Scientific Forecaster Discussion
fxus66 kmtr 260946
Area forecast discussion
National Weather Service San Francisco Bay area
246 am PDT Fri may 26 2017
Synopsis...deep marine layer with nearly all areas starting the
day cloudy which will keep temperatures on the cool side of normal
today. Saturday will trend back towards seasonable temperatures as
high pressure begins to build. Dry and warmer Sunday and Monday.
Another trough begins to approach by Tuesday and Wednesday with a
modest cooling trend and continued coastal clouds.
Discussion...as of 2:46 am PDT Friday...profiler data shows the
marine layer is very deep, around 4000 feet with fairly cool
temperatures aloft. This has allowed higher based marine clouds to
spread over nearly all locations in the district. The sfo to SAC
gradient is weaker this morning at 1.2 mb onshore with lighter
winds most locations. Nonetheless the widespread clouds and upper
trough just to our east will once again keep temperatures on the
cool side of normal today, especially inland.
The trough axis nudges inland over the Great Basin while high
pressure begins to build Saturday. This will allow inland
temperatures to trend back closer to normal with more readings
into the 70s vs the cool 60s forecast for today.
High pressure continues to build Sunday with inland areas warming
back into the 70s and lower 80s. So pleasant weather for the
upcoming Holiday weekend with no real hot weather to contend with
but still warm enough to use the pool. Beaches will remain cool
with onshore flow in place. SST have trended a few degrees warmer
the last few days as stronger NW winds have eased allowing SST to
warm back into mid 50s and in turn keep overnight lows a little
more mild near the coast and coastal valleys.
It'll stay seasonably warm inland for Memorial Day with inland
highs from the mid 70s to mid 80s. The beaches will stay in the
upper 50s and 60s as another trough will approach by Monday
afternoon with increasing onshore winds. The models almost want to
generate some qpf around the middle of next week with the next
trough but that seems dubious at this time so will keep the
forecast dry. Trend should be for cooling back to seasonable norms
Tuesday and weds with longer range ECMWF wanting to build a warm ridge
the second half of next week.
Aviation...as of 10:40 PM PDT Thursday...a deep marine layer and
southerly low level onshore flow will maintain widespread MVFR
ceilings across the region overnight and into Friday morning.
Low clouds are expected to scatter out in most areas by late
Friday morning or early Friday afternoon. Winds will generally be
light from the south and southwest.
Vicinity of ksfo...MVFR ceilings expected to develop by 07z and
continue until about 17-18z Friday. However, southerly flow over
the Santa Cruz Mountains may result in sufficient downslope
warming and drying to delay development of low clouds and lead to
earlier clearing on Friday. Light southwest winds overnight and
into Friday morning, increasing in the afternoon.
Sfo bridge approach...similar to ksfo except likely earlier
development of ceilings this evening.
Monterey Bay terminals...MVFR ceilings expected overnight and
through Friday morning with likely VFR conditions during Friday
afternoon, followed by early return of low clouds Friday evening.
Light south to southwest winds.
Marine...as of 02:24 am PDT Friday...light onshore flow and
moderate seas expected through tonight into Friday. Winds will
increasing over the Memorial Day weekend as high pressure
redevelop over the eastern Pacific.
Public forecast: rww
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