Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1004 am PST Sat Jan 31 2015
Synopsis...dry and mild conditions are expected to continue
through the middle of next week with rain chances confined to far
northern California. Temperatures will remain several degrees
above normal. There are indications that rain may move into the
area by the end of next week.
Discussion...as of 08:44 am PST Saturday...large scale pattern
features a strong ridge along the coast through tonight before
flattening on Sunday and Monday.
Main weather features this morning are gusty east winds in the
hills of the East Bay area with gusts around 40 miles per hour. Offshore flow
dominant this morning across the region with extensive radiational
fog in Salinas valley actually advecting over Monterey Bay with
downvalley winds. Some low clouds even reaching the Santa Cruz
region and patchy fog also in southern Santa Clara Valley. Hrrr
and WRF models in agreement with rapid decrease in boundary layer
relative humidity this morning...so expect clearing most areas by noon.
Picture perfect weather day across the Bay area with highs
reaching middle 60s to lower 70s across the region. East winds over
the hills should decrease quickly this afternoon as offshore
pressure gradients relax. Sfo to SAC gradient actually becomes
weakly onshore by late afternoon. However...look for continued
gusty east winds in the Bay area hills occasionally surfacing into
the valleys this morning before decreasing this afternoon.
NAM and WRF models support return of high relative humidity and possible stratus
to at least San Mateo coastline by late tonight and possibly
patchy fog into Bay area Sunday morning. GFS not as aggressive
with fog return and associated MOS guidance favors clear
conditions. Patchy fog will probably form late tonight in interior
valleys as dew points edge upward with brief onshore flow this
evening. No changes planned in the short term forecast for
now...and will evaluate chances for patchy fog and what locations
tonight with newer model guidance.
Previous discussion...slightly cooler temperatures are expected on Sunday
as the surface flow returns to onshore.
The dry weather will continue through at least the middle of next
week as the upper level ridge remains anchored over the west. A
system prognosticated to affect the Pacific northwest early in the week
could bring some rain to the extreme northern part of the state
but our district is expected to remain dry. Medium range models
continue to bring rain chances far enough south to reach our
district by the end of next week. There continue to be differences
in model solutions regarding this potential rain...but indications
are looking more favorable to finally seeing at least some
rainfall across the area by next weekend.
Aviation...as of 10:04 am PST Saturday...for 18z tafs. Skies have
cleared out under offshore flow. Some low level shear off the East
Bay hills is accounted for in koak taf. VFR through tonight. Lower
confidence by Sunday morning as onshore flow may allow return of
Vicinity of ksfo...VFR. Clear skies with moderate offshore winds.
Ksfo bridge approach...similar to ksfo. Low level wind shear
through 21z today.
Monterey Bay area terminals...clear today and tonight. Possible
return of stratus by Sunday morning but low confidence on that.
Marine...as of 10:04 am PST Saturday...generally light northwest wind
and seas are forecast the rest of the weekend and into early next
week with high pressure over the waters.
Public forecast: kbb/Sims
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