Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service San Francisco Bay area
434 am PDT Wednesday Apr 16 2014

Synopsis...dry conditions will continue through the weekend.
Patchy fog and clouds near the coast will become more extensive
Thursday night and Friday as a weak weather system moves onshore.
A stronger low pressure system will arrive late Monday and Tuesday
bringing a threat for showers...cooler temperatures...and gusty
winds.

&&

Discussion...as of 03:53 am PDT Wednesday...tonights viirs
satellite imagery around 230 am showed patchy low clouds near
Monterey Bay and Salinas valley. Latest GOES fog product imagery
indicating stratus has become a little more widespread in the
Salinas valley...near Half Moon Bay...and Monterey Bay the last
couple hours. Breezy northwest winds over the open waters have
kept the boundary layer well mixed and confined stratus to
convergence and upslope areas near the coast favored by northwest winds.

Short wave ridge will progress eastward across the state
today...keeping the marine layer under 1500 feet. Surface pressure
gradients will remain strong from the northwest to southeast with
sfo-acv over 6 mb today and winds will remain at least breezy over
the open waters. Hrrr model surface relative humidity field indicates limited
stratus again today. As the ridge shifts eastward the flow will
become more onshore Thursday with a better established marine
layer...so expect extensive stratus to return to coastal areas by
Thursday morning.

A weak trough in zonal flow will approach the coast Thursday night
deepening the marine layer and increasing onshore flow. This trough
splits over the area Friday...and the lack of upper level lift
should keep conditions dry. Cooler air aloft with 850 mb
temperatures dropping to 10 degree c should disrupt the marine layer
Friday but spread cooler air inland with continued onshore flow.

After a brief break Saturday under weak high pressure and mostly clear
skies...another minor system will brush by to the north of our area
Sunday with more coastal clouds.

A stronger trough will drop over California late Monday and Tuesday
bringing a threat for showers and much cooler conditions with
gusty winds. Forecast models are consistently advertising this
stronger system...and even though the system lacks a significant
moisture tap...cold air aloft will be plentiful and showers are
certainly possible especially over the mountains.

&&

Aviation...as of 4:30 am PDT Wednesday...satellite imagery shows
patchy low clouds in mry Bay and in the Salinas valley and along
the San Mateo coast this morning. Strong north-S pressure gradient indicates
dry northerly flow that will keep clouds out of the sfo Bay area
today.

Vicinity of ksfo...VFR. West afternoon winds to 20 knots after 20z.

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...MVFR ceilings through 17-18z.

&&

Mtr watches/warnings/advisories...
... Pt to pt pinos 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
glw...pt Arena to pt Reyes 10-60 nm
glw...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
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...Monterey Bay from 1 PM

&&

$$

Public forecast: kbb
aviation: west pi

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