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Displaying AFOS PIL: AFDMTR Received: 2018-01-12 16:28 UTC
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709 FXUS66 KMTR 121628 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 828 AM PST Fri Jan 12 2018 .SYNOPSIS...High pressure will build over California today and bring dry and mild weather to the area through the Martin Luther King Jr. Holiday Weekend. The next chance of rain will be on Monday night and Tuesday, with additional rain chances next Thursday and Friday. && .DISCUSSION...As of 8:20 AM PST Friday...Patchy fog continues around our region this morning with many spots under two miles. Worst conditions appear to be over the East Bay Interior valleys with less than 1/2 mile in many spots. Upper air sounding nicely showed the surface inversion which gave favorable conditions today for fog development. Conditions will improve later this morning with upper 50s to the mid 60s forecast. Latest models in are fairly close to the previous couple of runs. Look for rainfall to return on Tuesday with a second round slated for Thursday. .PREVIOUS DISCUSSION....Satellite fog product is showing low clouds over a portion of the coastal waters, and also spreading through most inland valleys at this time. There is also a fair amount of fog being reported at area airports with visibilities bouncing around from 1/4 mile to 7 miles at our TAF sites. A dense fog advisory may be needed towards dawn if 1/4 mile or less becomes more widespread. Otherwise, today should see warmer high temperatures with most locations seeing highs in the 60s. Even warmer temperatures are anticipated for Saturday and Sunday as high pressure aloft builds over the state, and warmest inland areas could see highs in the mid 70s. The next rain event is forecast to begin late Monday as an upper level trough approaches the coast. Light rain is expected to begin across much of the San Francisco Bay Area by late Monday night and early Tuesday, and then reaching the Monterey Bay area Tuesday morning. The heaviest rainfall is expected to be mostly north of our CWA but northern Sonoma and Napa counties could see periods of moderate rainfall at times. This system is expected to be through our area by midday Tuesday with perhaps some lingering early afternoon showers. Rainfall totals with the Monday Night/Tuesday system are currently forecast to range from 0.25-0.75" in the North Bay...locally up to 1.25" in the far northern coastal mountains...and generally a third of an inch of less south of the Golden Gate. A second system is forecast to impact the district with widespread rain on Thursday with showers continuing into Friday. This second system is currently expected to be about as wet as the first (or somewhat wetter for areas from San Francisco southward). Medium range models still indicate another system after next weekend. && .AVIATION...as of 3:51 AM PST Friday...For 12z tafs. Big concern for high impact fog event today at Bay Area terminals. Nearly all sites have been bouncing around from 1/4 mile to 6 plus at times overnight. Goes-16 fog product shows much of the Bay filled in at this hour. With light winds, moist boundary layer and inversion aloft the fog/low clouds will be slow to mix out. Optimistic taf will show late morning but that can easily turn to early afternoon this time of year with low sun angle. Vicinity of KSFO...Concern for dense fog at times from now through at least 16z and possibly beyond. Web cams show fog and there have been varying reports around the region all night. Satellite fog product looks ominous. Usually conditions get worse as the sun comes up. Potential that clearing may not occur until early afternoon. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...Dense fog in the Salinas Valley could briefly impact kmry as it burns off but main impact will be ksns this morning, otherwise mostly clear. && .MARINE...as of 03:44 AM PST Friday...Generally light winds over the waters today except south of Point Pinos where stronger north winds will persist. Long period swells will continue to pass through the waters heading into the weekend with seas building rapidly by Monday. Several storms and associated cold fronts will pass through the waters next week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm && $$ PUBLIC FORECAST: Bell/Sims AVIATION: RWW MARINE: RWW Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea