Area forecast discussion National Weather Service San Francisco Bay area 1030 PM PDT sun may 19 2013 Discussion...as of 8:20 PM PDT Sunday...clear skies prevail across all of our district with even the coast and coastal waters entirely free of any marine stratus. High temperatures this afternoon were generally in the 70s around San Francisco Bay and the 80s in the valleys...about 5 to 8 degree warmer than on Saturday. New 00z NAM very consistent with prior recent runs in its projection of moderate offshore winds developing in the higher hills of the north and East Bay late tonight. Latest output also remains largely unchanged in both its general depiction of the synoptic evolution over the next 24 hours...and in the resulting bias corrected gridded maximum temperature forecasts for Monday. Thus continue to expect that we'll see an additional 5 to 8 degree of warming for tomorrow afternoon...with highs then reaching into the upper 70s to middle 80s around sf Bay...and to the lower 90s in the warmest Bay area inland locations. Current forecasts appear on track and no updates are presently anticipated. From previous discussion...a significant weather change is in store for our area beginning Tuesday. An unseasonably cool upper trough dropping southeast out of the Gulf of Alaska will bring a much cooler airmass into northern and central California by late Tuesday and Tuesday night. 850 mb temperatures are forecast to plummet from near 20 degree c on Monday down to as low as 2 degree c by Tuesday night. In addition...strong onshore flow will develop by Tuesday afternoon. High temperatures on Tuesday will be 15 to 20 degrees cooler compared to Monday. Only the far southern interior part of our area will escape major cooling on Tuesday. But all areas will see temperatures fall well below normal by Wednesday. Northwesterly winds will quickly increase on Tuesday after a dry cold front sweeps across the region. By late Tuesday afternoon portions of our area may see wind gusts up to 50 miles per hour. The GFS MOS guidance is forecasting sustained winds of 32 knots at sfo at 21z Tuesday afternoon. Strongest winds on Tuesday afternoon and early evening will be near the coast of the sf Bay area. Winds will gradually decrease near the coast overnight Tuesday night...but remain strong and gusty in the coastal hills through much of Tuesday night. A hazardous weather outlook has been issued to draw attention to the possibility of locally strong winds for coastal areas of the sf Bay area on Tuesday and Tuesday night. A Wind Advisory may be needed for this event. Temperatures by Wednesday will be up to 10 degrees below normal and cool conditions will persist through the end of the week as the upper trough remains anchored near the West Coast. The models continue to keep all precipitation with this system to our north...so the main impact in our area will be cool and breezy conditions. Winds will likely be strongest on Tuesday and Tuesday night...but breezy conditions will persist through the end of the week. We will likely see a brief return of coastal low clouds late Monday night and Tuesday morning. But by Tuesday afternoon there will be enough cool advection to wipe out the marine layer and marine layer low clouds will be absent from our area for the remainder of the week. Temperature contrasts from the coast to inland areas by midweek will be much less than typical for this time of year...only about 10 degrees or so. The upper trough is forecast to lift to the northeast by next weekend...so temperatures should begin to warm then. However...the models maintain a weak upper trough near the West Coast and so temperatures will likely remain below normal into next weekend...especially for inland areas. && Aviation...as of 10:30 PM PDT Sunday...dry northerly flow will keep VFR conditions in the sfo Bay area through Monday. Weak marine layer exists near 1000 feet and there could be patchy stratus in the mry Bay area early Monday. Vicinity of ksfo...VFR through Monday. Wind gusts to 30 knots through 05z. Ksfo bridge approach...similar to ksfo. Monterey Bay area terminals...patchy stratus will be possible at kmry...similar to the past few evenings. && Mtr watches/warnings/advisories... ... Reyes to Pigeon pt 0-10 nm until 3 am Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 3 am Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm until 3 am Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm until 3 am Small Craft Advisory...pt Arena to pt Reyes 0-10 nm Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm && $$ Public forecast: dykema/blier aviation/marine: west pi Visit US at www.Weather.Gov/sanfrancisco Follow US on facebook, twitter, and youtube at: www.Facebook.Com/US.Nationalweatherservice.Sanfranciscobayarea.Gov www.Twitter.Com/nwsbayarea www.Youtube.Com/nwsbayarea