0615z
Just noticed a RAWS site just up the Bell Canyon from San Juan
Capistrano (southeast Orange County) had a gust to 56 mph from the
northeast (same orientation as the canyon) at 03z. Was gusting to 47 mph
as recently as 05z, but gusts had died down to 30 mph by 06z. Future
research may want to concentrate on the legitamacy of the observation or
on a reason for the gusts other than the pressure gradient given the
gradient across the Santa Ana Mountains was only about 1-2 mb at the
time. The apparent gust happened about the same time that San Diego's
wind was backing in direction from south to southeast due to an apparent
strengthening of the offshore low.
Haner
0546z
I was just looking at the Experimental RUC at 03Z and noticed
that it developed the low circulation further south off the San Diego
Coast than what the observations where indicating. Perhaps as you fly
northward, later updates to the RUC will make an adjustment.
Precipitation estimates are not even close to reality. It is still
showing the heaviest precipitation over northern baja the next few hours
with local three hour amounts less than one half inch.
Three hour output from O6Z RUC image for precipitaion estimates shows
less than 0.05 inches from LA county northward. Sepulveda Dam picked
up 0.40 inches last hour. RUC is generally showing less than a quarter
inch from orange county southward with an isolated amount between one
quarter to one hour inch near the border of Orange and San Diego County.
Also the 500 mb hieght/vort field did not pick up on the vort feature I
mentioned in earlier discussions that the mso eta picked up on over
the Santa Monica Bay. RUC has strongest vort lobe west of point
conception...near the flight path you took to point one. Latest ETA
run has this area in a weak NVA at 06Z. I'm not sure but there
may be a correlation to the flight path that was taken in why this is
showing up.
0540z
A surface low pressure center is now located in Santa Monica Bay south
of LAX. Winds at Buoy 46047 (Tanner Bank) have now backed from northwest
to WNW, suggesting the low may now be passing that latitude. The lowest
surface pressures yet with this system are now being observed at buoy
46025 with 1011.1 mb. As the low pressure center moves northeast toward
the LA/Orange County coasts, heaviest precip should shift inland through
midnight and the front will finally pass southeast through San Diego.
The 04-05z precip highlights include:
Ventural County Coast:
Conejo Creek above Hwy 101...0.43"
Ventura County (western valleys):
N Fork Matilija Creek...0.24"
Matilijia Dam...0.20"
Ventura County (eastern valleys):
Santa Clara at Piru...0.20"
Ventura County (mtns):
Nordhoff Ridge...0.47"
LA Metro:
Lechuza FS...0.28"
Beverly Hills...0.25"
Hollywood Resvr...0.20"
La Habra Heights...0.20"
LA County (s fernando and s clarita vlys):
sepulveda Dam...0.40"
Agoura...0.31"
Chatsworth Rsvr...0.24"
LA County (mtns and foothills)
Opids Camp...0.21"
San Diego County (deserts)
Coyote Creek...0.16"
Ocotillo Wells...0.16"
0400z
Here are the latest 02-03z rainfall highlights:
Santa Barbara County (south coast)
Montecito...0.41"
Ventura County (mountains)
Tommy's Creek...0.28"
Nordhoff Ridge...0.20"
LA Metro
Big Rock Mesa...0.24"
Ballona Creek at Sawtelle...0.20"
Beverly Hills...0.16"
LA County (S Fernando and S Clarita Valleys)
Sepulveda Dam...0.20"
Schoolhouse D.B...0.16"
LA County (San Gabriel Valley)
Fremont Hdqs...0.31"
Eagle Rock Reservoir...0.28"
Puddingstone Divide...0.24"
LA County(Mtns and foothills)
Live Oak Dam...0.24"
---------
Now for the 03-04z highlights:
Santa Barbara County (mtns and foothills)
San Antonio Ridge...0.20"
Ventura County (western valleys)
Fagan Canyon east...0.24"
Ventura County (eastern valleys)
Santa Susana Pass...0.20"
Nordhoff Ridge...0.28"
LA Metro:
Beverly Hills...0.31"
Compton...0.21"
La County (San Fernando Valley)
Canoga Park...0.28"
Sepulveda Dam...0.24"
LA County (San Gabriel Valley)
Santa Fe Dam...0.16"
Winds in coastal San Diego County have now been backing for the past 2-3
hours, suggesting that the front is either slipping south or that low
pressure is strengthening offshore, or both. Suspect it is actually a
combination of both. The RUC model actually shows the front slipping
south of San Diego late this evening. The precipitation has also
creeped west into far eastern Santa Barbara County as the whole system
pivots counter-clockwise, but the passage of the main vort max and upper
support later this evening should reverse this trend with the bulk of
precip moving inland overnight.
Other relatively minor feature of interest is the broken band of showers
over western Santa Barbara County extending offshore south from Point
Arguello. Believe this is being caused by convergence of easterly winds
in the Santa Barbara Channel and northwest winds sliding down the
westward-facing coasts of San Luis Obispo and Santa Barbara Counties.
Could be worth checking out if this feature still exists on the flight
back north. Surface obs due show a weak reflection of a possible surface
trough extending up the coast from Point Arguello.
Otherwise, the whole system continues to take on a more negative tilt
all the time with low-level cloud elements (and likely the front) behind
the vort max now shifting southeast. IR satellite imagery shows a
broken line of cumulus located from 30.0N 121.6W through 28.4N 123.8W to
27.5N 125.6W. This is far removed from the main precip shield but is
still of mild interest.
0409
I talked with LA forecaster a little while ago and he felt that the
surface low was increasing offshore. Surface observations At 03Z
Torrance 12015G20KT...LAX 0918G23KT...Santa Monica Basin Bouy
02015KT and Avalon(AVX) 17008KT. Note the circular pattern over Santa
Monica Bay!
The forecaster in San Diego so far has had mostly light rain with no
problems to report.
Montecito picked up another 0.41 inches last hour in southwest Santa
Barbara County. LA forecaster is considering issuing Flood Statement
for southeastern Santa Barbara County .
0250Z
LA office has issued a flood advisory for ventura and la counties
through 10 pm.
San Diego office has issued a Flash Flood Watch for tonight for
Orange and San Diego Counties...the Inland Empire and surrounding
Mountians.
Radar images indicate good enhancment taking place over the
Santa Monica Bay near where meso eta indicated the center of the vort
max would be by 03Z. Also a developing line of 40 DBZ extends from just
east of San Clemente Island....due south to 75 miles west of
Ensenada Mexico. This line has shown very little movment.
In General RADAR shows most precipitation moving almost due north as
upper low is slowly becoming more negativly tilted. IR image at 02Z
indicates greatest moisture plume extending from near San Nicoles
Island/33.4N 119.5W down to 28.9N to 119.5W. IR images shows
intermitent enhancements of cloud tops around this line...with embeded
heavier cells moving northward as the moisture plume
progesses very slowly to the east. Greatest enhancement is currently
over San Nicoles Island and moving northward.
Surface observations at 02Z indicate rain has spread further west into
Santa Barbara County. Orographics is enhancing
preciptation in southern Santa Barbara County...with last hour
Montecito recieving 0.40 inches and Mt Calvery 0.31 inches.
In Ventura County Mountains...Nordolf Ridge 0.20 inches. Upper
Matilija Canyon 0.24 inches.
In La County heaviest rain continues along the coast with numerous
reports around one quarter inch during the past hour. Rainfall rates
increase in the San Gabriel Valley with several locations reporting
around one quarter inch. In the Mountains the highest report was 0.20
inches at Thompson Creek Dam.
In San Diego County...rainfall amounts ranged from 0.04 to 0.12 inches.
METAR observations indicate surface winds almost south near San Diego
and curling to the east at LAX...and remaining east through the Santa
Barbara Channel.
0200Z
Compared the 0119Z P3 sounding to the 12z model runs this morning. The
P3 temperature profile is about 2C colder at 700 and 500 mb than what
the models forecasted. This is consistant with a slightly stronger upper
level system...and thus slightly lower surface pressures than what the
models forecasted this morning.
Dutter
0135z
To contrast the unidirectional southerly profile mentioned in the last
update from the San Diego sounding, the Simi Valley wind profiler has an
easterly wind of 10-15 knots through about 2k ft agl, then gradually
veers to southerly by about 4k ft agl. Just another sample from the
other side of the presumed front. Also, buoy 46047 (Tanner Banks, 137 mi
W of San Diego) now shows a MSL of 1012.7 mb which is 1-3 mb lower than
models from earlier today were forecasting, so this could be a tad more
potent a system than earlier thought. Finally, the last visible
satellite pictures of the day show a broken cumulus line (which could be
the front) extending WSW from the main rain shield from 31.1N 120.9W
through 30.0N 122.0W to 28.8N 123.8W.
0115z
Largest one-hour rainfall reports from 00-01z were along the
coast.
Here is a sampling:
LA River at Firestone...0.32"
Compton Creek at Greenleaf...0.30"
LAX International...0.28"
LA 96th and Central...0.24"
Santa Monica...0.20"
San Gabriel/San Fernando Valleys...0.04"-0.31"
Mountain and foothills...0.04-".16"
San Diego coast, foothills and mountains...0.04"-0.16"
except Oak Flats...0.28"
Heaviest rainfall should move inland in the next hour.
Several interesting things to note this hour. There was a 00z
ship
report from 38 miles northwest of KSAN with a SSE wind of 35
knots. Also
the wind at Avalon (KAVX) has shifted from 14013G19kt to 25009kt
from
23z to 01z. IR satellite pictures have also shown an enhancement
of
cloud tops in the general area of 29.8N 119.9W in the past two
hours.
Looks like this may be a sign of the approaching strong upper
level
divergence mentioned in the routine forecast discussion early
this
afternoon. Finally, the KNKX (San Diego) 00z sounding showed a
unidirectional southerly wind profile from the surface to 850 mb
(~4.7k
ft) with slight veering to SSW above that. As would be expected
in a
rainy regime, the temperature profile was nearly moist
adiabatic.
Haner
2335z
Latest METAR observations indicated light to moderate rain from
LA basin southward. At 23Z winds at San Diego from 15016KT...At
Avalon 14013G19KT...Calm at Point Mugu...and VRB04KT at
Santa Barbara.
Bouy Winds in Santa Barbara Channel...Point Conception 16002KT.
East Santa Barbara Channel 12006KT.
Tanner Banks 137 miles west of San Diego or 32.43N/119.32W
indicates
winds 33008KT.
Radar images indicate back edge of the front a little south of
Santa Barbara...with the Heaviest rainfall over LA county as
of 2345Z.
18Z meso eta shows vort max centered near 33.6N/119.2W at 03Z
with
north-south elongation into western Ventura county. Model moves
center
of vort max to just west of Palos Verdes by 06z or 33.7N/118.6W.
LA forecast office has extended Winter Storm Warning through
Monday...with San Diego continuing Winter Storm Warning through
tonight.Latest METAR observations indicated light to moderate rain from
LA basin southward. At 23Z winds at San Diego from 15016KT...At
Avalon 14013G19KT...Calm at Point Mugu...and VRB04KT at
Santa Barbara.
Bouy Winds in Santa Barbara Channel...Point Conception 16002KT.
East Santa Barbara Channel 12006KT.
Tanner Banks 137 miles west of San Diego or 32.43N/119.32W
indicates
winds 33008KT.
Radar images indicate back edge of the front a little south of
Santa Barbara...with the Heaviest rainfall over LA county as
of 2345Z.
18Z meso eta shows vort max centered near 33.6N/119.2W at 03Z
with
north-south elongation into western Ventura county. Model moves
center
of vort max to just west of Palos Verdes by 06z or 33.7N/118.6W.
LA forecast office has extended Winter Storm Warning through
Monday...with San Diego continuing Winter Storm Warning through
tonight.
1340
The main focus today will be in extreme southern California. Current
land-based surface observation and the most recent ship reports show a
surface front located from near the Orange-San Diego county line
offshore to near 30.0N 123.5W with land-based surface winds north of the
front from the east and surface winds from the south on the warm side of
the front. The latest AMSU data shows PW values of 1-1.1" in the axis of
a moisture plume corresponding well with the front. Land-based radars
show the heaviest precip moving onshore also co-located with the surface
front. An upper trough near 127W is already starting to take on a
negative tilt as a 120 knot 300 mb jet digs into the base of the trough.
Upper level divergence will increase dramatically this afternoon and
evening over the San Diego County and northern Baja coastal regions as
this area comes underneath the left exit region of the upper jet and the
upper trough takes on more of a negative tilt. Low-level moisture
convergence will also be maximized along the low-level boundary and will
be the other major forcing factor. There will be little in the way of
low-level temperature advection, so isentropic lift should not be a
major factor. However, a low-level theta-e axis will gradually shift
south from the San Diego coastal areas this afternoon and into the
northern Baja region this evening as the upper trough approaches and
kicks the front south. Otherwise, models agree in not showing further
deepening of the frontal wave approaching the coast this evening, and
models agree in not showing any significant low-level jet.
Extended forecast...long-term models agree in building an upper ridge
and northerly flow aloft across most of the west coast on Tuesday. The
flow across the northern Pacific starts to become more zonal on
Wednesday with a system approaching the Pacific northwest coast on
Thursday. While there are differences in the organization of that system
and even at what latitude it will arrive on the caost, the 12z AVN is in
general agreement with the 00z MRF on the timing with the most likely
time for operations on Thursday afternoon along the WA/OR coast.
Haner
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