EXTREME SOUTHWESTERN CALIFORNIA AREA FORECAST DISCUSSION
NWS SAN DIEGO CA
AFDSAN 410 AM PST TUE FEB 8 2000
...SYNOPSIS...
MOIST SOUTHERLY FLOW ALOFT WILL SPREAD CONSIDERABLE CLOUDINESS ACROSS
SOUTHWEST CALIFORNIA TODAY. THE OFFSHORE FLOW HAS ENDED AND DENSE FOG IS
PRESENT ALONG THE COAST. THE MARINE LAYER IS EXPECTED TO DEEPEN RAPIDLY
TONIGHT AND WEDNESDAY. A WEAK UPPER LEVEL TROUGH MOVING ACROSS THE AREA
MAY CAUSE SPRINKLES OR LIGHT RAIN LATE TONIGHT AND WEDNESDAY.
...DISCUSSION...
MODERATE SOUTHERLY FLOW IS BEING OBSERVED IN THE LOWER LAYERS WITH
STRONG SOUTHERLY FLOW ABOVE 10000 FEET BY BOTH WSR-88D VAD WINDS AND
ACARS. SURFACE PRESSURE GRADIENTS ARE REVERSING AND FORECAST TO INCREASE
TO +5 MB KSAN-KIPL BY 09/00Z. MODEL CROSS SECTIONS AND TIME SERIES SHOW
A CLASSIC WARM FRONTAL PATTERN WITH STEADY LOWERING OF THE BASE OF THE
SUBTROPICAL CLOUD SHIELD TODAY. THEN DUE TO INCREASED ONSHORE PRESSURE
GRADIENTS SIGNIFICANT COOLING AND MOISTENING IN THE LOWER LAYERS TONIGHT
THROUGH WEDNESDAY. WEAKENED AND ELONGATED UPPER LEVEL TROUGH MOVES
ACROSS WEDNESDAY GENERATING -3 UBAR UPWARD VERTICAL MOTION PER AVN
MODEL...POSSIBLY ENOUGH TO GENERATE PRECIPITATION. THE ETA/MESOETA
MODELS ARE MORE AGGRESSIVE ON THE MOISTENING OF THE AIR MASS AND THREAT
OF PRECIPITATION. CURRENT FORECASTS PRECIPITATION INTENSITY AND POPS
WERE MORE IN LINE WITH AVN SOLUTION. GIVEN AVN INITIALIZATION WAS MUCH
BETTER TONIGHT AND APPEARS TO BE VERIFYING WELL IN VIEW ON RECENT
SATELLITE IMAGERY AND HOURLY RUC MODEL UPDATES...ONLY PERFORMED MINOR
ADJUSTMENTS TO CUT BACK ON COVERAGE AND ONSET.
AS FAR AS EXTENDED....SYSTEM ON THURSDAY MORE LIKELY TO PASS TO THE
NORTH WITH MAIN EFFECT CONTINUING ONSHORE FLOW WITH GUSTY MOUNTAIN AND
DESERT WINDS. MODEL GUIDANCE DID HAVE POPS FOR THIS DAY...ALREADY IN
FORECAST SO LEFT IN BUT CONFIDENCE LOW. THE SYSTEM FORECAST BY MRF TO
MOVE ACROSS THE STATE ON SATURDAY IS MORE LIKELY TO PRODUCE THE NEXT
PRECIPITATION THREAT FOR SW CALIFORNIA.
SAN 011
.SAN...DENSE FOG ADVISORY UNTIL 8 AM...CAZ043...SEE LAXNPWSAN.
BALFOUR