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

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FXUS66 KMTR 080634
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1034 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 8:53 PM PST Wednesday...Rainfall spread
across the region this evening with precipitation lighting up the
KMUX radar across the entire forecast area. It took a while for
the boundary layer to moisten up earlier today resulting in little
rain actually hitting the ground until late afternoon/early
evening. However over the last 4 to 6 hours gauges across the
North Bay have been tipping with accumulation totals anywhere from
a few hundredths to just under two tenths of an inch. The Santa
Cruz mountain as well as the East Bay Hills have also reported a
few hundredths. Elsewhere scattered showers brought a hundredth of
an inch or less to select locations.

Models indicate warm frontal showers will spread south across the
district overnight into Thursday. Precipitable water values
remain between 1" to 1.3" off the coast. Unsettled showery
conditions will continue through Thursday morning with a lull in
the rainfall expected Thursday afternoon. With little in the way
of dynamic forcing with this system rainfall will be terrain
enhanced resulting in significantly less rainfall in the typically
rain shadowed valleys while the higher terrain of the coastal
ranges will see the most accumulation.

From previous discussion...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
expected.

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
normal.

&&

.AVIATION...As of 10:34 PM PST Wednesday...A warm front located
offshore will advance eastward resulting in additional wet weather
overnight. Residual lower level temperature inversions over the
Bay Area are effectively keeping surface based winds much lighter
while strong and gusty winds advance inland just above inversion
tops, thus expect at least several hours or more of strong surface
to lower level directional and speed shear tonight. A remote weather
station (Oak Ridge RAWS) at 1890 feet in the North Bay very recently
reports SE wind near 40 knots. Non-convective low level wind shear
(LLWS) has been added to all the Bay Area 06z tafs through early
Thursday morning. A few showers persist Thursday. Low cigs as well
as fog a possibility Thursday night.

Vicinity of KSFO...MVFR with tempo IFR cig/vsby in rain. LLWS tonight
and early Thursday morning. Rain turning to showers Thursday, MVFR
cigs.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Cigs becoming MVFR tonight. Off/on light
rain tonight turning to a steadier rain late tonight and Thursday
morning. Rain turning to showers Thursday. LLWS is a little less
likely here and not presently in 06z tafs, however surface winds
and winds aloft will be monitored.

&&

.MARINE...as of 10:07 PM PST Wednesday...A warm front will move
eastward over the area late tonight and thursday. strong and gusty
south to southeast winds tonight will then weaken and veer west on
thursday. expect gale force winds over the northern outer waters
tonight.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             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...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...SF Bay

&&

$$

PUBLIC FORECAST: CW
AVIATION/MARINE: Canepa


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