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

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FXUS66 KMTR 111119
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
419 AM PDT Tue Aug 11 2020

.SYNOPSIS...A slight cooling trend will continue today,
especially across the interior. Meanwhile, little change is
anticipated near the coast with the typical ebb and flow of low
clouds each night/morning. A warming trend is forecast to begin on
Wednesday and continue through the end of the week and into the
weekend.

&&

.DISCUSSION...As of 2:00 AM PDT Tuesday...Coastal profilers at
both Bodega Bay and Fort Ord indicate a slight deepening of the
marine layer over the past 24 hours. In addition, onshore surface
pressure gradients have increased. These developments are in
response to an upper trough settling into the Pacific Northwest
and weakening the ridge over California a bit. This process will
continue today and result in another 3 to 7 degrees of cooling,
with most cooling expected across the interior.

As the upper trough to our north shifts to the east on Wednesday,
surface high pressure will build off the northern California
coast, resulting in a return to more typical northwesterly surface
winds by Wednesday afternoon. These northwest winds may increase
sufficiently by afternoon to sweep low clouds away from the coast
north of the Golden Gate by late in the day. In addition,
increasing north-to-south surface pressure gradients will limit
onshore flow to some extent on Wednesday, which will result in the
start of a warming trend for much of our area.

The warming trend is then expected to continue through the
remainder of the week and into the upcoming weekend as an upper
ridge over the Desert Southwest gradually expands west and
northward across California. High temperatures in our warmest
interior valleys will climb to around 100 by Friday, with
additional warming possible over the weekend. Surface flow is
forecast to remain onshore and thus coastal areas will
experience less robust warming. But the marine layer will likely
compress to a depth of less than 1000 feet by late in the week,
allowing temperatures to warm into the 80s not all that far
from the coast, while 90s will be common in the coastal valleys
and hills by late in the week. Heat Risk is currently projected to
remain mostly in the moderate category, but scattered areas of
high Heat Risk are projected in the interior valleys and hills by
Friday and on into the weekend.

Remnant moisture from Hurricane Elida is forecast to be drawn
northward around the western periphery of the Desert Southwest
high and across the southern portion of our forecast area by late
Thursday and Thursday night. This moisture plume is then forecast
to lift northward across much of the rest of our forecast area by
early in the weekend. Additional moisture from a second tropical
system may then arrive over our area by early next week. Models do
not generate precipitation over our area from this moisture, and
the model blend currently keeps thunderstorm chances at less than
10 percent. In any case, this moisture and any possible mid-level
instability will need to be monitored closely due to the
potential for significant impacts if dry lightning were to
develop.

&&

.AVIATION....as of 4:20 AM PDT Tuesday...Marine layer has
deepened slightly but the stratus pattern and pressure gradients
are similar to yesterday. Little change expected today with
stratus clearing by 17Z.

Vicinity of KSFO...Becoming IFR after 12Z with bases 800-1000 ft.
Clearing after 17Z. Northwest afternoon winds to 15 kt.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...LIFR ceilings with occasional vsbys down
to 5 miles. Clearing after 17Z.

&&

.MARINE...as of 02:46 AM PDT Tuesday...A 1030 mb high centered
1300 miles west of Cape Blanco will move slowly closer to the west
coast through weaken on Friday as a low pressure system develops
in the Gulf of Alaska. Northwest winds will increase today through
Thursday before decreasing on Friday.  Mixed seas will continue
through the period with a short period  northwest swell and a
longer period southerly swell. Southerly  swell will increase
Tuesday and Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...SCA...SF Bay from 2 PM

&&

$$

PUBLIC FORECAST: Dykema
AVIATION: W Pi
MARINE: W Pi

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