FXUS66 KMTR 082006
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
106 PM PDT Sat Aug 8 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 104 PM PDT Sat Aug 8 2026
- Warm to hot conditions will result in moderate to major
HeatRisk for the interior through Sunday
- Near-critical fire weather conditions in the higher terrain
through Sunday
- Minor coastal flooding for bayshore locations along the San
Francisco, San Pablo, and Monterey bays through Thursday
morning
&&
.SHORT TERM...
Issued at 104 PM PDT Sat Aug 8 2026
(This evening through Sunday night)
The deeper marine layer, around 1600 feet in depth per the OAK
Upper Air Sounding, early this morning has resulted in slightly
cooler temperatures across the lower elevations. As high pressure
over the Four Corners region continues to build westward across
the Bay Area and Central Coast, temperatures aloft remain very
warm to hot! As such, the Heat Advisory remains in effect for much
of the interior through 10 PM PDT Sunday. This is as the marine
layer is forecast to eventually compress to around 500 feet by
Sunday morning under the building high pressure and 850mb
temperatures are between 27-30C Sunday afternoon. Afternoon
temperatures in the Heat Advisory are forecast to warm into the
mid 90s and up to 105 deg F in the warmest interior locations
where the most widespread moderate to isolated major HeatRisk are
present. Overnight lows are also forecast to be warm and range
from the mid 60s in the hills just above the marine influences to
low 80s (especially in the higher elevations). Afternoon
temperatures closer to the coast are forecast to be in the 60s to
mid 70s largely due to the onshore winds and marine influences.
Overnight lows near the coast are forecast to be in the 50s as
stratus returns overnight. If the depth of the marine layer is
higher than currently forecast, temperatures will be slower to
warm Sunday afternoon.
Minor coastal flooding is also expected around the time of the
highest high tide (evening/overnight) for bayshore locations along
the San Francisco, San Pablo, and Monterey bays through Thursday
morning. The Pacific Coast may need to be added Sunday through
Tuesday to the advisory. We are waiting to see how high the
observed levels are tonight (Saturday) before making that
decision. Please see the CFW product we have out for additional
details. Also, for more on the fire weather concerns this weekend,
please see the Fire Weather Section of the AFD below.
During this weekend's heat event, remember:
* Stay hydrated and drink plenty of fluids.
* Wear lightweight and light-colored clothing.
* Reduce time spent outdoors or stay in the shade.
* Never leave people or pets unattended in vehicles.
* Use sunscreen if going to the coast or the pool.
&&
.LONG TERM...
Issued at 104 PM PDT Sat Aug 8 2026
(Monday through next Friday)
Ensemble clusters are in decent agreement that a mid/upper level
shortwave trough will develop by Monday off of the West Coast.
However, the high pressure aloft will persist over the Four
Corners region and over the eastern Pacific. This will bring
temperatures closer to near seasonal norms by Monday and through
Wednesday, also lowering HeatRisk to the minor category across the
interior.
By late in the week, temperatures cool to below normal as a
mid/upper level through develops off of the Bay Area and Central
Coast. As this low pressure approaches the coastline late in the
week and monsoonal moisture advects northward around the high over
the Four Corners, there is the potential for high-based
convection. The main question is if there will be enough
instability. While this is still far out in time and low
confidence, any dry lightning would be problematic from a fire
weather standpoint. Be sure to check back for additional details
as we move closer to midweek.
&&
.AVIATION...
(18Z TAFS)
Issued at 1135 AM PDT Sat Aug 8 2026
Tricky forecast this TAF period. The marine layer overperformed this
morning at a depth of 1600 feet. Majority of model guidance kept
signaling a compression below 1000 feet, but considering the recent
observations and expected onshore wind support, it will likely be
closer to 1200-1500 feet tonight. That being said, a mixed bag of
borderline IFR-LIFR ceilings are expected after 02Z Sunday for
coastal sites and after 04Z Sunday for inland sites. SJC is the only
inland site that will see low-end MVFR ceilings this TAF period. Low
confidence on whether LVK will develop a brief MVFR-IFR ceiling as
it is dependent on how far inland the marine stratus travels. If a
ceiling does develop, it will likely be sometime after 10Z Sunday.
Overall, medium confidence on stratus arrival for Bay Area sites.
Aside from stratus, typical diurnal onshore wind pattern prevails
through the TAF period with most sites shifting to VFR by the early
afternoon.
Vicinity of SFO...VFR with northwest winds increasing to 12-18 kt
this afternoon and ease to 7-10 kt overnight. Marine stratus returns
again tonight with IFR ceilings. In terms of timing, relied on
persistence for SFO but expect a delayed arrival for OAK (~04Z
Sunday). Medium confidence on exactly when they will arrive, though
ceilings are expected to persist until 17-18Z tomorrow.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Stratus has receded to the coastline where
the otter eddy resides. VFR through the afternoon with high
confidence for IFR ceilings to roll in around 02-03Z this evening.
Overnight, ceilings may drop to LIFR (OVC003-004) though there is
low confidence on when and how long those conditions will last.
&&
.MARINE...
(Today through Thursday)
Issued at 918 AM PDT Sat Aug 8 2026
Fresh to strong northwest winds continue through the weekend into
the work week with building rough seas up to 12 feet across the
outer coastal waters. The northern coastal waters particularly
will remain hazardous to small craft with occasional near gale
force gusts through the middle of next week. Gusty onshore winds
are forecast through Sunday across the San Francisco Bay north of
the Bay Bridge to the Delta. A long period southerly swell of 15
to 17 seconds prevails through the weekend.
&&
.FIRE WEATHER...
Issued at 1206 AM PDT Sat Aug 8 2026
Near-critical fire weather conditions persist through the weekend
across the interior due to very hot and dry conditions. Strong
thermal belting, extended burn periods, elevated PIG, and near or
record BI/ERC values are expected. Temperatures will be 10 to 15
degrees above normal with a compressed marine layer. Poor minimum
daytime relative humidity as low as 10% in the afternoons with
little-to-no recovery overnight is expected with nocturnal drying in
the highest terrain. Even with critically dry conditions, wind is
the limiting factor preventing this from being a Fire Weather
Watch/Red Flag Warning event. Outside of the diurnal sea breeze that
will bring breezy conditions in the afternoons and evenings through
gaps and passes, onshore flow will be light. Additionally, critical
conditions are not expected to meet coverage or duration
requirements to warrant a product. Elevated fire weather conditions
are expected into next week as onshore flow increases on the heels
of the near-critical hot and dry event this weekend. The upper-level
pattern along with a resurgence in monsoonal moisture may be enough
to bring elevated rain showers/thunderstorms to the forecast as
early as Thursday and into next weekend.
Sarment
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506-
508-529-530.
Heat Advisory until 10 PM PDT Sunday for CAZ503-504-510-512>518.
PZ...Small Craft Advisory until 9 PM PDT this evening for SF Bay N of
Bay Bridge.
Small Craft Advisory from 9 AM to 9 PM PDT Sunday for Pt Arena
to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge.
Small Craft Advisory until 3 AM PDT Monday for Pt Arena to Pt
Reyes 10-60 NM.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Navarrete
MARINE...Navarrete
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Prepared by Boulder-Creek.com Weather at: Sat Aug 8 14:30:03 PDT 2026
From the National Weather Service
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