Technical NOAA Weather Discussion

FXUS66 KMTR 280457
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
957 PM PDT Wed May 27 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1215 PM PDT Wed May 27 2026

- Cooler, unsettled weather conditions continue through Thursday

- Warming and drying trend Friday and beyond

&&

.UPDATE...
Issued at 921 PM PDT Wed May 27 2026

We have been able to continue to benefit from the upper level 
disturbance that has been slowly churning overhead the past couple
of days with beneficial rainfall in the bumper portion of our
transition into the dry season. Most locations that have received
some rainfall got less than a tenth of an inch, but numerous 
locations in the Myacama's, Diablo Range and Santa Lucia's have 
seen 0.25"-0.50" or more the past 48hrs. The Santa Cruz Mountain 
are likely to catch up somewhat overnight into Thursday as the 
upper low ends its retrograde and starts to exit to the east on 
Thursday morning. Portions of the Santa Lucia's and Santa Cruz
mountains will see more rainfall tomorrow with ensembles 
indicating a roughly 30%-50% chance of exceeding 0.50" of rainfall
by sunset tomorrow across those areas.

&&

.SHORT TERM...
Issued at 1215 PM PDT Wed May 27 2026
(This evening through Thursday)

We have already seen showers and an isolated thunderstorm develop 
late this morning across the Eastern Santa Clara Hills and in the 
Mountains of San Benito County. As daytime heating continues, we are 
expecting convection to fire up in the East Bay Hills, Eastern Santa 
Clara Hills, the Santa Cruz Mountains and the Central Coast (County 
of Monterey/San Benito) this afternoon and evening. This is as the 
atmosphere becomes more unstable with CAPE values between 100-400 
J/kg. However, vertical wind profiles don't favor organized 
convection, with little to no 0-6km wind shear. Therefore, 
probabilities for thunderstorms remain less than 10% through the 
afternoon and early evening. Any stronger cell (shower and/or 
thunderstorm) that develops over any one given location has the 
potential to produce 0.25"-0.50" per hour of rainfall. 

The mid/upper level low will begin to retrograde back over the 
Pacific tonight into early Thursday morning and begin to pull in 
PWAT values of around 1.00". This will increase rain chances 
offshore late tonight and then will move onshore along the Central 
Coast through Thursday morning. However, with the loss of daytime 
heating, the thunderstorm threat will lessen. Forecast rainfall 
amounts have increased in the Santa Cruz Mountains and Santa Lucia 
Range now having a greater than 60% probability of seeing more than 
0.25" through Thursday afternoon (this would include rainfall from 
today). These probabilities of seeing greater than 1.00" (40%-75%) 
remain confined to the Santa Lucia Range. 

Conditions begin to dry out from north to south during the day 
Thursday as the mid/upper level low shifts further inland. However, 
rain showers look to linger over the Central Coast through the early 
evening. 

&&

.LONG TERM...
Issued at 1215 PM PDT Wed May 27 2026
(Thursday night through next Tuesday)

Cannot rule out rain showers to linger across the North Bay late 
Thursday night into early Friday morning as deeper moisture (PWAT 
values approaching 1.00") move across this region. In wake of the 
exiting trough, a warming and drying trend will kick off by Friday 
afternoon with temperatures gradually returning to near average this 
weekend as zonal flow develops over the region. Temperatures are 
currently forecast to warm above seasonal averages by Sunday and 
into the middle of the upcoming week. 

&&

.AVIATION...
(06Z TAFS)
Issued at 957 PM PDT Wed May 27 2026

Scattered showers are expected to arrive tonight becoming widespread 
rain by early morning. Rain generally continues through late 
morning/early afternoon before conditions dry out. There is some 
potential for isolated thunderstorms to develop again during the 
day. Any t-storms that develop would likely impact MRY and SNS with 
the highest thunderstorm probabilities across the interior Central 
Coast. Breezy onshore winds are expected again during the 
afternoon/evening before winds ease tomorrow night. Confidence has 
increased in widespread MVFR CIGs tonight with most sites seeing 
MVFR conditions through late morning. Temporary decreases in 
visibility are possible if a stronger shower moves directly over the 
airport.

Vicinity of SFO...Shower chances are expected to increase overnight 
and continue through late morning. Winds remain relatively light 
overnight before breezy onshore winds return during the 
afternoon/evening. MVFR CIGs generally expected overnight with CIGs 
rising to the MVFR/VFR border overnight. Winds ease tomorrow 
evening/night with some potential for MVFR CIGs to return.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Shower chances increase through 10Z with 
widespread rain returning afterwards through much of the day. There 
is some potential for thunderstorms to develop during the day. The 
highest chances for thunderstorms are to the south of MRY and SNS 
but cannot rule out the potential for a stray storm or two moving 
through the Monterey Peninsula (particularly during the morning into 
the early afternoon). Winds remain breezy during the 
afternoon/evening before starting to ease overnight. Winds at SNS 
are tricky with LAMP guidance highlighting strong valley winds 
during the early morning. For now put gusts to around 15 knots 
during the early morning but LAMP guidance seemed a little high with 
20+ knot gusts.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 921 PM PDT Wed May 27 2026

Winds diminish and waves abate across the coastal waters tonight
with a moderate northwest breeze expected late morning through
Friday. Strong to near gale force northerly winds return over the
weekend and continue into next week. Wave heights build as winds
restrengthen with wave heights between 10 to 12 feet expected this
weekend into early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from 9 AM PDT Thursday through late 
     Thursday night for CAZ006-505-509-529-530.

PZ...Small Craft Advisory until 3 PM PDT Thursday for Pt Arena to Pt 
     Reyes 10-60 NM.

     Small Craft Advisory until 3 AM PDT Thursday for Pigeon Pt to Pt 
     Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Kennedy
MARINE...Kennedy

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Prepared by Boulder-Creek.com Weather at: Wed May 27 22:30:02 PDT 2026
From the National Weather Service