Scientific Forecaster Discussion
fxus66 klox 252155
Area forecast discussion
National Weather Service Los Angeles/Oxnard California
255 PM PDT Tue Jul 25 2017
There is a slight chance of a thunderstorm or shower in the
mountains and deserts this afternoon and evening. Dry southwest
flow aloft and a building ridge will gradually warm temperatures
this week to a few degrees above normal. Overnight and morning
low clouds will continue along the coasts.
The remnants of a monsoonal surge remain over the area today as
southwest flow aloft continues to entrain drier air into the air
mass. Some cumuliform cloud development is taking place over the
mountains and desert. With enough moisture still in place, a
slight chance of showers and thunderstorms remains in the forecast
through this afternoon and evening across the Los Angeles and
Ventura County mountains and the Antelope Valley.
High pressure aloft to the east centered over the Texas will start
to nudge west through Thursday night and build across the area. An
onshore flow pattern should weaken into late week along with a
thinning marine layer depth. NAM-WRF time height sections at klax
reflect the trend well with the near-surface moisture getting
squashed each day through Thursday and remaining shallow into
Friday. A warming trend should take shape through the end of the
work week as 500 mb heights climb across the region. Temperatures
could reach toward dangerously hot levels across portions of the
area on Friday and a heat advisory could needed Friday for the Los
Angeles and Ventura County mountains, if this trend continues.
The ridge aloft weakens some while pushing into northern Arizona
over the weekend as the remnant moisture from Hurricane Hilary
could get embedded in the flow around the high pressure system.
GFS and European model (ecmwf) solutions hint at some semblance of an easterly wave
moving over the region. A slight chance of showers and
thunderstorms remain in the forecast over the weekend over the
mountains and desert and into early next week as a low confidence
forecast looks to develop.
Some model differences start to develop over the weekend and into
early next week. Both model solutions agree that the high pressure
system will strengthen to near 598 dm over the Great Basin some
time between Tuesday and late next week. While agreement exists
for further warming, timing will be difficult to place as much
will depend upon the movement of the remnants of Hurricane Hilary.
At 1733z, the marine layer depth was 1550 feet. The top of the
inversion was 3200 feet with a temperature of 21 degrees celsius.
Moderate confidence in 18z taf package. For tonight, high
confidence in return of stratus to coastal sites. There is less
confidence in the return of marine clouds to any valley sites.
Klax...moderate confidence in 18z taf. There is a 30 percent
chance of the marine clouds arriving plus or minus two or more
hours from the forecasted time.
Kbur...low to moderate confidence in 18z taf. There is a 40
percent chance of MVFR/IFR cigs 10z-17z.
For the outer waters, good confidence in current forecast. Winds
and seas will remain below Small Craft Advisory (sca) levels
through Thursday. For Friday and Saturday, winds may increase to
Small Craft Advisory levels in the far north portion.
For the inner waters, good confidence in current forecast. For the
waters north of Point Sal, winds and seas are expected to remain
just below Small Craft Advisory levels through Saturday. For the waters south of
Point Conception, winds and seas will remain below Small Craft Advisory levels
Hurricane Hilary is expected to become a major hurricane today. As
this system continues to strengthen, it will generate a
southeasterly swell that will impact Southern California beaches
this weekend. The southeasterly swell will move into the coastal
waters early Friday, then peak on Sunday. High surf conditions as
well as strong rip currents will be likely across south-facing
beaches this weekend. Isolated damaging sets of surf and beach
erosion cannot be ruled out for the south-facing beaches of Los
Angeles and Ventura counties.
Hazard potential outlook...(fri-tue)
A significant surf event could develop late Thursday as swells
from Hurricane Hilary arrive at the Southern California beaches.
High surf and strong rip currents will occur from Friday through