Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
FXUS66 KMTR 270436
Area Forecast Discussion
National Weather Service San Francisco Bay Area
936 PM PDT MON SEP 26 2016
.SYNOPSIS...Slight cooling is possible on Tuesday near the coast,
yet the strong high pressure aloft and lack of a persistent
onshore flow will result in another very warm afternoon across
much of the region. A more widespread cooling trend is forecast on
Wednesday and will extend into the upcoming weekend as an upper
level trough deepens along the West Coast.
.DISCUSSION...as of 9:36 PM PDT Monday...Record breaking heat was
felt across the region today with highs in the 90s reported across
most locations. 100 to 106 degree temperatures were observed in
the warmest inland locations with Corralitos coming in as our hot
spot at 106 followed by a record breaking 104 in Salinas. Several
records were tied or broken across the region today in the absence
of the marine layer and the influence of warm offshore flow. (See
RERMTR for more detailed information.) Temperatures remain in the
70s and lower 80s at this hour with mild overnight temperatures
expected once again tonight.
Hot and dry weather also help fuel a few wildfires across the
region today. The largest of these fires ignited in the hills
above Morgan Hill this afternoon with smoke and flames visible
across the Bay Area. The Loma Fire located near Loma Prieta has
grown to over 1000 acres and has destroyed one structure. For more
infomation on this fire follow us on Facebook and Twitter.
From previous discussion...The very warm and dry air mass aloft
will remain in place into Tuesday. With this, do expect another
very warm to hot day region- wide. However, some slight cooling is
possible near the coast as onshore winds are forecast to develop
earl in the afternoon. With this, should see about 10 degrees of
cooling at the coast while inland areas only cool a few to as much
as 5 degrees. The caveat will be if onshore flow does not develop,
then expect the heat to once again extend all the way to the coast
with little cooling. Regardless, tomorrow will once again see
temperatures well above seasonal averages.
Temperatures will finally cool down from Wednesday through the
upcoming weekend as the ridge aloft weakens ahead of an
approaching mid/upper level trough from our north. Conditions will
cool first near the coast on Wednesday and then spread inland late
in the week as onshore flow and associated marine influences
increase. By late week, temperatures will likely be 15 to as much
as 25 degrees cooler compared the past few days.
Further cooling is expected into the upcoming weekend with
temperatures falling back below seasonal averages as the upper
level trough off of the West Coast deepens and shifts inland. The
forecast models generally agree on a secondary mid/upper level low
dropping down the Pacific Northwest coast from Sunday into Monday
with the potential for precipitation as far south as northern Napa
and Sonoma Counties. With this, do have a slight chance mentioned
at this time. Will continue to monitor this upcoming change in the
weather pattern and analyze our chances for precipitation late in
the forecast period.
.AVIATION...As of 5:39 PM PDT Monday...High confidence VFR for
this period due to strong mid-upper level high pressure stretching
from the eastern Pacific to NV/UT/ID. A closed mid-upper level low
over the Baja will slowly drift northward through Tuesday. San
Carlos sodar shows a very shallow layer of marine air approx 800
feet deep, and no significant cooler marine air seen on the Fort
The latest NAM model has generally trended slower with the
weakening of the high across northern CA and slower with lower
level cooling forecast through Tuesday night and Wednesday thus
pretty good chances VFR persists at the Bay Area terminals into
mid-week. Patchy marine based fog and stratus may return to the
immediate coastline later Tuesday into early Wednesday morning.
Vicinity of KSFO...VFR. W-NW winds 10-15 knots til 04z, then lighter
W winds through late evening. Light NE wind Tuesday morning then NW
winds 10-15 knots returning Tuesday afternoon and early evening.
SFO Bridge Approach...Similar to KSFO.
Monterey Bay Terminals...VFR. SW-NW wind 5-10 knots this evening,
winds becoming light SE later this evening. W winds near 10 knots
return late Tuesday morning or early afternoon.
.FIRE WEATHER...As of 2:45 PM PDT Monday...In the grand scheme of
things, very little change from the previous forecast. Hot and
dry conditions will continue for one more day. Poor recoveries
will be possible again tonight with occasional offshore flow.
Latest model guidance continues coastal cooling Wednesday and more
widespread cooling later in the week.
For Sawmill fire - gusty southwest winds will be possible this
evening and then weakening overnight. Flow will switch to
northeast overnight with mild and dry conditions. Tuesday will be
hot and dry again.
Soberanes Fire...gusty conditions will be possible through this
evening and then weaken overnight. An overall offshore flow will
develop overnight with poor recoveries. Really no changes of note
on Tuesday with perhaps a few degrees of cooling but still dry.
Will need to wait until Weds for any appreciable inland cooling
but even that will be moderated for the interior portions of the
.CLIMATE...Here are the record highs for September 26.
Monterey Bay Area
.MARINE...as of 8:57 PM PDT Monday...A strong upper level high
pressure area stretches from the Eastern Pacific across
California to the northern Great Basin. An upper level low
pressure area was located over Baja and will drift northward
through mid-week reaching Southern California later Tuesday. Some
high clouds from this low may reach the southern forecast area
during the mid-week. The aforementioned upper level high will
gradually weaken through mid-week then become replaced by a fairly
robust upper level low pressure trough from the Gulf of Alaska
later this week and weekend.
PUBLIC FORECAST: CW
FIRE WEATHER: MM
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