Scientific Forecaster Discussion
fxus66 ksgx 130500
Area forecast discussion
National Weather Service San Diego California
858 PM PST Tue Dec 12 2017
high pressure aloft and offshore flow at the surface will continue
warm and dry weather into the middle of next week. Stronger Santa
Ana winds Thursday morning through Friday morning for the mountains,
foothills and passes. Skies will be mostly clear.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
A thin band of high clouds will skirt the edge of our area overnight
from the northernmost periphery of a subtropical moisture plume. No
changes were made this evening as the forecast remains on track,
and the previous forecast discussion is below.
An expansive upper ridge continues to dominate the weather across
the U.S. West Coast. This will continue through early next week,
promising a continuation of dry conditions with temperatures
averaging much above normal.
The main forecast change today was to indicate stronger winds for
early Thursday morning through Friday morning. An upper level
trough will be diving south from The Rockies and across Arizona on
Thursday morning. Surface high pressure will build in to our east
behind this feature. The surface pressure gradient trend since
yesterday has been increasing in the Thu-Thu night timeframe. This
means there is the potential for stronger northeast winds from
the mountain ridges to the foothills, passes, and into portions of
the valleys. Current forecast for these Santa Ana wind-prone areas
is now for northeast winds to increase to 20-30 mph with gusts to
50 mph and even isolated gusts to 65 mph possible (places such as
Sill Hill/South Dakota county). This presents fire weather concerns. See
fire weather discussion below.
Winds will relax later Friday and through the weekend with
tranquil weather prevailing. A brief period of light onshore flow
Saturday will quickly give way to offshore winds early next week.
Temps will cool some, but still remain above normal.
Global models indicate a break down in the ridge during the middle
to latter part of next week. Whether or not this translates to
some rainfall for socal remains to be seen.
offshore surface pressure gradient will be increasing Thursday
through Friday morning. The model tendency since yesterday is to
increase this gradient, which means that stronger winds are
possible. An extremely dry airmass will remain in place and be
re-enforced. Fuels are at record low moisture levels as well.
Given the higher wind potential, have issued a Fire Weather Watch
for all local mountains, the inland Empire, the inland valleys of
San Diego County as well as inland Orange County effective
12 am Thursday through 10 am Friday. Winds look to rev up first
across northern areas early Thursday morning-afternoon, then peak
into the San Diego mountains/portions of valleys Thursday night
through early Friday morning. Lighter winds are forecast later
Friday and through the weekend.
130430z...mostly clear with unrestricted vis through Wednesday
evening. Local surface northeast winds 20-30 knots with gusts to 40
knots will occur at times from the mountain crests to the coastal
foothills, including through/below Cajon Pass and the Santa Ana
no hazardous marine weather is expected through Sunday.
California...Fire Weather Watch from late Wednesday night through Friday
morning for Orange County inland areas-Riverside County
mountains-including the San Jacinto Ranger district of the
San Bernardino National Forest-San Bernardino County
mountains-including the mountain top and front country
Ranger districts of the San Bernardino National Forest-San
Bernardino and Riverside County valleys -the inland Empire-
San Diego County inland valleys-San Diego County mountains-
including the Palomar and Descanso Ranger districts of the
Cleveland National Forest-Santa Ana Mountains-including the
Trabuco Ranger district of the Cleveland National Forest.