Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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FXUS66 KMTR 260102 AAA

Area Forecast Discussion...UPDATED
National Weather Service San Francisco Bay Area
502 PM PST Sun Feb 25 2018

.SYNOPSIS...A cold front is forecast to sweep from north to south
through the region late Sunday night and Monday morning, bringing
a brief period of rain. Scattered showers and possible
thunderstorms are then expected behind it along with locally
breezy conditions. A stronger and wetter storm system will bring
widespread precipitation to the region Wednesday night through
Thursday, with showers continuing through at least Friday.


.DISCUSSION...As of 2:00 PM PST Sunday...Offshore flow combined
with mostly sunny conditions has lead to seasonably comfortable
readings this afternoon with many places running 3 to 8 degrees
ahead of Saturday. Temperatures will likely peak in the upper 50s
to the mid 60s for almost all spots.

A weak system to our north-northwest will quickly drop down into
our region starting tonight and bring rain back into the picture. Models
are in generally good agreement and have been fairly consistent
run-to-run. Timing has precipitation starting in the North Bay
late this evening and then down to the San Francisco Bay Area
close to morning rush. The system will progress southward into the
Monterey Bay Region by later Monday morning or early in the
afternoon. Rainfall amounts will be light -- generally under 1/4"
outside of higher elevation spots. Even the typical wet spots
should stay under 1/2" for the system.

Behind it and the associated cold front, cooler northwesterly
winds will move across as the atmosphere starts to destabilize.
Synoptically, it`s a fairly classic thunderstorm setup for our
region as the center of the cold core low quickly moves through
Monday afternoon and evening. Small hail and a slight chance of
thunder was added to the forecast. With snow levels locally
dropping to around 2,000 feet, many higher elevation spots could
see a dusting of snow. Gusty northwesterly winds of 15 to 25 mph
will be common. Even higher numbers potentially gusting to over 40
mph can be expected along the coast.

Cool and quiet weather returns by Monday night extending into the
first part of Wednesday. Overnight lows will once again drop into
the 20s and 30s for many areas. Many metro locations will see
lows in the 30s with highs just in the mid 50s to the lower 60s.

A much more potent system will track down the west coast and bring
widespread rainfall back to our region starting late on Wednesday
and continuing through Thursday. IVT values are not that
impressive (GEFS maxes out around 500 kg/m/s while the mean only
gets to around 350), so potential for high rain rates looks very
limited. Overall look for 1/2" to 1.5" in most spots with isolated
mountain areas picking up more than 2" from the main round of

Wind will once again increase due to the approaching cold front
with the strongest speeds likely late Wednesday night into
Thursday morning. Gusts over 30 mph look likely with local values
over 40 mph possible. A wind advisory will be considered as the
event gets closer. Showers will quickly return as an associated
front moves through later on Thursday with another shot of cooler
air. Showery conditions will continue into Friday. Additional
rainfall will generally be light behind the front -- under 1/2".

Worth noting that we have not had a substantial rain event in our
region since January 8th, and for the water year we have only had
one other (November 16th) event. Most locations are at least 5
inches drier than normal, so the system on Thursday will be
helpful, it will not be enough to bring us to where we should be.

&& of 4:20 PM PST Sunday for 00Z TAFs. Looks like
mainly clear skies for this evening through about 03-05z with
onshore winds at the terminals. Clouds will thicken and lower
overnight with mvfr conditions likely by 12-14z. Front will be
fast moving and drop rain on all the terminals Monday morning.
However fast moving nature should allow for precip to quickly turn
showery by around 18z with winds turning nw. Shower threat and
some mvfr cigs with continued nw flow Monday afternoon.

Vicinity of KSFO...West winds this evening with latest trends
suggesting low cigs will hold off until after the evening rush,
likely around 05z or so. Rain and low cigs to start the day Monday
between 12-15z. Precip turns showery by 18z with gusty nw post-
frontal flow developing.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR this evening. Cold front arrives
around 15z Monday with periods of rain before turning showery with
nw winds Monday afternoon.

&& of 03:43 PM PST Sunday...Moderate northerly winds
will continue over the coastal waters as high pressure resides
over the eastern Pacific. Late tonight and  Monday, a storm system
will drop southward through the area bringing rain, increasing
winds and building fresh swells. Strong N to NW  winds behind it
are expected to reach gale force over at least the northern outer


     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm from 10 PM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 1 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 4 AM
             SCA...Mry Bay until 9 PM




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