Scientific Forecaster Discussion
fxus66 kmtr 201136
Area forecast discussion
National Weather Service San Francisco Bay area
436 am PDT Thu Jul 20 2017
Synopsis...seasonable weather conditions are forecast to persist
today with a modest warming trend expected Friday into Saturday.
Expect areas of late night and morning low clouds giving way to
mostly sunny afternoon conditions. Temperatures then looks to cool
back to near seasonal averages early next week.
Discussion...as of 03:31 am PDT Thursday...a marine layer of
1000-1200 feet in depth continues to impact the region this
morning. This has resulted in more widespread cloud cover off of
the coast with some development inland over the Monterey Bay
region and into the city of San Francisco. Meanwhile, most North
Bay valley locations remain under clear skies with temperatures
generally in the 50s. Look for low clouds to continue to expand a
bit through sunrise before giving way to mostly sunny skies this
afternoon. Very little change in the overall pattern is expected
today as an upper level trough pushes inland to our north and
stronger high pressure persists over the southern portion of the
country. Thus, afternoon temperatures today will be similar to
those on Wednesday.
The ridge aloft will begin to build toward the California coast
late in the week as the upper level trough lifts northward. This
will result in a warming trend Friday into Saturday with inland
areas once again warming to above seasonal averages. Look for more
widespread 90s by Saturday with a few of the warmest inland
locations exceeding the 100 degree mark. This too should compress
the marine layer some late in the week and into the weekend
resulting in less overnight/morning cloud cover. Temperatures may
cool by a few degrees inland on Sunday as the ridge begins to
weaken and onshore flow increases slightly.
Temperatures are then forecast to cool back to near seasonal
averages by the beginning of next week as the ridge retreats back
to the east and upper level troughing returns to the Pacific
northwest and northern California. This too will likely allow for
the marine layer to return and result in more widespread
overnight/morning low clouds. The forecast models do show some
moisture wrapping around the upper level ridge early in the week
that will advect northward across the region. However, instability
appears limited with the best chance of any convection remaining
over the interior portions of the state. Nonetheless, something
Worth keeping an eye on in the coming days.
Aviation...as of 04:35 am PDT Thursday...for 12z tafs. Low
stratus has begun to develop along the coast and move inland into
the Salinas valley and East Bay. Currently IFR/MVFR cigs at koak,
kmry, and ksns. Not expecting clouds to move over ksfo.
Increasing westerly winds forecast for this afternoon with gusts
at ksfo around 25 kt.
Vicinity of ksfo...VFR. Gusty westerly winds resume this
afternoon and evening.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...IFR/MVFR cigs around both terminals.
Estimating clearing late this morning. Confidence on timing is
low. VFR conditions in the afternoon before the return of low cigs
late tonight and into Friday morning.
Marine...as of 04:28 am PDT Thursday...high pressure remains over
the eastern Pacific as high pressure also temporarily builds over
far northern California. As a result expect gusty northwesterly
winds to continue across the coastal waters.
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...mry Bay from 11 am
Public forecast: rgass
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