Dry fuels, strong winds and dry weather will continue to bring elevated to critical fire weather conditions to the areas of the Plains, Midwest and Southeast today. A Pacific storm system will bring low elevation rain and heavy high elevation mountain snow to California through early week, expanding into the Pacific Northwest, Great Basin, and southern California on Tuesday. Read More >
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266 FXUS66 KMTR 201850 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1150 AM PDT Mon Apr 20 2026 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 1210 AM PDT Mon Apr 20 2026 - Cool temperatures and beneficial rainfall today through Wednesday - Isolated to scattered thunderstorms on Tuesday - Seasonal temperatures and dry conditions for the later part of the week && .SHORT TERM... Issued at 1210 AM PDT Mon Apr 20 2026 (Today and tonight) High clouds continue to flow over the Bay Area and Central Coast tonight, an outgrowth of the cold front that will make Monday a pretty rainy day -- more on that a little bit later on. KMUX radar is showing returns from the first rain band off the coast of the Bay Area and Central Coast, and just now coming ashore in the northwestern corner of Sonoma County. Southerly winds are prevalent across the region as the front approaches, leading to some pretty abnormal nocturnal drying across the Silicon and Santa Clara valleys, where the southerly winds downslope from the Santa Cruz Mountains into the region. To give just one example, at 4 PM Sunday afternoon, San Jose reported a dew point of 48 degrees, a relative humidity of 40%, and a light northwest breeze. By 9 PM, San Jose reported a dew point of 8 degrees, a relative humidity of 11%, and a gentle southerly wind, with gusts reaching 20-24 mph over the previous couple of hours. Low temperatures this morning should hover around the middle 40s to the lower 50s, downslope warming effects notwithstanding, with the interior valleys and mountains dipping into the middle 30s to lower 40s. Looking into the big picture, a deep and large upper level low drives a massive circulation across the eastern Pacific with a pronounced and highly noticeable comma cloud wrapping up the California and Oregon coastlines before diverting away from Washington state into the Pacific. The 03Z, or 8 PM, WPC surface analysis shows a closed circulation that spans the ocean off the Central Coast all the way to offshore Washington State, and two surface lows embedded in the comma cloud, one located around 600 miles west of Cape Mendocino and one around 550 miles west of where the Columbia River empties into the Pacific Ocean, on the border between Washington and Oregon. This is the system that will approach the region through the night, increasing the cloud cover and placing a few scout showers into the North Bay overnight before light to moderate rain comes into the North Bay close to the end of the morning commute on Monday. The rain will start to spread south and east through Monday as the cold front approaches, with a messy evening commute expected as rain spreads across the SF Bay Area and Monterey Bay regions. As the front approaches, southerly flow should ramp up as the pressure gradient tightens, with the winds increasing across the coastal regions through the morning before they spread inland during the afternoon and evening hours. Winds are not expected to be strong enough for a Wind Advisory, but wind gusts of 25 to 35 mph, possibly up to 40 mph in favored coastal or ridgeline areas, are expected. Given the southerly flow, initial rain chances may be delayed across downslope and rain shadowed areas -- think the Petaluma region, the Santa Clara Valley, or the interior Salinas Valley. Highs in the North Bay will drop into the middle 50s to lower 60s in the lower elevations, to the upper 40s to middle 50s across the higher elevations, as the cold front passes through. South of the Golden Gate, temperatures remain relatively mild with the continuing warm sector influence and, for some areas, including the Monterey area, enhancement from the southerly downslope flow. Highs range from the middle 60s to the lower 70s in the SF Bayshore and Monterey Bay regions, to the lower to middle 70s in the inland valleys. && .LONG TERM... Issued at 1210 AM PDT Mon Apr 20 2026 (Tuesday through Sunday) With the frontal passage passing the Bay Area and Central Coast Monday night through Tuesday morning, the stage is set for a rather convective Tuesday afternoon and evening. The cold pool behind the frontal passage and the arrival of the upper level low will contribute to a destabilized atmosphere, while the placement of a left exit region from a jet streak (a pattern that typically results in upper level divergence) and potential low level shear provide sources of lift. The latest SPC outlooks continue to place the Bay Area and Central Coast in a general mention of thunderstorms for Tuesday. If any storms do develop, lightning, localized heavy rain, and small hail are the primary threats. Some lingering showers may hang on through Wednesday afternoon as a shortwave trails behind the upper level trough as it departs into the Intermountain West. In total, rainfall totals today through Wednesday remain generally beneficial, half an inch to an inch and a half in the lower elevations, up to 3 inches in the coastal ranges and the North Bay interior mountains. While there is no threat for widespread river flooding, minor flooding is possible in urban and poor drainage areas should particularly heavy showers or thunderstorms develop. As the frontal system passes, temperatures will warm slightly into a rather dry latter part of the week, close to or slightly below the seasonal averages as highs in the lower elevations range from the lower 60s to lower 70s. Ensemble model cluster analysis points to continued troughing across the state which, if nothing else, should help moderate the warming trend, particularly towards the latter part of the 7-day outlook. Extended guidance from the Climate Prediction Center leans towards temperatures and rain totals above seasonal averages for the last days of April into the first days of May. && .AVIATION... (18Z TAFS) Issued at 1149 AM PDT Mon Apr 20 2026 High clouds and scattered mid-level clouds are building as showers arrive head of the cold front. Shower activity increases through the afternoon for the North Bay and around the SF Bay, while the East Bay, South Bay, and Monterey Bay see better chances into the late afternoon and evening. Expect breezy to gusty southerly winds ahead and during the frontal passage. Winds reduce slightly into the night in the post-frontal environment with scattered lighter showers lasting through the late night. Another band of rain arrives Tuesday morning, bringing locally breezy winds and widespread light to moderate showers. Showers will continue to move through the area behind this band of rain, but will be more scattered. Chances for storms will be possible into Tuesday afternoon and evening. Vicinity of SFO...Expect overcast high clouds and building mid-level cloud cover into the afternoon as breezy south east winds build. Showers become a line of rain in the mid afternoon, with slight reductions in visibilities possible. Rain chances and winds reduce in the late evening, but scattered passing showers will still affect the area. Another band of rain arrives into early Tuesday with breezy south winds. Winds turn more southwest in the wake of this rain band with scattered showers continuing into the afternoon. Chances for storms will be possible in the afternoon and evening on Tuesday. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Showers are moving through the area, with better chances for rain arriving into the afternoon. Expect breezy to gusty south winds to build into the afternoon as rain chances increase.The main rain band arrives in the evening offering consistent rain and reduced visibilities. This band exits into the late night with winds reducing in its wake, but scattered showers will continue to move through the area. Shower become more widespread again in the mid morning with some chances for storms. && .MARINE... (Today through Saturday) Issued at 1149 AM PDT Mon Apr 20 2026 Breezy to gusty southerly winds are building as a cold front passes and winds shift to a moderate southwesterly breeze by Tuesday with some localized, but short lived gale force gusts possible. The front will also bring steady rain and showers through the day. Showers become more scattered into the night but continue into Tuesday with some chances for thunderstorms. As the weather breaks, winds will gradually shift back to the northwest Wednesday before increasing to a strong northwest breeze by Thursday. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory until 3 AM PDT Tuesday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. Small Craft Advisory from 9 AM to 9 PM PDT Tuesday for Mry Bay. Small Craft Advisory from 9 AM to 3 PM PDT Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...DialH LONG TERM....DialH AVIATION...Murdock MARINE...Murdock Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea |
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