FXUS66 KMTR 311854
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1154 AM PDT Tue Mar 31 2026
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1152 AM PDT Tue Mar 31 2026
- Seasonably cool conditions with rain chances through Thursday
- Above normal temperatures and offshore flow return Friday and
continue over the weekend
&&
.SHORT TERM...
Issued at 1152 AM PDT Tue Mar 31 2026
(This afternoon through Thursday morning)
It only took 29 days, but it's finally raining. A stationary front
is offering an area of convergence for its tropical moisture tap.
Rain shower activity will continue to drift south through the day as
surface high pressure tries to nose in from the Eastern Pacific
Ocean. A gale force low in the Gulf of Alaska will put a stop to
that as it heads to the Washington/Canada border. The attendant cold
front will bring us a winter-like feel with below normal
temperatures, gusty conditions, and rain. Southwesterly winds will
increase ahead of the cold front with northwesterly winds developing
in the post-frontal environment. Widespread gusts of 20-30 mph can
be expected with gusts up to 40 mph in the highest terrain. Rainfall
totals are expected to be in the 0.10"-0.25" range with locally
higher totals in the higher terrain of the North Bay and locally
lower totals in the Interior Central Coast. Slick roadways can be
expected due to the dry spell that has allowed oil to accumulate.
&&
.LONG TERM...
Issued at 1152 AM PDT Tue Mar 31 2026
(Thursday night through next Monday)
The pattern will quickly change Thursday afternoon as upper-level
shortwave ridging noses in from the Eastern Pacific Ocean. The short
wavelength of the aforementioned trough and ridge will tighten the
pressure gradient. Strong northerly winds will result, primarily
affecting exposed areas like the higher terrain and marine
environment. The SFO-WMC pressure gradient is expected to become
negative Thursday night as the wavelength moves inland, resulting in
offshore flow. At 5 AM Friday, the ECMWF Ensemble mean is
forecasting the gradient to be -9.81 mb while the GEFS mean is
forecasting the gradient to be -7.76 mb. The 2 mb discrepancy is due
to the ECMWF Ensemble showing a stronger high and stronger low
closer together than weaker features farther apart in the GEFS. This
uncertainty is propagated through Friday and Saturday with the ECMWF
Ensemble bottoming out at -10.96 mb at 5 AM Saturday while the GEFS
is well on its relaxing trend at -5.24 mb. Nonetheless, a moderate
offshore flow event can be expected Thursday night through the
weekend with a 35 knot 925 millibar jet streak across the North Bay.
This will translate to gusts of 40 to 50 mph in the higher terrain,
namely the North Bay Interior Mountains, East Bay Hills, and Eastern
Santa Clara Hills. The ridge will also send temperatures soaring
back to well above normal.
&&
.AVIATION...
(18Z TAFS)
Issued at 1104 AM PDT Tue Mar 31 2026
Mostly VFR across the region with ceilings between 5k-15k feet.
Winds are light and variable this morning but will become west-
southwest this afternoon with rain showers tapering off. Winds
ease overnight becoming light and variable as rain showers return
early Wednesday morning. The greatest potential for rain showers
will be over the North Bay and Bay Area terminals through 18Z
Wednesday, shifting southward later in the afternoon/evening.
Along with the rain, ceilings lower to sub-VFR with the greatest
potential for IFR across the North Bay.
Vicinity of SFO...VFR. West-southwest winds increase this
afternoon and early evening before easing overnight and into
Wednesday morning. This is when we expect MVFR conditions to
return to the region by around 12Z Wednesday. In addition, VCSH
has been added to the TAFs around 12Z Wednesday with -SHRA
returning by 18Z when we may see lower end MVFR ceilings at times
of heavier rain showers.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR. Lingering rain showers will persist
through about 21Z that may produce MVFR ceilings. Otherwise,
expecting west-southwest winds at KMRY with the potential for
northwesterly winds at KSNS this afternoon. Winds ease overnight
with MVFR ceilings returning late this evening and likely to
persist into Wednesday morning. Rain should stay to the north of
the Monterey Bay Terminals, depending on timing of our next
frontal system forecast to move through.
&&
.MARINE...
(Today through Sunday)
Issued at 1104 AM PDT Tue Mar 31 2026
Gentle southwesterly breezes today will increase to become
moderate to fresh tomorrow ahead of the cold front. Fresh to
strong northwesterly breezes will develop in the post-frontal
environment Wednesday night into Thursday morning. Strong
northerly breezes will develop Thursday afternoon and persist into
Friday. Moderate seas will build to become rough Thursday into
Friday. Widespread hazardous conditions are expected Thursday and
Friday. Conditions improve by the weekend.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...RGass
MARINE...Sarment
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Prepared by Boulder-Creek.com Weather at: Tue Mar 31 14:30:02 PDT 2026
From the National Weather Service
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