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851 PM PDT TUE JUL 26 2016


High pressure aloft centered over Southern Nevada will change
little through Saturday...resulting in hot conditions away from
the coast and a shallow marine layer at the beaches. The high will
shift to the east early next week bringing some cooling and an
increased chance of thunderstorms to interior areas.



The latest satellite imagery shows upper-level high pressure
centered over Southern Nevada this evening. At the surface,
weaker onshore flow combined with stronger high pressure aloft
brought a warmer day to the area today. With the weather pattern
changing little over the next several days, minimal changes will
occur. A warm air mass will remain in place through Wednesday,
possibly cooling on Thursday. 500 mb heights stay near 594 dm
over the next couples of days with little change in the onshore
flow strength.

Southeast flow aloft will continue over the area around the high
center. Some clouds developed over the San Gabriel Mountains
today, but no showers or thunderstorms were observed. The window
for monsoonal moisture remains open for now. While high confidence
exists for the moisture transport into Southern California, less
certain is the instability at this time. NAM-WRF solutions do not
a particularly great handle with the feature driving the cluster
of storms over the Sonoran Desert near the US-Mexico Border in
Arizona. That could add a wrinkle to the forecast for Wednesday
afternoon and evening. For now, the forecast will wait for more
data to arrive.

No updates are planned at this time.



SHORT TERM...With the weaker onshore flow, many valley areas may
see their warmest day of the week today, while mountain and desert
areas will see little change to their hot temperatures for the
next few days. While there is slightly more humidity in the air
today as compared to the last couple of days, heat index values
will generally remain below critical heat warning thresholds.
However, would not be surprised to see a few isolated locations
reach critical heat thresholds this afternoon. With continued hot
daytime temperatures and above normal minimum temperatures (with
some inland areas remaining in the 70s at night), there will be
some heat impacts with this current heat wave this week. A shallow
marine layer will keep low clouds and fog mostly confined to
coastal areas during the next few nights, helping to moderate
coastal temperatures.

Other item of note today is the increase in mid level moisture
across the mountains and deserts of Southern California, as
precipitable water values have risen to between 1.2 and 1.4 inches
across Los Angeles and Ventura counties. This added moisture,
combined with hotter and more unstable conditions resulting in
some cumulus cloud development over the local mountains. For our
forecast area, the eastern San Gabriel mountains will have a
20 percent chance of thunderstorms this afternoon and evening,
with a 10 percent chance for the remainder of the LA/Ventura
county mountains and Antelope Valley (including the Sand Fire
region). In addition, the hot and unstable conditions will make
conditions favorable for development of pyrocumulus clouds
at the Sand Fire burn location near Agua Dulce and Acton. 

And if any storms develop to our east this afternoon and
evening, the easterly flow at the mid and upper levels could drift storm
activity into the eastern portions of the LA county mountains and
Antelope Valley. If any storms were to develop today, the main
threats would be isolated dry lightning strikes and gusty
downdraft winds. With southeast flow aloft prevailing the next few
days, there will be a 10 percent chance of thunderstorms across
the LA county mountains and Antelope Valley each afternoon and
evening through Friday.

LONG TERM...The EC and GFS agree that the upper high will move
to the east over the weekend and then a little trof will ripple
overhead for Monday. The lower hgts will kick off a cooling trend.
Max Temps will fall to normal over the weekend.

The high will be in a slightly more favorable position for
monsoon moisture transport on Sat and Sun and there will be a
slight chc of afternoon convection over the VTA and LA mtns as
well as the Antelope Vly. Still the better chc of TSTMs will be
to the south and east of the area.

On Monday drier SW flow sets up as the upper trof rolls in to the
north. This will inhibit any monsoon flow and the slight chc of
convection will end.



At 00z, the marine layer was around 750 feet deep at KLAX. The top
of the inversion was near 2400 feet with a temperature around 29
degrees celsius.

LIFR to IFR conditions will spread into coastal terminals through
10Z. The highest likelihood on LIFR conditions exists for coastal
terminals north of KOXR. Conditions should improve to VFR between
14Z and 17Z.

KLAX...There is a 80 percent chance of IFR conditions by 10Z. VFR
conditions should redevelop between 16Z and 17z.

KBUR...High confidence in VFR conditions throughout the period.


.MARINE...26/815 PM.

Moderate confidence in winds and seas remaining below Small Craft
Advisory through tonight except for some local gusts up to 25 KT
near Point Conception. West to northwest winds will start
increasing some on Wednesday and Thursday with Small Craft
Advisory Likely between Point Conception and San Nicolas Island.
Moderate confidence in dense fog with visibility of 1 NM or less
will affect much of the coastal waters through Wednesday.


.FIRE WEATHER...26/900 PM.

The elevated fire weather conditions across interior mountains
and valleys will persist each afternoon and early evening through
Thursday or Friday due to low relative humidities and locally
gusty onshore to northwest winds. Elevated fire weather concerns
extend into the upcoming week weekend due to the possibility of
afternoon thunderstorms. Monsoon moisture aloft is expected to
gradually deepen over the area through the week with increased
moisture leading to higher relative humidities at the surface
beginning Friday or Saturday. The increasing moisture will bring
the slight chance of thunderstorms over the Los Angeles and
Ventura county mountains and Antelope Valley each afternoon
Saturday and Sunday.






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