Scientific Forecaster Discussion
fxus66 kmtr 231131
Area forecast discussion
National Weather Service San Francisco Bay area
431 am PDT Sat Jun 23 2018
Synopsis...very warm to hot temperatures are forecast for the
interior today as high pressure dominates the weather pattern.
Additionally, offshore winds will develop and result in heightened
fire weather concerns for portions of the region today through
Sunday. Cooling is then expected by Sunday and into early in the
upcoming week with increased onshore flow.
Discussion...as of 03:18 am PDT Saturday...mostly clear sky
conditions prevail over the region this morning with temperatures
ranging from the 50s at the coast to 70s inland and in the hills.
The exception is over the Monterey Bay where satellite imagery is
showing low clouds developing. Expecting low clouds to potentially
spread locally inland around the Bay through the morning before
retreating back to the coast by early afternoon.
With warming aloft in response to the building ridge, temperatures
will be warmer by at least a few degrees compared to yesterday
afternoon. Thus, a heat advisory has been issued for the interior
and higher elevation locations this afternoon as temperatures warm
into the 90s to around 105 for the hottest inland locations.
Meanwhile, weak onshore flow will keep conditions cooler at the
coast where heat risk will be significantly lower. As previously
mentioned...residents are advised to limit outdoor activities during
the hottest time of day, stay in air-conditioned areas, keep an eye
on pets and livestock, and drink plenty of water. Never leave kids
or pets in a vehicle unattended for any reason for any length of
time as temperatures will rapidly reach dangerous levels inside of
In addition to the heat, dry offshore flow will develop today and
persist into Sunday, especially in the North Bay hills/mountains and
across the Diablo Range. Northerly winds gusting to around 40 mph
will be possible and combine with low relative humidity values to
produce increased fire weather concerns. Thus, a red flag warning
remains in effect for the aforementioned areas from late this
morning through Sunday evening.
Onshore flow is then forecast to develop along the coast as a
southerly surge works northward up the Big Sur coast on Sunday. This
will bring cooler conditions first to the coast before spreading
inland through Sunday evening. Offshore winds will also decrease
late Sunday evening in the North Bay and East Bay hills/mountains,
lowering fire weather concerns. Region-wide cooling is then expected
into early in the upcoming week as onshore winds increase and a
marine layer becomes better established over the region.
Aviation...as of 4:31 am PDT Saturday...VFR. Coastal stratus
forming over the Monterey Bay could affect mry and sns after
Vicinity of ksfo...VFR. Winds becoming onshore with gusts up to
near 20 knots Saturday afternoon and early evening.
Sfo bridge approach...VFR.
Monterey Bay terminals...VFR, intermittent MVFR cigs possible
until 16z. Onshore winds likely redeveloping by afternoon.
Fire weather...as of 3:18 am PDT Saturday...a red flag warning
remains in effect for the north and East Bay hills from 11 am
through 8 PM this evening. The main concern will be for hot
inland temperatures and low relative humidity along with moderate
and dry northerly winds. To be clear the weather set-up is very
different and not nearly as critical in terms of winds to the
North Bay firestorm last October.
Temperatures will continue to warm this afternoon further drying
out fuels that are running near average in terms of seasonal
dryness. Even more widespread afternoon highs in the 90s and low
100s are expected. As temperatures warm, dry northerly winds will
come down the Sacramento Valley and spread over Napa County
by late this morning with wind gusts between 35-45 mph. Winds
will ease in the afternoon before the north and East Bay hills see
another round of increased north winds late this evening into
Sunday. During this time little to no relative humidity recovery
is expected and overnight lows will be warm in the 70s and 80s.
Afternoon highs on Sunday will remain warm to hot, but onshore
flow will return late in the day providing some cooling.
Those spending time outside this weekend are urged to be vigilant
with sources of ignition. Any new fire starts, especially in the
grassy fuels will spread rapidly.
Marine...as of 04:20 am PDT Saturday...high pressure over the
eastern Pacific and a thermal trough over the California interior
will maintain gusty northerly winds over the coastal waters
through today. Winds will decrease during the weekend over much
of the coastal waters as winds switch to southerly over the inner
coastal waters reaching the Golden Gate and Point Reyes by either
late today or early Sunday morning.
Small Craft Advisory...pt Arena to Pigeon pt 10-60 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...Pigeon pt to pt Piedras Blancas 10-60 nm
Public forecast: rgass
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