216 FXUS66 KMTR 300358 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 858 PM PDT Wed May 29 2019 .SYNOPSIS...Tomorrow a system dropping down from the north will generate some clouds over the hills but the best chance of showers will be over the Sierra and coastal ranges north of the wine country. The weather system will turn into a cut-off low over Southern California by Friday and Saturday keeping the Bay Area in a quiet and seasonable weather pattern. A warming trend will then begin late this weekend and continue into early next week. && .DISCUSSION...as of 08:58 PM PDT Wednesday...Satellite imagery shows stratus along the coast and moving inland as the marine layer remains at around 1500 ft AGL per the Fort Ord Profiler. Temperatures across the region this evening are within a few degrees of this time yesterday with most areas in the upper 50s to low 60s. Low clouds will continue to move inland and down the valleys overnight before conditions clear by tomorrow afternoon. Additionally, patchy fog and drizzle will be possible once again along the coast. An upper low continues to spin near the OR/WA border and is set to move southward overnight and tomorrow. This will bring some slight cooling to the region with highs along the coast forecast in the low to mid 60s and inland areas in the 70s. The warmest spots across the interior will still reach the low 80s. Showers and thunderstorms also remain a possibility tomorrow afternoon. The most likely locations to experience this will be over the Sierra and to the north of the North Bay, however, there is some chance of showers/thunderstorms over Napa/Sonoma counties and interior San Benito. As the system drifts southward and exits our area on Friday, enough lingering moisture and lift will remain in place to allow for the continued slight chance of showers and thunderstorms over the Southern Diablo and Gabilan Range. Seasonable weather is expected for the weekend with night and morning low clouds persisting. An upper ridge will build into northern California late this weekend and into early next week bringing about some warming. && .PREV DISCUSSION...as of 01:30 PM PDT Wednesday...Morning low clouds did clear back to the coast with mostly sunny skies across the interior. Lingering low clouds along the coast remain from the Golden Gate southward. Sunny skies continued the warming trend today. Highs will ultimately top out in the 60s to lower 80s or about 3 to 7 degrees warmer than Tuesday. The convective temperature is also being reached across the interior hills - Southern Diablo and Gabilan Ranges. Afternoon satellite imagery does reveal a nice CU field, but not sure there is enough lift and moisture to fully develop into a thunderstorm. Forecast point soundings keep a subtle inversion at about 5,000 feet. If this can be overcome then a pop up shower/thunderstorm is possible. Likelihood is less than 10-15% so will keep out of forecast at this time. For what it's worth KMUX radar is now picking up on convection firing over the Sierra and north of Clearlake Night and morning clouds will return again tonight with patchy drizzle possible along the coast. Forecast focus then turns upstream to an upper level low spinning near the WA/OR border. Latest 12z models bring this feature southward over the next 12-24 hours. Not much of a surprise at this point, but showers and thunderstorms are possible Thursday afternoon. Most likely areas continues to be over the Sierra and Mts north of Clearlake. Locally most likelihood is for Northern Napa and interior San Benito. Chances are still small 15%, but enough to keep in the forecast. The upper low continues to drift southward and exit the forecast area on Friday. As the low exits enough lingering lift and moisture will remain allowing for another small chance of showers/thunderstorms over the Southern Diablo and Gabilan Range. Summer like weather for the weekend with night and morning low clouds clearing to the coast each afternoon. More noted ridging and warming should develop by late in the weekend into early next week. Longer range 8-10 day simulations show a longwave trough into the Pacific Northwest implying no big ridges for CA with a well developed marine layer along the coast setting the stage for some June gloom. && .AVIATION...as of 6:45 PM PDT Wednesday...Visible satellite image hows low clouds increasing off the San Mateo coast. Onshore gradients are about as strong as yesterday. Strong winds are blowing through the San Bruno Gap and stratus has already spread into SFO. Stratus should reach the approach around 04Z which is in agreement with the WRF. Meanwhile stratus has already settled into the southern MRY Bay Area. Vicinity of KSFO...SCT-BKN clouds becoming MVFR cigs after 04Z with bases 1000-1500 ft. West winds 20-25 kt gusting to 30 kt decreasing after 04Z. SFO Bridge Approach...MVFR cigs will spread south along the approach after 05Z. Monterey Bay Terminals...MVFR cigs lowering to IFR after 06Z. && .MARINE...as of 08:57 PM PDT Wednesday...A robust onshore gradient will keep breezy to gusty northwest winds across the waters through the coming days. Steep fresh swell with squared seas at times will continue through the end of the week, especially in the northern and outer waters. A lighter long period southerly swell will be more evident in south facing sheltered bays. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm until 3 AM SCA...Pt Arena to Pt Reyes 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...Pt Reyes to Pigeon Pt 0-10 nm SCA...Rough Bar Advisory for SF Bar SCA...SF Bay until 9 PM SCA...Mry Bay until 9 PM && $$ PUBLIC FORECAST: AS/MM AVIATION: W Pi MARINE: W Pi 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