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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 181747

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1047 AM PDT Thu Apr 18 2019

.SYNOPSIS...Warmer temperatures are forecast for today, 
especially inland areas where widespread highs in the lower to mid
80s are expected. A cooling trend is then expected to begin 
Friday and continue into the weekend as onshore flow redevelops 
and strengthens. This will be followed by renewed warming for the 
first part of next week. No precipitation is expected through the 
forecast period.

&& of 09:23 AM PDT Thursday...High pressure over the
Bay Area started out a little stronger this morning than expected.
As such cloud cover over most land locations has been non-
existent. A few clouds are lingering in some isolated pockets of
coastal location, but should dissipate for a while late morning
into early afternoon.
Most sites have been running about 3 to 6 degrees over yesterday,
so far this morning. We continue to expect a rise of the mercury
into the 70s (coastal) and 80s (inland) for nearly all locations.
The main change to the forecast this morning was to bump up the 
temps away from the coast by a degree or two. Just a touch warmer 
than the early morning forecast. Enjoy the day as we will cool a 
bit going into the weekend and increase cloud cover a bit as a 
system clips our area.


.PREV DISCUSSION...As of 02:42 AM PDT Thursday...GOES satellite fog 
product reveals mostly clear skies around the Bay Area overnight 
with a few exceptions: developing stratus over the coastal 
waters, patchy low clouds developing along portions of the 
immediate coastline and patchy fog/low clouds North Bay Valleys. 
Current forecast will have some patchy low clouds/fog possible 
early this morning, but impacts will be minimal. 

The bigger weather story for the day will be the noticeable warm
up. Synoptically speaking, a large upper level ridge currently
along the West Coast will strengthen as it moves eastward. The 
building ridge can be seen by looking at increasing 500 mb heights
and warming temperatures at 850 mb. Observed highs on Wednesday 
were upper 50s to upper 60s near the coast and 70s to near 80 
inland. Generally speaking a modest 5 to 10 degrees of warming
will be seen today with a few spots approaching 15 degrees of
warming compare to Wednesday. In other words, highs in the 60s to
mid 70s along the coast and widespread 80s inland. It's possible
that a few interior locations in Monterey/San Benito Counties may
eclipse 90 degrees. Temperatures this warm are about 5 to 10
degrees above normal for mid April. One limiting factor for really
warm weather is the lack of offshore flow and continued onshore
flow, especially near the coast. From a heat risk standpoint,
there is enough cooling (relief) Thursday night and Friday that
impacts will be minimal. However, today could be the warmest day
so far this year for some locations so some precaution should be
used - stay hydrated, monitor activities during peak heating of 
the day, take breaks, etc.

The warm up will be short-lived as the ridge moves east, an upper
level low undercuts the ridge across SoCal and low level onshore 
flow ramps on Friday. A general cooldown of 3 to 5 degrees is 
expected on Friday with a slight increase of early morning 
clouds/patchy fog. Not a full force summer stratus push just yet, 
but more of a preview. 

An even bigger cooldown is expected on Saturday as an upper level
low swings through NorCal bringing increasing clouds, cooler 850 
mb temps and possible precipitation to CA. 00Z model suite
continues to show mixed results on potential precip impacting the
Bay Area on Saturday. Current forecast will remain dry at this
point as best chance still remains N and E of the forecast area.
Will keep a close eye on this and precip may added to the forecast
later. High temperatures will be cool and mostly in the 60s an
lower 70s. Interesting to see the temp swing from above normal on
Thursday to below normal for Saturday. 

Similarly to the initial warm up, the cooldown will be short-
lived as well. High pressure is forecast to re-build over the 
region Sunday into Monday. The warming trend is forecast to 
continue well into next week. If some of the medium range models 
and ensembles are correct the second round of warming may be even 
warmer than the Thursday warm up. Interior locations may hit the 
upper 80s to lower 90s next Wednesday and Thursday. 

Longer range forecast indicate that the wet season may be ending 
and the dry season is beginning. The latest 8 to 14 day CPC 
outlook has much of NorCal drier than normal through May 1.

&& of 10:47 AM PDT Thursday...for 18Z TAFs. VFR 
conditions are forecast to prevail through the day as an upper 
level ridge remains in control over the region. Light/variable 
winds this morning will gradually shift and become onshore this 
afternoon, generally at or below 12 kt. The VFR conditions should 
continue overnight and into tomorrow morning, though can't rule 
out the potential for some patchy fog in the North Bay valleys.

Vicinity of KSFO...VFR conditions are forecast to prevail through
the period with passing high clouds. Light northeast winds this
morning will become west to northwest in the afternoon up to
around 10-12 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR conditions are forecast to prevail
through the period. Light to moderate offshore winds this morning
will become onshore by the afternoon between 7-11 kt.

&& of 8:50 AM PDT Thursday...Weakening high pressure 
over the offshore waters will keep light to moderate northwest 
winds through Thursday night. High pressure will rebuild over the 
eastern Pacific on Friday resulting in increasing northwest winds 
over the coastal waters that will last through the weekend.





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