Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000 FXUS66 KMTR 202210 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 210 PM PST Fri Jan 20 2017 .SYNOPSIS...
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Scattered showers are expected to continue today in the unstable airmass behind the front that moved through this morning. In addition, isolated thunderstorms will be possible. A few showers will then linger into Saturday morning with another, likely wetter system arriving late Saturday into Sunday. Given the antecedent conditions from recent rainfall, this system will have the potential to result in additional flooding concerns across portions of the region. Showers will then linger behind this cold front into Monday with dry conditions returning by Tuesday.
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&& .DISCUSSION...
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as of 2:10 PM PST Friday...showers continue to move across the area in the unstable post-frontal airmass. There have also been recent reports of pea-sized hail and thunder across portions of the East and South Bay associated with a robust line of showers currently moving across that area. Expect showers to persist through this evening and slowly taper off by Saturday mid day. At this time, showers will likely be ending with a bit of a break in precipitation for a good portion of the region through the rest of the day. The next system in this series remains on track to impact the area from late Saturday into Sunday morning. This system appears to have a deeper moisture tap with PWAT values forecast to range between 1 to 1.25 inches. Given this, expecting rainfall amounts to be greater than the previous two systems which will likely lead to a greater threat for flooding issues. Additional rainfall amounts from Saturday into Sunday will range from 0.75 to 1.50 inches in most urban areas and upwards of 2 inches in the North Bay Valleys. Meanwhile, the coastal ranges and North Bay Mountains will likely see 2 to 4 inches with isolated amounts upwards of 5 inches. A Flash Flood Watch has been issued for the entire CWA effective from midnight Saturday through 6 pm Sunday. Considering a few creeks went to flood stage with last night`s storm, additional moderate to heavy rain is likely to cause flooding issues. Along with the additional rainfall, southerly winds will also increase and become gusty at times ahead of the frontal boundary that will sweep through late Saturday night into early Sunday morning. A High Wind Watch is in effect for the entire CWA for the time frame from late Saturday evening through Sunday morning. The areas most likely to see the strongest winds will be the coasts and hills, however, with the frontal passage, strong winds are possible everywhere. Showers will then likely linger into Sunday night and even through much of the day Monday as the main mid/upper level low drops southward down along the northern California coast. By Tuesday, the trough will shift inland while a ridge begins to develop off of the West Coast. This ridge will maintain dry weather conditions through the remainder of next week with temperatures near seasonal averages.
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&& .AVIATION...As of 5:03 AM PST Friday...A very strong and fast moving cold front is pressing eastward across the forecast area this morning accompanied by heavy rain and wind. Pressure falls along the coastal waters and over land have been commonly 2-3 mb per hour since late last evening /pressure falling rapidly/. Cold unstable air is quickly moving in this morning, expect a continuation of heavy showers and t-storm development through this morning and afternoon. IR imagery shows lots of open cellular clouds to our W-NW, a signature of plenty instability to arrive today. Vicinity of KSFO....Airport weather warning valid through 15z, may need to extend warning if winds remain strong and gusty. Model guidance indicates possible lull then re-energized westerly winds developing later this morning into the afternoon. Expect downpours and possible additional t-storms with reduced visibilities and ceilings to MVFR possibly briefly IFR visibilities. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Strong and gusty southeast winds prior to cold front moving through early this morning. MVFR possibly briefly IFR visibilities in downpours and t-storms. && .MARINE...as of 8:56 AM PST Friday...Strong southerly gale force winds will continue across the coastal waters through this morning ahead of an approaching cold front. As a result rough and hazardous seas will continue through today. After the front passes this morning winds will shift to the west but remain moderate and gusty. Winds will increase again Saturday night as another frontal system approaches. Very large swells arrive Friday afternoon with swell heights building to 25 to 30 feet Friday night and Saturday. Rogue waves of 30 feet or greater are possible during this timeframe. && .MTR WATCHES/WARNINGS/ADVISORIES...
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.Tngt...High Surf Warning...CAZ006-505-509-529-530 SCA...Mry Bay SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Reyes to Pigeon Pt 0-10 nm SCA...Pigeon Pt to Pt Pinos 0-10 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm SCA...Rough Bar Advisory for SF Bar SCA...SF Bay until 10 PM
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&& $$ PUBLIC FORECAST: Sims AVIATION: Canepa MARINE: CW Visit us at www.weather.gov/sanfrancisco Follow us on Facebook and twitter at: www.Facebook.com/nwsbayarea www.twitter.com/nwsbayarea

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