000 FXUS66 KMTR 151527 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 827 AM PDT Tue May 15 2018 .SYNOPSIS...Typical "May Gray" weather conditions with seasonably cool temperatures will persist over the region today in advance of an approaching upper level system. A few showers will be possible over the interior portions of the region Wednesday morning as the weather system pushes inland. A drying and slight warming trend is then forecast late in the week under a weak ridge of high pressure. && .DISCUSSION...as of 08:27 AM PDT Tuesday...Satellite imagery continues to show low clouds over most of the region with bases of 1,500 to 2,500 feet. Persistent overnight cloud cover has kept low temperatures across the region in the 50s this morning with higher elevation areas reporting in the 40s. Afternoon high temperatures today are expected to remain relatively cool as clouds only partially mix out ahead of an approaching mid/upper low. Some inland areas may experience clearing this afternoon while most coastal locations and parts of the North Bay remain under cloudy skies throughout the day. Expect highs this afternoon in the 50s to 60s along the coast with mid to upper 60s for most inland areas. No changes to the forecast are needed at this time. For additional details refer to the previous discussion below. && .PREV DISCUSSION...as of 03:00 AM PDT Tuesday...Low clouds with a base of 1,500 to 2,500 feet continue to impact much of the region this morning in response to a deep marine layer and moist, onshore flow from the Pacific. This has helped to keep temperatures in the 50s for much of the region with a few 40s reported in the higher elevations. Temperatures will be slow to warm this afternoon as clouds only mix out partially in advance of an approaching mid/upper level low. As the upper level low pushes onshore over the San Francisco Bay Area late tonight into Wednesday morning, low clouds will once again spread over much of the region. However, a well defined marine layer will not be as likely tonight into Wednesday morning in response to slightly cooler air moving in overhead. A few rain showers cannot be ruled out over the interior portions of the region as the upper level low pushes inland. However, the latest forecast models show the best chances to remain over Northern California and into the interior portion of the state. Seasonably cool conditions are likely again on Wednesday in response to cold air advection associated with the low. Look for daytime temperatures to only warm into the 60s for most locations. Dry weather conditions return to the entire region late Wednesday into Thursday as the mid/upper level low shifts inland to our east. With the marine layer likely to be mixed out, temperatures will be on a warming trend with weak high pressure building over the eastern Pacific. This will allow for temperatures to warm back to near seasonal averages by Saturday. Medium range guidance suggests another mid/upper level trough will drop southward out of the Pacific Northwest late Sunday which would result in some cooling early next week. && .AVIATION...As of 4:47 AM PDT Tuesday...For 12z TAFs. Satellite imagery reveals widespread low clouds across all area terminals this morning. The Fort Ord Profiler depicts a deep 3000 ft marine layer. MVFR cigs will persist through the morning with low level cigs scattering out around noon over most terminals. Light onshore flow will strengthen this afternoon. High confidence. Vicinity of KSFO...MVFR cigs will persist through the morning with low level cigs scattering out around noon. Moderate onshore flow around 10 mph will continue through the morning hours then increase once again this afternoon. SFO Bridge Approach...Similar to KSFO. MVFR cigs will impact the approach until around 18z-19z this morning. Monterey Bay Terminals...MVFR cigs will persist through the morning with low level cigs scattering out around noon. Light winds will continue through the morning hours then increase this afternoon. KSNS wind sensor is down for maintenance therefore no amendments are scheduled. && .MARINE...as of 2:37 AM PDT Tuesday...Relatively light winds will prevail through midweek as a weak disturbance gradually makes its way across the region over the next few days. Winds will strengthen during the later half of the week as the surface gradient tightens on the backside of this system. A small mixed swell will persist through the forecast period. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tday...None. $$ PUBLIC FORECAST: AS/RGass AVIATION: CW MARINE: CW 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