Marine Weather and Tide Forecast for Piedmont, CA

UPDATE
Issued at 912 PM PDT Fri Apr 25 2025

The surface low pressure centered about 220 miles to our west continues to meander to the SE tonight. Light showers are mostly diminishing aside from some lingering showers over terrain. A line of heavier showers currently seen on radar will continue towards the Central Coast overnight. Much of the Central Coast south of the Monterey Bay should see some measureable rainfall through sunrise Saturday. The current forecast remains on track with no updates needed this evening.

Behringer

SHORT TERM
(This afternoon through Saturday Night)
Issued at 1247 PM PDT Fri Apr 25

-Short Term Key Messages *Cool and cloudy conditions *Showers and isolated thunderstorm chances *Mountain top light snow

Showers will continue this afternoon and evening across southern portions of the Bay Area as well as the Central Coast. The primary culprit appears to be a couple of PV anomalies along the 2PVU surface rotating around the main upper low/trough. Rain will still remain on the "lighter" end and 12 hour rainfall amounts have largely tallied around a few hundredths of an inch across the region.

As the main upper trough digs southward, we'll see a re-invigoration of marine showers that will slide eastward. Guidance has been rather insistent on the Big Sur Coastline being the favored region for convection and given the range in the forecast, I'll nudge PoPs upward. As the upper low continues to pinwheel down the Central Coast, some modest 850-700mb WAA or trough of warm air aloft may result in some precipitation across the North Bay early Saturday morning. Currently, the greatest PoPs reside down across the Central Coast with rain chances ranging from 60-70% with PoPs around 30-50% across the North Bay. This leaves the heart of the Bay Area in a minimum PoP wise, but even here, a few sprinkles or light showers will remain possible (albeit around 20%).

As far as the potential for isolated thunderstorms, this remains a possibility, though the probability is diminishing. Forecast soundings indicate lapse rates may not be quite as steep (likely do to some slight shifts in the location of the coldest air aloft), but still supportive of more vigorous showers with a few isolated lightning strikes. For now, have confined the risk for a few storms to southern Monterey and San Benito counties. At this time, widespread severe weather is not anticipated, but brief bouts of accumulating hail may result in slick driving conditions.

There still remains an opportunity for some snow across the higher terrain of the Santa Lucia Range and potentially portions of the Diablo Range. Overall, not anticipating much in the way of significant impacts due to snow.

LONG TERM
(Sunday through next Thursday)
Issued at 1247 PM PDT Fri Apr 25 2025

-Long Term Key Messages *Lingering rain chances on Sunday Morning *Modest warming trend, 'Minor' HeatRisk next week

A slight change to the long term forecast and there now remains a potential (20-30% chance ) for lingering precipitation after sunrise Sunday. As the upper low departs, large scale ascent should ramp down. However, low level moisture remains plentiful and there's still an opportunity for largely light drizzle with some breezy conditions (10-20 mph wind gusts) as the surface pressure gradient remains a little tight.

Longer term model projections support a handful of days that will be dominated by shortwave ridging. This will mean a gradual warming trend, with "minor" HeatRisk returning. This type of heat isn't overly impactful, except to those that are exceptionally sensitive to heat (very young and elderly). As we progress into the first weekend of May, there are some signs that the pattern evolve such that a couple of upper troughs slide through the area. This may mean additional rain chances in the day 8-10 time frame according to a couple of the ensemble clusters. For now, we'll hold serve with a largely rain-free forecast given the time of year and the consensus of a dry period among a majority of the NWP. Of course, early May rains will be beneficial as it pertains to delaying the start of our dry/spring fire season.

AVIATION
(00Z TAFS)
Issued at 700 PM PDT Fri Apr 25 2025

Scattered light rain continues this evening as an upper level low tracks south along the California coastline this evening. VFR is expected to prevail, with some cigs lowering to MVFR if a shower passes overt the terminal.

Vicinity of SFO...VFR conditions are expected to prevail through the overnight with occasional drops to MVFR if/when a shower passes over the terminal, especially early Saturday morning when an increase in rain coverage around the Bay Area is possible. VFR is expected for the remainder of the TAF period from Saturday afternoon onward.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Rain coverage is expected to gradually increase across the Monterey Bay area overnight into early Saturday morning but still be scattered in nature. There is slight chance for an isolated thunderstorm, but confidence is too low for mention in the TAF. Expect VFR conditions to prevail through the forecast period with occasional cig drops into MVFR if a rain shower moves over any of the terminals.

MARINE
(Today through Wednesday)
Issued at 842 AM PDT Fri Apr 25 2025

A chilly upper level low arriving from the northwest will result in scattered showers across the coastal waters and bays today through Sunday morning. Gusty northwest winds and rough seas return across the northern outer coastal waters late Saturday. Dry weather returns early next week due to an eastward moving high pressure system over the Pacific.

MARINE
(Tonight through next Thursday)
Issued at 912 PM PDT Fri Apr 25 2025

Shower activity over coastal waters is easing this evening after sunset and the center of the upper level system continues its track southward. Rough seas are expected to develop Saturday afternoon and evening with breezy north winds across the northern waters. High pressure begins to build in by the end of the weekend into next week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory from 3 PM to 9 PM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM.