Scientific Forecaster Discussion
fxus66 kmtr 110027
Area forecast discussion
National Weather Service San Francisco Bay area
427 PM PST Sat Dec 10 2016
Synopsis...rain will continue to progress to the south through
our region. Some light rain will linger across the central coast
overnight with rapid clearing Sunday for all areas. Increasing
clouds Monday with seasonable temperatures. Rain returns by
Tuesday and may continue on and off for much of next week.
Discussion...as of 3:00 PM PST Saturday...widespread rainfall
across our region has slowly been shifting to the south through
the day today. Rainfall is now mostly confined to San Francisco
southward to around the Monterey County line. Over the next few
hours it will continue to shift with the bulk of the rain
forecast for the southern half of our region. By late tonight
rain will generally be out of the entire County Warning Area with just a few
showers possible over far southern sections.
Rainfall amounts over the past 24 hours have been impressive in
some locations with coastal areas picking up 2 to 4 inches in most
spots with locally more than 5" reported in Marin County. Urban
locations have also done fairly well with many spots between 1/2"
and 1". Please see sfopnsmtr for the entire list of unofficial
Dry weather will return to the San Francisco and Monterey Bay
region for Sunday through Monday afternoon as the moist air overhead
moves to the south. Precipitable water values currently 1"-1.40" will be replaced
by .25" to .65" for both days. This will help to produce cooler
overnight temperatures for tonight and Sunday night.
By Monday evening moist air will return again from the west with
precipitable water values forecast to jump back to the 1" to 1.30" range through
at least Wednesday night as a stationary front sets up from our
region directly to the west. Rain will return to the North Bay
Monday night then down to the sf Bay area Tuesday morning. The
rain will slowly work down to the Monterey Bay region by Tuesday
evening. Rainfall amounts by early Wednesday morning will range
from 1 to 3 inches for the North Bay and Santa Cruz Mountains, to
75" to 1.50" for the sf Bay area with less than .75" for
locations to the south.
Rain will continue through the reminder of Wednesday through
Thursday although models disagree on where the main moisture
plume will be focused. Depending on whether or not the plume
remains nearly stationary or moves through will greatly dictate
how much rainfall we end up getting. Some of the solutions due
produce enough rainfall that Hydro issues would be a possibility.
Needless to say, this will need to be closely monitored.
Aviation...as of 4:20 PM PST Saturday...rain is decreasing over
the area but low-level moisture will keep MVFR cigs in through at
least 06z. Some uncertainty in the forecast late tonight as models
want to dry things out quickly after 06z. Normally the nighttime
cooling allows low cigs to linger through the night but if the
models verify it may clear out sooner.
Vicinity of ksfo...MVFR cigs with rain diminishing. Southwest
winds to 10 kt. Confidence is high that MVFR cigs will linger
through 06z but low to medium after that. Cigs expected to linger
through the night but it may clear out during the night.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...MVFR cigs with vsbys down to 2-3 miles at
times. Rain diminishing after 02z but MVFR cigs lasting through
the night. Confidence is not high after 08z as it may clear out
sooner than expected.
Marine...as of 02:19 PM PST Saturday...winds will continue to
weaken and veer towards the northwest. Increasing southwest winds
will not return until early next week. A small to moderate west to
northwest swell will move through the coastal waters through the
Public forecast: Bell
aviation: west pi