Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 072157
Area Forecast Discussion
National Weather Service San Francisco Bay Area
157 PM PST Wed Dec 7 2016
.SYNOPSIS...A change in the weather pattern will result in
unsettled weather conditions across the region through Saturday.
Periods of rain can be expected at times, especially tonight into
Thursday morning and again late Thursday night into Friday. The
greatest rainfall totals will likely be along the coastal ranges
and across the North Bay through this event. Periods of dry
weather will be possible this weekend with rain returning to
northern California early next week.
.DISCUSSION...as of 01:53 PM PST Wednesday...Plenty of returns
showing up the the KMUX Radar this afternoon with only a few
locations around the region picking up precipitation. This is
likely due dry conditions in the lower levels with higher moisture
content aloft. The forecast models continue to show dry,
northwesterly flow becoming westerly with the lower levels
moistening through the afternoon/evening. At this point, light
precipitation will being to increase in coverage generally north
of the Monterey Bay late this evening and spread inland/southward
across the Central Coast overnight tonight.
Rain will then persist through much of Thursday morning with the
greatest rainfall amounts along the coastal ranges and across
portions of the North Bay. Meanwhile, many inland valley locations
including the Santa Clara Valley, Southern Salinas Valley and East
Bay Valley will likely see much less rainfall. Light rain will then
diminish in coverage and intensity by Thursday afternoon and
evening. However, with PWAT values still near 1.00" or so, upslope
flow and orographic lift will result in continued rainfall along the
coastal ranges through Thursday.
Another round of precipitation is then expected late Thursday into
Friday as another weak impulse pushes across the region. The focus
of heaviest rainfall will be from the Santa Cruz Mountains southward.
Through Saturday, 2" to 5" will be possible along the coastal ranges
with about 1" to 1 3/4" for San Francisco Bay Area and points
northward. Meanwhile, storm total amounts will likely range from
1/4" to 1" for inland valleys and around the Monterey Peninsula.
Mostly dry conditions return during the day on Saturday and will
likely persist into Sunday.
Another band of deeper moisture will then push into Northern
California late Sunday into early next week. At this time, the best
chances for rainfall over our region will mainly be across the
North Bay and down into portions of the San Francisco Bay Area.
However, confidence remains low at this time regarding the
southward progression of this system and how much rainfall can be
Aside from rainfall, temperatures will remain near or slightly below
seasonal averages during the daytime hours while the increased
cloud cover and moisture will keep overnight conditions above
.AVIATION...As of 9:30 AM PST Wednesday...VFR conditions expected
for this morning into early afternoon ahead of an approaching
storm system. Cigs will begin lowering later this afternoon with
rain developing. Intermittent rain will continue through the
remainder of the day and into the weekend, leading to wet runways
and reduction to visibility. East to southeast winds will prevail
through the day while some TAF locations will gradually veer
towards the south by the end of the TAF period. Winds will become
briefly gusty at times as the storm system pushes through the
Vicinity of KSFO...VFR thru early afternoon. High clouds early
this morning will gradually lower to 2500-4000 ft range by this
afternoon. Offshore wind will prevail. Rain possible as early as
21-22Z. Rain will persist through the end of TAF period. MVFR
later this afternoon and overnight possible.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR thru early afternoon. MVFR cigs
possible by this evening. Intermittent rain through the end of
the TAF period.
.MARINE...as of 8:12 AM PST Wednesday...An approaching storm
system will bring increasing south to southeast winds across the
waters today with the strongest winds over the northern outer
waters. Gale force winds will be possible over the northern outer
waters. Winds weaken and veer west overnight and into Thursday.
.Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm from 9 PM
SCA...Pt Arena to Pigeon Pt 10-60 nm from 3 AM
GLW...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...SF Bay from 9 PM
PUBLIC FORECAST: RGass
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