Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service San Francisco Bay area
919 am PDT Thursday Apr 24 2014

Synopsis...a storm system will bring cooler temperatures and
chances for precipitation to the region late Thursday night
through Friday. Another weaker system could bring rain chances to
northern California Saturday night and Sunday. Then high pressure
will bring dry and significantly warmer conditions to the area
next week.

&&

Discussion...as of 9:19 am PDT Thursday...active weather through
the entire forecast period with rain...thunderstorms...poss patch
frost Saturday morning and the first real warm up of the season
next week.

First and foremost...a cold front is entering norcal as we speak.
Rain is currently being reported in Arcata. For the Bay area...mix
of sun and clouds ahead of the approaching front today. By this evening
the front is forecast to push south into the North Bay late this
evening with light rain spreading north-S overnight. Behind the
front...the upper trough swings through the County Warning Area on Friday with
much colder air aloft. In addition to the cold air advection aloft...a jet maximum
moves overhead as well. That being said...the current forecast for
thunderstorms on Friday still seems plausible. For what it/S Worth
model guidance has very little cin and a few hundred cape...Li/S
less than 0c and steepening lapse rates for Friday
afternoon/evening. Storm Prediction Center included much of the
North County warning area in a general risk for convection as well. The chances for
thunder quickly diminishing Friday night into Saturday as the
atmosphere begins to stabilize. Given the cold air aloft storms
that do develop will be capable of producing small hail. Overall
rainfall will be rather light with a few tenths to possible a half
inch in the high spots. Clearing will occur Friday night into
Saturday morning...which produces a new concern...cold temperatures
Saturday morning. MOS guidance suggests temperatures Saturday morning
across the North Bay in the middle 30s. A few of the cold/protected
valley may even approach freezing. This could be problematic given
that plants could be blooming/budding.

For the second half of the weekend things continue to be
interesting as another weak boundary moves through. Still some
uncertainty with the southern extent of precipitation...but latest models
drag at least some precipitation through the much of the County Warning Area. Persons
with outdoor activities Sunday morning may get wet with light rain
and/or drizzle...especially coastal locations. Will likely fine
tune the forecast and increase coverage/chances for precipitation early
Sunday morning.

Now onto next week...model guidance and pattern recognition is
shaping up to show the first real warm up of the season. Latest
guidance has several days of of above normal temperatures with
many interior locations in the 80s and 90s.



&&

Aviation...as of 4:35 am PDT Thursday...mostly clear skies are
being reported around the forecast area this morning. GOES-west MVFR
probability image is showing stratus along the coast this morning.
This makes sense since Halfmoon Bay is reporting bkn013 at this
hour. The Fort Ord profiler is indicating a very shallow marine
layer less than 200 feet deep with a fairly well mixed atmosphere
above. Therefore...stratus is not expected to impact the Monterey
and Salinas terminals tonight. In the sf Bay area the sql sodar
does show evidence of a marine layer approximately 1000 feet deep.
Therefore cannot rule out stratus as a sun rise surprise for koak
and ksfo.

Vicinity of ksfo...VFR is expected to prevail this morning with a
slight possibility of stratus impacting the terminals tempo
2412/2416 bkn005 bkn012. MVFR is anticipated by 0300z with a light
shower. West winds will increase to 15 to 20 knots this afternoon
with gusts to 25 knots possible.

Confidence is moderate

Ksfo bridge approach...similar to ksfo.

Monterey Bay area terminals...VFR is expected this morning with
MVFR expected to begin around 0300z. Light showers are anticipated
to begin around midnight. Winds will increase out of the west this
afternoon reaching 10 to 15 knots.

Confidence is high

&&

Marine...as of 04:39 am PDT Thursday...generally light west to
northwest winds will prevail along the central coast into the
weekend. However...winds will be locally stronger south of Point
Sur through tonight. A mixed swell will enter the coastal waters
Friday featuring a moderate sized medium period westerly swell and
a long period southerly swell. The mixed swell will last into the
weekend.

&&

Mtr watches/warnings/advisories...
... Francisco Bay north of the Bay Bridge from 2 PM
Small Craft Advisory...San Francisco Bay south of the Bay Bridge from 2 PM
Small Craft Advisory...Monterey Bay from 2 PM
Small Craft Advisory...Pigeon pt to pt pinos 0-10 nm from 2 PM
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 10-60 nm

&&

$$

Public forecast: mm
aviation/marine: Larry

Visit US at www.Weather.Gov/sanfrancisco

Follow US on facebook, twitter, and youtube at:
www.Facebook.Com/US.Nationalweatherservice.Sanfranciscobayarea.Gov
www.Twitter.Com/nwsbayarea
www.Youtube.Com/nwsbayarea