Scattered severe storms are expected in the Midwest this afternoon/tonight, with another threat possible in the central/southern Plains. Late-season snow is expected over parts of the central Rockies including the Denver Metro into Wednesday. Severe thunderstorms are expected Tuesday and Wednesday across Texas and the mid-South, with threats of damaging winds, large hail, tornadoes, and flooding. Read More >
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176 FXUS66 KMTR 042345 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 445 PM PDT Mon May 4 2026 ...New AVIATION... .KEY MESSAGES... Updated at 1204 PM PDT Mon May 4 2026 - Cooler temperatures and cloudy mornings through Tuesday with light rain expected tonight through Tuesday morning for the SF Bay Area - Warmer and drier conditions return for the middle of the week through the weekend && .SHORT TERM... Issued at 1204 PM PDT Mon May 4 2026 (This evening through Tuesday) The satellite image shows some lingering low and mid-level clouds throughout the Bay Area and Central Coast, accompanied by a east-to- west band of high clouds entering the North and East Bays. Zooming out to the synoptic level pattern, an upper level low is crawling into the state, centered near the coast of Monterey County. This is bringing cool conditions throughout the region and rain across the SF Bay Area through Tuesday morning, as warm air advection driven by the low pressure system interacts with the cooler air aloft. As noted by the previous forecaster, lower surface pressures over the Great Basin are practically canceling the offshore flow effects that a east-to-west flow over the Sierra Nevada would typically produce. In fact, the SFO-WMC pressure gradient is strongly positive (that is, much higher pressure at the San Francisco Airport compared to Winnemucca in north-central Nevada -- 9.8 mb higher as of 11 AM) and will remain so through the overnight period. The rain band will come into Sonoma and Napa Counties this afternoon into the evening commute, steadily moving into the SF Bay Area this evening and overnight before dissipating Tuesday morning. Rain totals have continued to trend upwards, and the latest forecast now has totals of around half an inch for the interior mountains of the North Bay, around a quarter to half an inch for the North Bay in general, and a tenth to a quarter of an inch south of the Golden Gate through the southern reaches of San Mateo and Alameda counties. Localized rain totals near one inch, as suggested by some high-resolution model output, are very possible if the rain band overproduces. In addition, there remains a 5 to 10% chance for thunderstorms through the early part of Tuesday morning, with the chance for enhanced rainfall intensity where storms set up. Temperatures remain rather cool today with highs in the middle to upper 60s across the inland valleys, and the upper 50s to lower 60s along the coast. There may be a slight warm up in the most interior valleys on Tuesday as highs go into the lower 70s, but otherwise similar conditions are expected on Tuesday. && .LONG TERM... Issued at 1204 PM PDT Mon May 4 2026 (Tuesday night through next Sunday) By Wednesday, the upper level low moves into the Great Basin and southern Rockies with ridging building back behind it, leading to a warming and drying trend across the region. Highs in the inland valleys will steadily climb from the middle 70s to lower 80s on Wednesday up to the middle 80s to the lower 90s for the upcoming weekend, while locations near the Bays will warm from the middle 60s to lower 70s on Wednesday, to the lower 70s to the lower 80s for the weekend. These rising temperatures could bring Moderate HeatRisk for the inland valleys on Sunday, corresponding to a moderate chance for heat-related illnesses in sensitive populations (including children, the elderly, pregnant women, and people who work or live outdoors). Towards the latter part of the work week, a decaying front will sweep through the far northern parts of California, which may bring gusty conditions for the coast, ridgelines, and favorably oriented valleys and passes Thursday through Saturday. The CPC extended outlook shows that temperatures above the seasonal averages are likely to persist through the middle of May, while precipitation totals lean below the seasonal average. For context, the seasonal average high in downtown San Francisco is around 64 degrees, while the seasonal average precipitation total for the May 11 to 17 period, as covered in the CPC 8-14 day outlook, falls a shade under two tenths of an inch for the same station. && .AVIATION... (00Z TAFS) Issued at 432 PM PDT Mon May 4 2026 Simply put, a mix of MVFR to VFR conditions over the TAF period. Details of the MVFR and VFR are lower confidence due to a finicky upper low passing over the region. Seeing some light rain across the N Bay and the rain will slowly drift S toward SF Bay and then fade after that. Precip will drop CIGs to MVFR and low chc (20%) for IFR. After 18Z Tuesday CIGS do lift and then SCT to VFR. Vicinity of SFO...VFR this evening with light rain and MVFR CIGs arriving toward the tail end of the evening rush and lingering through early Tuesday. VFR expected for Tuesday afternoon with a few CU. SFO Bridge Approach...Similar to SFO. Timing of precip maybe just a tad later than SFO. Monterey Bay Terminals...VFR with some blue sky for the moment. Not expect rain per se, but some MVFR CIGs in the forecast late tonight. && .MARINE... (Today through Saturday) Issued at 438 AM PDT Mon May 4 2026 A light to gentle breeze continues over the waters with winds to become more moderate by Tuesday. A weak upper level disturbance lingers over the region through midweek. This disturbance will bring light, scattered showers and a non-zero chance of thunderstorms Monday into Tuesday. Northerly winds and seas strengthen Thursday into next weekend as high pressure rebuilds. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...DialH LONG TERM....DialH AVIATION...MM MARINE...RW 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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