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000 
FXUS66 KMTR 202011
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
111 PM PDT Wed Sep 20 2017

.SYNOPSIS...A cool, upper level trough will dominate the western 
portion of the country through the workweek maintaining cooler 
than average temperatures and breezy conditions. Aside from the 
potential for isolated showers offshore or near the coast tonight 
through Thursday, dry weather conditions will prevail. A gradual 
warming trend is then expected to begin this weekend and persist 
into early next week.

&&

.DISCUSSION...as of 01:09 PM PDT Wednesday...A weak frontal 
boundary continues to slowly move through the region this 
afternoon with reports of light rainfall ongoing from the North 
Bay down through coastal San Mateo County. However, rainfall 
amounts have generally been a few hundredths of an inch or less. 
Scattered clouds also persist around and north of the frontal 
boundary while sunny conditions prevail over much of Monterey and 
San Benito County. Overall, temperatures from the mid 60s to upper
70s are being reported along with breezy to locally gusty winds. 
These breezy conditions will continue through the late evening, 
especially in the hills and higher elevations with gusts to around
35 MPH possible. 

As colder air advect southward into the region overnight, 
temperatures will be noticeably for locations away from the 
immediate coastline. Many locations will cool into the 40s to 
lower 50s both overnight tonight and again Thursday night into 
Friday morning. Cannot rule out some of the highest elevations 
falling into the low 40s or even upper 30s briefly before sunrise 
each morning, especially if the winds begin to ease. Daytime 
temperatures for the remainder of the week will also struggle to 
warm out of the mid 60s to lower 70s. While most locations will 
remain dry in wake of today's frontal passage, the forecast models
do show some weak disturbances dropping southward over the 
coastal waters both late tonight into early Thursday morning as 
well as Friday morning. Given the cool air mass aloft, cannot rule
out isolated showers over the waters through late week which 
could potentially bring a few showers to coastal areas of the 
Central Coast. With that said, most locations across the region 
will remain dry. Will continue to monitor any potential for 
isolated showers over the next 24 to 48 hours. 

High pressure is then forecast to build over the Eastern Pacific 
and nudge inland as the mid/upper level trough currently impacting
the region shifts to the east. This will result on drying 
conditions and a warming air mass aloft. Look for temperatures to 
warm back to near seasonal averages through the weekend and likely
back above average by early next week. Thus, widespread 80s to 
lower 90s are currently forecast by Tuesday and Wednesday of next 
week. Cannot rule out brief offshore winds as well at times which 
will help bring the warmer conditions to the coast. 

&&

.AVIATION...As of 10:44 AM PDT Wednesday for 18Z TAFs. A 
challenging TAF package as overcast conditions blanket most TAF 
sites with ceilings ranging from IFR to VFR. Do think we'll see a 
rather continuous feed of BKN/OVC clouds through the day -- 
especially for San Francisco Bay Area terminals -- and have 
updated the TAFs accordingly. Ceilings are expected to be MVFR 
through the day, but then approach back toward IFR levels after 
sunset as cold air advects into the area. Overall confidence in 
the ceiling forecast remains low. Winds are expected to increase 
from the west to northwest this afternoon.

Vicinity of KSFO...Ceilings have improved back to MVFR through 
the morning. Expect mostly overcast conditions to persist through 
the day with ceilings around 2000 to 3000 ft in the afternoon. 
Expect ceilings to decrease by evening and continuing overnight 
with the possibility of IFR conditions overnight. Confidence 
remains low on ceilings, particularly after 00Z Thursday. Winds 
will increase this afternoon to around 15 kt with possible gusts 
around 25 kt.

SFO Bridge Approach...similar to KSFO. 

Monterey Bay Terminals...VRF conditions as of the 18Z TAF 
issuance, though do expect increasing cloud cover through the day 
with MVFR ceilings becoming more likely. Breezy conditions 
expected this afternoon.

&&

.MARINE...as of 10:25 AM PDT Wednesday...Moderate long-period
northwest swell will continue to affect the coastal waters today 
as swell periods slowly decrease over the next 12 to 24 hours. 
Swell heights will remain above 8 feet through this evening, 
particularly for the northern outer waters, then decrease through 
the remainder of the week. Northwest winds will increase again 
this afternoon/evening throughout the waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 9 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm from 9 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...SF Bay until 3 AM

&&

$$

PUBLIC FORECAST: RGass
AVIATION: Rowe
MARINE: Rowe

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