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Area Forecast Discussion
National Weather Service San Francisco Bay Area
513 PM PDT SAT SEP 24 2016

...VERY WARM TO HOT WEATHER CONDITIONS SUNDAY AND MONDAY...

.SYNOPSIS...A strong ridge of high pressure over the region and weak
offshore flow will result in very warm to hot conditions through the
weekend and into Monday. In addition, mostly sunny conditions will
prevail region-wide. A cooling trend is then forecast for the second
half of next week. 

&&

.DISCUSSION...as of 01:52 PM PDT Saturday...A warm and dry air
mass is in place over the region this afternoon as high pressure
builds in from the eastern Pacific. This has resulted in
temperatures running 5 to as much as 15 degrees above those 24
hours ago along with clear skies region-wide. However, a slight
onshore flow has caused temperatures to cool by a few degrees near
the coast and will limit coastal warming for today. Meanwhile,
inland areas will continue to warm into the upper 80s to lower 90s
while coastal areas experience mid 60s to lower 80s away from the
immediate coastline.

The warming and drying trend will continue into Sunday and Monday as
the ridge builds closer to the California coast and temperatures
aloft warm. In addition, weak offshore flow is forecast through
early tomorrow afternoon and will allow for the warm inland
temperatures to extend to the coast. Have increased temperatures by
a few degrees region-wide for Sunday with upper 80s to low 90s
briefly possible even in downtown San Francisco and around the
Monterey Bay. Temperatures near the coast will greatly depend on
when/if the sea-breeze develops during the afternoon hours the next
few days. Widespread 90s are also forecast for inland areas with
some of the warmest locations reaching into the 100-105 degree
range. In addition to the weak offshore flow and warm temperatures,
sunny skies will prevail through early next week. The forecast
models are no longer showing much relief from the heat on Monday as
weak offshore flow continues and onshore winds do not return early
enough to cool coastal temperatures until Tuesday. With this, a heat
advisory continues for the entire forecast area from 11 AM to 8 PM
PDT for both Sunday and Monday. On the flip side, overnight
conditions will cool into the 50s each night and allow for relief
from the daytime heat. 

Onshore flow is forecast to increase slightly by Tuesday and allow
for coastal temperatures to cool some while inland areas remain
above seasonal averages. The cooling trend will then spread inland
through the second half of next week as the ridge shifts eastward
ahead of an approaching mid/upper level trough to our northwest. By
late week, daytime temperatures will likely cool as much as 20
degrees compared to Monday. Dry weather conditions are also forecast
through the entire work week ahead with the potential for coastal
clouds to return as early as Tuesday night and Wednesday morning.

&&

.AVIATION...As of 5:05 PM PDT Saturday...VFR is expected to
prevail across the region over the next 36 to 48 hours. The main
item will be the winds. Onshore flow late this afternoon will ease
then turn offshore across the area overnight. Offshore flow
tonight should not be very strong, but could bring gusty
conditions to STS, OAK, and LVK. Will be interesting to see how it
plays out. Conditions will turn onshore again late Sunday morning
into the early afternoon. This pattern will prevail into Sunday
night as well.

Vicinity of KSFO...VFR. Winds will ease this evening then turn
light offshore overnight and last into the morning hours. Onshore
winds will develop again late Sunday morning into afternoon.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR through the period. Light offshore
winds overnight then light onshore flow again by Sunday afternoon.

&&

.FIRE WEATHER...As of 5:05 PM PDT Saturday...Models continue to
trend towards stronger offshore winds tonight and Sunday morning,
especially in the North Bay mountains. 12Z WRF model forecasts
sustained northeast winds of around 32 kt at 925 mb over Napa and
eastern Sonoma counties late tonight into Sunday morning. This
equates to about 38 mph. Gusts may be as high as 55 mph. These
winds will be following and preceding very warm to hot daytime
temperatures. No nighttime humidity recovery is expected. Ridges
will actually see a RH minimum overnight. As a result of the
strong offshore flow and forecast low RH the red flag warnings
remains in place for the North Bay Mountains (Fire Weather Zone
507). Otherwise, expect the warming and drying trend to continue
through Monday across the entire district. Winds will generally be
light after Sunday. A cooling trend will begin on Tuesday.

In the vicinity of the Soberanes Fire: Portable RAWS stations
above 3000 feet are already showing light offshore flow. The local
WRF is indicating east winds picking up tonight as the thermal
trough offshore strengthens. By late Sunday morning winds in this
area are forecast to decrease slightly then gradually turn to the
south. Temperatures will climb during the day Sunday and again
Monday while RH values drop into the single digits. Monday will
likely be the warmest and driest day, with gradual improvement
expected to begin on Tuesday.

&&

.CLIMATE...Here are the record highs for September 25 and
September 26. 
 
                   September 25                September 26
                   Record/Year                 Record/Year
Bay Area

Kentfield.............100/1964.....................99/1921
San Rafael............100/1964.....................99/1963
Napa..................101/1960....................105/1963
San Francisco..........93/1954.....................94/1992 
SFO....................91/1970.....................95/1958
Oakland Museum.........95/1978.....................93/1973 
Oakland Airport........94/2010.....................97/1958 
Richmond...............95/1964.....................95/1963
Livermore.............101/1978....................103/1952 
Mountain View..........91/1978.....................95/1999 
San Jose...............97/1952.....................98/1963
Gilroy................106/1978....................104/1963

Monterey Bay Area

Monterey...............95/1954.....................98/1970
Santa Cruz............100/2010....................101/1970
Salinas................97/1960....................100/1970
Salinas Airport........99/1937.....................99/1970
King City.............105/1975....................105/1963

&&

.MARINE...as of 10:54 AM PDT Saturday...A gradually easing
pressure gradient will continue to result in moderate northwest
winds through the day today for most of our waters. The strongest
winds will be this afternoon and this evening along the sonoma and
big sur coasts. Locally generate fresh swell may also result in
hazardous conditions. Winds decrease sunday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 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

&&

$$

PUBLIC FORECAST: RGass
AVIATION: BFG
MARINE: DRP
CLIMATE: BAM 
FIRE WEATHER: BFG


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