FXUS66 KMTR 271047
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
347 AM PDT Fri Mar 27 2026

...New CLIMATE...

.KEY MESSAGES...
Updated at 900 PM PDT Thu Mar 26 2026

 - Above normal temperatures persist into the weekend

 - Offshore winds across the North Bay Interior Mountains thru
   Friday morning

 - Pattern change with chances for largely beneficial rain and
   increased breezes next week

&&

.SHORT TERM...
Issued at 900 PM PDT Thu Mar 26 2026 
(Tonight through Friday Night)

Above normal warmth is anticipated to continue as we end the
work-week. The current expectation is that we'll see a modest push
of offshore breezes through the pre-dawn hours on Friday. 925mb
flow of 20 to 30 knots is forecast to extend from the northern 
Sacramento Valley southward through the Bay Area and portions of 
the Central Coast. This could translate to wind gusts at the
highest elevations of the North Bay exceeding 35-45 mph thanks to
mountain wave activity through sunrise Friday. In addition to the
compressional warming associated with offshore wind patterns, the
marine layer will remain nearly non-existent. With a dry airmass 
in place, there should be a large diurnal temperature range with 
MinT values in the 40s (a few upper 30s cannot be discounted) with
Friday afternoon MaxTs in the 70s and 80s, even across coastal 
regions. 

&&

.LONG TERM...
Issued at 900 PM PDT Thu Mar 26 2026 
(Saturday through next Thursday)

The weekend will be largely pleasant with the start of our 
cooling trend expected to commence early next week. Highs on 
Saturday and Sunday are expected to remain above normal, 
especially for areas away from the coast. That said, there are 
some signs that onshore flow may be a *slightly* stronger on 
Saturday which may equate to MaxTs a few degrees lower than 
Sunday. In fact, higher resolution NWP from PGE/SJSU WRF hint that
a very shallow and compressed marine layer may try to invade 
coastal regions (Pacific Coast and SF/Monterey Bays) on Saturday 
with potentially some morning drizzle/patchy fog. We'll fine tune
this in future forecasts. By Saturday afternoon, however, most of
the shallow moisture should be scoured out with mostly sunny skies.
Depending on the breadth/inland extent, this could modulate MaxTs
by 2-5 degrees. Still, it'll be largely pleasant on Saturday. 
Offshore surface to 925mb flow appears more organized on Sunday, 
and while morning low clouds/fog cannot be discounted during this 
time,especially along the coast, Sunday for sure looks to be the 
warmest day this weekend.

After an extended time of above normal warmth, there will be a 
very noticeable change as unsettled conditions take shape. This
will mean opportunities for rainfall and increased onshore winds.
Our stubborn area of high pressure will be dislodged eastward by 
our longwave pattern that is well-advertised by a majority of 
deterministic and ensemble guidance. There are some differences
with respect to the overall amplitude/depth of the upper trough.
That said, the greatest spread in the NWP is due to differences in
the progression of various upper troughs. What this translates to
is high confidence that we'll see widespread cloud cover and 
rainfall with lower confidence in specific onset/end times. 

A discernible plume of precipitable water (above 150% of normal 
for this time of year) will stretch from the Central Pacific 
eastward toward the West Coast by the time we get into Monday. 
Confidence is increasing that a bulk of the more widespread 
activity will be later Monday and into Tuesday as a ribbon of 
50-70 knot mid-level flow develops ahead of a positively titled 
upper trough. This corridor of greater winds has shifted a bit 
farther south compared to what was forecast yesterday by NWP. Not
surprisingly, the richest plume of moisture appears that it's 
aimed a bit more at the Central Coast compared to areas north of 
the Golden Gate. In fact, the latest QPF through Thursday evening 
has increased across the Santa Lucia Range/Big Sur Coastline while
ticking down slightly across the Western Sonoma Hills. This 
aligns well with both GEFS and EPS probability of Integrated Vapor
Transport above 250 kilogram/meter/second maximized south of the 
Golden Gate (and probably south of Monterey Bay), at least with 
this initial upper trough on Tuesday.

A second, more compact upper trough will swing through the region
early Wednesday. This second opportunity for precipitation will 
be what allows totals to tick up a little higher across the North
Bay. In total, rain amounts across the Coastal Ranges in Sonoma 
County still have the best chance of eclipsing 1" (around a 40% 
chance), with the probability of 1" lower farther south. Of 
course, areas such as the Santa Cruz Mountains and Santa Lucia 
Range are likely to be the spots where rain totals could rival 
regions farther north. Instability does build a little bit more 
with this second system. While the probability of thunder remains 
around 10%, the convective nature of activity does complicate rain
amounts some due to the isolated to scattered nature of precip.

It does appear that ridging will return sometime Thursday and 
into Friday, but timing of when this trough will progress eastward
is highly uncertain. Total rain amounts are forecast to average 
between one tenth of an inch across inland areas (including the 
population centers) to half an inch across coastal regions of the 
Central Coast and portions of the North Bay. As noted above, 
western Sonoma County will have the best chance for rain amounts 
at or above 1 inch. It should be restated that if this second 
system amplifies more than currently anticipated, then the window 
for rainfall could be extended into Friday which could drive 
totals upward. Still, rain amounts appear largely beneficial as 
even the 90th percentile QPF (reasonable-worst case scenario) are
largely 1-2" across the region which shouldn't translate to a
major flood risk given the recent dry spell.

This second system will have the potential to produce the 
stronger non-convective winds (largely across the higher terrain) 
as the breadth of higher momentum resides through the column. 
Probability of 40 mph winds are around 60-80% across the North Bay
Mountains, East Bay Hills, Sonoma Coastal and Gabilan Range(s).

Ridging is expected to return toward the end of next week. At the 
surface a cold front will slide southward and dry out the low 
levels. As surface pressures rise across the Great Basin, we may 
find ourselves in another period with modest offshore winds. We'll 
examine this a little closer with time. 

&&

.AVIATION...
(06Z TAFS)
Issued at 948 PM PDT Thu Mar 26 2026

VFR with widespread high clouds across the region. Winds are 
gradually diminishing in a generally onshore pattern, except in the 
higher elevations, particularly in the North Bay, where breezy 
offshore winds persist. Light winds develop overnight, along with 
LLWS concerns in the interior North and East Bays as the winds aloft 
remain strong. Widespread onshore flow resumes Friday afternoon. 
High resolution models depict the return of marine layer stratus 
Friday night into Saturday morning, although the greatest confidence 
for impacts, especially for locations away from the immediate coast, 
comes after the end of the 24-hour TAF period.

Vicinity of SFO... VFR with thin high clouds through the TAF period. 
Breezy west-northwest winds persist through the evening hours. Winds 
gradually diminish in the late evening with light winds Friday 
morning, before the breezy west-northwest winds resume during the 
afternoon. Beyond the TAF period, monitoring the potential for 
stratus impacts at the terminal early Saturday morning, although 
confidence is very low.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... Moderate to high confidence of VFR 
throughout the TAF period. Light drainage winds overnight before 
breezy northwest winds resume Friday afternoon. Marine layer stratus 
expected to develop Friday night, but the greatest confidence for 
impacts to the terminals comes after the end of the TAF period on 
Saturday morning.

&&

.MARINE...
(Tonight through next Wednesday)
Issued at 948 PM PDT Thu Mar 26 2026

Fresh to strong gusts continue through the far outer waters
overnight, diminishing on Friday before strong gusts return to the
northern outer waters Friday night. Rough seas will begin to
subside into Friday, becoming moderate by the weekend. Relatively
light onshore winds develop Friday into the weekend with light
rain returning by the middle of next week.

&&

.CLIMATE...
Issued at 301 AM PDT Fri Mar 27 2026

Here are the record high temperatures at the long term sites for
March 27th and March 29th.

Location          March 27th          March 29th

Santa Rosa        87 in 1930          86 in 2018
San Rafael        82 in 1969, 1951    85 in 2018
Kentfield         90 in 1923          84 in 1935
Napa              86 in 1930          83 in 2018, 1968
Richmond          82 in 1952          79 in 1968
Livermore         82 in 1969, 1930    85 in 2015
San Francisco     84 in 1923          81 in 2018
SFO Airport       77 in 2021, 1986    81 in 2018
Redwood City      83 in 1969          85 in 2018, 1968
Half Moon Bay     76 in 1952          77 in 2004
Oakland           79 in 1986          79 in 2003
San Jose          85 in 1923          82 in 2018
Salinas Airport   80 in 1969, 1952    86 in 2018

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Fri Mar 27 04:30:03 PDT 2026