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

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS66 KMTR 250542 AFDMTR Area Forecast Discussion National Weather Service San Francisco Bay Area 1042 PM PDT SAT SEP 24 2016 ...RECORD HIGH TEMPERATURES OVER THE BAY AREA AND NORTH CENTRAL COAST SUNDAY AND MONDAY... ...HEAT ADVISORY FOR THE BAY AREA AND NORTH CENTRAL COAST 11 AM PDT TO 8 PM PDT SUNDAY... ...RED FLAG WARNING FOR THE NORTH BAY MOUNTAINS THROUGH 3 PM PDT SUNDAY... .SYNOPSIS...
-- Changed Discussion --
A strong upper level ridge of high pressure over the eastern Pacific, Pacific Northwest and California will result in record high temperatures Sunday and Monday. Moderate levels of mugginess will accompany hot temperatures again Sunday, possibly Monday as well. Strong offshore flow is also in early stages of development this evening. Expect offshore flow to persist through at least Monday with exception of very minor and localized intrusions of cooler marine air on the immediate coastline. Record warmth through early next week will be followed by subtle cooling, mainly on the immediate coast, by the middle to later part of next week.
-- End Changed Discussion --
&& .DISCUSSION...
-- Changed Discussion --
as of 10:42 PM PDT Saturday...Strong high pressure for late September /and early October/ time frame is over the eastern Pacific with overlap onto the Pacific Northwest and California. 593-595 decameter 500 mb geopotential heights through Sunday evening are close to the seasonal maximum for all KOAK soundings back to 1948 per SPC`s sounding climatology page. Based on model guidance, relatively high sun angle for late September, and 850 mb temps brought to sea level via the dry adiabat high temperatures will quite likely climb close to record levels Sunday and Monday; high temps 90s/lower 100s. Record highs are listed below. Temperatures Sunday and Monday will warm primarily through large scale subsidence coinciding with a period of offshore wind flow. Also of note, the NAM model and to some degree the GFS model both have had an ongoing onshore bias with respect to the SFO-WMC gradient. For the NAM model this onshore bias, upwards of 7 mb to 8 mb, has been present through the summer. The WMC-SFO gradient will thus likely sustain well up over 10 mb tonight through early next week, then decrease in strength by the middle of next week. Also, noting a precipitable water value 0.70" on KOAK upper air sounding and area dewpoint temps hovering in the 50s this evening; sort of unusual to see high levels of moist air trapped surface to lower levels given the developing offshore flow pattern. Origin of this water vapor is from central Pacific advected latitudinally northward then southeastward into northern California out ahead of the eastern Pacific high pressure system. New 00z GFS PW forecasts show the PW only decreasing to approx 0.60" through early next week, thus remaining a bit elevated for the given pattern we`re entering thus expect at least moderate levels of mugginess to hold in the air Sunday and Monday for locations nearest sea level, much drier air will be along hill tops and in the mountains. Made an update earlier this evening. Update was made to increase the winds somewhat for this evening through Sunday evening for the North Bay mtns, East Bay hills/mtns, Santa Cruz mtns and Santa Lucia mtns and along the San Francisco Peninsula coast. High resolution WRF model indicates increasing E-NE winds developing in the coastal gaps along San Mateo county by early Sunday morning. Hot temps peak Sunday and Monday.
-- End Changed Discussion --
&& .AVIATION...
-- Changed Discussion --
As of 10:12 PM PDT Saturday...VFR. Non-convective low level wind shear is a possibility late tonight/Sunday at KOAK. Offshore wind during the period with minor influxes of onshore flow possible on the immediate coast late Sunday afternoon. Vicinity of KSFO...VFR. Light winds. SFO Bridge Approach...Similar to KSFO. Monterey Bay Terminals...VFR. Light offshore winds overnight then light onshore flow again by Sunday afternoon.
-- End Changed Discussion --
&& .FIRE WEATHER...As of 5:05 PM PDT Saturday...Models continue to trend towards stronger offshore winds tonight and Sunday morning, especially in the North Bay mountains. 12Z WRF model forecasts sustained northeast winds of around 32 kt at 925 mb over Napa and eastern Sonoma counties late tonight into Sunday morning. This equates to about 38 mph. Gusts may be as high as 55 mph. These winds will be following and preceding very warm to hot daytime temperatures. No nighttime humidity recovery is expected. Ridges will actually see a RH minimum overnight. As a result of the strong offshore flow and forecast low RH the red flag warnings remains in place for the North Bay Mountains (Fire Weather Zone 507). Otherwise, expect the warming and drying trend to continue through Monday across the entire district. Winds will generally be light after Sunday. A cooling trend will begin on Tuesday. In the vicinity of the Soberanes Fire: Portable RAWS stations above 3000 feet are already showing light offshore flow. The local WRF is indicating east winds picking up tonight as the thermal trough offshore strengthens. By late Sunday morning winds in this area are forecast to decrease slightly then gradually turn to the south. Temperatures will climb during the day Sunday and again Monday while RH values drop into the single digits. Monday will likely be the warmest and driest day, with gradual improvement expected to begin on Tuesday. && .CLIMATE...Here are the record highs for September 25 and September 26. September 25 September 26 Record/Year Record/Year Bay Area Kentfield.............100/1964.....................99/1921 San Rafael............100/1964.....................99/1963 Napa..................101/1960....................105/1963 San Francisco..........93/1954.....................94/1992 SFO....................91/1970.....................95/1958 Oakland Museum.........95/1978.....................93/1973 Oakland Airport........94/2010.....................97/1958 Richmond...............95/1964.....................95/1963 Livermore.............101/1978....................103/1952 Mountain View..........91/1978.....................95/1999 San Jose...............97/1952.....................98/1963 Gilroy................106/1978....................104/1963 Monterey Bay Area Monterey...............95/1954.....................98/1970 Santa Cruz............100/2010....................101/1970 Salinas................97/1960....................100/1970 Salinas Airport........99/1937.....................99/1970 King City.............105/1975....................105/1963 && .MARINE...
-- Changed Discussion --
as of 9:01 PM PDT Saturday...Moderate northwest winds will persist into the evening and then taper off through the night as the surface pressure gradient weakens over the coastal waters. Winds are forecast to continue easing through Sunday. A small to moderate mixed swell will persist through the upcoming week.
-- End Changed Discussion --
&& .MTR WATCHES/WARNINGS/ADVISORIES... .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM SCA...Pt Arena to Pigeon Pt 10-60 nm && $$ PUBLIC FORECAST: Canepa AVIATION: BFG MARINE: BFG CLIMATE: BAM FIRE WEATHER: BFG Visit us at www.weather.gov/sanfrancisco Follow us on Facebook and twitter at: www.Facebook.com/nwsbayarea www.twitter.com/nwsbayarea

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.