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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 211725
AFDMTR

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

.SYNOPSIS...Dry conditions return today 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.

&&

.DISCUSSION...as of 08:57 AM PST Thursday...Just about all rain
showers are now well offshore at this hour with dry weather
conditions forecast through the remainder of the day. Temperatures
will warm into the middle 50s for most coastal and valley 
locations this afternoon while 30s and 40s will be common in hills
and higher elevations. The ongoing forecast for the day remains 
on track with no updates anticipated at this time. For full 
details, please see the previous forecast discussion below.

&&

.PREV DISCUSSION...as 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 09:25 AM PST Thursday...For 18z tafs. VFR
conditions through the period with mostly clear skies. Breezy to
locally gusty winds this afternoon, although not as strong as
yesterday. Generally expecting gusts this afternoon 20 to 25 kt.

Vicinity of KSFO...VFR with mainly clear skies. West to northwest
winds gusting 20 to 25 kt this afternoon.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals....Showers have moved out. VFR conditions
through the period with mostly clear skies. Breezy onshore winds
this afternoon gusting to around 20 kt.

&&

.MARINE...as of 08:12 AM PST Thursday...Gusty northwest winds 
will persist today across the waters with gale force gusts 
expected over the outer waters. These winds will generate steep 
fresh swell creating hazardous conditions, especially for smaller 
vessels. Winds will diminish Friday and through the weekend. 
Moderate northwest swell will continue into next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm
             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
             GLW...Pt Arena to Pigeon Pt 10-60 nm
             GLW...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Mry Bay from 1 PM

&&

$$

PUBLIC FORECAST: RGass/MM
AVIATION: AS
MARINE: AS

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