Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1015 PM PST Sat Jan 24 2015
Synopsis...strong high pressure over the region will result in
dry weather and potentially record breaking daytime temperatures
through Sunday. Cooling will occur early in the work week as the
high pressure shifts to the east. Light precipitation is possible
late Monday night and Tuesday as a weak system approaches from
the south. Rain chances will be highest across Monterey and San
Discussion...as of 8:55 PM PST Saturday...warm conditions
developed across much of the region today...but not all.
Persistent fog in the Central Valley crept westward into the
Delta...around northern sf Bay and locally into the North Bay
valleys last night. Even after fog cleared today...a light east
wind continued to advect a damp chilly airmass out of the Central
Valley and into areas around San Pablo and northern sf Bay. The
result: highs of only 57 degrees in San Rafael and at the Napa
Airport today. Meanwhile...not far away in Oakland...dry downslope
conditions helped push highs into the lower 70s...resulting in a
record high at the Oakland museum.
The warmest temperatures today were from Monterey Bay southward
where highs were generally in the 70s. The Monterey climate
station tied a record with a high of 74. The warmest location was
Carmel Valley at 78.
Fog and low clouds persist across the southern Sacramento and San
Joaquin valleys this evening...as well as across eastern Contra
Costa County. Evening dewpoints are running close to what they
were last evening and light east winds continue across the area.
Thus...it's likely the same areas that were foggy last night and
this morning will see fog once again tonight and Sunday morning. A
forecast update earlier this evening included the addition of fog
to portions of the north and East Bay tonight and Sunday morning.
Patchy dense fog is likely.
Guidance continues to forecast warmer conditions in most areas on
Sunday...even though offshore flow is forecast to weaken and the
airmass aloft will begin to cool. However...both the NAM and WRF
models indicate drier air will make its way into the boundary
layer by tomorrow afternoon which should help boost temperatures. Do
think...however...that guidance is too warm tomorrow for
locations around northern sf Bay and eastward into the Delta as
these areas will once again be impacted morning fog and proximity
to the persistent Central Valley fog bank. Evening forecast
update included an downward adjustment in maximum temperatures for places
like San Rafael...Concord and Napa...and other slight modification
elsewhere. In any case...record highs are once again possible on
Sunday...especially in portions of the south and East Bay...around
Monterey Bay...and into the Salinas valley.
Water vapor satellite imagery currently shows that an upper low
has developed off the coast of western Baja California. By Monday the high
pressure ridge currently centered over northern California will have moved
off to the east. This will result in cooler conditions on
Monday...but will also allow the low off Baja California to lift northward
into Southern California by Monday night. The models have not
been particularly consistent regarding precipitation with this
area of low pressure...nor have then been in very good agreement.
However...both the 00z NAM and 00z GFS agree that light rain will
spread northward into Monterey and San Benito counties late Monday
night into Tuesday. Compared to the GFS...the NAM forecasts more
widespread rainfall...generating scattered light precipitation as far
north as the sf Bay area on Tuesday. The NAM also generates higher
quantitative precipitation forecast with rain totals as high as 0.75" in San Benito County...while
the maximum GFS rainfall is only about a quarter of an inch. The
most recent European model (ecmwf) (12z) is more in line with the GFS. The upshot
is that all three of these models are currently forecasting
measurable rain across Monterey and San Benito counties late
Monday night and Tuesday. Have therefore increased rain chances
across the southern portion of our area...and chances may need to
be increased further depending on what the 00z European model (ecmwf) shows.
A weak splitting system approaching from the west around the
middle of next week is expected to leave our area dry.
Aviation...as of 10:00 PM PST Saturday...offshore winds strong
enough to mix out any fog or low clouds through Sunday.
Vicinity of ksfo...VFR. Light offshore winds.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...VFR.
Climate...record high temperatures are possible over the area today
and Sunday. Here is the list of records along with the January warmest
high temperature readings and the latest year they occurred.
Sf Bay area...
Location today Sunday January warmest
Kentfield 69/1974 77/1934 79/1962
San Rafael 75/1948 70/2014 82/1962
Napa 72/1924 83/1899 85/1962
San Francisco 74/1948 74/1899 79/1962
sfo Airport 72/1948 68/2011 73/2014
Oakland 71/2014 73/2014 78/2014
Oak Airport 72/1948 70/2014 77/2014
Richmond 71/1974 69/2011 76/1962
Livermore 73/1975 73/1911 77/1911
Mountain View 76/1948 72/2014 76/1948
San Jose 76/1948 71/2014 79/1962
Gilroy 74/1968 77/2014 80/2014
North central coast...
Monterey 74/2006 78/1942 84/2014
Santa Cruz 76/1988 80/1899 84/2014
Salinas 76/2011 78/2014 87/2014
sns Airport 80/1948 78/2014 86/2014
King City 78/1968 77/2014 86/1976
Marine...as of 10:00 PM PST Saturday...high pressure over the
Great Basin will weaken and move south over the next few days.
Winds will remain light switching to east to southeast from Sunday
through Tuesday. Weak high pressure will build off the Pacific
northwest Wednesday and Thursday for a return to northwest winds.
A large long period swell will continue to impact the coastal
waters through Sunday afternoon. This long period swell will
result in large breakers near bars...Shoals and jetties leading to
hazardous conditions along the coast. As of 10 PM...buoys along
the California coast are reporting seas in the 7 to 10 foot range
with a 14 to 16 second period. High surf advisory is in effect
through Sunday afternoon when swells are expected to decrease.
... Surf advisory...entire coast from Sonoma County
south to Monterey County.
Public forecast: dykema
aviation: west pi
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