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

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000 FXUS66 KMTR 241711 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 1011 AM PDT SUN JUL 24 2016 .SYNOPSIS...Modest cooling is forecast for inland areas today and Monday as high pressure over California weakens slightly. Warmer weather is then forecast for Tuesday and Wednesday before a cooling trend develops late in the week and into next weekend. && .DISCUSSION...as of 08:46 AM PDT Sunday...No significant updates to the forecast today as the inherited forecast has the current trends handled well. Modest downward temperature modification currently in the forecast due to weakening ridging and strengthening onshore flow which will cool down the inland areas Sunday and Monday in comparison to temperatures we saw on Saturday. Temperatures will rebound beginning on Tuesday as high pressure rebuilds across the region. Conditions however will remain warm and dry over inland areas and above the marine layer over the coastal sections. Models are hinting at some Monsoon moisture swinging into California later in the period but the flow pattern seems unfavorable for any meaningful intrusion of moisture into our area. && .PREV DISCUSSION...As of 3:35 AM PDT Sunday...Patchy low clouds began to develop along the coast shortly after midnight as northwest winds eased over the coastal waters and the low levels became more stable. Expect low clouds to become somewhat more widespread in coastal areas prior to sunrise. However, little inland development of low cloud cover is expected given that the marine layer remains shallow with a depth of 1000 feet or less. Early morning water vapor satellite imagery shows that a weak upper level shortwave trough has settled in across the Pacific Northwest and northern California, weakening the upper ridge slightly. However, this has not resulted in any notable modification of the airmass over our area which remains very warm and dry. Early morning temperatures in the hills are in the 70s and lower 80s with relative humidity values as low as the single digits above 2000 feet. So it`s likely that very warm and dry conditions will persist in the hills today. However, some cooling is expected at the lower elevations today. This is because the relatively strong north-to-south surface pressure gradient we have seen along the northern California coast during the past few days is beginning to wane. And short-term forecast models indicate this trend will continue today...which will allow for stronger onshore flow by afternoon and thus modest cooling. The inland cooling trend will continue into Monday as the low level flow takes on a southerly component which will enhance the inland influx of marine air. Inland high temperatures by Monday are forecast to be as much as 10 to 15 degrees cooler compared to Saturday, especially in the North Bay Valleys. Temperature trends are expected to reverse on Tuesday as high pressure strengthens over California once again and the surface thermal trough migrates close to the coast during the late night and morning hours, thereby reducing onshore flow. Locations near the coast are expected to warm into the 70s on Tuesday and Wednesday while the warmest inland areas will see highs up near 100 again. The longer range models agree that gradual cooling will begin late in the work week, but for the most part very warm conditions will persist inland through Friday. More significant cooling is then expected next weekend as an upper trough settles in along the West Coast. Monsoon moisture is forecast to increase across far southern California by late in the week as the upper flow turns to the southeast. But the arrival of the upper trough by next weekend will turn the upper flow to the southwest and likely prevent that monsoon moisture from making it anywhere near our area. && .Fire...As 3:30 AM PDT Sunday...High pressure aloft remains strong enough this morning to confine marine air to a shallow layer near the coast. Above the marine inversion the airmass remains very warm and dry with early morning temperatures in the hills in the 70s and lower 80s. Humidity recoveries have been poor above 1500 feet. In fact, early morning relative humidity values are in the 10 to 20 percent range at some of the higher peaks and as low as the single digits at Chew`s Ridge in Monterey County. One bright spot is that winds have generally been easing in the hills and should remain relatively light through this morning. Winds are then expected to turn to the west and southwest and increase this afternoon. Winds on Monday are forecast to turn more southerly and this may be accompanied by a modest increase in the depth of the marine layer, allowing for cooling and better humidity recoveries, at least below 1500 feet. Warming is then expected to occur Tuesday and Wednesday as high pressure strengthens over our area. However, winds on Tuesday and Wednesday should be relatively light. && .AVIATION...
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As of 10:12 AM PDT Sunday...Shallow marine layer persists near 1000 feet. Low clouds and patchy fog have are still along the coast. Impacts persist near the Monterey Bay. VFR this afternoon. More widespread stratus seems likely tonight. Vicinity of KSFO...VFR. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...IFR cigs this morning with clearing by 19Z. VFR this afternoon with cigs returning early this evening.
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&& .MARINE...as of 08:46 AM PDT Sunday...Strong high pressure off the coast and low pressure inland will continue to produce gusty northerly winds along the coast. the strongest winds will be over the outer waters and locally nearshore north of point reyes and south of point sur. steep wind waves will be possible due to the gusty winds. gusty winds will continue into early next week. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...SCA...Pt Arena to Pt Reyes 0-10 nm SCA...Pt Arena to Pigeon Pt 10-60 nm SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm SCA...SF Bay from 2 PM SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm && $$ PUBLIC FORECAST: JAH AVIATION: Sims MARINE: Sims FIRE WEATHER: Dykema 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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