Red Flag Warning 3, NWS San Francisco Bay Area, CA

246 
WWUS86 KMTR 201117
RFWMTR

URGENT - FIRE WEATHER MESSAGE
National Weather Service San Francisco CA
417 AM PDT Thu Sep 20 2018

...Red Flag Warning through 5 pm this afternoon...

.A weather pattern shift will bring increased northerly winds and
low humidities. In addition, very dry fuels will result in critical
fire weather conditions during this period. The strongest northerly
winds and critical humidity levels are expected to be in the North
Bay Mountains, as well as the East Bay Hills and Diablo Range, and
the Santa Cruz Mountains.

CAZ507-511-512-210000-
/O.CON.KMTR.FW.W.0003.000000T0000Z-180921T0000Z/
North Bay Mountains-East Bay Hills and the Diablo Range-
Santa Cruz Mountains-
417 AM PDT Thu Sep 20 2018

...RED FLAG WARNING REMAINS IN EFFECT UNTIL 5 PM PDT THIS
AFTERNOON FOR GUSTY OFFSHORE WIND AND LOW HUMIDITY FOR FIRE 
WEATHER ZONES 507, 511, AND 512...

* AFFECTED AREA...Fire weather zones 507, 511, and 512.

* WIND...Northerly. Ridgetops up to 20 mph sustained with gusts to
  35 mph mainly this morning. Winds will weaken but remain  
  northerly late morning into the afternoon. Light offshore winds 
  elsewhere. 

* HUMIDITY...Poor recoveries early this morning. Locally as low as
  25 to 35 percent in the driest areas. Daytime minimum humidities
  as low as the upper single digits to low teens in the driest
  areas. 

* IMPACTS...any fires that develop will likely spread rapidly. 


PRECAUTIONARY/PREPAREDNESS ACTIONS...

A Red Flag Warning means that critical fire weather conditions
are either occurring now...or will shortly. A combination of
strong winds...low relative humidity...and warm temperatures can
contribute to extreme fire behavior.

&&

$$

120 
WWUS86 KMTR 210000
RFWMTR

URGENT - FIRE WEATHER MESSAGE
National Weather Service San Francisco CA
500 PM PDT Thu Sep 20 2018

CAZ507-511-512-210100-
/O.EXP.KMTR.FW.W.0003.000000T0000Z-180921T0000Z/
North Bay Mountains-East Bay Hills and the Diablo Range-
Santa Cruz Mountains-
500 PM PDT Thu Sep 20 2018

...RED FLAG WARNING WILL EXPIRE AT 5 PM PDT THIS AFTERNOON FOR
GUSTY OFFSHORE WIND AND LOW HUMIDITY FOR FIRE WEATHER ZONES 507,
511, AND 512...

Winds in the hills had diminished by late Thursday afternoon.
Therefore, the Red Flag Warning has been allowed to expire at 5 pm.
Warm and very dry conditions will continue in the hills through 
Friday, but winds are forecast to remain light. 

Slightly cooler weather is forecast over the upcoming weekend,
with renewed warming expected during the first half of next week. 

$$

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1041 AM PDT Wed Sep 19 2018

.SYNOPSIS...A warming and drying trend will begin over the area
today and continue into Thursday as onshore flow weakens. Gusty
northerly winds in higher elevations will result in enhanced fire
weather concerns from tonight into Thursday morning, mainly in
the hills of eastern Napa County. Temperatures moderate slightly
over the upcoming weekend but will remain near to slightly above
seasonal averages.

&&

.DISCUSSION...as of 9:16 AM PDT Wednesday...The marine layer has
deepened overnight to around 2000 feet, and satellite imagery
shows coastal stratus has pushed well inland through the Monterey
Bay area filling the Salinas Valley, and also extending northward
into southern Santa Clara county. Stratus coverage is much more
patchy over the San Francisco Bays with OAK being the only Bay
Area airport affected by low ceilings at this time. Surface
pressure gradients are still predominately onshore with 1.1 mb
from SFO to SAC, but the northerly gradient from ACV-SFO is much
tighter versus 24 hours ago with 5.3 mb compared to 1.9 mb
yesterday at this time. This tight northerly gradient will
produced gusty winds across the north Bay mountains, where a Fire
Weather Watch remains in effect through tonight for gusty winds
and poor RH recoveries. Gusty winds are also possible tonight over
the East Bay Hills as well as the Santa Cruz mountains.

The upper level trough currently over California will continue to
move to the east as high pressure aloft builds in from the Eastern
Pacific. This will produce a warming trend over the next few days,
peaking on Thursday when high temperatures are forecast to edge
into the 90s across the warmest inland areas, with 60s and 70s
along the coast.

Latest medium range model runs bring a weak trough across the
PacNW over the weekend with high pressure rebuilding over the
Eastern Pacific early next week. Thus, temperatures should remain
around normal or slightly above.

&&

.AVIATION...As of 10:35 AM PDT Wednesday...For 18z tafs.
Trending VFR at all terminals as low clouds continue to erode.
Expect VFR this afternoon tonight. Offshore flow is forecast to
develop overnight leading to dry of the low levels. This should
keep the SF Bay are clear. Monterey Bay area on the other hand
could have some low clouds early in the night before clearing
early tomorrow morning. Decided to include LLWS for KOAK for
tomorrow morning. Light and vrb at the surface with gusty NE winds
over the East Bay Hills.

Vicinity of KSFO...VFR. Gusty onshore this afternoon. VFR tonight
with gusty offshore flow.

SFO Bridge Approach....Similar to SFO.

Monterey Bay Terminals....VFR this afternoon. Some cigs poss early
tonight then clearing early tomorrow.

&&

.MARINE...as of 8:34 AM PDT Wednesday...Moderate to locally
strong northerly winds will prevail over the coastal waters today
as high pressure remains over the eastern Pacific. Gusty winds
will generate steep wind waves creating hazardous sea conditions,
especially for smaller vessels. Winds will then diminish late this
week as the high pressure weakens and the thermal trough shifts
towards the coast.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 11 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm
             SCA...Mry Bay from 2 PM

&&

PUBLIC FORECAST: Sims
AVIATION: MM
MARINE: MM

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