FXUS66 KMTR 242032 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 132 PM PDT Fri May 24 2019 .SYNOPSIS...Mainly dry conditions are forecast through Saturday, along with continued cooler than normal temperatures. Unseasonably cool and unsettled conditions are forecast to develop later in the weekend as a system drops in from the north, with scattered showers maybe a stray thunderstorm possible on Sunday. Dry weather should return by Memorial Day, but temperatures will remain cool into early next week. && .DISCUSSION...as of 1:32 PM PDT Friday...Visible satellite imagery shows some areas of low clouds lingering over parts of the San Francisco and Monterey Bay areas this early afternoon. These low clouds are preventing efficient solar heating thus far this afternoon for some locations. For example, the Sonoma County Airport (KSTS) is running 12 degrees cooler than this time 24 hours ago as a consequence to the marine stratus. The most recent satellite trends reveal that clearing is occurring in the North Bay Valleys, but with the delayed sunshine, have gone ahead and dropped afternoon maximum temperatures for most North Bay locations by several degrees. The East Bay south of the Bay Bridge as well as the South Bay have been mostly sunny since mid- morning, and are actually running several degrees warmer than 24 hours ago. By the time the afternoon wraps up, high temperatures along the coast will warm to the upper 50s to 60s while interior locations will warm to the middle/upper 60s to middle 70s. These values equate to about 3 to 9 degrees below late May climatological normal values. If you're looking for warm weather in the Bay Area for the holiday weekend, I do not have good news for you. There is high confidence of continued below normal temperatures through Memorial Day as another upper level low drops south from the Pacific Northwest by the second half of the weekend. This upper low will bring a reinforced shot of cooler air, as well as another opportunity of rain showers on Sunday. Snow levels will drop to around 5,000 ft, per the official forecast and the National Blend of Models (NBM); however, the 12Z run of our local in-house WRF drops snow levels to 4,200 to 4,500 ft for some locations. Just to quantify how anomalous this upper low is -- the 850 mb geopotential height levels over our area are forecast to correspond to about -3 to -4 sigma (standard deviations) with respect to the 1979-2009 Climate Forecast System Reanalysis (CFSR). At the surface, these temperatures will translate to about 10 to 20 degrees below normal. Hikers, campers, and outdoor enthusiasts with plans to head to the higher elevations on Sunday should plan accordingly for cold temperatures and rain showers, as well as the possibility of isolated snow showers if snow levels drop lower than the present official forecast. Will also have to keep a close eye on the possibility of thunder for parts of the area, but for now think the best odds will be to our east in the Sierra. For Memorial Day, temperatures should begin to rebound as the upper low exits the area with highs in the 50s and 60s along the coast and middle 60s to near 70 for inland communities. Can't rule out some lingering showers in the mountains during the day, but think most locations will be dry for the holiday itself. Temperatures will continue to moderate through the middle of next week with the NBM bringing back some 80 degree readings returning to the warmest locations by Wednesday or Thursday. With that said, though, both the GFS and ECMWF are keeping a trough over the West Coast, so temperatures will likely just return back to near normal values. There is hope for those waiting for warmer weather -- the Climate Prediction Center's 8-14 day outlook does begin to favor the likelihood of experiencing above normal temperatures for the June 1 to 7 period. && .AVIATION...as of 10:33 AM PDT Friday...South flow will keep clouds lingering for STS and Monterey Bay. Strato-cu continues to fill in across portions of SF Bay, which may impact ops at times. VFR for most locations later today, but STS may struggle to clear. Cigs return tonight, but conf is low for SFO. Gusty winds develop overnight too. Vicinity of KSFO...A few cu spilling over SFO at 2k may briefly impact operations, but it should be shortlived. Will keep BKN for tonight, but conf is low as some models keep cigs just N of SFO. Cigs more likely for OAK. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...slow burn off today and will keep cigs late into the afternoon. A few hours of SCT before early return of cigs this evening. && .MARINE...as of 09:57 AM PDT Friday...Southerly flow will prevail near the coast and with northerly flow over the outer waters today. Low pressure will move inland over the Great Basin Friday night through the weekend and lead to gusty northwest winds over the coastal waters. Moderate northwest swell will continue through the weekend with steep fresh swell generated by the gusty winds. && .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM GLW...Pt Arena to Pigeon Pt 10-60 nm from 3 AM SCA...Pt Arena to Pt Reyes 0-10 nm from 9 PM until 3 AM GLW...Pt Arena to Pt Reyes 0-10 nm from 3 AM SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM && $$ PUBLIC FORECAST: Rowe AVIATION: MM MARINE: MM 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