Union City, CA 94587 Weather

Key Messages

Updated at 1200 PM PDT Mon Oct 19 2026

- Cooling trend continues through the end of the week

- Beneficial light rain showers expected mid-week

- Thunderstorms possible mid-week across southern Central Coast

Update

Issued at 856 AM PDT Tue Oct 20 2026

Looking out the window, yes sometimes we do just look out the window, we can see cirrus and even some accas. Both of these cloud types can be precursors to a pattern change. If we take a broader look at satellite the bands of clouds currently west of Monterey are the leading edge of an occluded low pressure parked off the coast. Additionally, the bands east of Monterey are likely tied to the position of an upper level jet (GOES West shows strong winds in the 250-450mb range). The accas can be a good indicator of moisture and lower-mid level instability. If you haven't noticed, KMUX is still in precip mode. We are now picking up a few echoes well offshore closer to the low pressure and surface boundaries.

No changes in the near term forecast for today. Will be focusing on the next 24-48 hour as the offshore system moves east bringing dynamics with it. Early look still suggest some precip across the entire CWA. The biggest impacts will be tied to the potential convective threat along the Central Coast. Will coordinate with SPC to any updates on SVR Outlooks. Still looks like a low chc for some rotating cells to develop over the coastal waters off Big Sur Wednesday.

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Short Term

Issued at 1203 AM PDT Tue Oct 20 2026 (Today through Wednesday)

The low pressure system is already making its presence known as it nears our coast. Not only were there various cloud layers present on Monday, but some measurable rainfall has been observed in Northern California nearby Eureka (as of 10 PM PDT Monday). Given that the center of the low is still to our northwest, these rainbands are not expected to impact us just yet...

Overnight, the upper-level trough continues to dig southward along the coast and becomes fully cut-off from the main airflow by Tuesday. During the day, calm conditions are expected with below normal temperatures and infrequent wind gusts up to 20-25 mph. Later tonight, the cut-off low begins to slowly propagate eastward with the first few rainbands possibly impacting the southern Central Coast first. Through the overnight hours, these rainbands begin to make their way across the rest of the Central Coast and Bay Area.

Rain chances increase Wednesday with the North and East Bay less likely to experience wetting rain (>0.10 inch) during the event. Chances for wetting rain increase towards the Central Coast where the center of the cut-off low is expected to enhance moisture transport onshore. The eastern portion of the system is forecast to have stronger wind speeds than the western portion, likely due to a tighter pressure gradient downstream as well as a surge in momentum flux from the subtropical jet stream. This roughly coincides with where the most moisture, instability, and lift can be found. As a result, thunderstorm potential (<20%) remains the greatest along the Central Coast. The exact timing is uncertain, though model guidance is suggesting the highest probabilities are during Wednesday afternoon. Most unstable CAPE has trended slightly downward compared to yesterday, though it is still highlighting the Big Sur Coastline. The latest SPC convective outlook has upgraded Central and Southern California to a marginal severe thunderstorm risk, just south of the Monterey County border... Even though we are not included in the marginal severe risk, this is too close to comfort considering the proximity to the Timber and Plaskett fire burn scars. As the event draws closer, this will be an area of special interest not only for the potential of debris flows if rainfall thresholds are met, but also gusty and erratic winds that may result from low-topped thunderstorms.

Long Term

Issued at 1203 AM PDT Tue Oct 20 2026 (Wednesday night through Monday)

Overnight, the center of the low gradually moves across the region resulting in diminishing rainfall chances, though the Central Coast still remains with a 60-80%. Lingering rain showers persist through Thursday as the system continues its eastward track. Across the Bay Area, 20-40% rain chances persist with a 40-60% chance across the Central Coast.

By Friday, the trough center will be east of our area as high pressure gradually builds in its wake with a mean northerly wind flow. To balance out the recent disturbance, a slightly warmer and drier air mass settles over the region this weekend with seasonal temperatures in the 60s and 70s.