Scientific Forecaster Discussion
fxus66 ksgx 291500
Area forecast discussion
National Weather Service San Diego California
800 am PDT Mon may 29 2017
a low pressure trough along the West Coast will bring slow deepening
of the marine layer into Wednesday, with nocturnal marine clouds
and patchy fog spreading a little farther into the valleys each day.
Slightly cooler today, with greater cooling midweek. Warmer again
into the weekend under a weak high pressure ridge aloft, then cooler
early next week as a trough redevelops.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Marine clouds were more extensive inland this morning. Satellite
imagery and sfc observations indicate some penetration into southern
portions of the inland Empire and over much of western San Diego and
Orange counties. However, high clouds drifting east off the Pacific
were limiting their detection by 8 am PDT. These higher clouds
extended up to 250 miles west of San Diego. The morning Miramar
sounding indicated a moist layer and near saturation below 2500 feet
msl, topped by a Ten Degree c inversion. Cooling of up to 3 degrees
c was indicated below 5k ft, along with a continuation of weak
northerly flow. East winds had increased above, from 6k-10k feet at
15-20kt. Moderate onshore sfc pressure gradients to the lower
deserts were supporting peak wind gusts 25-30 miles per hour through and below
the desert passes.
Expect slightly cooler weather today west of the mts based on the
sounding, and perhaps the high clouds, if they are thick enough to
affect the insolation. The marine clouds may be slow to clear
coastal areas due to the strong inversion and to a lesser extent,
the high clouds. Suspect clearing over the western valleys and coast
will become more elusive as the week progresses. No forecast changes
at this time.
From previous discussion...
Short term (today through wednesday)...
a developing weak trough of low pressure near the West Coast will
bring slow deepening of the marine layer into Wednesday with areas
of night and morning coastal low clouds and patchy fog spreading
farther into the valleys each night.
Early this morning...satellite imagery shows widespread stratus
over the eastern Pacific extending inland to the western valleys.
There are also some high clouds spreading into Southern California
ahead of a weak trough of low pressure off the California coast.
The low clouds will clear back toward the coast this morning...but
with somewhat less and slower clearing expected for the beaches
than on Sunday afternoon...especially for central and southern San
Diego County. By Tuesday night into Wednesday morning...the low
clouds are expected to extend into the far inland valleys and
possibly onto the lower coastal mountain slopes.
Slow cooling will begin to spread inland today with cooling
continuing into Wednesday with inland high temperatures on
Wednesday around 5 degrees below average.
Long term (thursday through sunday)...
weak high pressure aloft will bring slow warming for Thursday and
Friday with inland high temperatures on Friday returning to near
average. The marine layer will become a little shallower with night
and morning coastal low clouds not extending as far into the
valleys. For next weekend through early next weekend...a trough of
low pressure moving inland to the north will bring slow cooling
and slow deepening of the marine layer.
291445z...coast/valleys...low clouds with bases near 1000 ft msl and
tops around 2000 ft msl will continue over the coast and portions of
the valleys through 17z. Clearing for the valleys after 17z with
lingering patches of low clouds along the coast through the
afternoon. Ceilings should scatter out at ksan, kcrq and ksna around
20z, with light westerly winds and scattered at or above 20,000 ft msl through 00z
Tuesday. Low clouds should increase along the coast after 00z
Tuesday with bases near 1,000 ft msl, and linger through 21z Tuesday.
Mountains/deserts...light winds, unrestricted visibility and scattered at or above
20,000 ft msl will prevail through 00z Wednesday.
quiet conditions are anticipated through Friday with a mixed swell
(2-4 ft at 7-10 sec from the northwest and 2 ft at 12-15 sec from
the south). Winds will remain light this week, with a mix of
southwesterly winds in the mornings/early afternoons followed by
more west northwest winds in the late afternoons/evenings.
Skywarn activation will not be needed today.