Scientific Forecaster Discussion
fxus66 kmtr 220422
Area forecast discussion
National Weather Service San Francisco Bay area
922 PM PDT Fri Jul 21 2017
Synopsis...temperatures will continue to warm into the weekend as
an upper level ridge of high pressure strengthens over California.
Temperatures will moderate next week as the ridge progresses to
Discussion...as of 9:20 PM PDT Friday...our expected warming
trend got off to a very tentative start today as afternoon highs
in most locations were only a few degrees warmer than yesterday.
Warming is expected to be more robust on Saturday as the upper
ridge centered over the Desert Southwest continues to build to the
west and over California. The marine layer, currently at a depth
of about 1500 feet per Fort Ord profiler data, is expected to
compress by tomorrow and the overlying airmass is forecast to warm
by a couple of degrees c. In addition, models indicate that winds
near the top of the boundary layer will veer from westerly to
northerly by tomorrow morning which should help bring drier air
into the lower levels by then. Our current forecast calls for
warming of about 5 to 10 degrees tomorrow, which seems about
right. Afternoon highs tomorrow will warm into the 90s in the
inland valleys and in the hills above 1000 feet. Meanwhile,
continued onshore surface flow will keep coastal areas seasonably
cool with highs mainly in the upper 60s and 70s. Late night and
morning low clouds are expected to remain patchy in the short-
term, and confined mainly to areas near the coast.
Although the airmass over our region is forecast to remain warm
going into Sunday, the development of southerly flow by then will
mean at least slight cooling for most locations during the second
half of the weekend, with more significant cooling expected in
locations such as the North Bay valleys and coastal Santa Cruz
Warmer weather this weekend will raise heat risks into the
moderate category for many inland areas, especially on Saturday.
However, we are not expecting temperatures this weekend to be
nearly as oppressive as last weekend.
An upper level low is forecast to develop just off the northern
California coast by late Sunday, remain there through Monday, and
then shift inland across northern California by late Tuesday or
Tuesday night. At the same time, the upper ridge will retreat to
the east. These developments will result widespread cooling
across inland areas during the first few days of the work week.
Temperatures are then expected to warm gradually during the second
half of the week.
Southerly flow late in the weekend and into the early part of next
week may bring mid/upper level monsoon moisture over our area.
Due to model inconsistencies, there is currently a quite a bit of
uncertainty as to whether this moisture will make it far enough
west for any chance of showers/thunderstorms in our area. The 00z
NAM keeps the bulk of the monsoon moisture and mid level
instability to our east, but it's certainly close enough to watch
carefully for any signs this may shift farther to the west.
Aviation...as of 4:45 PM PDT Friday...similar conditions to
yesterday with the marine layer near 1000 feet and a strong N-S
gradient keeping skies clear along the coast. Stratus clouds will
reform late along the coast and will spread into the mry Bay area
terminals and through the Golden Gate into Oak and possibly sfo
early Saturday morning.
Vicinity of ksfo...VFR. Possible MVFR cigs between 13z and 16z.
West winds gusting to 28 kt through 04z.
Sfo bridge approach...similar to ksfo.
Monterey Bay terminals...IFR cigs after 10z.
Marine...as of 01:30 PM PDT Friday...gusty northwesterly winds
will continue into Saturday before decreasing somewhat during the
remainder of the weekend as high pressure off the California
coast begins to weaken.
... Arena to pt Reyes 0-10 nm
Small Craft Advisory...pt Arena to Pigeon pt 10-60 nm
Small Craft Advisory...Pigeon pt to pt Piedras Blancas 10-60 nm
Small Craft Advisory...pt pinos to pt Piedras Blancas 0-10 nm
Small Craft Advisory...pt Reyes to Pigeon pt 0-10 nm until 3 am
Public forecast: dykema
aviation: west pi
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