FXUS66 KMTR 171207
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
505 AM PDT Fri Apr 17 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1201 AM PDT Fri Apr 17 2026

 - Periods of gusty offshore winds, especially at higher
   elevations, continue through early this morning

 - Seasonably warm temperatures expected today through the 
   weekend

 - Cooler temperatures and beneficial rain for the beginning of
   next week

&&

.SHORT TERM...
Issued at 1201 AM PDT Fri Apr 17 2026
(Today and tonight)

Offshore flow produced gusty winds across our area today, but 
especially higher elevations of the North Bay and East Bay Hills.
The highest measured wind gust was at Mt St Helena (~4400ft) shortly 
after 3pm at 63mph, but is still gusting at 57mph late tonight. The 
fetch of offshore flow will persist overnight through mid-morning 
Friday as the upper trough responsible continues moving east. 
Overnight lows from the East Bay Hills south through San Benito and 
Monterey County will be chilly, especially at higher elevations, 
where winds aloft are weaker and more efficient radiational cooling 
will occur under clear skies. Morning winds will gradually ease by 
the afternoon as progressive ridging approaches the West Coast. 
Temperatures will jump about 5 degrees inland, and remain similar to 
yesterday along the coast as weak onshore flow is reestablished.

&&

.LONG TERM...
Issued at 1201 AM PDT Fri Apr 17 2026
(Saturday through Thursday)

Overnight lows tonight into Saturday morning will shift closer to 
normal as the progressive upper ridge moves across our area and 
gradually amplifies as it moves east. Temperatures will be in the 
mid-70s to near 80 inland, once again not much increase along the 
coast with onshore flow. Deterministic guidance is still struggling 
with the evolution and timing of the developing offshore 
disturbance. Sunday now looks dry and relatively pleasant, just 
slightly cooler as cloud cover increases out ahead of the upper low. 
The North Bay is likely to receive rainfall Monday, however there is 
plenty of uncertainty for the remainder of our area wrt to the 
initial ave ejecting east onshore. Tuesday has the best chance for 
scattered showers and possible thunderstorms, especially if the 
trough becomes negatively tilted by Tuesday morning. Scattered 
showers may linger into Wednesday, with no clear signal for what the 
pattern looks like beyond the extended forecast.

&&

.AVIATION...
(12Z TAFS)
Issued at 505 AM PDT Fri Apr 17 2026

Offshore winds and a deeply dry air (continental air) intrusion 
support VFR for the 12z TAFs. Gusty offshore winds in the hills 
and mountains will gradually subside through morning, resulting 
in a decrease in low level wind shear. Currently the ACV-SFO and 
UKI-STS pressure gradients are 5.2 mb and 2.2 mb respectively. 
The WMC-SFO pressure gradient is 9.6 mb. These gradients are 
forecast to weaken later today and tonight with at least locally 
onshore winds returning during this time. Model forecasts show a 
few patchy coastal low clouds possible while high clouds move in 
tonight and Saturday.

Vicinity of SFO...VFR. North wind 10 to 15 knots shifting to
northeast at times later this morning while also decreasing, 
however timing the decrease in wind is a low confidence forecast.
It's very cold over the Great Basin, offshore winds are well 
entrenched at this time. Cold, dense basin air has steepened the 
WMC-SFO pressure gradient to 9.4 mb. The large scale pattern is 
progressive, this should help flip the surface wind to onshore in 
the afternoon. Westerly wind steadily decreasing to less than 10 
knots tonight and Saturday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Dry air supports radiative cooling and 
chilly, denser air drainage winds through daybreak then steadily 
easing through morning. As mentioned for SFO the large scale pattern 
is progressive and this should help flip surface winds to onshore in 
the afternoon for the Monterey Bay terminals as well. Light and 
variable winds shifting to light southeasterly tonight and Saturday 
morning.

&&

.MARINE...
(Today through Wednesday)
Issued at 422 AM PDT Fri Apr 17 2026

Northwest winds and seas will gradually subside today through
Saturday. On Sunday winds will shift to southerly ahead of a
Pacific low pressure system that will bring rain to the area
beginning early next week.

&&

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

$$

SHORT TERM...JM
LONG TERM....JM
AVIATION...Canepa
MARINE...Canepa

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Prepared by Boulder-Creek.com Weather at: Fri Apr 17 10:30:03 PDT 2026