周四下午在湾区高点,Ce登录必赢亚洲ntral Coast and Sacramento Valley, with widespread 70s by the shoreline and bays, 80s in the foothills and delta and 90s in some of the inland valleys.
Baron/LynxThe firstheat waveof the year is expected to peak in the Bay Area on Thursday. Rounds of hot and dry air from a powerful high-pressure system are flowing into the region, clearing out the spring’s marine layer. This will especially be the case in the region’s inland valleys, where temperatures are expected to soar to the upper 80s and lower 90s.
These are unusually warm temperatures for April, even for inland cities like Napa, Livermore and Santa Rosa. And depending on the timing of some of the hot air, a few spots will be just shy of temperature records for the day — one city might even surpass its record.
Scorching hot afternoon
The ridge of high-pressure that’s driving this week’s heat wave feels like something Californians experience in September or October, not so much April.
欧洲整体的分析脊of high pressure over California, suggesting that the ridge will peak in strength by Thursday afternoon — its strength is looking to fall two standard deviations from the average for late April.
Baron/LynxThe European weather model even signals the anomaly, with several of its most recent runs highlighting that this system’s intensity is well over what’s normal for a high pressure system around this time of year, bringing above-average temperatures.
Plenty of weather stations in the North Bay and East Bay will be flirting with temperature records for the day. Santa Rosa’s official station is looking to reach the upper 80s — close to its record high of 93 degrees set back in 2004. Cities like Livermore and Concord will be in a similar situation, reaching daytime temperatures that will be around 3 to 5 degrees shy of some of their record highs for April 27.
But the hottest air in the region is looking to settle over the South Bay.
Thursday’s daytime highs across the South Bay, 101 corridor between Morgan Hill and Gilroy and the Santa Cruz Mountains.
Baron/LynxThe high-pressure system’s apex — or center — will be oriented in the right direction to reel in enough warm air so that cities like Milpitas, Cupertino and San Jose can reach the lower 90s. In fact, if this air gets to San Jose just before San Francisco Bay’s afternoon breeze arrives, the record at the weather station at San Jose International Airport — 91 degrees set back in 2004 — is likely to be tied. Both the European and American weather models are leaning toward that outcome, while a few runs even hint at the record being broken by a degree or two.
The only surefire way for the record to be broken is for the high-pressure system to completely compress the marine layer Thursday morning, keeping it out over the Pacific Ocean and away from the Santa Clara Valley. For now, that's looking pretty likely.
Thursday breakdown
San Francisco:The warm-up continues Thursday as a high-pressure system compresses the cool, misty fog that normally forms around this time of year. Shallow layers of clouds in the hills and west side will quickly fizzle away, making room for hot and dry air that’s likely to raise daytime temperatures to the upper 60s in the Outer Sunset and Richmond districts, lower 70s in Golden Gate Park, Lake Merced and the rest of the west side.
Commuters taking Muni between the West Portal and Castro stations are in for a sharp temperature, with most neighborhoods east of Sutro Tower expected to reach daytime highs in the mid-70s — including Dolores Park, most of the Mission and SoMa. That’s roughly 7 to 10 degrees warmer than April’s average daytime high of 63 at the city’s official weather station.
A couple weather models are suggesting that as pressure levels begin to fall after 6 p.m., some of the compressed marine clouds off the coast will be able to expand back into the west side. If that plays out, then you can expect a cloudy evening in west-facing hills and summits in Twin Peaks, Mount Davidson and Diamond Heights.
Pacific Coast and Peninsula:A faint layer of fog is likely to settle along Highway 1 between Half Moon Bay and Pacifica Thursday morning, ushering in brief instances of reduced visibility — down to half a mile at times. This will be in sharp contrast to the sunnier and warmer air that will spread across most of the Peninsula over the course of the day. That said, most of the fog is likely to burn off after 9 a.m., allowing coastal temperatures to gradually rise to the mid-70s — between 12 and 15 degrees above Half Moon Bay’s April average high of 61 degrees.
Residents along the San Bruno Gap, including Daly City, Mllbrae and immediately by San Francisco international Airport can expect widespread upper 70s for highs Thursday afternoon while wind-shielded cities along the I-280 and 101 corridors are expected to reach the lower 80s after 1 p.m.
The warmth is looking to steadily drop off Thursday evening as the marine layer’s clouds and winds flood the coast and eventually spill into the rest of the Peninsula, bringing temperatures back down to the 60s by 6 p.m. and 50s after sunset.
North Bay:Bits of the marine layer’s clouds are set to sit off the coast of Point Reyes and Bodega Bay Thursday, sending just enough of a sea breeze to keep daytime temperatures in the Sonoma and Marin County shoreline in the upper 60s to lower 70s. A sharp difference in warmth is on tap for most of the region, with temperatures quickly rising to the mid-80s as you head farther inland into Vallejo, Novato and San Rafael.
Weather models are suggesting that there will be sufficient levels of warm air overhead to raise daytime highs to the 90-degree mark across swaths of the Napa, Santa Rosa and Petaluma valleys Thursday afternoon — about 5 to 7 degrees short of Napa State Hospital’s record high for the day of 95 degrees set back in 2004.
A breeze off the coast, bays and delta is looking to sweep the North Bay after 5 p.m., allowing temperatures to gradually return to the 60s by this evening and 50s overnight.
East Bay:Some of the hottest air in the Bay Area is looking to set up shop in the San Ramon and Livermore Valleys Thursday, with residents in Walnut Creek, Dublin and Pleasanton likely to experience temperatures in the lower 90s. This warmth will result in a couple weather stations like Livermore running just a few degrees shy of their daily records. Cooler air off San Francisco Bay and the delta will keep Alameda, Richmond and most of the bayside below the 80-degree mark, though some of the Oakland and Berkeley hills are likely to reach the lower 80s after 1 p.m.
The cooling effect off the bayside is then looking to spread inland after 5 p.m., quickly dropping temperatures back down to the 60s and 70s across Alameda and Contra Costa Counties. Look for a more comfortable evening as nighttime temperatures fall to the lower 50s by the water and mid-50s farther inland.
South Bay and Santa Cruz:The heat is on for the Santa Clara Valley Thursday as the hot ridge of high pressure stomps out any traces of clouds and cool air and replaces it with an air mass that will raise temperatures to the lower 90s. San Joseé’s official weather station at the airport has a high chance of reaching 90 degrees. If warm winds off the foothills of the valley have their way, there is a good possibility that the station will tie its record highest temperature for the day of 91 degrees — potentially even surpassing it by a degree or two. That said, cool air is looking to quickly return to San Jose after 4 p.m., which could keep the station from reaching that milestone.
Warm air will also settle across the Santa Cruz Mountains, though a light breeze off Monterey Bay is looking to spread north of Pasatiempo Thursday afternoon. This will keep daytime temperatures in the mountains closer to the mid-70s while residents in Capitola, Soquel, Aptos and Watsonville can look forward to cool daytime highs in the lower 70s.
Reach Gerry Díaz: gerry.diaz@sfchronicle.com; Twitter: @geravitywave
