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000 
FXUS66 KMTR 231131
AFDMTR

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 
vehicles. 

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
sunrise.

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.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Heat Advisory...CAZ506>508-510>513-516>518
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Sims
MARINE: Sims

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