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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 170008
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
508 PM PDT Tue Apr 16 2019

.SYNOPSIS...This afternoon will feature cool temperatures and 
breezy conditions under partly cloudy skies. A warming trend is 
forecast for Wednesday and Thursday, with temperatures expected to
climb well above normal by Thursday with widespread 80s for 
inland locations. A cooling trend is forecast to begin on Friday 
and continue into the weekend. Generally dry conditions are 
expected over the weekend and early next week.

&&

.DISCUSSION...as of 01:55 PM PDT Tuesday...Showers have exited 
the region with dry conditions in all areas this afternoon. 
Sunshine and low level moisture are creating widespread 
stratocumulus clouds, especially over the higher terrain. A 
subsidence inversion is forming about 5000 feet MSL limiting the 
vertical development of these clouds. Temperatures this afternoon 
are on the cool side, ranging from the upper 50s along much of the
coast to the middle 60s inland. Our region is situated between a 
surface high to the west and a surface trough to the east, and as 
a result breezy northwest winds have developed this afternoon. 
These winds will become strong at times through the evening along
the coast where gusts up to 30 mph are possible. Overnight 
tonight, areas of stratus are likely to develop along the coast.

On Wednesday, an upper ridge currently over the eastern Pacific
will begin to move overhead. This will bring a warmer airmass and
weaker onshore flow, resulting in about 10 degrees of warming
inland and up to 5 degrees along the coast. The ridge will 
continue to shift east on Thursday, when the ridge axis is 
expected to transverse the region. A surface trough will develop
along the coast on Thursday as high pressure develops over the
Great Basin, resulting in weak offshore flow. Thursday is expected
to be the warmest day of the week with widespread 70s at the coast
and 80s in the inland valleys. The warmest locations, such as the
southern Salinas Valley, are forecast to reach the upper 80s with
a 90 degree reading not out of the question. These high 
temperatures are about 7-15 degrees above normal for mid-April. 
These warm temperatures are expected to remain several degrees shy
of record highs. For reference, the record high on Thursday for 
Downtown San Francisco is 83 and San Jose is 91 degrees, which we 
are not expecting to approach. 

On Friday, a cutoff low will move onshore over southern
California, and onshore flow will increase. Cooling will be most
pronounced along the coast, while some inland areas could see
temperatures similar to Friday. Additional cooling is expected on
Saturday as a Pacific trough brings with it a cooler airmass. 
Highs are expected to range from the mid 60s to the mid 70s, or
about a 10 degree drop from Thursday. Precipitation chances with
this system will be minimal with showers expected to remain to our
north.

Another weak shortwave trough will move through the area on
Sunday, with continued minimal chances of precipitation. A low-
amplitude ridge of high pressure will then replace the trough on 
Monday and Tuesday with warming temperatures expected. With a 
return to ridging, the forecast looks to remain dry through the 
end of the forecast period.

&&

.AVIATION...as of 05:00 PM PDT Tuesday...VFR conditions prevail 
districtwide, with just some small cumulus clouds over the hills 
and areas of thin midlevel clouds drifting through. Current light
to locally moderate onshore winds will diminish during the 
evening hours and become light overnight. 

Key forecast question is ceiling development during the late night
and early morning hours. Mixed signals from models and statistical
guidance, and thus lower than average confidence. Upshot is that 
it appears more likely for the Monterey Bay terminals and less 
likely for those in the San Francisco Bay Region. 

Vicinity of KSFO...Breezy west winds through early evening, with 
sustained winds 15-20 kt and gusts 20-25 kt possible. Latest 
model output indicates diminished chances of late night/early 
morning ceiling development so am maintaining VFR conditions 
throughout the forecast period, but confidence is low.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...Onshore winds 10-15 kt through early
evening, then becoming light. MVFR ceilings projected to develop
overnight and persist into the morning hours, but low confidence.

&&

.MARINE...as of 02:09 PM PDT Tuesday...Strong and gusty northwest
winds are forecast to persist trough the evening and into tonight
before diminishing slightly on Wednesday. However, gusty winds 
will remain possible along the coast and just offshore Wednesday 
afternoon and evening. A moderate northwest swell will continue 
through the forecast period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Mry Bay until 11 PM
             SCA...Pigeon Pt to Pt Pinos 0-10 nm until 11 PM
             SCA...Pt Arena to Pt Reyes 0-10 nm until 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm until 3 AM

&&

$$

PUBLIC FORECAST: ST
AVIATION: Blier
MARINE: RGass

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