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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 221159

Area Forecast Discussion
National Weather Service San Francisco Bay Area
459 AM PDT Sat Jun 22 2019

.SYNOPSIS...Dry north winds will persist in the hills through
this morning. The marine layer will continue to erode and 
compress through the day as an upper level ridge builds over 
California. The result will be a continued warming trend this 
weekend, especially inland, along with mostly clear skies. A 
distinct cooling trend is then forecast from Monday through 
Wednesday, resulting in much cooler temperatures by the middle of 
next week. 


.DISCUSSION...As of 3:19 AM PDT Saturday...Satellite imagery 
shows mainly clear skies over most of the district. Coastal 
stratus does extend along the Monterey county coast, through the 
Monterey Bay, and northward along the San Francisco Peninsula. 
Inland, low clouds are extending into the Salinas Valley. The 
offshore surface pressure gradient has increased somewhat with 5.4
mb from WMC to SFO, but there is still an onshore component with 
2.1 mb from SFO to SAC. 

Offshore winds have ramped up in the North Bay Mountains, and to 
a lesser extent in the East Bay Hills. Generally, northeast winds
from 25-35 mph with some higher gusts are being observed in these
higher hills. This is resulting in dry conditions this morning,
and warm temperatures are anticipated across inland areas today. 
High temperatures today are forecast to be anywhere from 5 to 12 
degrees warmer than those on Friday, with the most significant 
warming expected inland. Light onshore flow is expected to persist
at the surface and this will likely keep temperatures near the 
immediate coast limited to the lower to middle 70s. The warmest 
inland areas are expected to warm into the lower to middle 90s. 
Little change is expected on Sunday.

A switch back to cooler summer weather is expected to begin early
next week as an upper level trough approaches the coast. This 
will bring much cooler temperatures, with highs forecast to be as 
much as 15-20 degrees cooler than this weekend and from 5 to 10 
degrees cooler than normal. The upper trough is forecast to linger
through the end of next week, keeping temperatures on the cool 
side of normal through the end of the extended forecast period. 


.AVIATION...As of 05:00 AM PDT Saturday...VFR conditions exist 
this morning at the SF Bay Area terminals as offshore flow aloft 
brings dry air into the region. A 1500 foot marine layer is 
impacting the Monterey Bay terminals with stratus forming north 
along the coast to the Golden Gate. Under continued offshore flow 
and a strong northerly gradient, VFR expected to continue this 
morning through the day at the SF Bay terminals. Any stratus this 
morning is expected to erode by late this morning with only patchy
stratus remaining along the coast this afternoon. Light winds 
this morning will turn onshore this afternoon and increase to 
10-15 kt at most sites. 

Vicinity of KSFO...VFR. Light northwesterly winds this morning
expected to become light north-northeasterly late this morning. 
Northwesterly winds of 15-20 kt are expected this afternoon 
through early evening to around 04z.

SFO Bridge Approach...Similar to SFO but lighter winds are 
anticipated away from the San Bruno gap. 

Monterey Bay Terminals...IFR cigs at the terminals this morning
with bases around 500-700 feet. Cigs expected to begin clearing
around 16-17z this morning with VFR expected by 18z. Light winds
this morning becoming onshore this afternoon with speeds up to
10-15 kt. 


.FIRE WEATHER...As of 3:50 AM Saturday...Moderate and gusty north
winds are forecast for the higher hills in the North and East Bay
through this morning, with gusts up to 30-35 mph expected over 
the exposed ridges above 2000 feet. These north winds are ushering
a drier airmass into the region and relative humidity recoveries 
in the higher hills both this morning and Saturday night will be 
poor. In terms of offshore wind events, this one looks to be on 
the weak/light side in terms of winds, coverage, and humidity. 
Would need to see more widespread coverage and extreme 
winds/lowering humidity to put our region into critical fire 
weather conditions. Nonetheless, a very warm and dry weekend will 
mean increased concerns for fire spread of any new fire starts. 
Winds in the hills are expected to be lighter tonight and Sunday 
morning. Much cooler conditions, and greatly improved nighttime 
humidity recoveries, are forecast to develop from Monday through 

&& of 02:13 AM PDT Saturday...High pressure over the 
eastern Pacific extends to the Pacific Northwest coast with low 
pressure across central California. Breezy to gusty northwesterly 
winds will occur across the northern outer waters through Sunday 
with lighter winds elsewhere. Steep fresh swell will result from 
gusty winds over the northern outer waters with moderate 
northwesterly swell elsewhere. 


     .Tday...SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 9 AM




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