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

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467
FXUS66 KMTR 081246
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
446 AM PST Thu Dec 8 2016

.SYNOPSIS...Periods of rain will continue this morning and taper
to showers this afternoon and evening. Shower threat continues on
Friday but not as widespread. Next front arrives Saturday with
another chance of rain. Mainly dry Sunday and Monday then more
rain possible by middle of next week.

&&

.DISCUSSION...as of 3:50 AM PST Thursday...Radar still picking up
plenty of returns this morning but rain rates and totals have been
light to moderate. Some of the wettest locations around Marin
county and the Santa Cruz mtns are approaching 1 inch storm totals
so far. In addition to the beneficial rains overnight the warm
front has allowed for much milder overnight lows compared to last
night with readings in the 40s to around 50...feeling much warmer.

The overall pattern remains pretty complex and models are still
showing fairly significant run to run changes. In the short term
expect steady light...to locally moderate rain to continue through
the morning rush hour. Then the activity should start to become
less widespread in nature and more focused over the coastal hills
as synoptic forcing ends.

Have scaled back pops for tonight to just show lingering showers
overnight with the scattered shower chances continuing into
Friday. Models now bring another warm frontal type feature in by
early Saturday morning spreading from north to south...not to
different from our current event. It finally appears the nam/gfs
and euro are all on board with rain chances but exact timing and
location of rainfall remains frustratingly difficult to pinpoint
given the lack of a surface cold front and typical cold core upper
low. These warm advection rains lack the upper dynamics and
surface cold frontal passage to really crank up the rain rates.

Rain will end from north to south by Saturday afternoon/evening
and latest guidance now suggests things dry out for Sunday and
Monday. Even thats a low confidence forecast as with this fast
moving zonal flow the timing of individual shortwaves can change
dramatically.

Mid range forecast remains pretty generic with some type of precip
chances in the Tue/Wed time frame...best chance in the north bay.
Rather than try and time individual model runs thinks it prudent
to just keep some low pops in the forecast for now. Models do seem
to be honing in on a potentially deep and cold trough by about
next Thu. The good news is continued early season beneficial rain
and mountain snow looks to continue for the foreseeable future.

&&

.AVIATION...As of 04:40 AM PST Thursday...Eastward moving warm
sector rain showers continue to advance inland this morning...
albeit with lesser coverage than earlier in the night. As a
result... seeing a wide range of ceilings and visibilities coming
in from regional TAF sites... with predominately IFR-VFR
conditions w/ BR and -SHRA. Additionally, LLWS posbl at some TAF
sites through around sunrise as light surface winds increase to
25-35kt AOA 2000-2500 FT AGL. Moist quasizonal flow expected to
continue through the day today with isolated to scattered light
rain showers in the vicinity. Ceilings and visibilities will
fluctuate through the day, however, model data points towards
generally IFR to MVFR cigs for most areas throughout the day.
Specific timing and conditions in TAF will be very difficult to
place today as a result of disorganized but moist air mass over
area.

Vicinity of KSFO...IFR will prevail through early to mid morning,
then intermittent IFR/low MVFR possible for remainder of the day
as -SHRA move through the area. LLWS posbl thru around sunrise.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR to IFR cigs and visbys posbl
throughout the day today as on/off rain showers move through the
area.

&&

.MARINE...as of 04:32 AM PST Thursday...A warm front will move
eastward over the area through the morning. strong and gusty south
to southeast winds this morning will then weaken and veer west
today. the strongest winds are expected along the coast today. a
dominate westerly swell train will move across the waters today
through the remainder of the work week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Mry Bay until 3 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm until 3 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 AM
             SCA...SF Bay

&&

$$

PUBLIC FORECAST: RWW
AVIATION: DRP
MARINE: DRP


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