FXUS66 KMTR 272027
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
127 PM PDT Thu Aug 27 2026
...New SHORT TERM, LONG TERM, FIRE WEATHER...
.KEY MESSAGES...
Updated at 125 PM PDT Thu Aug 27 2026
- Slight chance of thunderstorms through Friday afternoon,
especially across the Central Coast
- Cooling trend continues Friday into next week
&&
.SHORT TERM...
Issued at 125 PM PDT Thu Aug 27 2026
(This evening through Friday night)
Looking at satellite imagery, seeing more widespread mid-to-high
level cloud cover spreading across the Central Coast and southern
portion of the greater San Francisco Bay Area. The greatest
potential for high-based convection will be across the Central Coast
as the OAK Upper Air sounding reported MUCAPE (instability aloft)
slightly greater than 400 J/kg. This is also where the CAMs and
higher resolution deterministic models show the greatest MUCAPE
values today through early Friday morning. Thus, have added isolated
thunderstorms to the official forecast for the Central Coast. Further
north across the Bay Area, seeing less threat for thunderstorms, yet
remains a non-zero chance.
The Precipitable Water (PWAT) values increase to around or slightly
above 1.5" across the Central Coast by Friday morning with a greater
potential for wetting rains. However, rainfall amounts are projected
to largely be less than 0.10" throughout this event. Thus, we have
issued a Red Flag Warning for much of the Central Coast including
the Santa Cruz Mountains from 5 AM to 3 PM Friday. Fuels remain dry
from the recent warm and very dry conditions above the marine
influences, especially in areas above 1000 feet in elevation. This
is also where the CAMs have the greatest instability on Friday.
Given the Timber and Plaskett fires ongoing, any lightning strikes
and/or erratic/gusty outflows would make for difficult firefighting
efforts. Will closely monitor the latest forecast models and adjust
accordingly.
As the mid/upper level trough deepens off of the Pacific Northwest
coast Friday evening into Saturday morning, expecting this deeper
moisture plume to shift eastward resulting in PWAT values lowering
to near 0.50". Thus, ending the threat for high-based convection.
The mid/upper level low off of the Pacific Northwest will push
inland Friday night into Saturday, leading to a tightening pressure
gradient which will result in breezier winds Friday and into the
weekend. Thus, wind gusts are forecast to reach 25 to 35 mph along
the coast and through favored gaps, valleys, and passes. This
pattern will also usher in cooler temperatures. Zonal flow develops
over the weekend holding temperatures steadily below normal.
&&
.LONG TERM...
Issued at 125 PM PDT Thu Aug 27 2026
(Saturday through next Wednesday)
A reinforcing trough deepens off of the Pacific Northwest coast by
Monday, allowing afternoon temperatures to be some 5 to 15 degrees
below seasonal averages. The current forecast has the potential for
rain showers returning towards the middle of next week. However, the
evolution of things across the tropical Eastern Pacific remains in
question, mainly in the form of remnant tropical moisture to be
pulled in from the south. Thus, forecast confidence remains low at
this time.
&&
.AVIATION...
(18Z TAFS)
Issued at 1222 PM PDT Thu Aug 27 2026
Quite an interesting set up today. A moisture plume is moving across
our region from the southwest and is producing lightning offshore as
well as some light rain. Whether rain will reach the ground over the
terminals is uncertain, but high confidence for virga at the very
least. Overall, there is low confidence on the forecasted ceilings
towards the end of the TAF period and exact timing of potential
vicinity showers, but medium confidence for it to remain south of
the Golden Gate. The potential for lightning to impact terminals
this TAF period is low, around a 10-15% chance, and TAFs will be
updated as needed.
Despite the current set up, VFR conditions prevail through the day
with a parade of high level clouds associated with the high-based
convective system. Moderate onshore breezes increase through the day
and ease overnight. If thunderstorms do develop over land, we will
monitor for gusty outflows and amend as needed.
Vicinity of SFO...VFR through the afternoon with onshore winds
increasing to 15-20 kt and ease to around 10 kt overnight. SFO and
OAK are currently on the edge of the previously mentioned convective
system, so there is not an immediate concern for lightning or VCSH.
However, this moisture plume is expected to become a bit more
widespread early Friday morning. As of writing this, there is a
great deal of discrepancy in model guidance, so the timing will be
refined in following TAF issuances.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Moderate onshore winds prevail this
afternoon and ease overnight. MRY and SNS have the highest chance of
remaining under the influence of the moisture plume this TAF period.
MRY may be close enough to the coast to still experience some marine
influence, but medium confidence on the timing of IFR ceilings.
Lightning is still being observed via satellite offshore and will
continue to be monitored.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 1222 PM PDT Thu Aug 27 2026
Fresh northwest breezes with occasional near gale force gusts
persist through the weekend and ease by early next week. Wind
driven seas remain moderate into next week as a long period
southerly swell around 16 to 18 seconds approaches our coastal
waters by Friday morning.
&&
.FIRE WEATHER...
Issued at 125 PM PDT Thu Aug 27 2026
One more day of near-critical fire weather conditions above 1000
feet, especially across the Central Coast, as warm and dry
conditions continue above the marine layer inversion and overnight
humidity recoveries remain poor into Friday morning. There still is
a non-zero chance for thunderstorms across the Central Coast today
through tonight. By tomorrow, with the increasing potential for
lightning, we have issued a Red Flag Warning for much of the Central
Coast including the Santa Cruz Mountains from 5 AM to 3 PM Friday
given the low confidence for wetting rains to develop. By Friday
night and into the weekend, the cooling trend will continue and
bring cooler temperatures and likely a deeper marine layer, bringing
progressively more relief to some of the higher elevations.
RGass
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Red Flag Warning from 5 AM to 3 PM PDT Friday for Caz516-516-517-
528>530.
PZ...Small Craft Advisory until 2 PM PDT Friday for Pigeon Pt to Pt
Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt
Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt
Piedras Blancas 0-10 nm.
Small Craft Advisory from 3 PM Friday to 9 AM PDT Saturday for
Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60
NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60
NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Navarrete
MARINE...Navarrete
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Prepared by Boulder-Creek.com Weather at: Thu Aug 27 14:30:03 PDT 2026
From the National Weather Service
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