FXUS66 KMTR 210030

Area Forecast Discussion
National Weather Service San Francisco Bay Area
530 PM PDT Wed Mar 20 2019

.SYNOPSIS...Rain showers will diminish in strength and coverage
through the remainder of the day. Isolated showers may linger
across the Central Coast tonight into early Thursday morning yet
most locations will remain dry. Another frontal system pushes
across the region on Friday with mainly dry weather expected
Saturday into Sunday. Cool, unsettled weather possible throughout
most of next week.


.DISCUSSION...as of 02:30 PM PDT Wednesday...A slow moving,
negatively tilted trough approached California from the west last
evening and brought gusty southerly winds before pushing ashore
after midnight. Light to moderate broken rain bands were wrapped
tightly around the core of the upper low as it shifted ashore,
delaying the onset of rain for some in the North Bay until the
upper disturbance lifted northward this morning. The majority of
the rain and wind from this storm system has now passed, however,
a second disturbance rounding the broader trough later today
through tonight will allow gradually weakening rain showers to
persist through the next 12 to 18 hours. Latest radar/satellite
imagery shows the deepest convection has now shifted farther
inland over the Central Valley, where lightning pulses have been
observed near Los Banos, Tracy, and Stockton.

Scattered to widespread showers through the day added to the
overnight rain totals with the Big Sur peaks leading the storm
total rainfall accumulations (generally around 1.50-2.00"). Other
higher elevation locations in the North Bay (such as Venado) and
the Santa Cruz mountains (such as Ben Lomond) picked up between
1.00 and 1.50". Elsewhere, lower elevation urban areas reported
lesser amounts between 0.10" on the low end (in rain shadowed
areas) and up to 1.00" on the high end (typically along the coast
or near orographically enhanced areas). Peak gusts ranged from 40
to 50mph out of the south in the windiest locations and occurred
last evening ahead of the cold front. Winds this afternoon have
weakened but remain breezy and primarily out of the west on the
lee of the trough.

Despite the relatively warm start to the day, afternoon
temperatures are 5 to 15 degrees cooler than the same time
yesterday with 2pm temperatures in the mid 50s to low 60s. These
afternoon high temperatures are 4 to 8 degrees below normal
readings for this time of the year. And speaking of this time of
the year... spring officially begins at 258pm this afternoon!
Happy vernal equinox!

A transitory ridge arrives tomorrow which will bring dry weather
conditions and a slight warming trend for the day. Despite this
warming trend, afternoon temps are forecast remain a few degrees
below normal tomorrow.

Another storm system arrives from the Gulf of Alaska by sunrise
Friday, impacting the North Bay first before shifting southward
throughout the day Friday. Precipitation amounts will be highest
over the North Bay (around 1.00" over the North Bay coastal range,
ie Venado, and 1/2-2/3" in the North Bay valleys) with progressively
lower accumulations the farther southward/inland the system
progresses. A few lingering showers are possible into early
Saturday however most of the weekend will see a general
drying/warming trend as another ridge passes overhead.

High pressure redevelops throughout most of the weekend which will
bring generally dry weather conditions and a moderate warming
trend regionwide. Sunday afternoon temperatures rebound to nearly
normal with highs ranging from the low to upper 60s.

A third storm system will impact the region early next week. Mid
to long term models and ensemble members are peppering the Monday
through Thursday period with various amounts of precipitation
though there is little consensus on the coverage or intensity of
this rain. Models do seem to be converging on the Monday morning
timeframe for an initial arrival time of the rains, though they
disagree on the duration or when/if there will be breaks in the
rain through Thursday. As it now stands, the data shows a clear
trend towards an extended period of cool, unsettled weather
throughout most of next week.


.AVIATION...As of 4:30 PM PDT Wednesday...Scattered showers
and a few thunderstorms over southern Monterey and San Benito
Counties and in the Central Valley this afternoon could impact LVK
through 02Z. SCT-BKN clouds through this evening with cigs
staying 3500 ft or above. The upper low will move southeast across
the coastal waters later tonight. Rain expected to stay offshore
but cigs near 3000 ft are possible at MRY which will be closest to
the low. Also cannot rule out fog at STS tonight.

.CWSU SFO Approach Forecast...

.VAPs this afternoon through the evening.

.Confidence:  MED-HIGH

Update. VAPS have occured and are expected to continue through the
evening hours. The area remain conducive for low clds to develop as
moisture and an unstable atmosphere remain inplace. Expect cloud
bases between FEW-SCT 020-030 with cigs around 050 or higher. Expect
the winds to remain out the WSW for the rest of the afternoon

Vicinity of KSFO...SCT clouds at 3000 ft with cigs 4000-5000 ft.
Clouds will decrease after 04Z as we lose the daytime heating but
will increase again early Wednesday morning as the upper low
reaches its closest point to the area. West winds to 15 kt
decreasing after 09Z.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Clouds over the coastal hills could bring
MVFR conditions to MRY after 03Z with cigs around 3000 ft. Better
chance of VFR at SNS with cigs remaining at or above 5000 ft.


.MARINE...as of 04:21 PM PDT Wednesday...Light to moderate west to
southwest winds will continue this evening across the coastal
waters before winds diminish overnight. Winds will increase and
turn southerly again tomorrow night and Friday as the next weather
system approaches. Moderate period west swell will continue today
and tomorrow before a longer period  west to northwest swell
arrives on Friday.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 6 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 6 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 6 PM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 6 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 9 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 PM
             SCA...Rough Bar Advisory for SF Bar until 9 PM




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NWS MTR Office Area Forecast Discussion