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

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FXUS66 KMTR 202246
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
246 PM PST Thu Feb 20 2020

.SYNOPSIS...Warming temperatures continue through the end of the
week as the next system passes to the south. A chance of rain is
possible for the Central Coast late Friday into Saturday morning,
though accumulations are forecast to be minimal. The Bay Area
will see dry conditions and mild temperatures are forecast to
continue through next week.

&&

.DISCUSSION...as of 03:00 PM PST Thursday...Another dry and mild
February day is now well underway with increasing high clouds from
the west and slightly warmer temperatures versus this time
yesterday. Current observations are generally running with
temperatures in the mid 60s near the shorelines up to the low 70s
inland, which are about 3-7 degrees above normal.

For tomorrow, 850mb temperatures are forecast to rise by another
1-2C which will directly result in further warming at the surface
by an additional 3-7 degrees (F). Consequently, tomorrow will run
approximately 6-14 degrees above normal, with shoreline
temperatures forecast in the mid to low 70s and up to the mid 70s
farther inland. High clouds will lower and thicken later in the
day and the farther southward a location is.

The primary weather system in the region is a 553dm 500mb low
pressure system approximately 500 miles WSW of San Francisco.
Moist southwesterly flow on the southeastern flank of the low is
responsible for todays increasing high clouds. This system has
trekked roughly 120 miles southward since this morning which is in
line with the varying forecast model trajectories that guide it
into Southern California late Friday into early this weekend. Wrap
around moisture on the north/eastern periphery of the upper low
may bring the first measurable rain of the month for some portions
of Santa Cruz, southern Santa Clara, Monterey, and San Benito
counties as it slides well to our south of our location and into
Southern California. Moderate amount of uncertainty remains on
which areas will pick up any area, with the highest certainty for
the coastal ranges of Monterey (Big Sur) for picking up at least a
hundredth. Elsewhere, areas such as Monterey, Salinas, Hollister,
and the Santa Cruz mountains will be looking in the range of
0.01-0.10", while the peaks of Big Sur could see 0.05-0.50" per
latest ensemble member output. That said, dry ensemble members
remain for all locations, meaning there is still a possibility of
the system coming in slightly farther southward, or weaker/drier
than anticipated, resulting in less or no precipitation for
some/all areas mentioned. Any rain that does fall with this system
would be the first for the area this month, aside from any trace
amounts accumulated during the morning fog events. Winds should
remain light to occasionally breezy with this system.

In the wake of this low passing to our south, a short lived, low
amplitude (weak) high pressure will develop over the area later
Saturday. This will be the driving factor for the increase in
850mb temperatures previously discussed and will also tighten the
pressure gradient, causing locally moderate winds along the coast
and through coastal gaps, such as near KSFO from later Saturday
and throughout Sunday. A low pressure trough will sweep across the
Pacific Northwest late this weekend but will not bring a tangible
impact to the local weather. A broader, higher amplitude high
pressure system will then develop early next week, pushing 850mb
temperatures up to 10-13C from Tuesday through Thursday --
resulting in further dry, mild weather for the region.


&&

.AVIATION...as of 9:34 AM PST Thursday...For 18Z TAFs. VFR
conditions are forecast to prevail through the period with
passing high clouds. Winds are forecast to remain rather light
today.

Vicinity of KSFO...VFR conditions expected with passing high
clouds. Light winds this morning will eventually become
west/northwest this afternoon around 10 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...VFR with increasing high clouds. Light
offshore winds this morning will become onshore later today.

&&

.MARINE...as of 02:00 PM PST Thursday...Light northwesterly winds
are forecast to prevail over the coastal waters today. A low
pressure system will arrive on the Central  Coast on Friday,
bringing with it a chance of light rain to the  waters south of
Point Pinos. Dry weather returns Sunday and  Monday. A moderate
northwest swell persists through the week along with a light
southerly swell.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...None.

$$

PUBLIC FORECAST: DRP
AVIATION: Sims
MARINE: Sims

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