Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
109 PM PST Tuesday Jan 27 2015
partly cloudy for the region today as high pressure aloft moves
in...then dry and a little warmer for Wednesday. For Thursday
through Saturday...a weak low pressure system from the southwest
will likely bring increasing clouds and periods of scattered light
showers to the region. Drier and warmer with offshore flow and
locally gusty northeast winds for Sunday and Monday.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
Visible satellite imagery this afternoon shows scattered low and
high clouds across the region as the upper trough that brought the
showers yesterday is now over western Nevada. The 12z Miramar
sounding showed a lot less in the way of moisture...with a surface
inversion and some moisture in the 820-750 mb layer. The cool air
mass left behind by the departing trough has brought temperatures
several degrees lower than 24 hours ago for most coastal...valley
sections and the San Bernardino County and Santa Ana
Mountains...with temperatures actually a few degrees higher in other
locations...likely due to less cloud cover than at this time
Warmer and continued sunnier on Wednesday as a transitory upper
ridge moves through the area. On Thursday...the forecast models
continue to show an elongated trough approaching and moving inland
into the Southern California coast...developing into a closed low
over Southern California on Friday...moving southeast into Sonora
Mexico on Saturday...and continuing to move south on Sunday. This
trough will bring increasing clouds and likely periods of scattered
light showers across portions of the forecast area mainly late
Thursday through Saturday morning...with some showers beginning as
early as Thursday morning. Looking at a cross-section...the GFS and
European model (ecmwf) both show deep moisture advecting into the area in the middle and
high levels early Thursday...and then deepening to the surface by
early Friday morning...and continuing through early Saturday.
Although initially on Thursday...most precipitation will favor areas
over and west of the mountains...models show that as the core of the
low moves into extreme southeast California/western Arizona late
Thursday into Friday...850 and 700 mb flow turns out of the north to
northeast direction...which would result in wrap-around
precipitation focusing more over the deserts and mountains during
that time. This wrap-around precipitation could continue into
Saturday afternoon. The 12z European model (ecmwf) and 12z GFS are both a little
wetter than their previous runs...and both show relatively deep
moisture with this system. Considering this...have increased probability of precipitation a
little...especially for the ridges...desert slopes and deserts
during the wrap-around portion of the trough. Rainfall accumulations
look to be light to locally moderate with this event. Snow levels
look to be at around 7000-7500 feet or so...with a few inches or
more of snow possible above that elevation. The cloud cover and
colder air mass will lead to a cooling trend...as high temperatures
fall to slightly below normal by Friday.
The showers should be gone for the most part by Saturday evening as
the low moves into Sonora and we get northeast flow aloft with a
ridge nudging into central California. Offshore flow and increased
ridging aloft will bring warming and increased sunshine Sunday into
next Monday. The offshore flow looks to be weak to possibly moderate
on Sunday...with some gusty conditions in the favored
passes...canyons and coastal foothills.
272100z...coast/valleys/mountains...sct080 sct250 through Wednesday
afternoon. Areas of ground fog with visible below 3sm between 12-18z in the
inland valleys near krnm...kajo and kcno.
Deserts...sct-bkn030-050 through 04z...after 04z sct030.
100 PM....no hazardous marine weather is expected through Saturday.
Skywarn activation will not be needed today.