Flash Flood Warning 1, NWS Hanford, CA

INTERIOR CENTRAL CALIFORNIA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HANFORD CA
310 PM PDT WED JUL 17 2002

THE WESTERN EDGE OF THE MONSOON SHOWS UP VERY WELL ON THE CURRENT
VISIBLE SATELLITE...WHERE THUNDERSTORMS FIRED UP ALONG THE CREST
OF THE SIERRA NEVADA THIS AFTERNOON. THE ANVIL TOPS OF THESE
THUNDERSTORMS HAVE BEEN DIRECTED TOWARD NEVADA...AN INDICATION
THAT STEERING WINDS ALOFT ARE BLOWING FROM THE SSW. THE MECHANISM
HELPING TO DRIVE THESE THUNDERSTORMS IS AN UPPER LEVEL LOW...
ESTIMATED TO BE CENTERED JUST WEST OF THE BAY AREA ON CURRENT WATER
VAPOR IMAGERY.

THE MODELS TRACK THE UPPER LEVEL LOW SLOWLY EASTWARD ACROSS INTERIOR
CENTRAL CA DURING THE NEXT 24 HRS...DURING WHICH TIME WINDS ALOFT
WILL GRADUALLY BECOME MORE WESTERLY AND FINALLY PUSH THE BACK EDGE
OF MONSOONAL MOISTURE EAST OF THE SIERRA. HOWEVER...AS THE LOW DRIFTS
ONSHORE TONIGHT...THE MODELS DO FORECAST RATHER HEALTHY PVA ACROSS
INTERIOR CA. THIS WARRANTS CONCERN THAT THERE WILL BE ENOUGH INSTABILITY
AND ATMOSPHERIC LIFT TO KEEP TSTM ACTIVITY ALIVE OVER THE HIGHER
ELEVATIONS THRU AT LEAST THE EARLY PART OF TONIGHT...AND PERHAPS
INTO WEE HOURS THURSDAY MORNING. HAVE DWINDLED POPS IN THE MTN ZONES
AFTER THIS EVENING...HOWEVER...SWING SHIFT FORECASTERS WILL NEED TO
MONITOR AND REASSESS IF TSTM ACTIVITY DOES NOT DIMINISH MUCH TONIGHT.
AND IF THE 18Z MESO-ETA IS RIGHT...CONVECTION MAY NOT NECESSARILY BE
CONFINED TO THE HIGHER ELEVATIONS TONIGHT. THIS PARTICULAR MODEL
FORECASTS A MODEST INCREASE IN 700MB REL HUM OVER THE SOUTHERN AND
EASTERN SJ VLY TONIGHT AS THE NOSE OF THE 300MB JET CUTS UNDERNEATH THE
UPPER LEVEL LOW. ON THURSDAY...THE BEST CHANCE OF AFTN CONVECTION
WILL BE NEAR THE SIERRA CREST WITH MESO-ETA FORECASTING CAPES APPROACHING
700 JOULES/KG AND LIFTED INDICES BETWEEN -2 AND -4.

IN THE LOW LEVELS...THE MARINE LAYER HAS REMAIN ESSENTIALLY UNCHANGED
SINCE THIS MORNING...AVERAGING ABOUT 1500 FT DEEP ON THE FORT ORD
PROFILER. NEITHER HAS THERE BEEN ANY INCREASE IN ONSHORE FLOW THRU
THE DELTA. SO A MARINE INTRUSION INTO THE SJ VLY TONIGHT WILL AGAIN
BE TOO SHALLOW TO BRING ANY SIGNIFICANT COOLING. IN FACT...MOS GUIDANCE
FORECASTS NO CHANGE IN 1000-500MB THICKNESSES OR LOWER BOUNDARY LAYER
TEMPS IN THE SJ VLY DURING THE NEXT 24 HRS. WILL THEREFORE BUMP UP
TEMPS FIRST TWO PERIODS IN VLY ZONES TO MATCH RECENT DIURNAL RANGES.

WHILE THE MEDIUM RANGE MODELS LIFT THIS UPPER LEVEL LOW NORTHEASTWARD
INTO THE NORTHERN ROCKIES FRIDAY...MOST ARE STILL SHOWING A WEAK
TROUGH HANGING BACK OVER THE EASTERN PACIFIC THRU THE WEEKEND. THIS
SHOULD HAVE LITTLE IMPACT ON CENTRAL CA EXCEPT TO KEEP COASTAL AREAS
COOL WITH CONTINUED ONSHORE FLOW WHILE TEMPS IN THE INTERIOR VALLEYS
CONTINUE TO AVERAGE SLIGHTLY ABOVE NORMAL. BY THE MIDDLE OF NEXT WEEK...
TEMPERATURES ARE LIKELY TO AVERAGE WELL ABOVE NORMAL AS A STRONG
RIDGE OF HIGH PRESSURE ALOFT BUILDS WESTWARD OVER CALIFORNIA FROM THE
FOUR-CORNERS REGION.

.HNX...NONE.

DURFEE