Issued at 1239 AM PDT Thu Apr 24 2025
Cooler trend continues today into the weekend. Patchy drizzle and fog are possible within the marine layer clouds. Light rain, drizzle, and isolated thunderstorms are possible throughout the region Friday and Saturday.
, (Today and tonight) Issued at 1239 AM PDT Thu Apr 24 2025
Marine layer stratus has developed across the Bay Area and Central Coast. The latest data from the Point Sur profiler suggests that the marine layer has thickened to around 2500-3000 feet, a depth that would support stratus intrusion well into the interior. Some of the far interior locations could see some transitory sunshine for a few hours in the afternoon, but the coastal region and the coastal valleys should remain socked in through the day.
A cooling trend continues across the region with a strengthening upper level trough approaching California. High temperatures range from the lower to middle 60s in the inland valleys, with southern Monterey County seeing temperatures up to the lower 70s, while the coasts and the bays see temperatures reach the middle 50s to the lower 60s. Onshore winds this afternoon will be breezy and gusty, with gusts of 20-30 mph at the coast and through the gaps and passes. In some favored regions, particularly Altamont Pass, Pacheco Pass, and the Mayacamas, the gusty winds could last well into the evening.
..(Friday through Wednesday) Issued at 1239 AM PDT Thu Apr 24 2025
An upper level low should impact the state on Friday and Saturday, with the trends for a stronger and more southerly low continuing as of the latest model outputs. The ensemble model clusters are finally coming into agreement on the location of the low coming in, if not the exact strength. As a result, while we're more confident in where the rain will fall, there's still some variation in the exact rain amount. The current forecast calls for around 0.10-0.25" of rain in the Monterey Bay region, the Santa Cruz Mountains, and the Salinas Valley, with rainfall totals as high as 0.5-0.7" in the Santa Lucia mountains. Elsewhere, rain totals across the Bay Area will be very light, especially across the North Bay where upper level offshore flow will limit the precipitation chances, and outside of the southern and eastern mountains of Santa Clara County, wetting rains (over 0.1" of rain) are not likely.
We're also noting an steady increase in the likelihood of convection across the region. While still slight, the probabilities of thunderstorms have risen to 10-20%, mainly across the Central Coast, extending from Friday night through Saturday. From the previous forecaster: Forecast soundings show a few hundred J/kg of CAPE across the Central Coast overnight Friday into Saturday with forecasted CAPE values to peak Saturday morning. To have a thunderstorm you need four main ingredients: moisture, instability, lift, and wind shear (speed or directional). With this system incoming, we have a source of moisture, a source of lift (cold frontal passage), and some instability forecast. The questionable ingredient is wind shear. As of right now during the time of the highest thunderstorm probabilities (5AM-5PM Saturday), forecast soundings show some directional wind shear (winds veering with height indicating some warm air advection is occurring) but not very much speed wind shear. The surface to 500 mb bulk shear shows much higher speed shear values located just to our south in San Luis Obispo County (NWS Los Angeles' CWA). While the current trend for this cut-off low has been to shift southwards, if the low were to shift just slightly northward we could potentially see those higher bulk speed shear values shift into Monterey County. If this were to occur, it would increase confidence that we may see some thunderstorms across southern Monterey County given the alignment of wind shear with our area of moisture, lift, and instability. It's worth watching over the next few days to see where this cut- off low tracks (further south or further north) and how our thunderstorm risk along the Central Coast changes this weekend.
Ridging should return after the trough moves out, with daytime highs rebounding to near to slightly above the seasonal averages in the early and middle part of next week.
(12z TAFS) Issued at 448 AM PDT Thu Apr 24 2025
Widespread MVFR CIGS are affecting the region with IFR CIGs for STS. Winds stay light to moderate through the morning and increase slightly into the afternoon. Cloud cover snuggles to erode in the late morning and into the afternoon, with CIGs scattering in most areas, but mid level clouds continue to build. MVFR CIGs become widespread into Thursday evening, with slight reductions in wind. The next approaching rain system will cause some coastal drizzle and some shower chances into early Friday.
Vicinity of SFO, MVFR CIGS rise into the afternoon to around 2300 ft AGL before scattering into the late afternoon but mid-level cloud cover remains. MVFR CIGS return into the evening and last through much of Friday before some slight lifting as the low pressure system and light rain chances approach. Expect moderate west winds through the TAF period.
SFO Bridge Approach, Similar to SFO
Monterey Bay Terminals, MVFR CIGs last through the late morning before scattering. West winds increase into the afternoon but reduce in the early evening and MVFR CIGs re-fill over the terminals.
(today through Tuesday) Issued at 448 AM PDT Thu Apr 24 2025
Winds and seas continue to abate. Expect quiet into the late work week with some light rain moving across the waters starting Friday morning and lingering into that night. Strong northwesterly breezes and rough seas return late Saturday.
Ca, None. PZ, None.
