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

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FXUS66 KMTR 242131
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
231 PM PDT Sat Aug 24 2019

.SYNOPSIS...High pressure will bring a fairly seasonable weather
pattern to the Bay Area this weekend into early next week. The
marine layer will persist along the coast along with onshore flow
keeping temperatures warm near the coast and bays. Inland
temperatures will trend hotter as the strong high pressure builds.
Remnants of Tropical Storm Ivo will pass offshore Tuesday and
Wednesday with increasing clouds and higher humidity developing.

&&

.DISCUSSION...as of 2:31 PM PDT Saturday...After an overcast
morning for many, GOES-West visible imagery reveals mostly clear
skies for most land areas throughout the region this afternoon.
Locations along the immediate Pacific coast are still experiencing
cloudiness, including coastal Sonoma and Marin Counties, parts of
San Francisco, coastal San Mateo and points south through
Monterey County. 1-minute imagery shows the low clouds pushing
through the Golden Gate from Alcatraz to Treasure Island as the
onshore gradients from San Franciso to Sacramento are around 2
millibars.

A broad 594 dm ridge at 500 mb located off the California coast
continues to be the main synoptic feature for our area. This
morning`s 12Z upper air sounding at Oakland measured the 500 mb
height at 593 dm, ranking climatologically for this day in the
99th percentile. Ordinarily this would start to raise concerns
about excessive heat; however, the temperature at 850 mb was only
21.4 deg C, ranking around the 75th percentile climatologically.
For comparison, earlier in August when much of the interior
recorded highs near or above 100 deg F, 850 mb temperatures were
in the 24-25 deg C range. These "cooler" temperatures at the low
levels combined with onshore flow will together prevent widespread
upper 90s to 100s from becoming realized for the interior. Highs
will instead warm to the 80s and some 90s this afternoon,
particularly in the region`s hottest areas. Temperatures along the
immediate coast will hold in the upper 60s to 70s. Compared to
yesterday, high temperatures will likely be a few or several
degrees cooler.

Over the rest of the weekend and into early next week, 850 mb
temperatures are forecast to gradually warm as the ridge remains
just off the California coast. We`ll likely see the marine layer
compress as well, which will generally prevent widespread the
inland intrusion of the morning stratus. Inland temperatures are
expected to warm day-to-day with widespread 90s more likely by
Monday. Locations such as Pinnacles National Park and the far
North Bay near Lake Berryessa and Cloverdale will likely be near
100 degrees. For late August, these values correspond to low to
moderate heat risks. Coastal communities will continue to benefit
from the marine-cooled air with little or no heat impacts
anticipated.

We`re continuing to keep a close eye on Tropical Storm Ivo,
presently located about 420 miles west of the southern tip of the
Baja Peninsula. Ivo is forecast to continue its northward
trajectory over the next several days, weakening as it encounters
cooler waters. Moisture from what will be the remnants of Ivo will
advect towards California around the Tuesday-Wednesday timeframe.
Models generally keep the bulk of the moisture off the mainland
for most of Tuesday, but by late Tuesday and into Wednesday, the
latest runs of the ECMWF and GFS bring increased mid/upper level
RHs and even some instability closer to home. The tail end of the
latest run of the NAM is beginning to capture our time frame of
interest, and over the next 24 hours, we should be able to get a
better idea with the potential for convection over our area. At a
bare minimum, we should expect increased mid/high clouds as the
remnants approach the region. Stay tuned for more details...

&&

.AVIATION...As of 10:53 AM PDT Saturday...For 18Z TAFS. The
marine layer remains around 1500-2500 feet near the coast.
Conditions are improving across the area with VFR expected at all
terminals within the next hour. Winds this afternoon will turn
onshore and increasing to 10-15 kt during the afternoon. Stratus
will likely reform overnight impacting most terminals by Sunday
morning.

Vicinity of KSFO...VFR through today and most of the overnight
with winds increasing to near 15 kt during the afternoon. Stratus
to reform by Sunrise tomorrow.

SFO Bridge Approach...MVFR cigs until 1730Z, otherwise similar to
KSFO.

Monterey Bay Terminals...VFR. IFR cigs returning by 03-04Z.
Northwest winds to 10 kt during the afternoon.

&&

.MARINE...as of 8:26 AM PDT Saturday...Light northerly winds will
persist over the northern outer waters while light southwesterly
winds will develop elsewhere through the weekend. Steep, short
period northwesterly swell will continue to decrease through the
weekend with periods becoming 7 to 8 seconds. Moderate period
southerly swell will increase to 2 to 3 feet on Sunday and persist
through early next week with light to moderate period
northwesterly swell continuing through the period.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pigeon Pt 10-60 nm from 10 PM

&&

$$

PUBLIC FORECAST: Rowe
AVIATION: Sims
MARINE: Sims

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