Scientific Forecaster Discussion
Area forecast discussion
National Weather Service San Diego California
930 am PST Tuesday Dec 10 2013
the areas of strong east winds will gradually diminish today. High
clouds will move over the region as a weak area of low pressure
approaches from the southwest. Otherwise...there will be fair but
warmer weather the rest of this week as the big low pressure trough
moves from the western to eastern United States. However...the
nights will remain chilly in wind protected areas due to the low
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
East winds continued overnight...with local gusts around 60
miles per hour...but most areas were having some decrease in the wind speeds
this morning. The high wind warnings/wind advisories will be allowed
to expire at 10 am. High clouds and the areas of winds kept the near
freezing temperatures rather local in the valleys and lower deserts...but
thermal still dropped to 23. Meanwhile...Ramona...which is usually a
cold spot...never dropped below 45 due to the persistent wind. For
tonight...while there will be quite a few high clouds...wind will be
less widespread so more valley/desert locations will probably drop
to near freezing than last night. Will evaluate any need for a frost
advisory by early afternoon.
A closed upper low was centered near 28n/135w...with the models
showing it moving towards a point just south or east of San Diego by
Thursday. AMSU images show some precipitation rates with this low of up to 1/2
inch per hour...but relative humidity in the 850-700 mb layer generally decreases
with this system through Thursday...mostly due to dry air entrainment
from the Continental air to the northeast. However...there should be
enough moisture for quite a bit of cloud cover and perhaps if the
low takes a track a bit further west than the models show...some
light precipitation. This will help with nighttime temperatures due to the cloud
cover...especially Wednesday night. There probably will not be much
negative impact on daytime temperatures as temperatures at 850 mb increase through
the period as the effects of that big western/central US trough wane
as the trough moves east.
Overall...there will be a blocking ridge off the West Coast through
early next week...with a cutoff low south of the ridge. So...expect
mild weather late this week and over the weekend. There will be a
brief period of weak onshore flow either late Thursday and/or Friday...then
another surface high over the Great Basin will turn US back offshore
over the weekend...though without any strong gradients.
Models...including ensembles...are not in very good agreement after
about Monday/Tuesday of next week...but some solutions suggest a deeping
trough over the West Coast around midweek.
101600z...few-sct clouds between 10000 and 15000 feet mean sea level and
unrestricted visible will continue through tonight. Areas of northeast
winds 15-25 kts with local gusts to 45 kts in west and southwest
facing mountain foothills this morning...weakening during the day.
Weak to moderate offshore flow will continue tonight into Wednesday
over inland areas.
Fire weather...from previous discussion...
widespread low humidities and gusty offshore winds will continue
this morning...but recent rainfall and low temperatures will limit
the wildfire threat. For Wednesday through Friday...humidities
will increase a little and the offshore winds will weaken then
turn onshore briefly on Friday. Periods of gusty offshore winds
will return for the weekend into early next week.
Wind Advisory until 10 am PST this morning for the Coachella
Valley...Riverside County mountains.
High Wind Warning until 10 am PST this morning for the Orange
County coastal areas...San Bernardino County mountains...San
Bernardino and Riverside County valleys-the inland Empire...San
Diego County mountains...San Diego County valleys...Santa Ana
Mountains and foothills.