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fxus66 kmtr 121806 
afdmtr

Area forecast discussion
National Weather Service San Francisco Bay area
1006 am PST Tue Dec 12 2017

Synopsis...strong high pressure will remain in place through much
of the week and result in dry weather conditions along with above
average daytime temperatures. Clear skies and weak offshore flow
will allow for cool overnights which will warm slightly late in
the forecast period as onshore winds return.

&&

Discussion...as of 9:18 am PST Tuesday...the mostly clear skies
have again helped to produce another chilly start to the day
across the region. Morning lows fell as low as sub-freezing in the
North Bay, 30s for the interior East Bay communities, and 40s for
most coastal locations. This morning's Oakland sounding recorded
a precipitable water (pwat) value of 0.15", which according to the
storm prediction center's sounding climatology Page, would be the
driest reading at Oakland for all past 12 Dec 12z soundings. This
dry airmass combined with the long, clear December nights are
helping to produce the large diurnal temperature swings for
interior locations. Temperatures will rebound back to above normal
values region-wide this afternoon with highs generally in the 60s
and 70s. Some areas in interior Monterey County and San Benito
County will likely reach the low 80s. No major changes planned for
the forecast package this morning. For additional details beyond
day 1, please refer to the previous discussion section.

&&

Previous discussion...as of 2:30 am PST Tuesday...dry and mild conditions
continue across the Bay area as high pressure remains in control.
Simply put, only minor tweaks to the forecast as guidance keeps
much of California dry through early next week.

Now for the details...latest longwave pattern shows a classic Rex
block across the west with high pressure over the Great Basin and
low pressure over the Gulf of California. The blocking pattern has
kept stagnant weather in place the last few days. However, the
ridge of high pressure is forecast to shift westward today
weakening the blocking pattern and possibly a transition to a
pattern change this weekend and early next weak.

High pressure overhead has led to another chilly morning across
interior/protected valleys with temperatures in the upper 20s to
lower 30s. Patchy frost will be possible in these locations, but
nothing too widespread given how dry the airmass is. On the flip
side, temperatures are much warmer and in the upper 50s to lower
60s across the hills.

Given the retrograding high pressure, warming 850mb temps and
continued offshore flow above normal temperatures will continue
into the weekend. Daytime highs will be 5 to 15 degrees above
normal with readings in the mid to upper 60s across the sfo Bay area
with 70s from the Santa Clara Valley south. A few interior spots
may even approach 80 across Monterey/San Benito. Overnight lows
will remain chilly with patchy frost and readings near freezing.
Warmer temps near urban areas, the coast and higher terrain.

Medium range models flatten the ridge as a weak boundary slides
into the pacnw Friday into Saturday. The Canadian is the most
aggressive with precip near the California/or border, but the ec and GFS
are much drier. For the Bay area, no mention of precip, but cooler
temps and some clouds possible this weekend.

The ridge rebuilds Sunday/Monday with continued warm and dry
conditions. The million dollar question continues to be, when will
it rain? For several days now long range models have suggested a
pattern shift and possibly some precip around December 20. The 00z
model run of the ec and GFS still shows that thinking, but the
Canadian not so much.

&&

Aviation...as of 010:10 am PST Tuesday...for 18z tafs. VFR. Very
light winds except breezy offshore winds through mountain gaps
and over ridges. Thin layer high clouds. Fog possible in the North
Bay valleys tonight.

Vicinity of ksfo...VFR. Light winds through the forecast period.

Sfo bridge approach...similar to ksfo.

Monterey Bay terminals...VFR. Generally light winds except for east-southeast
winds around 10 knots into the afternoon at ksns.

&&

Climate...

Here is a list of record high temperatures along with the most
recent date it occurred.
*Signifies there are additional years the record was set.

Sf Bay areadecember 13december 14
location................
Healdsburg..............76/191177/1942
Santa Rosa..............74/195872/1956
Kentfield...............73/191170/1942
San Rafael..............69/195070/1959
Napa....................72/193473/1959
San Francisco...........71/191169/1988
sfo Airport.............69/195869/1958
Oakland Airport.........70/195865/1958
Richmond................75/195867/1983
Livermore...............73/195875/1958
Moffett field...........68/195372/1958
San Jose................70/195873/1958
Gilroy..................78/195872/1988

Monterey Bay area
location................
Monterey................77/195378/1953
Santa Cruz..............77/194482/1953
Salinas.................79/195880/1988
Salinas Airport.........80/195381/1953
King City...............79/193683/1958

&&

Marine...as of 10:04 am PST Tuesday...increasing northwest winds
over the waters beginning later today through the upcoming
weekend. The strongest winds today will be primarily be located
south of Half Moon Bay through Davenport and as well as from Point
Sur and southward. Steadily larger, long period swell will impact
the coast mid to late this week as well.

&&

Mtr watches/warnings/advisories...
... Pinos to pt Piedras Blancas 0-10 nm from 3 PM

&&

$$

Public forecast: Rowe/mm
aviation: drp
marine: drp

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