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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
737 
FXUS66 KMTR 260530
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1030 PM PDT Mon Mar 25 2019

.SYNOPSIS...A weak front continues to slowly push through the Bay
Area resulting in showers this evening. The front will stall over
the South Bay and Central Coast on Tuesday keeping a chance of 
showers in the forecast for southern areas. The next front will 
push into the area later Tuesday night into early Wednesday with 
another organized chance of rain. Shower and isolated 
thunderstorms will be possible Wednesday before ending by 
Thursday. Drying trend Friday into the weekend.

&&

.DISCUSSION...as of 08:58 PM PDT Monday...A weak cold front 
continues to slowly move south and east through the Bay Area this 
evening. Latest surface analysis indicates the front has push 
through San Francisco and is now moving through the Santa Cruz 
Mountains. Rainfall since this morning has been greatest across 
the North Bay, coastal Santa Cruz Mts and higher terrain of the 
East Bay. Latest KMUX radar imagery still indicates rain showers 
ahead and along the cold front. Recent trends on radar do show the
front is starting to lose some steam. Taking a closer look one 
can see a nice rain shadow effect happening on the lee side of the
Santa Cruz Mts. Based on trends from radar and latest hi-res 
model (HRRR) decided to update evening forecast lowering rain 
potential Monterey southward and over San Benito county. Lowered 
rainfall amounts to a tenth or two. 

Take a sneak peak at the 00Z models - the NAM really dries things
out overnight while the GFS is a little wetter. That being said,
both models continue shower activity tomorrow as the frontal
boundary continues to weaken and small waves/vort maxes moves
through the region.

&&

.PREV DISCUSSION...as of 1:51 PM PDT Monday...A frontal boundary is 
weakening as it passes through the Bay Area this afternoon and 
evening. Showers will continue to impact the afternoon/evening 
commute but mainly be light to occasionally moderate in intensity.
Shower activity will decrease this evening and overnight. The 
surface boundary will wash out over the South Bay and Central 
Coast by early Tuesday morning. 

As the main upper trough approaches on Tuesday, there may be
sufficient upper lift/divergence over the left over surface
boundary to allow for more showers to develop on Tuesday. In
contrast to today the best chances will be from the far East Bay
counties through the South Bay and around the Central Coast in the
vicinity of the surface moisture boundary. The nam model remains
most bullish on generating showers Tuesday while the ecmwf and gfs
are drier.

Rain chances will then increase again later Tuesday night into
Weds, especially across the North Bay as another surface front
approaches the region. This will lead to increased shower chances
right through Weds morning. Enough cold air aloft by Weds to allow
thunderstorm chances be put into the forecast (as inherited from
overnight shift).

The parent upper low responsible for all the shower chances the
next few days will finally move onshore late Weds night into
Thursday morning. Precip chances should rapidly end by late
Thursday afternoon and evening. For all the talk of showers the
next few days, amounts in general look to be light with some
portions of interior Monterey/San Benito potentially seeing no
rainfall at all. Daytime highs will be on the cool side of normal
with cloud cover and cool temps aloft. However, any peaks of
sunshine will allow temps to jump into the 60s most days.

High pressure to build Friday into the weekend with dry and mild
weather. Storm track remains somewhat active next week but right
now the best precip chances remain north of I-80.

&&

.AVIATION...As of 10:55 PM PDT Monday...For 06z TAFs. The cold 
front will continue to slide south across the region spreading 
rain to area terminals from KSFO south. Showers will lingering 
through tonight and likely through Tuesday. Winds will remain 
light veering to the west behind the front...otherwise winds will
be calm and variable overnight. MVFR to VFR cigs will prevail 
through much of the period. 

Vicinity of KSFO...MVFR cigs will prevail with showers gradually
tapering to vicinity showers overnight. Light west winds will 
becoming light and variable overnight. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR to MVFR cigs will prevail with 
showers possible overnight as the front slides south. Light winds.

 
&&

.MARINE...as of 9:00 PM PDT Monday...Low pressure off the Oregon 
coast will keep light to moderate southerly winds through Tuesday 
night. Stronger winds can be expected over the northern waters 
Tuesday night. Winds will switch to southwest on Wednesday and 
Thursday as high pressure builds off the California coast.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...NONE.

&&

$$

PUBLIC FORECAST: MM/RWW
AVIATION: CW
MARINE: W Pi/CW

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