Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
839 am PST Tuesday Jan 27 2015
patchy dense fog in the deserts will clear out today...with
increasing sunshine for the region as a high pressure aloft moves
in. Dry and a little warmer for Wednesday. For Thursday through
early 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
Radar imagery this morning shows no shower activity in our forecast
area...with the nearest showers located over l... and Kern
counties. The upper trough that brought the showers yesterday is now
over central California and moving north...according to water vapor
satellite. The 12z Miramar sounding shows a lot less in the way of
moisture...with a surface inversion and some moisture in the 820-750
mb layer. With this low-level moisture...there are scattered to
broken clouds across the region this morning...with some fog in the
deserts. This fog should clear up as the day progresses...while
better sunshine sneaks through across the rest of the area also. The
cool air mass left behind by the departing trough will bring some
cooler conditions today.
Warmer and 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. Models show
the best precipitation/moisture moving into Arizona...but also show some
light precipitation over our area as well Thursday afternoon into
Saturday morning. Rainfall accumulations look to be light to locally
moderate with this event...with the models focusing the better
accumulations over the mountains valleys and deserts...with less for
the coast. Snow levels look to be at around 7000 feet or so...with a
few inches 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 by Saturday afternoon as the low moves
into Sonora and we get strong 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.
271630z...sct050 bkn080 with areas of 3-5sm br in the deserts and
some sections of the inland Empire through 19z. After 19z...p6sm
sct070 through tonight. Areas of ground fog between 12-16z in the
inland valleys near krnm...kajo and kcno.
830 am....no hazardous marine weather is expected through Saturday.
Skywarn activation will not be needed today.