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(EXTRACTED FROM FXUS66 KMTR 031259)


    As of 4:59 AM PST Sunday...For the 12z TAFs. It's
    VLIFR-IFR across much of the cwa. Conditions are favorable for
    ongoing morning low ceilings and fog /VLIFR-IFR/ due to positive
    heat and water vapor flux from sea surface to air and from plenty
    of residual near surface based water vapor from recent rain and
    drizzle, winds are light and overall the cool air mass supports
    near surface air reaching saturation both over water and land.
    
    Webcam at KSFO shows fog, visibility has lowered to 1/2 to 1/4
    mile, 12z taf recently amended to IFR-LIFR for much of the morning.
    
    At peak diurnal mixing potential near midday, cloud layers aloft
    will be returning before the arrival of a cold frontal passage and
    rain late tonight and Monday morning. Some rollover of warmer air
    aloft occurs over near surface based cooler air which may sustain
    stratiform cloud layers a bit longer into the afternoon before
    seeing appreciable improvement to MVFR-VFR, caveat is it'll likely
    be slow going in cloud lifting and improvement today. Thereafter,
    cloud layers return and lower with rain developing north to south
    late tonight and Monday with frontal passage; cigs and vsbys again
    deteriorating during this time.
    
    Vicinity of KSFO...1/2 to 1/4 mile in fog in recent observations,
    as discussed conditions are favorable for ongoing poor visibilities
    and low ceilings through much of the morning. Will have to wait
    for improvement to coincide with max potential diurnal mixing
    today, which may be difficult to attain given how saturated the
    air is at the moment. Low sun angle, cloud layers aloft today will
    slow mixing potential since winds will be mainly light too.
    Overall expect slow improvement today. If after any appreciable
    improvement today expect ceilings and visibilities to lower ahead
    of the late night and Monday cold frontal passage with rain.
    
    SFO Bridge Approach...Similar to KSFO.
    
    Monterey Bay Terminals...VLIFR-IFR in nearly ideal conditions for
    fog and low cloud ceilings through morning. Some improvement during
    midday with diurnal mixing attempting to start, but expect slow
    going if any appreciable lifting today given low sun angle, light
    winds. For tonight and Monday ceilings then lowering to IFR in
    light rain ahead of Monday's cold front.

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