Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 250218

Area Forecast Discussion
National Weather Service San Francisco Bay Area
718 PM PDT Fri Mar 24 2017

.SYNOPSIS...Showers can be expected into the evening behind a
departing cold front.  A break in the rain is expected Saturday
with showers anticipated to return starting late on Sunday as a
low pressure system moves through.

&& of 1:40 PM PDT Friday...Widespread rainfall
across our CWA today as a moderate cold front quickly advances
through our region. So far rainfall reports have generally been a
bit lower than forecast in most locations which has meant fewer
hydro reports than expected. Even when the main band of moderate
rainfall went through the Bay Area late a couple of hours ago,
reports of roadway flooding or hydro issues were less than what we
typically would typically see. One possible reason is as expected
the front went through at an ideal time between the morning rush
and evening commute -- typically when traffic is quite a bit less.
Regardless, still decent values that will add to our impressive
totals for the winter of 2016/17.

Winds also increased as the front approached, however outside of a
few isolated spots, speeds have been lower than advisory criteria.
Latest analysis suggests that the peak winds have already
occurred, so the wind advisory was cancelled for all locations.

Post-frontal Scattered showers can be expected into tonight
especially for far southern portions. However, amounts will
generally be very light -- less than 1/10" for urban locations
with locally up to 1/4" for higher elevation spots.

Dry weather will return for Saturday through most of Sunday as a
weak ridge of high pressure builds back to the coast. Highs will
mostly be in the upper 50s to mid 60s on Saturday with a few
degrees of cooling on Sunday as the ridge flattens out. At the
same time a minor system will drop down from the north and
quickly move through our region. Scattered showers can be expected
with the majority of the rain over the North Bay. In fact, many
locations south of the Bay Area will likely see a tenth or less.
Light showers will mostly come to an end by Monday morning.

Continues to look like next Monday through the following weekend
will be fairly quiet as a ridge of high pressure builds to the
coast and is then replaced by a dry northwesterly flow. Models
show possibly two shots at getting light scattered showers,
however any associated precipitation should be very light.
Temperatures will range from near normal to a bit above normal.

.AVIATION...As of 7:18 PM PDT Friday...Residual scattered showers
persist per radar data and area metar obs while some clearing is
taking place local IFR is also now developing; it`s rare for KSJC
to have IFR cig/vsby in the early evening for instance. A surface
cold front located in an ill-defined and weakening surface trough
has decelerated perhaps temporarily stalled over the south Bay to
north Central Coast. Amended KSJC for tempo IFR til 04z based
mostly on a persistence forecast, thereafter should begin to see
some improvement back to MVFR/VFR by 04z with light W-NW flow. The
mid-upper levels dry out significantly tonight and Saturday while
boundary layer humidity remains quite high thus likely to see
MVFR cigs persist with patchy LIFR/VLIFR developing in valley fog.

A secondary slow moving and dry cool front slides SE across the Bay
Area Saturday evening; preceding frontal passage it`s a low confidence
cloud cover forecast though due to a lack of near surface inversions
if there is cloud cover best guess would be that primarily MVFR/VFR
prevails. Post frontal drier air intrusion should help with keeping
VFR going Saturday night.

Vicinity of KSFO...MVFR/VFR. Wind light onshore this evening. 10-15
knots onshore winds Saturday 21z to 04z Sunday.

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...Southeast to south winds becoming light this
evening as showers gradually diminish. MVFR/VFR.

&& of 4:51 PM PDT Friday...Winds will return to northwest
and continue to ease this evening in the wake of the frontal boundary
that moved through the coastal waters earlier today. Southerly winds
are forecast to return Sunday as the next system approaches. Fresh
short period swells will make for choppy conditions over the coastal
waters through the weekend.


     .Tngt...SCA...Mry Bay until 9 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 9 PM
             SCA...SF Bay until 5 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 5 PM




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