FXUS66 KMTR 202121 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 221 PM PDT Mon Apr 20 2026 ...New SHORT TERM, LONG TERM... .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 200 PM PDT Mon Apr 20 2026 (This evening through Tuesday) The much advertised wet weather has finally arrive - began with a few showers last night through early this morning and more widespread precip this afternoon. A cold front knocking on the Bay Area's doorstep has led to an increase in precip over the North Bay stretching south to SF Bay and finally Santa Cruz the last 3-6 hrs. Monterey Bay and points E and SE remain dry at this time. Decent precip totals over the last 12 hrs with 0.25-0.75 inches North Bay Coastal Mts and a few hundredths to 0.25" elsewhere. In addition to the precip, the frontal structure and associated pressure gradient led to gusty southerly winds. Gusts since midnight range from 20-40 mph most areas with gust 40-50 mph along the coast and and higher terrain. Rest of today through tonight: The front off the coast will finally makes its way inland with a nudge from an upstream sfc low and upper level jet. As such, the more stratiform precip will move through the Bay Area and Central Coast with impacts to the evening commute. Wet roads and windy conditions. By late this evening the steadier rainfall will transition to more convective nature/shower behind the front. Tuesday: Post frontal regime on Tuesday will be mainly be driven by the trailing upper level trough moving overhead, cold pool associated with trough, a phasing jet aloft around 200-250mb, and a jet max near 850-700mb. Lastly, some increased insolation during the afternoon due to less clouds. The combo of colder air aloft and daytime heating will increase sfc and ML CAPE. Factor in some of the wind fields and there's an increase for late morning/early evening thunderstorms. While there is some large 0-6km shear values it appears to be more confined to the 3-6km layer. Would like to see high shear below 3km for waterspout/tornado concerns. That being said, we'll be watching closely. Regardless, stronger storms will be capable of producing gusty winds, heavy rain, and small hail given the temp profile. SPC is not highlight tor/hail/wind like they were earlier in the month. They do have a general mention of thunder though. && .LONG TERM... Issued at 219 PM PDT Mon Apr 20 2026 (Tuesday night through next Sunday) Once the sun sets Tuesday evening the threat for thunderstorms quickly fades, but lingering showers will persist through early Wednesday. We will have to wait for the upper trough and embedded/trailing weak shortwave to exit before shower activity ends Wednesday. Thursday into next weekend. Warm and drier conditions will be trend. However, that trend will be tempered by persistent trough/broad upper low settling over the EPAC and CA. Conf with the forecast decreases for next weekend. Current forecast has a passing shower late Saturday due to another trough swinging through CA. Ens members are scattered on amounts, but most members at least show something. This will be fine tuned over the next few days, but for now cannot rule out some precip. && .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...MM LONG TERM....MM 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