Scientific Forecaster Discussion
fxus66 ksgx 170945
Area forecast discussion
National Weather Service San Diego California
245 am PDT Tue Oct 17 2017
today will be rather hot again, but a cooling trend will get
started. Low pressure will bring onshore flow and cooler air into
the region through Friday. The marine layer and coastal low clouds
will redevelop each night and morning, along with some winds in
the mountains and deserts. On Saturday the flow turns offshore as
high pressure builds. That will bring Santa Ana conditions, clear
skies and hot weather next week.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
High pressure aloft continues to grip our area and maintain the
dry interior air over our area. To our west there is a weak cutoff
low that is drawing up some high level moisture that will manifest
itself as thickening high clouds across Southern California
today into Wednesday. For two reasons the cooling trend will get
started today. Offshore flow drops off and allows the onshore
flow to spread more marine air farther inland. And we'll have more
high clouds occasionally filtering out the sunshine. This blob of
clouds will track through California Wednesday and there is some
instability in the blob. Elevated convection is expected, but any
showers at 10-15 thousand feet will try dropping rain through the
really dry air below that, and evaporate. That's why we are only
carrying slight chances of precip in the mountains (less dry air
to fall through before hitting the ground) where a few sprinkles
or light showers are possible. Coastal clouds don't seem to get
the message to form until Wednesday night and Thursday. That's
when a big low pressure trough moving through the northwest will
increase the onshore flow and generate a pretty decent coastal
eddy. The coastal clouds never really establish a foothold
Thursday before the cooler air aloft appears to erode whatever
marine inversion can get established. All that means we'll have
partly cloudy skies Thursday into Saturday. The trough will boost
winds through mountains and into deserts, particularly Friday.
Temperatures will drop well below average on Friday. The trough
axis gets through our region Saturday morning and flow turns
offshore over the weekend while high pressure aloft builds quite a
bit. Yes, another Santa Ana event, complete with the hot and dry
weather. Right now it doesn't appear to be too windy, but the
usual foothills and adjacent valleys will get some locally strong
winds that for now appear strongest on Monday and Tuesday.
Temperatures will head back into the 90s and approach or hit the
century mark on those days for many spots west of the mountains.
170910z...few-sct clouds at or above fl200 and unrestricted vis through
no hazardous marine weather is expected through Thursday. Winds will
increase to around 20 kt or more in the outer waters on Friday.
a south southwest swell from 200 degrees will peak today-Wednesday
at 3-4 ft/16-18 seconds. This will produce 3-6 ft surf with sets to
7 ft north of del Mar. Highest surf will occur along southwest
facing beaches. Strong rip and longshore currents will accompany the
elevated surf. Swell and surf will begin to lower on Thursday. A
beach hazard statement is in effect for elevated surf and strong rip
currents today and Wednesday.
very warm and dry weather will continue today, but with light
winds. A very slight chance of an isolated shower or thunderstorm
Wednesday is forecast for the mountains, with a very small chance
of isolated dry lightning strikes. Cooler and more humid onshore
flow will take control Thursday and Friday. Gusty westerly onshore
winds in mountains and deserts Thursday and Friday. On Saturday
and Sunday flow turns offshore and lower elevations heat up. Dry
Santa Ana conditions are forecast for west of the mountains,
strongest on Monday and Tuesday.
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.
California...beach hazards statement from 6 am PDT this morning through
Wednesday evening for Orange County coastal areas-San Diego
County coastal areas.