Marine Weather and Tide Forecast for Sunnyvale, CA

UPDATE
Issued at 803 PM PST Sat Dec 7 2024

Widespread high cloud cover encompasses the entire Bay Area and Central Coast this evening with lurking low-level clouds just offshore. These low clouds may approach coastal areas later this evening and into the overnight hours while high clouds may limit low clouds and/or visibilities over the North Bay. This too will limit radiational cooling with temperatures expected to be a few degrees warmer than this morning's lows. The approaching frontal boundary will dissipate as it approaches the Central Coast by mid-to-late tomorrow morning. That said, the ongoing forecast remains on track this evening with no updates anticipated at this time. For complete details, please see the short and long term discussions below.

SHORT TERM
(This evening through Sunday)
Issued at 241 PM PST Sat Dec 7 2024

Temperatures are generally running on track today. Current obs show temperatures in the upper 50s to mid 60s for most locations with the exception being the warmest locations in the interior Central Coast where temperatures are reaching into the low 70s. We see a brief break from upper level ridging today as a shortwave trough moves through the Pacific Northwest. At the surface, this trough is associated with a weak surface low and a trailing cold front. The cold front will reach the Bay Area and Central Coast overnight tonight and bring with it a low (generally < 15%) chance of drizzle along the coast and over the marine environment. No real precipitation accumulation is expected with this system as it continues to weaken moving southward. While our rain chances are negligible, we will still see some effects from it namely in terms of high level clouds. Looking at the satellite, we can see a wide bank of overcast high level clouds moving into Northern California ahead of the cold front. As the front continues to move south, high clouds will become more widespread over our area with some low to mid level clouds expected to develop overnight. The increase in overnight cloud cover should help to decrease radiational cooling and keep overnight temperatures a few degrees (2-3) warmer than last night. Increased fog potential continues for the North Bay and directly along the marine/bay shoreline where there is a 20-40% chance of fog. All in all, today is shaping up to be a pleasant, if a bit warmer than normal, day.

LONG TERM
(Sunday night through next Friday)
Issued at 241 PM PST Sat Dec 7 2024

As the shortwave trough moves east, it will deepen moving into the intermountain west and create a setup favorable for gusty offshore winds across the North Bay interior mountains, East Bay Hills, and Santa Cruz Mountains Monday through early Tuesday. Gusts between 30 to 40 mph are possible across the North Bay interior mountains while gusts between 20 to 30 mph are more likely across the East Bay Hills and Santa Cruz Mountains. Widespread fire concerns remain low but dry conditions do continue to persist across the interior Central Coast.

After our weak surface cold front exits, we will see a return to clear skies through at least mid week as upper level ridging builds back in over the region. Daytime high temperatures will be fairly similar Sunday and Monday with highs generally remaining in the mid to upper 60s across the interior and upper 50s to low 60s directly along the coast. Wednesday through Friday, the pattern begins to shift (more below) with high temperatures dropping into the low 60s to upper 50s across the region. While daytime highs will be pleasant, morning lows Monday and Tuesday will be particularly chilly due to increased radiational cooling stemming from the lack of overnight cloud cover. Confidence is increasing that a Frost Advisory will be needed on Tuesday morning, potentially Monday as well, for at least portions of the North Bay and the interior Central Coast. Tuesday will be the coldest morning this week with most locations across the interior expected to drop into the 30s.
Far interior southern Monterey County looks as though it will be the coldest location in our CWA, with the official forecast showing lows dropping to 30 degrees Tuesday morning. Probabilistic NBM guidance does show a 15-30% chance of temperatures dropping below 30 degrees in this region. We can expect slight improvements in morning lows beginning Wednesday through the end of the week with lows generally remaining in the upper 30s to mid 40s as high clouds move back into the region.

As the pattern becomes more active mid to late week, we will start to see some rain in the forecast again. A weak shortwave trough is expected to move through late Wednesday into Thursday with some potential for light drizzle over the coast and marine environments.
This initial system will likely not produce much in the way of rain accumulation and confidence is decreasing as models keep delaying the onset of rain associated with the shortwave. In contrast, confidence is increasing that a stronger upper level low will move into the West Coast late Friday into next weekend. Initial storm totals look to be around 0.5"-0.7" closer to the coast and generally less than a quarter of an inch across the interior Bay Area and Central Coast. It is too far out at the moment to place much stock in the current storm totals for Friday into next weekend, but, they serve as a useful reminder that we are in the middle of our rainy season and we will continue to see more storms as the pattern gets more active.

AVIATION
(06Z TAFS)
Issued at 857 PM PST Sat Dec 7 2024

Mostly VFR/MVFR conditions with mostly high clouds over the terminals but some terminals are experiencing lower visibility due to some haze. KMRY is seeing temporary LIFR conditions but there is uncertainty if conditions will remain due to poor satellite imagery.
The weak front continues to bring chances for MVFR/IFR conditions near the coastal terminals late tonight going into early Sunday morning but confidence is low to moderate. VFR conditions are expected to return for most terminals between 15-18Z if MVFR/IFR conditions develop. Winds will continue to be fairly light to moderate through the TAF period.

Vicinity of SFO...VFR expected to prevail through most of the TAF period but there is a chance that MVFR conditions will develop near 13-14Z as haze has developed near the terminal. Some models show VFR through the TAF period, but if vis and cigs lower, expect VFR near 18-19Z.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR but KMRY is experiencing some low clouds that can potentially become LIFR, therefore TEMPO group was included in the TAFs, but confidence is low. Overall, there is some uncertainty for conditions becoming lower than VFR as some models show VFR through the TAF period.

MARINE
(Tonight through next Friday)
Issued at 857 PM PST Sat Dec 7 2024

Northerly winds will continue to increase tonight as approaching cold front moves over our area. For Sunday, look for a fresh to strong N breeze, with near gale force gusts at times, and building rough seas on Sunday. Winds will decrease Sunday night, allowing seas to abate by Monday afternoon. Gentle, shifting wind and a moderate NW swell will persist through the remainder of next week.

MTR WATCHES/WARNINGS/ADVISORIES
CA...None.
PZ...Small Craft Advisory until 9 AM PST Monday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.