Marine Weather and Tide Forecast for Piedmont, CA

SHORT TERM
Issued at 200 PM PDT Mon Apr 20 2026 (This evening through Tuesday)

The much advertised wet weather has finally arrive - began with a few showers last night through early this morning and more widespread precip this afternoon. A cold front knocking on the Bay Area's doorstep has led to an increase in precip over the North Bay stretching south to SF Bay and finally Santa Cruz the last 3-6 hrs. Monterey Bay and points E and SE remain dry at this time.
Decent precip totals over the last 12 hrs with 0.25-0.75 inches North Bay Coastal Mts and a few hundredths to 0.25" elsewhere. In addition to the precip, the frontal structure and associated pressure gradient led to gusty southerly winds. Gusts since midnight range from 20-40 mph most areas with gust 40-50 mph along the coast and and higher terrain.

Rest of today through tonight: The front off the coast will finally makes its way inland with a nudge from an upstream sfc low and upper level jet. As such, the more stratiform precip will move through the Bay Area and Central Coast with impacts to the evening commute. Wet roads and windy conditions. By late this evening the steadier rainfall will transition to more convective nature/shower behind the front.

Tuesday: Post frontal regime on Tuesday will be mainly be driven by the trailing upper level trough moving overhead, cold pool associated with trough, a phasing jet aloft around 200-250mb, and a jet max near 850-700mb. Lastly, some increased insolation during the afternoon due to less clouds. The combo of colder air aloft and daytime heating will increase sfc and ML CAPE. Factor in some of the wind fields and there's an increase for late morning/early evening thunderstorms. While there is some large 0-6km shear values it appears to be more confined to the 3-6km layer. Would like to see high shear below 3km for waterspout/tornado concerns. That being said, we'll be watching closely. Regardless, stronger storms will be capable of producing gusty winds, heavy rain, and small hail given the temp profile.
SPC is not highlight tor/hail/wind like they were earlier in the month. They do have a general mention of thunder though.

LONG TERM
Issued at 219 PM PDT Mon Apr 20 2026 (Tuesday night through next Sunday)

Once the sun sets Tuesday evening the threat for thunderstorms quickly fades, but lingering showers will persist through early Wednesday. We will have to wait for the upper trough and embedded/trailing weak shortwave to exit before shower activity ends Wednesday.

Thursday into next weekend. Warm and drier conditions will be trend. However, that trend will be tempered by persistent trough/broad upper low settling over the EPAC and CA. Conf with the forecast decreases for next weekend. Current forecast has a passing shower late Saturday due to another trough swinging through CA. Ens members are scattered on amounts, but most members at least show something. This will be fine tuned over the next few days, but for now cannot rule out some precip.

AVIATION
(00Z TAFS)
Issued at 451 PM PDT Mon Apr 20 2026

The cold front is now right along the coast, with prefrontal rain ongoing across the majority of the terminals. This light to moderate steady rain will continue through the night before a break in the early morning hours. This won't last long, however, as a band of stronger showers and possible thunderstorms is expected to roll through late morning through early afternoon.
After this finale, showers will become much more isolated as the sun comes back out.

Vicinity of SFO...Prefrontal rain will continue through the night with moderate southerly winds. There will likely be a break in the rain from around 12-17Z as the southerly winds start to increase.
The main band of showers and possible thunderstorms is expected to reach the terminal vicinity around 17Z and continue for 2-4 hours. In addition to the heavy rain, lower visibility, and lightning potential, winds will be gusty and erratic during this window. Conditions will improve in the early afternoon, but there is a chance for the atmosphere to recharge for another round of showers in the late afternoon or early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...The impacts are more or less the same across the southern terminals, although the timing is slightly later with the onset of rain this evening, the break mid Tuesday morning, and the arrival of the strong band of showers late Tuesday morning.

MARINE
(Tonight through next Saturday)
Issued at 451 PM PDT Mon Apr 20 2026

Expect breezy to gusty southerly winds to continue as a cold front and low pressure move through the area. Light to moderate rains will move along the front with spotty showers expected in its wake. Winds begin to reduce from the north to south this afternoon and into the night a moderate southwesterly breeze by Tuesday. Shower chances increase again into Tuesday with some chances for thunderstorms lasting into that night. As the weather breaks, winds will gradually shift back to the northwest Wednesday before increasing to a strong northwest breeze by Thursday.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge.

Small Craft Advisory until 3 AM PDT Tuesday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory from 9 AM to 9 PM PDT Tuesday for Mry Bay- Pigeon Pt to Pt Pinos 0-10 nm.

Small Craft Advisory from 9 AM to 3 PM PDT Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.