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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 211109

Area Forecast Discussion
National Weather Service San Francisco Bay Area
309 AM PST Thu Feb 21 2019

.SYNOPSIS...Lingering showers continue early Thursday morning 
especially over the Central Coast and East Bay Hills with snow 
showers above 3,000 feet elevation. Dry conditions return 
Thursday into Friday with near record lows possible Friday 
morning. The next chance of rain returns to northern California 
over the weekend and early next week.

&& of 3:08 AM PM PST Thursday...Meteorological term
for the night shift - orographic lift. Impressive to watch the 
KMUX radar imagery from late Wednesday evening through early 
Thursday morning as showers continue to impact the Central Coast.
Moist air over the coastal waters is being forced upward over the
terrain of the Central Coast leading to a training effect of 
precipitation. The training effect is most notable over the Santa 
Lucia Range where peaks exceed 5500 feet. Interesting factoid - 
the highest coastal peak in the lower 48 is Cone Peak along the 
Big Sur Coast. There are no snotel gauges in the Santa Lucia Range
so it's hard to say how much snow has fallen, but MRMS data 
suggests possibly 5-10" with a greater than 10:1 ratio. Impacts 
are minimal as population base is rather small compare to the rest
of the Bay Area, but interesting nonetheless. The rest of the Bay
Area did see some precip earlier in the night, but shower 
activity has diminished. Gusty winds still remain over the higher 
peaks with gusts in the 25-35 mph range. Temperatures did cool off
compare to 24 hours ago, but some linger winds are keeps 
temperatures from really dropping. Sheltered valleys may dip below
freezing with some patchy frost. 

Based on latest hi-res models will keep orographic showers going
through the morning hours before complete drying N to S by this
afternoon. It should be noted that given the lower snow levels any
vertically developed shower could drop small hail. Increased 
sunshine this afternoon, but daytime highs will be below seasonal 
levels and in the 50s - 30s- 40s higher terrain.

Winds will taper off under clearing skies Thursday night leading
to a cold night. Overnight lows will drop into the 30s for most
locations, including some urban centers, and low 40s for
SF/coastline. The coldest locations will be the interior valleys
and higher peaks with temps dropping into the 20s. Widespread
frost will be possible. Dry weather with slightly warmer
temperatures are expected on Friday. Next chance for precipitation
returns to the Bay Area Saturday afternoon over the North Bay.
Latest model guidance keeps showers confined to north of the
Golden Gate through early Sunday, but spreading precipitation
southward. At this point, medium range models keep the heaviest
rain north of the Bay Area on Sunday, but some precip is possible
as far south as San Jose.  

More widespread precip is expected on Monday as a better moisture
plume drifts southward. Confidence is medium as medium range
models have been flipping on precip amounts and potential for an
Atmospheric River. Most likely location for moderate to heavy rain
early next week will be across the North Bay. Will keep rain
chances in the forecast through the middle of next week with some
gradual drying possible late in the week. Stay tuned as details
will likely change between now and then.


.AVIATION...As of 10:00 PM PST Wednesday...Drier air will move
into the area overnight resulting in decreasing clouds. Winds are
slowly decreasing but will pick up again Thursday afternoon. 

Vicinity of KSFO...VFR. West winds gusting to 25 kt through 11Z. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals....Clouds over the hills may bring sct-bkn
to MRY through 12Z otherwise VFR. 

&& of 10:05 PM PST Wednesday...Low pressure over the
desert southwest will keep strong northwest winds through Thursday
night. Winds will decrease Friday through Sunday as the low moves
east and high pressure builds over the district. Gusty winds will
generate steep fresh swell causing  hazardous conditions
especially for smaller vessels. Moderate  northwest swell will
continue through the end of the week.


     .Tday...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 until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM
             GLW...Pt Arena to Pigeon Pt 10-60 nm
             GLW...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
             GLW...Pt Arena to Pt Reyes 0-10 nm until 3 AM
             GLW...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Mry Bay from 1 PM




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