Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1057 PM PDT Friday Aug 29 2014
Synopsis...normal to slightly above normal temperatures and dry
weather will persist through the Holiday weekend.
Discussion...as of 9:25 PM PDT Friday...middle and high level
clouds continue to shear eastward from the remnants of tropical
cyclone "marie" as the entire system moves higher in latitude. The
00z Oakland sounding showed the total precipitable water value
also increasing to 0.98" this evening up from 0.70" 24 hours ago.
All the extra clouds in the sky today made for picturesque
conditions and a decent finale with a colorful sky right at
As the remnants of"marie" continue to meander north in latitude
the middle-upper level circulation center will detach and move with
the middle-latitude westerlies then merge with a shortwave trough from the
higher latitudes. The newly merged system will pass over northern
California next Wednesday into Thursday. The surface to low level
circulation will meander and diminish over the Pacific sending
higher tpw air north in latitude eventually north over the epac
ridge with some of this more humid air possibly returning
southeast over the offshore waters by late next week or weekend.
Recent runs of the Gem...GFS and European model (ecmwf) models show some spotty
light quantitative precipitation forecast...a few hundredths here and there...over the forecast
area from Wednesday-Thursday fitting the time frame when the aforementioned
middle-upper level circulation passes over norcal. The models show it
to be stratiform precipitation not convective which seems to fit the
scenario as the models do not show very much humidity below 500 mb
on the cross-sections therefore chances for middle level convection
appear to be near zero percent. It's not in our forecasts
currently but if subsequnet model runs show very light quantitative precipitation forecast in
similar Wednesday-Thursday timeframe...we may need to think about adding low
end chance probability of precipitation for the middle-later part of next week.
Middle to upper level troughing will continue over northernmost California
and the Pacific northwest into late next weekend. This will be followed
by a strengthening closed high over the Gulf of Alaska by days 9 or
Aviation...as of 10:45 PM PDT Friday...middle and high clouds are
obscuring the coastal stratus coverage at the moment. Model forecasts
indicate additional stratus redevelopment overnight but there is also
an appreciably drier layer developing just above the marine inversion.
This drier layer should help mix out the stratus clouds fairly
quickly Saturday morning.
Vicinity of ksfo...VFR has been holding through the evening so
far. Taf indicates broken ceiling by 07z which may be a bit early but
confidence in forecast lower tonight due to obscured lower cloud
field. Moderate to high confidence VFR forecast for Saturday.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...there has been scattered-broken cloud cover
so far this evening. IFR is forecast tonight. The stratus clouds
should mix out by late Saturday morning.
Marine...as of 2:50 PM PDT Friday...high pressure will build off
the northern California coast resulting in increasing northwest
winds that will last through early next week. Residual southerly
swell from Hurricane Marie will continue to diminish.
... 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 pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm
Public forecast: canepa
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