fxus66 ksgx 130500 

Area forecast discussion 
National Weather Service San Diego California 
858 PM PST Tue Dec 12 2017 

high pressure aloft and offshore flow at the surface will continue 
warm and dry weather into the middle of next week. Stronger Santa 
Ana winds Thursday morning through Friday morning for the mountains, 
foothills and passes. Skies will be mostly clear. 


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

A thin band of high clouds will skirt the edge of our area overnight 
from the northernmost periphery of a subtropical moisture plume. No 
changes were made this evening as the forecast remains on track, 
and the previous forecast discussion is below. 

An expansive upper ridge continues to dominate the weather across 
the U.S. West Coast. This will continue through early next week, 
promising a continuation of dry conditions with temperatures 
averaging much above normal. 

The main forecast change today was to indicate stronger winds for 
early Thursday morning through Friday morning. An upper level 
trough will be diving south from The Rockies and across Arizona on 
Thursday morning. Surface high pressure will build in to our east 
behind this feature. The surface pressure gradient trend since 
yesterday has been increasing in the Thu-Thu night timeframe. This 
means there is the potential for stronger northeast winds from 
the mountain ridges to the foothills, passes, and into portions of 
the valleys. Current forecast for these Santa Ana wind-prone areas 
is now for northeast winds to increase to 20-30 mph with gusts to 
50 mph and even isolated gusts to 65 mph possible (places such as 
Sill Hill/South Dakota county). This presents fire weather concerns. See 
fire weather discussion below. 

Winds will relax later Friday and through the weekend with 
tranquil weather prevailing. A brief period of light onshore flow 
Saturday will quickly give way to offshore winds early next week. 
Temps will cool some, but still remain above normal. 

Global models indicate a break down in the ridge during the middle 
to latter part of next week. Whether or not this translates to 
some rainfall for socal remains to be seen. 


Fire weather... 
offshore surface pressure gradient will be increasing Thursday 
through Friday morning. The model tendency since yesterday is to 
increase this gradient, which means that stronger winds are 
possible. An extremely dry airmass will remain in place and be 
re-enforced. Fuels are at record low moisture levels as well. 
Given the higher wind potential, have issued a Fire Weather Watch 
for all local mountains, the inland Empire, the inland valleys of 
San Diego County as well as inland Orange County effective 
12 am Thursday through 10 am Friday. Winds look to rev up first 
across northern areas early Thursday morning-afternoon, then peak 
into the San Diego mountains/portions of valleys Thursday night 
through early Friday morning. Lighter winds are forecast later 
Friday and through the weekend. 


130430z...mostly clear with unrestricted vis through Wednesday 
evening. Local surface northeast winds 20-30 knots with gusts to 40 
knots will occur at times from the mountain crests to the coastal 
foothills, including through/below Cajon Pass and the Santa Ana 


no hazardous marine weather is expected through Sunday. 


Sgx watches/warnings/advisories... 
California...Fire Weather Watch from late Wednesday night through Friday 
morning for Orange County inland areas-Riverside County 
mountains-including the San Jacinto Ranger district of the 
San Bernardino National Forest-San Bernardino County 
mountains-including the mountain top and front country 
Ranger districts of the San Bernardino National Forest-San 
Bernardino and Riverside County valleys -the inland Empire- 
San Diego County inland valleys-San Diego County mountains- 
including the Palomar and Descanso Ranger districts of the 
Cleveland National Forest-Santa Ana Mountains-including the 
Trabuco Ranger district of the Cleveland National Forest. 


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