2:45 update – over 6,000 lightning strikes across the west in the last hour per Bay Area NWS.

…RED FLAG WARNING FOR DRY THUNDERSTORMS IN EFFECT BEGINNING
THIS EVENING…

.DISCUSSION…AS OF 8:40 AM PDT SUNDAY…AN UPPER LEVEL CUTOFF LOW
REMAINS JUST WEST OF THE BIG SUR COAST…AND THIS WILL DICTATE THE
WEATHER SITUATION FOR THE NEXT SEVERAL DAYS. VISIBLE SATELLITE
IMAGERY SHOWS STRATUS CLOUDS OVER THE COASTAL WATERS FROM CENTRAL
SONOMA COUNTY SOUTH THROUGH POINT CONCEPTION…AND INTO THE SAN
FRANCISCO AND MONTEREY BAYS…PLUS THROUGH THE SALINAS VALLEY. THE
MARINE LAYER DEPTH IS STILL AROUND 1200 FEET DEEP…AND SURFACE
PRESSURE GRADIENTS ARE STARTING TO TREND MORE NORTHERLY OR
OFFSHORE (ACV-SFO: 4.2 MB…WMC-SFO: 2.9 MB…AND SFO-SAC: 1.2
MB.) VISIBLE SATELLITE ALSO SHOWS A SWATH OF MID CLOUDS ROTATING
AROUND THE UPPER LOW…EXTENDING FROM SANTA BARBARA AND VENTURA
COUNTIES NORTHWARD INTO THE SAN JOAQUIN VALLEY.

MOISTURE AND INSTABILITY WILL CONTINUE TO ROTATE INTO CALIFORNIA
FROM AROUND THE CUTOFF LOW AS IT CONTINUES TO WOBBLE OFF THE
CENTRAL CALIFORNIA COAST. THE BEST CHANCES FOR CONVECTION ACROSS
OUR DISTRICT WILL BE LATE MONDAY THROUGH WEDNESDAY AS THE UPPER
LOW BEGINS TO APPROACH THE AREA. HOWEVER DUE TO THE INITIAL
DRYNESS OF THE ATMOSPHERE…A HEIGHTENED RISK OF DRY LIGHTNING
PROMPTED THE ISSUANCE OF A RED FLAG WARNING FOR ALL INLAND AND
HILLY AREAS BEGINNING AT MIDNIGHT TONIGHT AND EXTENDING INTO
WEDNESDAY. SHOWER/THUNDERSTORM CHANCES WILL MOSTLY BE CONFINED
TO THE NORTHERN HALF OF THE CWA FROM LATE TUESDAY NIGHT INTO
WEDNESDAY AND CHANCES WILL END IN ALL AREAS BY THURSDAY AS THE LOW
MOVES OFF TO THE NORTHEAST.

.FIRE WEATHER…AS OF 8:40 AM PDT SUNDAY…AN UPPER LOW OFF THE
CENTRAL CALIFORNIA COAST WILL BEGIN TO GENERATE SHOWER AND
THUNDERSTORM CHANCES ACROSS MOST OF OUR DISTRICT BY LATE THIS
EVENING WHEN THE FLOW ALOFT BECOMES MORE EASTERLY…BRINGING IN
GREATER MOISTURE AND INSTABILITY. INITIALLY…THE SUB-CLOUD LAYER
WILL BE QUITE DRY AND SO ANY THUNDERSTORMS THAT DEVELOP ON SUNDAY
NIGHT WILL LIKELY PRODUCE DRY LIGHTNING. A RED FLAG WARNING
IS IN EFFECT FOR MOST OF THE DISTRICT BEGINNING THIS EVENING AND
EXTENDING THROUGH EARLY WEDNESDAY MORNING. THE UPPER LOW WILL
REMAIN NEARLY STATIONARY THROUGH TUESDAY MORNING WHICH WILL MEAN
CONTINUED THUNDERSTORM CHANCES FOR MOST AREAS. SHOWER/THUNDERSTORM
CHANCES WILL GRADUALLY END FROM SOUTH TO NORTH FROM MIDDAY TUESDAY
THROUGH WEDNESDAY NIGHT AS THE LOW MOVES TO THE NORTHEAST. WILL
THEREFORE MAINTAIN A RED FLAG WARNING FOR MONTEREY AND SAN BENITO
COUNTIES ONLY THROUGH MIDDAY TUESDAY…BUT CONTINUE THE WARNING
THROUGH AT LEAST TUESDAY NIGHT FOR THE SF BAY AREA. THUNDERSTORMS
WILL LIKELY PRODUCE DECENT RAINFALL BY LATE MONDAY…BUT EVEN THEN
NEW FIRE STARTS WILL STILL BE POSSIBLE GIVEN HOW DRY THE FUELS

MAIN FORECAST CONCERN REMAINS FOR SUNDAY NIGHT THROUGH THE FIRST
HALF OF NEXT WEEK AS MOISTURE WORKS ITS WAY IN FROM THE SOUTHEAST
AS THE UPPER LEVEL LOW REMAINS NEARLY STATIONARY. INSTABILITY WILL
INCREASE THROUGH THE DAY TOMORROW AND BY TOMORROW NIGHT THE MODEL
GUIDANCE CONTINUES TO SUGGEST THE POSSIBILITY OF NOCTURNAL
CONVECTION ESPECIALLY OVER THE EASTERN THIRD OF THE CWA.
CONVECTIVE PARAMETERS ARE FAIRLY IMPRESSIVE WITH MODIFIED TOTAL
TOTALS UP TO 34C AND MUCAPE UP TO 300 J/KG) HOWEVER, BY MONDAY,
THE COVERAGE WILL CONTINUE TO SPREAD AND LIKELY BRING AT LEAST A
SLIGHT CHANCE FOR SHOWERS AND THUNDERSTORMS TO THE ENTIRE CWA.

ALTHOUGH THIS IS FAR FROM A SLAM-DUNK (CUT-OFF LOWS ALWAYS PRESENT
CHALLENGING FORECASTS) THERE REMAINS ENOUGH CONFIDENCE BASED OFF
OF REPEATED MODELS RUNS PLUS GOOD INITIALIZATION AND 48 HOUR
FORECAST OF THE PLACEMENT OF THE LOW, TO GO WITH A FIRE WEATHER
WATCH FOR ALMOST THE ENTIRE AREA. THE MAIN IMPACTS FROM THIS WILL
BE POSSIBLE NEW FIRE STARTS, GUSTY WINDS, AND BY LATER MONDAY INTO
TUESDAY, SMALL HAIL AND BRIEF HEAVY RAIN. THE LOW WILL VERY SLOWLY
PROGRESS TO THE NORTHEAST AND BE OUT OF OUR AREA BY WEDNESDAY
NIGHT. AS THE LOW MOVES TO THE NORTH, THE MAIN FOCUS FOR
CONVECTION WILL ALSO MOVE FROM SOUTH TO NORTH (IN FACT, SOME
GUIDANCE QUICKLY REMOVES CHANCES FOR SHOWERS BY MONDAY EVENING
ACROSS MONTEREY AND SAN BENITO COUNTIES).