textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1247 PM PDT Wed Mar 18 2026

- Early season, long duration heat wave continues to bring record- breaking temperatures and Moderate HeatRisk through Friday

- Elevated potential for grass fires through the week due to warm and dry conditions with periods of moderate offshore winds

- Gradual cooling trend begins this weekend

UPDATE

Issued at 825 AM PDT Thu Mar 19 2026

The main weather impact message for today continues to be focused on the ongoing heat wave. Latest probabilistic data shows highest potential for cracking 100 degs remains over the Santa Cruz Mts (Boulder Creek/Scotts Valley) and interior Monterey county near Pinnacles. Heat Advisory remains in effect. However, as noted below the marine layer is making a return. Satellite imagery and cams show a very shallow marine layer hugging the immediate coastline from Point Arena southward to near Pigeon Point. As such, near the coastline will be a day of micro- climates with bust potential for max temps being forecast too warm. We'll need a offshore push to nudge the marine layer to west to keep the hotter temps on track. We'll leave the forecast as is for now, but watch it closely.

Given the ongoing heat, here are a few safety reminders.

* Stay hydrated and drink plenty of fluids. * Wear lightweight, light-colored clothing. * Reduce time spent outdoors or stay in the shade. * Never leave people or pets unattended in vehicles. * Use sunscreen if going to the coast or the pool. * Use caution at the beach, the water is still cold.

MM

SHORT TERM

Issued at 1218 AM PDT Thu Mar 19 2026 (Today and tonight)

While the heat wave continues to bring another day of record breaking temperatures inland, there is some nuance along the coast. The Half Moon Bay buoy is reporting 51F air temp, 50F dew point, and 56F water temp. That combination of air temp near dew point but lower than the SST is a canary in the coal mine for a cloud filled marine layer. Not only is the air 5 degrees cooler than this time yesterday and nearly saturated, it's also now significantly 5 degrees cooler than the SST. That means there is a latent heat flux (of moisture) from the warmer ocean to the cooler boundary layer air. Due to the warmer temperature, the sea surface-air interface has a higher saturation vapor pressure (capacity to hold water vapor) than the air at 2 meters. This drives evaporation from the sea surface to the air, increasing the dew point until the air is fully saturated. At this point any further latent heat flux will force the water vapor in the air to condense into cloud droplets.

And wouldn't you know it, fog rolled into Half Moon Bay just prior to 10 PM Wednesday night. The IR satellite image shows low clouds extend along the entire coast from Bodega Bay to Big Sur. The Bodega Bay vertical profiler doesn't quite have the resolution to capture the shallow depth, other than it's less than 100 meters (328 ft). ALERT California cameras show the top of the fog monster is around the Golden Gate Bridge deck, which is around 220 feet. That's very shallow for a marine layer, which averages around 1,500 - 2,000 feet in the Summer. If the onshore winds persist through the day, this marine layer will bring morning clouds and fog with much cooler and more humid air along the coast and adjacent low-lying areas today. If offshore winds become reestablished, we may still get a warm afternoon at the coast. Since the wind speed is so light, it's really hard to predict these direction changes. The most likely outcome is the return of offshore winds through the day, but the exact timing is unknown. Either way the shallow nature of the marine layer will significantly limit it's inland progression.

LONG TERM

Issued at 1218 AM PDT Thu Mar 19 2026 (Friday through Wednesday)

Friday still looks like the last day of the heat wave before a cold front brings some relief on Saturday. That being said, Friday may be the hottest day of the week for inland areas as the ridge reaches it's most powerful form. The 850 mb temperature is now expected to reach 22C. That's 2.8 standard deviations above the mean. Before this week, we've never seen anything over 19.2C in March. 22C is roughly the 75th percentile for August. The hottest spots (Ben Lomond, Gilroy, King City) will likely reach the mid to upper 90s. After the grand finale Friday afternoon, some high clouds will start to move in, signaling the approaching cold front. The surface front should move through Saturday morning, effectively ending the heat wave. Inland temperatures will drop around 10 degrees Saturday, and a further 5 degrees Sunday. Next week will still be warmer than normal, but nothing compared to this week. The next chance for rain is around the first of the Month, but the forecast trend has been pushing that back. While the rainy season is winding down, we still normally get 1-2 inches in April.

AVIATION

(12Z TAFS) Issued at 431 AM PDT Thu Mar 19 2026

Satellite shows areas of fog and low stratus clouds /VLIFR-IFR/ along the immediate coastline. Inland it's VFR. Clearing will occur along the immediate coastline during late morning and afternoon. Patchy fog and low stratus /LIFR-IFR/ return tonight and Friday morning.

Vicinity of SFO...VFR. West wind near 10 knots becoming light and variable late morning then west 12 knots in the afternoon and early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Patchy fog and low stratus /VLIFR-IFR/ along the coastline. Inland it's VFR. Highest probability of VFR will be late morning and afternoon. Stratus likely redeveloping tonight and Friday morning. Southeast winds 5 to 10 knots this morning shifting to onshore in the afternoon. Light southeast winds tonight and Friday morning.

MARINE

(Today through Tuesday) Issued at 412 AM PDT Thu Mar 19 2026

Gentle breezes continue across the inner waters with moderate north to northwest breezes over the outer waters. Northwest winds will begin to increase tonight and Friday and persist through the weekend, with hazardous seas developing by Friday night in response to the strengthening winds.

CLIMATE

Issued at 421 AM PDT Wed Mar 18 2026

The following are the record high temperatures at the long term sites for March 18th, 19th and 20th.

Location Mar 19 Mar 20

Santa Rosa 83 in 2004 84 in 2004 San Rafael 81 in 1964 82 in 1960 Kentfield 83 in 1996 82 in 2001 Napa 86 in 1914 86 in 2004 Richmond 80 in 1996 81 in 2004 Livermore 82 in 2015 87 in 1915 San Francisco 80 in 2010 78 in 2004 SFO Airport 78 in 2010 78 in 2004 Redwood City 81 in 2010 82 in 2004 Half Moon Bay 79 in 2010 75 in 2010 Oakland Museum 81 in 1984 78 in 2001 San Jose 82 in 1988 78 in 2004 Salinas Airport 87 in 1997 80 in 1934

The following are the record high temperatures at the long term sites for the entire month of March.

Location

Santa Rosa 91 on March 16, 2004 San Rafael 88 on March 25, 1952 Kentfield 91 on March 28, 1923 Napa 92 on March 17, 1914 Richmond 88 on March 18, 2026 Livermore 90 on March 25 and 26, 2025 San Francisco 87 on March 11, 2005 SFO Airport 85 on March 25, 1952 and March 17, 2026 Redwood City 93 on March 17, 2026 Half Moon Bay 83 on March 31, 2000 and March 17, 2004 Oakland Museum 89 on March 17, 2026 San Jose 89 on March 14, 2015 Salinas Airport 93 on March 18, 2026

MTR WATCHES/WARNINGS/ADVISORIES

CA...Heat Advisory until 8 PM PDT Friday for CAZ006-502>506-508>510- 512>518-528>530.

PZ...Small Craft Advisory from 3 PM Friday to 9 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory from 9 PM this evening to 9 AM PDT Saturday for Pt Arena to Pt Reyes 10-60 NM.