECTED FOR THE REST OF THE WEEK AND THROUGH THE WEEKEND.
INTERIOR NORCAL WILL BE UNDER AN UPPER LEVEL RIDGE BETWEEN AN
OFFSHORE LOW OVER THE EASTERN PACIFIC AND A WEAK LOW OVER THE
GREAT BASIN. THE ECMWF MODEL IS MORE PROGRESSIVE WITH HAVING THE
OFFSHORE LOW MOVE INTO NORCAL SATURDAY NIGHT/EARLY SUNDAY. BUT THE
GFS DOESN'T HAVE THE OFFSHORE LOW MOVING INLAND UNTIL LATE SUNDAY
NIGHT INTO MONDAY MORNING. HAVE TRENDED THE FORECAST SO THAT
SUNDAY TEMPERATURES SHOW FURTHER COOLING SINCE A TROUGH PATTERN
OVER THE AREA SUNDAY INTO MONDAY IS LOOKING INCREASINGLY LIKELY.
AT THIS POINT THE LOW LOOKS RELATIVELY DRY SO THE MAIN AFFECTS
SHOULD BE COOLER TEMPERATURES. PRECIPITATION WITH THE CURRENT
TRACK WOULD REMAIN TO THE NORTH OF THE FORECAST AREA. EK/JBB

&&

.AVIATION...

HI PRES OFSHR EXTDS INLD WITH NLY FLOW ALF. VFR CONDS OVR INTR
NORCAL NXT 24 HRS EXC LCL MVFR/IFR POSS VCNTY RIM FIRE. ISOLD N-E
SFC WND GSTS UP TO 25 KTS POSS TDA INTO TUE MRNG...MNLY OMTNS AND
THRU CANYONS.

&&

.STO WATCHES/WARNINGS/ADVISORIES...
NONE.
&&