FXUS66 KMTR 280057
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
557 PM PDT Thu Aug 27 2026

...New AVIATION...

.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...
(00Z TAFS)
Issued at 557 PM PDT Thu Aug 27 2026

It's VFR with widespread mid and high level clouds over much of 
the forecast area. There are high based showers as well. A few 
showers have been reaching the ground over the north Central Coast
based on webcam and spotter reports. Increased cloud cover i.e. 
water vapor will interfere with and decrease radiative cooling; 
coastal stratus and fog will be limited tonight and Friday. 

It's a complex forecast over the next 12-24 hours. Subtropical jet
stream winds and upper level divergence are aligned with the current
water vapor plume with a 700 mb to 500 mb shortwave trough arriving
from the southwest Friday morning. Stay tuned to the latest updates.

Vicinity of SFO...VFR. A few showers are possible tonight and/or 
Friday. Currently, the 00z TAF advertises vicinity showers (VCSH)
11z-20z Friday. West to northwest wind 8 to 14 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Vicinity showers (VCSH) tonight, with
tempo showers 10z-15z Friday morning and showers prevailing until
late Friday morning at the terminals. Winds will be a mix of west to
northwest 5 to 15 knots and light and variable.

&&

.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 CAZ512-516-517-
     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...Canepa
MARINE...Navarrete

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea


  
Prepared by Boulder-Creek.com Weather at: Thu Aug 27 20:30:03 PDT 2026