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000 FXUS66 KSGX 242043 AFDSGX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN DIEGO CA 200 PM PDT WED SEP 24 2008 .SYNOPSIS... A SHALLOW MARINE LAYER AND ONSHORE FLOW WILL CAUSE AREAS OF COASTAL LOW CLOUDS AND FOG DURING THE NIGHTS AND MORNINGS...EXTENDING LOCALLY INLAND. IT WILL BE WARM INLAND THROUGH FRIDAY UNDER HIGH PRESSURE...THEN A LITTLE COOLER THIS WEEKEND AND EARLY NEXT WEEK AS THE HIGH WEAKENS. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... SIMILAR WEATHER IS EXPECTED THU UNDER A RIDGE OF HIGH PRESSURE. THE RIDGE WILL KEEP THE MARINE LAYER SHALLOW AND THE DAYTIME TEMPS HIGH AWAY FROM THE COAST. AREAS OF DENSE FOG WILL SHROUD THE COASTAL MESAS LATE TONIGHT AND IN THE MORNING...BUT WITH MINIMAL FOG COVER. ON FRI THE UPPER HIGH BEGINS TO SLOWLY BREAK DOWN AND ONSHORE FLOW INCREASES SLIGHTLY. THAT WILL MEAN A GENTLE COOLING TREND. WEAK UPPER LOW PRESSURE OFF THE COAST WILL DRIFT ALMOST IMPERCEPTIBLY THROUGH CA OVER THE WEEKEND WHICH WILL DEEPEN THE MARINE LAYER AND EXTEND THE COASTAL CLOUDS AT NIGHT. A FAIRLY STRONG JET STREAM SETS UP ACROSS THE EASTERN PACIFIC NEXT WEEK WHICH WILL PUSH THE HIGH PRESSURE RIDGE OVER THE INTERIOR EASTWARD. THIS WILL START THE WET SEASON IN THE PACIFIC NORTHWEST...BUT SOCAL WILL REMAIN SOUTH OF THE ENERGY WITH WEATHER CLOSE TO SEASONAL. && .AVIATION... 241900Z...MARINE LAYER DEPTH REMAINS 1000 FEET OR LESS OVER THE AREA. STRATUS WITH BASES AROUND 500 FEET MSL" onClick="return popup(this, 'notes')">MSL SHOULD REFORM ALONG THE COAST AROUND SUNSET AND SPREAD LOCALLY INLAND OVER THE COASTAL VALLEY AND SOME MESA AREAS BETWEEN MIDNIGHT AND SUNRISE ON THURSDAY. BREAK UP ON THURSDAY SHOULD BY BY 16Z. ABOVE THE MARINE LAYER...A MOSTLY CLEAR SKY WITH UNRESTRICTED VISIBILITIES WILL CONTINUE THROUGH THURSDAY. KSAN...STRATUS WITH BASES AROUND 500 FEET MSL SHOULD MOVE BACK OVER THE AIRPORT BY 12Z THURSDAY. CEILING WILL LIKELY REQUIRE ILS RUNWAY 9 ARRIVALS UNTIL BREAKUP AROUND 16Z ON THURSDAY. HORTON && .FIRE WEATHER... THURSDAY EXPECTED TO BE THE WARMEST AND DRIEST DAY THIS WEEK UNDER STRONG HIGH PRESSURE ALOFT. DURATIONS OF HUMIDITY BELOW 10 PERCENT EACH DAY WILL NOT MEET OR EXCEED 10 HOURS BUT THERE WILL BE POOR OVERNIGHT RECOVERY OF HUMIDITY TONIGHT AND AGAIN THURSDAY NIGHT FOR ELEVATIONS ABOVE 1000 FEET AND NOT LOCATED IN WIND SHELTERED AREAS...ONLY A FEW HOURS EXPECTED EACH NIGHT WITH RELATIVE HUMIDITY ABOVE 25 PERCENT. ON FRIDAY THE RIDGE BEGINS TO BREAK DOWN. DRY AND WARM WILL STILL BE IN PLACE THIS DAY BUT WEST TO SOUTHWEST WINDS WILL BE GUSTING OVER 25 MPH THROUGH PASSES AND ALIGNED CANYONS AND VALLEYS. BOTTOM LINE...ANOTHER 48 TO 60 HOURS OF CRITICAL FIRE WEATHER CONDITIONS FOR ALL BUT COASTAL AREAS OF SOUTHWEST CALIFORNIA. && .SGX WATCHES/WARNINGS/ADVISORIES...NONE. && $$ PUBLIC...MM AVIATION/MARINE...HORTON FIRE...BALFOUR