Scientific Forecaster Discussion
Southwest California area forecast discussion
National Weather Service Los Angeles/Oxnard California
750 PM PDT Monday Jul 28 2014
A slight chance of thunderstorms will continue in the mountains and
deserts through this evening due to the monsoonal flow. Overnight
low clouds and fog are expected for most of the week with above
normal temperatures. A cooling trend is expected for the weekend.
Short term (tonight-thu)...update
looks like storm activity will remain well to the east this evening
and tonight as the atmosphere becomes a bit more stable overnight.
There will continue to be some high level clouds across portions of
the forecaster area...but not anticipating any convection tonight
including the coast and valley areas. Although there was decent
instability potential over the mountains and Antelope Valley earlier
today...too much of a cloud shield prevented convection to
initiate...and best storm convergence and convective parameters
continued to be east of la County into San Bernardino County this
Latest acars soundings out of lax indicated a relatively strong
inversion around 700 feet deep. Normally this would be conducive for
widespread low clouds to develop if there was any sort of eddy to
help with lift. At this point it looks like low clouds will be
scattered in nature and should only affect southern la County
coastal areas and the central coast late tonight or early Tuesday
morning with a quick burnoff if low clouds develop at all. Patchy
dense fog could be an issue a few hours before sunrise along the
For Tuesday...the middle levels should be drying out with more stable
SW flow aloft. There will be less in the way of high clouds but a
few flat cumulus will be possible across some mountain
ridges...otherwise expect a few degrees of warming across interior
areas although it will not fell as humid. Coastal areas will
experience a degree or two of cooling. By Tuesday evening...latest
models continue to be consistent with remnants from what is
currently Tropical Storm Hernan bringing a slug of middle level
moisture across much of the forecast area from the southwest. The
earlier discussion captures the details of this well Tuesday night-Thu.
***From previous discussion***
Late Tuesday night into Wednesday we should start seeing high level
moisture moving into the area again from the south as a little
energy from what was briefly Hurricane Hernan reaches US. Models
don't typically handle these situations very well so for now i've
just added some clouds and sub-10 probability of precipitation to the area. Certainly has
the potential for kicking off some overnight and early morning
convection, especially over the outer coastal waters, but confidence
just too low at this time to pull the trigger. Increased cloud cover
during the day Wednesday could lead to a slight reduction in highs
that day but likely compensated somewhat by the increase in humidity
in terms of how it feels out there.
Air mass starts to dry out Thursday as moisture shifts to the south.
Still pretty warm though as the 4 corners high remains in place. So
temperatures about the same but lower humidity.
Increasing northwest flow offshore will lead to some mini-sundowners
for the sba area this week. Very light tonight and tomorrow, but
stronger Wednesday and Thu, possibly near advisory level. This will also
boost temperatures there as well, possibly to near 90 for the southern sba
Long term (fri-mon)...very little change Friday. However, over the
weekend both the GFS and European model (ecmwf) show a weakening of the high over the
4 corners as a trough pushes into northern California. This will lead to a
decent cooling trend for most areas that should last through early
next week. The shift to westerly flow aloft will also keep
thunderstorms out of the forecast.
S of Point Conception...latest acars sounding near lax was around
600 feet deep. There will continue to be plenty of middle level moisture
over the area through tonight. Low clouds expected to be confined to
south la coast after 10z. But confidence is very low due to the
moist middle layer. Expect IFR ceilings. 30 percent chance for low MVFR
ceilings if inversion raises. Otherwise expect VFR conds.
North of Point Conception...low confidence with 00z taf package along
central coast in respect to IFR/LIFR ceilings developing between 8z-12z
tonight. High clouds will make it difficult for widespread stratus.
There should be some patchy dense fog...especially between 10z-14z.
Otherwise expect VFR conds after 18z Tuesday.
Klax...high confidence in VFR conds through 09z...less confidence
with IFR ceilings after 09z. There is a 40 percent chance that only
scattered stratus early Tuesday morning.
Kbur...high confidence in VFR conditions.
Isolated showers and thunderstorms are still possible into this
evening. Weak to locally moderate winds are expected across the
coastal waters through Tuesday.
Stronger winds are expected later this week with small craft
advisories possible in the outer waters Wednesday afternoon.