Marine Weather and Tide Forecast for Napa, CA

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
(18Z TAFS)
Issued at 1110 AM PDT Fri Apr 25 2025

Low pressure spins offshore leaving much of the area with VFR cigs, though a few areas have seen cigs fall to MVFR for a few hours. This should generally remain the trend for the forecast period, unless a shower moves over the region. Tomorrow morning, when rain chances look to pick up, we may see longer stretches of MVFR for terminals around KSFO and down the Central Coast, though confidence is low on timing and exact locations of showers.

Vicinity of SFO...VFR conditions should prevail through much of the day, with VCSH being possible through the evening. Showers should start to increase by Saturday morning and perhaps bring a brief period of MVFR conditions. Conditions look to improve mid to late morning with VFR conditions prevailing through the day.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Similar story as the rest of the TAF sites, though Monterey Bay Terminals likely have the best shots of showers through the forecast period and into Saturday. Generally VFR conditions will prevail, though MVFR conditions will be possible with any stronger showers that move through. There is a small chance for thunderstorms for the southern half of Monterey and San Benito counties.

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.

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.