SOUTHWEST CALIFORNIA AREA FORECAST DISCUSSION
NWS LOS ANGELES/OXNARD CA
AFDLOX 310 AM PST FRI MAR 1 2002
PERSISTENT EDDY CIRCLN HAS DEEPENED THE MARINE LAYER INTO THE COASTAL
SLOPES OVERNIGHT. 00Z NKX SOUNDING SHOWED MARINE LAYER DEPTH NEAR 2500
FEET...BUT RECENT ACARS SOUNDINGS FROM THE L.A. BASIN AND RAWS DATA
INDICATE THAT THE MARINE LAYER HAS DEEPENED TO BETWEEN 3500 AND 4000
FEET. MESO-ETA SHOWS THE EDDY CONTINUING THRU THE MORNING HOURS
TODAY...BEFORE FINALLY DISSIPATING THIS AFTERNOON. PRESSURE GRADIENTS
REMAIN ONSHORE AT THIS TIME...ALTHOUGH OFFSHORE TRENDS HAVE BEGUN TO
DEVELOP DURING THE LAST FEW HOURS. COMPARISON OF 00Z AVN/MESO-ETA 6
HOUR FCSTS TO THE 06Z SFC OBS SHOWS THAT BOTH MODELS WERE CONSIDERABLY
OVERDONE WITH THE STRENGTH OF THE SFC HIGH BUILDING INTO NEVADA...WITH
THE AVN MUCH WORSE THAN THE MESO-ETA. 06Z MESO-ETA APPEARS TO HAVE
INITIALIZED BETTER...AND IS PREFERRED. BOTTOM LINE IS THAT THE DEEP
MARINE LAYER WILL CONTINUE ACROSS THE COASTAL AREAS THIS MORNING...
WHILE GRADUALLY BEING FORCED OUT OF THE MTNS AND THEN THE VALLEYS BY
THE INCREASING OFFSHORE FLOW. COLD ADVECTION WILL WEAKEN THE INVERSION
AS WELL...AND WOULD EXPECT THE MARINE LAYER TO BE GONE FROM THE FCST
AREA BY TONIGHT...EXCEPT FOR SOME PATCHY LOW CLOUDS/FOG WHICH MAY
SNEAK INTO THE L.A. COUNTY COAST. MAX TEMPS TODAY WILL REMAIN A FEW
DEGREES BELOW NORMAL ACROSS THE LOWER ELEVATIONS DUE TO THE MARINE
INFLUENCE...WHILE THE MTNS/DESERTS WILL COOL OFF CONSIDERABLY AS COLD
ADVECTION TAKES HOLD. WOULD EXPECT WINDS TO INCREASE ACROSS THE MTNS
TODAY...BUT WINDS WILL PROBABLY HAVE A DIFFICULT TIME SURFACING IN THE
VALLEYS AS THERE WILL STILL BE A MARINE LAYER TO OVERCOME. WIND SPEEDS
ACROSS ALL AREAS SHOULD REMAIN BELOW ADVISORY LEVELS THROUGH TODAY.
AS FOR TONIGHT AND SATURDAY...MODELS CONTINUE TO HAVE MAJOR
DIFFERENCES WITH THE HANDLING OF THE SECONDARY S/W DROPPING THROUGH
THE ROCKIES...WHICH ULTIMATELY WILL DETERMINE THE STRENGTH OF OUR
OFFSHORE FLOW. 00Z AVN IS SLOWER...MORE CLOSED OFF...AND FURTHER WEST
WITH THIS FEATURE...WHILE THE 00Z ETA AND 06Z MESO-ETA ARE FURTHER
EAST AND MORE PROGRESSIVE. BY 18Z SAT...THE AVN DEPICTS A 1044 MB HIGH
CENTERED OVER SOUTHERN IDAHO...WHILE THE ETA MODELS HAVE MUCH WEAKER
HIGH PRESSURE CENTERED OVER MONTANA OR SRN CANADA. AS A RESULT...THE
ETA MODELS HAVE MUCH LESS OFFSHORE SURFACE FLOW...COLD ADVECTION AND
UPPER SUPPORT THAN DOES THE AVN. IF THE AVN WERE TO VERIFY WE COULD
SEE HIGH WIND WARNING CRITERIA MET ACROSS THE MTNS AND SOME OF THE
VALLEYS...WHILE THE 06Z MESO-ETA SUGGESTS PROBABLY ONLY WIND ADVISORY
CONDITIONS. BEST COURSE FOR THE FORECAST APPEARS TO BE A COMPROMISE.
WILL INDICATE WIND ADVISORY TYPE CONDITIONS ACROSS THE MTNS...VALLEYS
AND VTU COAST ON SATURDAY...BUT WILL NOT ISSUE ANY HIGH WIND WATCHES
AT THIS TIME. TEMPS ON SATURDAY WILL BE QUITE TRICKY DEPENDING ON THE
STRENGTH OF THE OFFSHORE FLOW. WILL GENERALLY STICK WITH THE PREVIOUS
IDEA OF WARMING FOR THE COASTS...LITTLE CHANGE FOR THE LOWER VALLEYS...
AND COOLING FOR THE UPPER VALLEYS...MTNS AND DESERTS.
OFFSHORE FLOW WILL CONTINUE SAT NIGHT AND SUNDAY...ALTHOUGH THE UPPER
SUPPORT APPEARS MARGINAL ACROSS MY FORECAST AREA...AND THE MORE
EASTERLY FLOW DIRECTION WOULD BE MORE FAVORABLE FOR THE INLAND
EMPIRE. STILL WOULD EXPECT AT LEAST LOCALLY WINDY CONDITIONS IN THE
MTNS AND SOME OF THE LOWER ELEVATIONS. THERE IS SOME POTENTIAL FOR A
LATE SEASON FREEZE ACROSS THE CENTRAL COAST...BUT THIS WILL DEPEND ON
THE STRENGTH OF THE COLD AIRMASS AND IS QUITE UNCERTAIN AT THIS TIME.
MAX TEMPS SHOULD BE ABLE TO WARM UP SOMEWHAT ACROSS THE LOWER
ELEVATIONS SUNDAY AFTERNOON AS THE COLD ADVECTION WEAKENS...WITH MOST
LOCATIONS RANGING FROM THE UPPER 60S TO MID 70S.
EXTENDED...WEAK OFFSHORE FLOW WILL CONTINUE SUN NIGHT AND MONDAY
MORNING...TRANSITIONING TO ONSHORE BY MON EVENING. UPPER RIDGE
FLATTENS WITH CONTINUED ONSHORE FLOW TUE AND WED...WHICH WILL ALLOW
FOR THE RETURN OF THE MARINE LAYER AND A COOLING TREND. MEDIUM RANGE
MODELS HAVE COME INTO BETTER AGREEMENT ON THE PATTERN FOR NEXT WEEK...
WITH A GENERAL CONSENSUS FOR A MOIST WESTERLY FLOW INTO CA BY THU.
CONSIDERING THE DRYNESS OF THE WINTER TO DATE...AM STILL RELUCTANT TO
FULLY BELIEVE THIS SOLUTION JUST YET...BUT GIVEN THE DECENT MODEL
AGREEMENT AND RUN-TO-RUN CONSISTENCY OF THE MRF...AND TO BETTER BLEND
WITH MTR AND HNX...WILL INTRODUCE A CHANCE OF RAIN TO THE CENTRAL COAST
ZONES FOR THURSDAY. FURTHER SOUTH...WILL INDICATE MOSTLY CLOUDY SKIES
AND COOL CONDITIONS BUT KEEP THINGS DRY FOR NOW.
LAX 000. JACOBSON
.LOX...SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS (SEE LAXCWFLAX).