Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Francisco Bay area
1047 PM PDT Friday Oct 31 2014
Synopsis...a slow-moving cold front will continue to produce rain
across Monterey and San Benito counties through Friday evening.
Behind the front...showers and isolated thunderstorms will develop
overnight Friday night...mainly south of San Francisco. Showers
will linger into Saturday. Dry conditions are forecast to return
on Sunday and continue through much of next week as high pressure
builds over the region.
Discussion...as of 8:55 PM PDT Friday...a cold front produced
widespread much-needed rainfall across our region today.
Significant enhancement occurred along the front as it pressed
south into Monterey and San Benito counties this afternoon. The
frontal rain band also slowed considerably as a wave developed along
the front off the central California coast. These developments resulted in
rainfall totals that were opposite of the norm...with heavier
amounts to the south and lighter amounts to the north. Rainfall
totals today across the San Francisco Bay area were generally
between a quarter and a half inch...while areas from Monterey Bay
southward picked up between 0.75 and 1.5 inches. There was one
report of nearly 2 inches of rain near Laguna Seca raceway between
Monterey and Salinas.
The cold-frontal rain band continues to gradually push to the east
this evening and should exit our forecast area entirely by
midnight. Radar and satellite show scattered shower activity
offshore in the cold unstable airmass associated with the upper
trough. There have also been several lightning strikes detected
offshore this evening. A line of showers is currently approaching
the Monterey County coast and latest model data suggest that the
most widespread shower activity overnight will be across the
southern part of our County Warning Area. In fact...the models agree that nearly
all of the showery precipitation tonight and into Saturday will occur
south of the Golden Gate. Thunderstorm chances appear greatest
across our southern-most counties tonight...but the best chance of
thunderstorms will be over the coastal waters where surface temperatures
are warmer and instability greater.
Showers will taper off from north to south late Saturday afternoon
and evening and end by midnight Saturday night. Dry weather will
return to all areas by Sunday as an upper level ridge builds just
offshore. Temperatures will remain cool through the weekend.
The upper ridge will build inland over California and result in a
warming trend during the first half of the work week. Daytime
temperatures are expected to warm above normal by midweek. The ridge will
also keep our area dry through most of the week...perhaps the
entire week. A weak system is forecast to approach northern California
late in the week...but most model data now indicate this system
will remain too far north to bring rain to our area.
Aviation...as of 10:40 PM PDT Friday...showers off the coast in
association with the upper trough. Several lightning strikes have
been detected offshore with more over the San Joaquin Valley.
These showers will be moving inland tonight through Saturday
but most of the showers will be south of the sfo Bay area.
Winds will stay light westerly through tonight then turn more
southerly after 12z.
Vicinity of ksfo...VFR with ceilings remaining above 4000 feet.
Thunderstorms expected to stay south of the approach but cannot
rule out the possibility of a stray thunderstorm getting into the
sfo Bay area after 12z. Winds will be light west switching to the
south after 12z then Switch Back to west Saturday afternoon.
Ksfo bridge approach...similar to ksfo.
Monterey Bay area terminals...lots of shower activity off the mry
Bay will impact mry and sns through Saturday. VFR ceilings
occasionally lowering to MVFR in showers.
Marine...as of 8:55 PM PDT Friday...a frontal system has moved
through the area. An upper level trough behind the system will
bring showers and possibly a few thunderstorms tonight. Northwest winds
will gradually increase Saturday night and Sunday as high pressure
builds behind the trough. Seas of up to 10 feet will develop
creating some hazardous seas for the start of crab season.
Public forecast: dykema
aviation/marine: west pi
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