EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN DIEGO CA
925 AM PDT SAT MAY 15 1999
...SYNOPSIS...
A BROAD UPPER TROUGH OF LOW PRESSURE OVER THE WEST WILL BEGIN TO
MOVE EAST ON SUNDAY WITH WEAK HIGH PRESSURE BUILDING INTO
SOUTHERN CALIFORNIA FOR MONDAY. A COASTAL EDDY WILL ONCE AGAIN BRING
LOW CLOUDS AND PATCHY FOG TO AREAS WEST OF THE MOUNTAINS TONIGHT
THROUGH SUNDAY MORNING. FOR THE MOUNTAINS AND DESERTS... BREEZY
TODAY...WITH A LITTLE WARMER TEMPERATURES FOR SUNDAY.
...DISCUSSION...
COAMPS AND OFF TIME ETA RUNS (PROBABLY 00Z AND 12Z RUNS AS
WELL...XCP OUTPUT FM THOSE RUNS IS ON A COARSE 80 KM GRID
EFFECTIVELY MASKING SUBSYNOPTIC DETAIL) CONTINUE TO PERFORM WELL IN
SHOWING THE DIURNAL TRENDS OF THE EDDY WITH THE ETA PERFORMING
REASONABLY WELL IN SHOWING TRENDS WITH THE MARINE LYR DEPTH.
ACARS SOUNDINGS SHOW THE BASE OF THE MARINE INVERSION BETWEEN 4000
AND 4500 FEET...SIMILAR OF SLIGHTLY LWR THAN 24 HOURS AGO.
HOWEVER...COOLING IN THE LYR FM 850 MB TO 700 MB FM THE INLAND
EMPIRE AND ORANGE COUNTY N HAS WEAKENED THE INVERSION IN THOSE
AREAS...WITH RESULTING PATCHIER STRATUS COVERAGE IN THOSE AREAS
VERSUS THE PAST FEW NIGHTS. HOWEVER...A 15Z ACARS SOUNDING FM LAX
SHOWED THAT THE MARINE INVERSION IS BEGINNING TO STRENGTHEN WITH
STRATUS COVERAGE ACTUALLY GREATER NOW THAN OVERNIGHT.
CSTL LOW CLOUDS...COAMPS AGAIN SHOWS THE EDDY DECAYING TODAY...THEN
REFORMING TONIGHT...A TYPICAL DIURNAL CYCLE FOR THE EDDY.
HOWEVER...S WINDS ALG THE CST THIS MORNING ARE ACTUALLY STRONGER
THAN 24 HOURS AGO AND HENCE DECAY OF EDDY AND ASSOCD CLEARING TODAY
MAY BE SLOWER THAN SHOWN BY MDLS AND THAT INDICATED IN THE CURRENT
PACKAGE. HAVE UPDATED TO INDICATE A SOMEWHAT SLOWER AND LESS
EXTENSIVE CLEARING PATTERN FOR TODAY. 00Z ETA SHOWED A GRADUAL DECR
IN MARINE LYR DEPTH...TO AROUND 3000 FEET...DURG THE FORECAST PD.
HOWEVER...GIVEN THAT HEIGHTS ALF ARE FORECAST TO CHANGE LTL DURG THE
NEXT 24 HOURS...WOULD NOT EXPECT MUCH CHANGE...OTHER THAN DIURNAL
CHANGES...THRU SUN MORNING. ETA ALSO SHOWS THAT MOST 850 MB COOLING
HAS ALREADY OCCURRED (ALSO SUPPORTED BY THE 15Z ACARS SOUNDING FM
LAX)...SO COOLING SUFFICIENT TO BREAK THE MARINE INVERSION APPEARS
UNLIKELY. HENCE...AREAS OF LOW CLOUDS AND FOG SHOULD ONCE AGAIN PUSH
INLAND TONIGHT TO THE LOWER CSTL SLOPES. FOR AFTERNOON FORECAST
ISSUANCE...WL EVALUATE INCOMING 12Z GUIDANCE FOR INFO ON EDDY
PERSISTENCE FOR SUN AND RESULTING IMPACTS ON CLRG W OF MTNS FOR SUN.
TEMPERATURES...HEIGHTS/TEMPERATURES ALF ARE LWR/COOLER TODAY THAN
FRI...WITH SOME INCR/WARMING SHOWN FOR SUN. FOR MTNS AND DESERTS...
THIS SHOULD RESULT IN SOME COOLING TODAY VERSUS FRI WITH SOME
WARMING FOR SUN. FOR AREAS W OF THE MTNS...THE MARINE INFLUENCE
SHOULD MODULATE THESE TRENDS SOMEWHAT WITH SLIGHT COOLING
TODAY...AND LIKELY A SLOWER WARMUP ON SUNDAY THAN SHOWN IN THE MOS
GUIDANCE OR IN THE CURRENT FORECAST PACKAGE...ESPECIALLY IF THE EDDY
THAT DEVELOPS TONIGHT PERSISTS WELL INTO SUN. WL NOT MAKE ANY
CHANGES FOR THE LATTER PERIODS NOW...BUT WL TAKE A CLOSER LOOK FOR
THE AFTERNOON ISSUANCE.
WINDS...STRONGEST GRADIENTS TO SUPPORT WINDS IN THE MTNS AND DESERTS
ARE TODAY WITH WEAKENING OF THE GRADIENTS SHOWN FOR SUN. EVEN
TODAY...HOWEVER...WINDS SHOULD REMAIN BLO ADV LVLS.
SAN 000
.SAN...NONE.
MARTIN