Scientific Forecaster Discussion
fxus66 kmtr 300355
Area forecast discussion
National Weather Service San Francisco Bay area
855 PM PDT Sat Apr 29 2017
Synopsis...sunny and seasonably warm weather will continue across
our region through the remainder of the weekend. Another round of
offshore winds is forecast during the first half of the work week,
which will push temperatures even warmer from Monday through
Wednesday. A cooling trend is then forecast next Thursday and
Friday as the upper ridge over California is replaced by a trough.
Discussion...as of 8:55 PM PDT Saturday...a building upper ridge
offshore brought a warmer and drier airmass into our region today.
Highs today were 5 to 10 degrees warmer than yesterday and ranged
from the 70s to lower 80s in most locations, values that were
about 10 degrees warmer than normal.
The upper ridge centered offshore along 135w is forecast to
continue edging slowly to the east for the remainder of the
weekend, and the airmass aloft over our area is expected to
continue to warm. However, surface gradients have turned slightly
onshore this evening and the incoming marine air will probably
offset the overall airmass warming under the ridge. The net result
for temperatures tomorrow will likely be persistence. The upshot
is that Sunday will probably be a day much like today. Although
light onshore flow has developed this evening, the boundary layer
remains very dry and it's unlikely there will be any coastal fog
or low cloud development.
Surface high pressure is forecast to strengthen to our north and
east by late Sunday night. This will set the stage for another
round of offshore flow across our region from late Sunday night
through midweek. Gusty north winds are likely in the hills from
late Sunday night through Tuesday night, mainly during the late
night and morning hours when local gusts up to 30 mph are
possible. This offshore flow will bring a drier airmass into our
area once again. At the same time, the upper ridge offshore will
gradually shift inland, warming the airmass over our area further.
850 mb temperatures, which were at 12 degrees c over Oak today,
are forecast to climb as high as 19 c by Wednesday. These
developments will result in a warming trend during the first half
of the work week with widespread 80s expected by Tuesday and
Wednesday and a few lower 90s likely in the warmest inland areas.
Coastal areas will mostly see high temperatures in the 70s, but
lower 80s are possible in San Francisco, especially on Wednesday.
Temperatures during the first half of the week will be the
warmest of the year so far.
The models agree that that an upper trough will approach the West
Coast later in the week, resulting in robust cooling on Thursday
Aviation...as of 5:23 PM PDT Saturday...it's a gorgeous afternoon,
not a cloud to be seen. VFR tonight and Sunday. There is the chance
for patchy coastal low stratus and fog to develop much later tonight,
but confidence in its development is low at this time, will monitor
it through the evening. The acv-sfo pressure gradient is 5.6 mb and
forecast to reach 7 mb to 8 mb tonight and Sunday as a surface ridge
edges in over far northwestern California. If stratus and fog do
develop it would quite likely either brush the immediate coastline
at times or parallel the coast staying just offshore under a stronger
northerly wind and trapped beneath strengthening marine inversions.
The wmc-sfo gradient will be increasing later Sunday into Monday
morning which may tend to push the surface thermal trough over
interior California to the coast in which case these conditions
would strongly favor VFR to continue from later Sunday into Monday.
Vicinity of ksfo...VFR. Westerly wind gusts to 25 knots til 04z
this evening, lighter winds tonight. Westerly winds become gusty
again Sunday afternoon and evening. Near high confidence.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...VFR. Westerly winds becoming light later
this evening. Boundary layer rhs increase to near 100% very early
Sunday morning along the immediate coastline along the southern
Monterey Bay area to the Carmel Highlands per latest WRF model
run, it may be overdone in tonight's case, but will monitor it.
Marine...as of 8:50 PM PDT Saturday...high pressure will
continue to bring strong, gusty northwest winds to the coastal
waters this evening. The strong winds will drive hazardous seas in
the form of steep fresh swells with relatively short periods.
Strong winds will continue through the weekend and into early part
of next week.
... Pt to pt pinos 0-10 nm until 3 am
Small Craft Advisory...pt Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...mry Bay until 9 PM
Public forecast: dykema
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