Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1013 am PST Sat Feb 28 2015
Synopsis...a storm system will bring showers and cooler
temperatures to the area through tonight. Another weak system will
bring additional shower chances to the area on Monday.
Discussion...as of 8:20 am PST Saturday...as expected showers
across our County Warning Area this morning have mainly been focused on the
southern third of our County Warning Area. Issued a pns earlier with 24 hour
rainfall totals highlighting amounts up to half an inch in
Monterey County. Koak sounding this morning came across with
lifted values of -.6 and cape near 400 j/kg so the atmosphere is
primed for showers and possible thunderstorms for today. 15z hrrr
is in good agreement with the forecast with keeping most of the
shower activity south of the sf Bay region through the day as the
upper low progresses north to south through our area. Small hail
and brief heavy rain will remain the main risks with minor
snow accumulations likely for elevations over 4000 feet.
Current forecast appears to be generally on track so main focus
will be monitoring radar plus social media and product updates.
Previous discussion...an upper trough continues to sag south
over northern California. Two upper level low centers are rotating
within this trough. Showers associated with the southern-most low
center continue to move southeastward over the coastal waters and
over San Mateo...Santa Cruz and Monterey counties. Measurable
rainfall so far has been limited to Monterey County...Mount Toro
has picked up the most thus far with 0.35 over the last 12 hours.
Expect shower activity to increase today...but continue to be most
numerous across the southern half of the district. Thunderstorms
will be possible today through this evening in this unstable
airmass. Rainfall amounts are expected to be less than one-tenth
of an inch for the sfo Bay area with one- quarter to one-half inch
to the south.
Shower chances will diminish over the sfo Bay area during the
night Saturday but chances will continue south of the sfo Bay
area along with possible thunderstorms and small hail. Snow
levels will lower to around 4000 feet so the higher mountains could
see a dusting of snow. Shower activity is expected to largely end by
Sunday except for residual showers possible over the Santa Lucia
and San Benito mountains.
A second upper level system will move into the area Monday
bringing additional rain chances to the area. Latest computer
models have this system tracking quickly southward along the coast
with precipitation exiting the district by Tuesday morning. Temperatures
will remain cool through early next week. High pressure is
prognosticated to rebuild over the West Coast from midweek on. This will
usher in a warming and drying trend. Will build back to our region
Wednesday as the storm track move
Aviation...as of 10:00 am PST Saturday...a storm system moving
across the forecast area today will bring showers to area
terminals through this afternoon. Wet runways are expected through
the evening rush. Showers will be periodic in nature with a slight
chance of isolated thunderstorm this afternoon.
Vicinity of ksfo...vicinity showers with intermittent period of
moderate showers expected through the afternoon. Ceilings will
remain VFR with occasional MVFR during periods of heavier showers.
Westerly winds of 10 to 15 knots are expected to prevail through the
Confidence is moderate.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...periods of light to moderate showers
are expected through the day today. Ceilings will remain VFR with
occasional MVFR during periods of heavier showers. Variable winds
will turn westerly to around 10 knots this afternoon.
Confidence is moderate.
Marine...as of 8:49 am PST Saturday...a storm system will
continue to move over the coastal waters today with showers and
isolated thunderstorms...mainly south of Point Reyes. Northerly
winds will decrease throughout the day as the center of the storm
system passes by. The decreasing winds will result in improving
sea conditions overnight into Sunday. Northerly winds will
increase once again Monday as the surface pressure gradient
... Arena to pt Reyes 10-60 nm
Small Craft Advisory...pt Reyes to Pigeon pt 10-60 nm until 3 PM
Small Craft Advisory...Pigeon pt to pt pinos 10-60 nm until 3 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm until 3 PM
Public forecast: Bell/Sims
aviation/marine: CW/rain shower
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