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fxus66 ksgx 242128 

Area forecast discussion
National Weather Service San Diego California
127 PM PST Fri Feb 24 2017

continued dry and cool through Saturday with frost possible in the
valleys again Saturday morning. For Sunday and Monday...cooler, with
a chance of rain and snow showers as low pressure develops along the
coast. High pressure aloft and weak offshore flow will bring dry and
warmer weather again Wednesday through Friday of next week with
periods of offshore flow.


Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino

Skies were mostly clear across socal this afternoon, except for a
few high clouds. At noon...surface pressure gradients were weak and
winds light.

It was a chilly start to the day with morning lows falling into the
30s and 40s west of the mountains. It was around freezing in the
colder spots. Due to the dry air in place, clear skies and light
winds again overnight tonight, minimum temperatures are forecast to
fall to similar levels. The most widespread cold will be in the
valleys, but patchy frost will also be possible in the San Diego
County deserts, and in colder spots along the coastal strip.

A frost advisory has been issued for the inland valleys tonight.
Otherwise, fair and continued cool on Saturday with Max temps 2 to 8
degrees below average.

A strong upper-level ridge over the Gulf of Alaska will favor
troughing downstream along the West Coast through early next week.
This keep temperatures below average. We will stay dry through
Saturday, but after that, disturbances dropping south along the east
side of the eastpac ridge will begin to affect our weather.
Forecasting the timing, track, and variations in intensity of the
disturbances moving through this flow has been difficult due to the
variety of model solutions being generated. This keeps confidence
compromised through about Tuesday, so probability of precipitation are still in the slight
chance/chance category sun through Tue.

The overwhelming trend over the last few runs has been for less
precip across socal, but most solutions still indicate some showers
will develop, with snow levels low enough to affect mountain
communities and resorts. Please see the hydrology section below for
further discussion.

The Sharp Ridge over the eastpac subsides early next week, allowing
heights to build over the west and a return to fair, dry, and warmer
conditions by the middle of next week.


242104z...p6sm vis through Saturday morning. Few-scattered clouds at or above
20000 ft msl becoming scattered-broken by 25/1200 UTC.


latest model guidance is showing weaker winds and lower seas Sunday
and Monday as a weak storm-system moves through the region, with
just some light to locally moderate showers possible. Thus, no
hazardous marine weather is expected through Wednesday.


despite the lack of forecast confidence, the model trends are
unmistakable, less precip across socal. So for now, it does not
appear that we will have any significant runoff impacts. Showers are
forecast to develop on Sunday and continue off and on into Tuesday.
Rainfall rates west of the mts should be less than one-quarter inch
per hour at any time, but my be locally higher on the coastal slopes
at times where upslope flow can enhance amounts.

Latest 12z NAM quantitative precipitation forecast through Monday shows one-tenth of an inch or less
along the coastal strip, up to one-third of an inch in the valleys
and foothills, one-half to one inch in the mts, and less than one-
tenth in the deserts. The 12z wrfems is a bit less. Additional
amounts of around one-quarter inch are possible through Tuesday
west of the mts, based on the more coarse 12z European model (ecmwf) run.

Due to the shallow depth of atmospheric moisture forecast, large
amounts of snow are not likely in the mts, but given the continued
uncertainty, it would not be surprising for a few inches to
accumulate between Sunday and Tuesday in some spots.


Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.


Sgx watches/warnings/advisories...
California...frost advisory from midnight tonight to 8 am PST Saturday for
San Bernardino and Riverside County valleys-the inland
Empire-San Diego County valleys.



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