Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 230402
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
902 PM PDT Sat Jun 22 2019

.SYNOPSIS...High pressure will continue to produce above average
temperatures through the remainder of the weekend, especially
inland. 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 9:00 PM PDT Saturday...Our warming trend
became more robust today as building high pressure aloft and light
offshore flow away from the coast combined to boost temperatures.
Warming was most pronounced inland where afternoon temperatures
were as much as 15 degrees warmer than Friday, topping out in the
low to mid 90s in the warmest inland valleys. Persistent light 
onshore flow near the coast kept temperatures mild close to the 
ocean, where afternoon highs were mostly in the 60s and lower 
70s.

Not much change is anticipated for the second half of the weekend.
Early evening satellite imagery looks almost identical to 
yesterday evening, with low clouds confined only to coastal areas 
from Monterey Bay southward. Expect an increase in low clouds and 
fog near the ocean overnight, but given the relatively shallow 
depth of the marine layer (approx 1200 feet deep at Fort Ord) and 
an ACV-SFO surface pressure gradient of 6 mb, expect very little 
inland development of marine layer fog/low clouds overnight. 
Temperatures on Sunday are forecast to be similar to today. 
Southern inland areas will likely warm a few more degrees as the 
upper ridge continues to strengthen over California. However, the 
North Bay Valleys are projected to cool slightly due to an 
increasing southerly component to the low level flow.

The ridge will start to break down on Monday as an upper trough 
off the coast of British Columbia begins to move to the southeast.
Expect stronger onshore flow by Monday afternoon, an increase in
coastal low clouds, and a decrease in high temperatures of at 
least 5 degrees in most areas. Another 5 to 10 degrees of cooling 
is then expected on Tuesday as the trough digs south along the 
West Coast, triggering a rapid deepening of the marine layer. A 
few additional degrees of cooling is likely on Wednesday, 
especially inland, when the upper trough axis if forecast to be 
aligned along the California coast. By Wednesday, high 
temperatures are forecast to be as much as 20 degrees cooler than 
Sunday and as much as 10 degrees cooler than normal. Temperatures 
are then expected to rebound a bit late next week, but still 
remain at least slightly below normal as the longwave trough 
position remains near the West Coast. 

In the longer range, the ensemble mean H5 pattern forecast by both
the GEFS and ECMWF indicate that an upper ridge over the Desert 
Southwest will build towards the west, bringing warming to our
region by the end of next weekend.

&&

.AVIATION...as of 5:00 PM PDT Saturday...Northerly gradient
continue to dominate over the east-west gradient. This will keep
VFR conditions in the SFO Bay Area through Sunday. 
Low clouds have hung around MRY Bay today and should spread into
MRY and SNS earlier tonight.

Vicinity of KSFO...VFR. Northwest winds around 15 kt decreasing
after 04Z. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR after 04Z. 

&&

.MARINE...As of 8:54 PM PDT Saturday...High pressure over the 
eastern Pacific extends into the Pacific Northwest with low 
pressure across central California. This will result in gusty 
northwest winds over the northern outer waters through Monday with
weaker winds elsewhere. Winds will decrease Tuesday as the high 
weakens and low pressure sets up off the Pacific Northwest. 

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi

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