Area Forecast Discussion
Issued by NWS San Diego, CA

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FXUS66 KSGX 290350

Area Forecast Discussion
National Weather Service San Diego CA
850 PM PDT Wed Jun 28 2017

Seasonal Summer weather will prevail through the 4th of July. Brief
periods of elevated fire weather conditions are anticipated over and
east of the mountains ridges each afternoon and evening. Otherwise
no hazardous weather conditions are expected.



Marine stratus covered the CA Bight and extended inland for several
miles along the coast at 8 PM PDT. At sunset...smoke from the
Cristianitos Fire near San Clemente was overspreading much of SW
Orange County. The 00Z Miramar sounding showed the marine inversion
base had lifted to nearly 2K FT MSL. Significant cooling was noted
below 5K FT. Surface pressure gradients were trending onshore,
supporting westerly winds over the mts/through the passes/and into
the deserts. Peak gusts were in the 40-50 MPH range, but an isolated
gust of 57 MPH was logged at the Whitewater West RAWS site in the
San Gorgonio Pass. No forecast changes this evening.

From previous discussion...

At 130 PM, Low amplitude ridging remained in place over the
Southwest US. Skies were mostly clear, with low clouds limited to
the coastal waters. Winds remained breezy through the passes with
local gusts of 30-45 mph. As expected temperatures are noticeable
cooler than this time yesterday, with some locations over the
valleys running 10-15 degrees F cooler than this time yesterday.

The low stratus currently hovering off the coast should make a
push inland after sunset, bringing increasing low cloud cover to
the coast and western valleys through early Thursday morning.
Patchy dense fog is possible over the higher valley terrain.
Cooling will continue Tuesday, with 3-5 degrees F of cooling in
the 950-850 mb layer leading to an additional 3-6 degree F drop in
afternoon highs over the valleys.

Friday through the middle of next week, the forecast can be
described by one word "seasonal". Upper level ridging will
generally remain in place over or just off the West Coast, as a
few weak troughs ride over the ridge. This will result in minor
day to day temperatures fluctuations, standard afternoon sea
breezes, and night and morning low clouds over the coast and
western valleys.

Toward the second half of next week, both the ECMWF and GFS
suggest a shift in the position of the upper level ridge axis
toward the Four Corners or western Plains. Along with the
potential development of a weak mid level (850-500 mb) trough off
the West Coast, this may allow for a push of monsoonal moisture
into the AZ/CA/NV region. Though uncertainty on the specifics of
the forecast remain high, moderate run-to-run consistency in the
global models lends itself to modest forecaster confidence in the
general synoptic pattern for this period.


290200Z...Coast/Valleys...Low clouds with bases 1000-1500 ft MSL and
tops near 2000 ft MSL will continue to move inland overnight,
continuing to affect KSAN and KCRQ, and moving into KSNA around 10
and eventually KONT after about 2-3 AM. Expect the clouds to spread
into the western valleys overnight, with vis 1-3SM where clouds and
terrain intersect. The inversion height is at 1500 FT with a +5.8C
inversion strength. Clouds should clear the coast mid-late morning
on Thursday with VFR prevailing for the afternoon before the low
stratus deck fills back in again much the same for Thu night.

Mountains/Deserts...Clear skies with unrestricted vis will prevail
through Thursday. West winds locally gusting 20-25 kt will produce
LLWS and weak-mdt up/downdrafts over and east of the mountains
this evening. Winds will weaken by late evening.


No hazardous marine weather is expected through Sunday.


Despite the improving conditions and deepening marine layer, a
wildfire developed on Camp Pendleton near Sen Clemente this
afternoon. IR satellite imagery showed the fire still burning at 8
PM PDT, even with light winds, temps in the low 60s and an RH of 85%.

Critical fire weather conditions were occurring much farther to the
east early this evening...near the passes/along some desert slopes/
locally into the desert, with RH values at or below 15%, winds of
25 MPH or greater, and gusts of 40-50 MPH. But west of the mtn
crests, RH values were rising as the onshore flow draws modified
marine air farther inland. Westerly winds will continue to be quite
gusty across the mts/deserts each afternoon/evening, but the areas
with critical RH/wind combinations will become more localized and
last for only a few hours in any one spot through the weekend.
Still, the wildfire risk will remain elevated at times over the back
country through the Holiday weekend due to the dry fuels, heat and
gusty winds.


Skywarn activation will not be needed on Thursday.




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