Technical NOAA Weather Discussion

FXUS66 KMTR 211146

Area Forecast Discussion
National Weather Service San Francisco Bay Area
446 AM PDT Thu Jun 21 2018

.SYNOPSIS...A robust warming trend will begin over the next 
several days as high pressure builds off the West Coast. This will
lead to hot conditions on Saturday with moderate to locally high 
heat risks across parts of the region. Additionally, winds will 
turn offshore, bringing heightened fire weather concerns to parts 
of the area on Saturday. Cooling will commence on Sunday along 
with the redevelopment of the marine layer for early next week.


.DISCUSSION...As of 3:15 AM PDT Thursday...GOES-East fog product 
reveals areas of stratus again impacting parts of the San 
Francisco Bay Area and central California coast this early 
Thursday morning. The Fort Ord profiler along the Monterey Bay 
shoreline indicates the marine layer is running around 1,000 ft 
deep, similar to what it was 24 hour ago. Despite the similar 
marine layer depth, the stratus coverage doesn't appear to be 
quite as widespread as it was yesterday morning.

Synoptically-speaking, an upper level high is presently centered 
in southwestern Arizona. A quick shortwave trough is currently 
pushing through the outer periphery of this high across northern 
California, and will quickly exit the state within the next 6-12 
hours. Some weak ridging is expected to occur behind this 
shortwave during the day, which should allow for some warming 
across interior locations this afternoon.

By Friday, an upper level ridge will begin to amplify off the 
California coast, resulting in further warming across interior 
locations. We'll likely see some locations in the interior North 
Bay, interior East Bay, and southern reaches of Monterey and San 
Benito Counties reach the triple digits for Friday afternoon. The 
warming will continue on Saturday for what should be the hottest 
day as the ridge continues to strengthen offshore. The hottest 
areas of the county warning area -- far northern Sonoma and Napa 
Counties, far interior East Bay, and far southern Monterey + San
Benito Counties -- may flirt with 105 degrees on Saturday. The 
warm-to-hot conditions will likely creep toward the San Francisco
Bay shoreline as well -- 90s to low 100s seem quite probable 
along the US 101 corridor from Gilroy north through San Jose and 
continuing toward Redwood City. Temperatures farther north toward
SFO and San Francisco will likely be cooler with highs along the 
bay shoreline in the 80s with cooler conditions along the 
immediate Pacific coast. These temperatures are expected to 
produce moderate to locally high heat risks across much of the
interior, and will likely see heat advisory headlines launched 
later today for certain zones as a result of these forecasted hot

Another concern for late Friday night/Saturday will be locally 
breezy north to northeast winds over the North Bay Mountains. 
High-resolution models are starting to capture this event, and are
showing wind speeds around 15 to 25 mph with local gusts around 
35 mph across far Northern Napa and Sonoma Counties. Combined with
poor relative humidity recoveries, this will likely lead to 
heightened fire weather concerns.

For Sunday, models have consistently been advertising appreciable
cooling across the region as the ridge axis pushes east into the 
North American continent. Additionally, the GFS, NAM, and local 
in-house WRF model have suggested the potential for a southerly 
surge pushing north along the Monterey County coast and continuing
toward the Golden Gate during the day. Cooling will continue into
the first half of next week with highs gradually returning close 
to late June climatological normals.


.AVIATION...As of 4:46 AM PDT Thursday...For 12z TAFs. Marine 
layer currently sits slightly below 1,000 feet, per the Ft. Ord 
Profiler. GOES-16 fog product shows patchy stratus affecting the 
Greater SF Bay terminals (BKN/OVC deck around 1,200 feet), as well
as Monterey Bay terminals (BKN/OVC deck around 500 feet). The 
shallow stratus should erode by 16-17z for most terminals this 
morning. Building ridge of high pressure will compress the marine 
layer even more by this evening. Therefore, not expecting cigs to 
form tonight. However, there could be some patchy dense fog that 
may reduce vsby around the Monterey Bay region overnight tonight, 
low confidence on exact timing. Light to moderate west/northwest 
winds this afternoon, locally gusty at times.

Moderate-high forecast confidence. 

Vicinity of KSFO...MVFR cigs becoming VFR by 16-17z. Onshore winds
15-20 kt, with higher gusts possible by this afternoon. A very
compressed marine layer should keep cigs from forming tonight.

SFO Bridge Approach...Approach remains clear for now (per SMB ob),
but intermittent MVFR cigs possible before 16z. 

Monterey Bay Terminals...LIFR/IFR cigs through about 16-17z, then
VFR. Light to moderate west/northwest winds this afternoon, around
10-12 kt. Compressed marine layer may produce fog tonight, 
reducing horizontal and vertical vsby by Friday morning.


.FIRE of 3:15 AM PDT Wednesday...A pronounced 
warming and drying trend is forecast for the end of the week as 
high pressure builds in and winds turn offshore. Saturday 
presently looks to be the hottest day, with poor overnight 
relative humidity recoveries for both Friday night and Saturday 
night. Locally gusty north to northeast winds are possible in the 
North Bay hills Friday night and Saturday morning. A return to 
cooling and redevelopment of the marine layer appears in store for
Sunday into the first part of next week as flow shifts back 

&& of 2:40 AM PDT Thursday...High pressure over the 
Eastern Pacific will continue to strengthen through the rest of 
the week and into the weekend. In response, strong and gusty 
northwest winds are expected to affect the majority of the coastal
waters zones through this period. Winds are expected to be 
strongest over the northern outer most coastal waters, 
strengthening to near gale force, with gale force gusts, by Friday
evening through Saturday morning. As a result of the strong 
winds, steep and hazardous seas are likely for the majority of the
coastal waters through at least the first half of the weekend.


     .Tday...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             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...Mry Bay from 12 PM




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Prepared by Weather at: Thu Jun 21 08:30:02 PDT 2018
From the National Weather Service