fxus66 kmtr 202348 

Area forecast discussion 
National Weather Service San Francisco Bay area 
448 PM PDT sun may 20 2018 

Synopsis...upper low over California will keep temperatures below 
normal at least through Tuesday. Weak ridge builds around midweek 
with temperatures near normal before another trough approaches 
Friday through Sunday with onshore winds keeping temperatures on 
the cool side of normal while mainly dry conditions are forecast. 


Discussion...as of 1:42 PM PDT Sunday...below normal 
temperatures and breezy onshore winds continue to be the main 
forecast trend. So far this afternoon temps generally running from 
the upper 50s beaches, 60s around the Bay and 70s well inland. 
Cloud decks are around 2500 feet deep along the coast due to an 
upper low over the region. The Ben Lomond RAWS up in the Santa 
Cruz Mountains is sitting in the cloud layer and so far reporting 
a high of only 49 degrees so far this afternoon. Onshore gradient 
of 2.5 mb from sfo to SAC is pushing some gusty winds from the 
Golden Gate out into the Delta with sfo gusting to 33 mph last 

Looking forward the last few NAM runs have generated some coastal 
drizzle tonight with cyclonic flow aloft and moist onshore flow 
lifting the boundary layer. Coastal hills from San Mateo southward 
to Monterey that are exposed to NW winds off the ocean is where 
the modeling is showing some measurable drizzle type qpf that 
should it develop will be localized. 

Main forecast theme to start the work week will be continued below 
normal temps and breezy onshore winds. The North Bay may see the 
most sunshine on Monday with drier north/northeast flow around 
the upper low. MOS data showing 79 degrees for Santa Rosa on 
Monday while most cities around the Bay will see 60s once again 
with some lower 70s for the Santa Clara Valley. 

The upper low slowly ejects inland by Tuesday but a deep marine 
layer and onshore flow will likely remain in its wake with 
continued trend of below normal temps and onshore breezes. 

Some weak ridging or zonal type flow develops weds afternoon into 
Thursday sending temps back to near normal. 

Longwave trough approaches by Friday afternoon with onshore winds 
and approaching upper low sending inland temps back below normal 
once again for Saturday and Sunday of the upcoming Memorial Day 
weekend. Latest ECMWF does indicate system may be progressive 
with warmer high pressure by Memorial Day Monday but that scenario 
may be dubious with developing tropical system in the Gulf of 
Mexico potentially slowing the large scale west to east flow 
across the US. 


Aviation...as of 4:48 PM PDT Sunday...it's VFR with a few areas 
MVFR ceilings mainly on the coast this afternoon. Low clouds will 
generally fill in again tonight and Monday morning. Mid to high 
clouds with a 500 mb closed low will slowly move eastward this 
evening into Monday. 

Vicinity of ksfo...MVFR ceiling tonight into Monday morning, westerly 
wind gusting to 30 knots this evening. Gusty westerly wind resumes 
Monday afternoon and evening. 

Sfo bridge approach...similar to ksfo. 

Monterey Bay terminals...MVFR ceilings tonight into Monday morning. 
Partial clearing possible either by late Monday morning or early 


Marine...as of 01:17 PM PDT Sunday...a strong north to south 
pressure gradient along the California coast will maintain 
moderate to strong northwesterly winds over the coastal waters 
through Monday. As a result, steep wind waves will produce 
hazardous conditions for small crafts. A long period southerly 
swell will increase and mix with northwesterly swell by Monday 
morning, gradually increasing through much of the week. 


Mtr watches/warnings/advisories... 
... Bay until 9 PM 
Small Craft Advisory...mry Bay until 9 PM 
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm until 9 PM 
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm 
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm 
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm 
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm 
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm 



Public forecast: rww 
aviation: canepa 
marine: rgass 

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