Scientific Forecaster Discussion
fxus66 ksgx 180405
Area forecast discussion
National Weather Service San Diego California
905 PM PDT Tue Sep 17 2019
low pressure over the west will bring cooler weather this week,
with more extensive coastal clouds during nights and mornings.
Gusty winds are expected in parts of the mountains and deserts
each afternoon and evening. The low pressure weakens Friday,
bringing warmer weather and less coastal cloudiness this weekend.
Discussion...for extreme southwestern California including Orange...
San Diego...western Riverside and southwestern San Bernardino
evening water vapor satellite imagery shows a short wave trough
moving through the California bight and the main upper level low off the
Washington/or coast. The weak trough and strengthening onshore pressure
gradients are contributing to breezy conditions in the mountains
and deserts where a few gusts to 35 mph are being reported. Patchy
low clouds are developing along the coast and should become a
little more widespread overnight. The 00z knkx sounding shows the
marine inversion is fairly weak, so expect rather quick clearing
in the morning. No big changes to the forecast this evening.
Onshore wind flow will strengthen through Thursday as a closed
upper low off the Pacific northwest opens up and dives
southeastward over the intermountain west. The result will be
cooler weather through Thursday as the onshore pressure gradient
The trough will pull away from the region ahead of another trough
poised to dig southeastward this weekend into early next week.
Weak offshore flow will ensue Friday and into the weekend with
GFS and European model (ecmwf) both show a significant (pw near 2 inches) tropical
moisture surge into Arizona ahead of this upper feature during
the early to middle part of next week before the upper trough
moves east. GFS and ec ensembles favor dry weather for our socal
service area, in line with wpc quantitative precipitation forecast next 7 days, showing no rain
over socal. However, it is Worth noting that a few members do show
1"+ of rain into the lower deserts centered around next Tue-Wed.
So this will be something that we will be keeping an eye on over
the next few days...to see the placement of the upper trough and
moisture pull from the south early/mid part of next week.
As that trough pulls away from the region during the latter part
of next week, another period of weak offshore winds could occur
with warm temperatures prevailing.
Looking ahead through month's end, above normal temps are favored
with no strong signal for precipiation.
180400z...coast/valleys...areas of broken-overcast stratus will occur near
the coast through 17z Wed with bases 1100-1500 ft mean sea level and tops to
1700 ft mean sea level. San/crq will likely have cigs by 08z Wed. But sna
will be later, probably after 10z Wed. Local vis 3-5 miles will
occur in the valleys 11z-17z Wed. Stratus will likely develop
along the coast Wed evening.
Mountains/deserts...mostly clear skies will prevail through Wed
evening with unrestricted vis. Areas of surface west winds 20-30 kt
with local gusts 40 kt will occur during the late afternoons and
evenings through Wednesday on the Desert Mountain slopes and east of
San Gorgonio Pass, with local low level wind shear and moderate up/downdrafts.
no hazardous boating conditions are expected through Sunday.
gusty and locally strong westerly winds are expected each
afternoon and evening through Thursday. Top gusts should reach 35
to 45 mph. These local winds will combine with low inland humidity
to elevated fire weather conditions for favored pockets along
mountain ridges, through mountain passes and into adjacent
Skywarn activation is not requested. However weather spotters are
encouraged to report significant weather conditions.