textproduct: San Diego

SYNOPSIS

Mostly cloudy skies with isolated drizzle this afternoon will make way to Santa Ana winds this evening with clear skies, and cold temperatures overnight. Weak to moderate Santa Ana winds come and go in two pulses, the first through Sunday morning, then the second Sunday night through Tuesday. Weaker offshore winds continue thereafter yielding to low relative humidity, dry conditions and high temperatures hovering a few degrees above average.

SHORT TERM

As of 1:10 PM, satellite shows mostly cloudy skies throughout the coastal basin, with some clouds scattering out in northern areas. Accumulating precipitation has effectively fully come to a close, and the latest HRRR run has completely removed showers from the 48 hr forecast in the region. Clouds will continue to gradually retreat this afternoon from northwest to southeast, leaving behind clear skies for northern areas and patchy cloud cover over inland San Diego County by this evening. This clearing can be attributed to the synoptic scale positively tilted shortwave trough axis - embedded within the larger eastern US polar vortex - moving east of us and leaving us in the subsidence quadrant. The trough is dragging along the surface high pressure from Canada into the Northern Rockies / Great Basin and increasing our North/South pressure gradient here locally.

North/Northeasterly Santa Ana winds have begun to spill through the Cajon Pass as of this afternoon and will continue through the pass and Santa Ana / San Bernardino County mountain foothills through Sunday morning. Winds will be moderate at times in these areas, gusting 30-40 mph in the Inland Empire and up to 60 mph in the Cajon Pass, San Bernardino County foothills and in wind prone canyons of the Santa Ana mountains like Fremont Canyon. Other mountain foothills won't be quite as gusty during this first pulse, gusting up to 40 mph.

North winds weaken Sunday afternoon, then re-intensify out of the east Sunday night as the strong surface high (around 1042 mb) drops down into the southern Great Plains, thereby increasing our East/West pressure gradient. This gradient remains strong through at least Tuesday morning, yielding to periods of strong easterly wind gusts through the Banning Pass and Peninsular Range foothills around 30-45 mph during the early part of the weak.

Very dry air will accompany these Santa Ana winds, dropping humidity down to 20-30% tonight and ultimately down to 10% by Sunday where the winds blow. Morning temperatures will also be on the colder side for Southern California standards, with moderate chances for Sunday morning lows dipping below 35F in the interior valleys and good confidence for below freezing temperatures in the high desert.

LONG TERM

Medium range models show high confidence in the redevelopment of a ridge over the mountain West, with a center axis over eastern Washington, Oregon and California on Tuesday. High temperatures will only reach a few degrees above average - in the low 70s for the coastal basin - as high clouds will be passing through intermittently and as mid-level temperatures will remain cool, despite the ridge.

Wednesday, around 30% of WPC model ensemble cluster runs show a closed low developing in the Pacific and moving though Southern California. In all ensemble runs, this trough is weak and embedded within the greater stubborn West Coast ridge. High temperatures may cool slightly Thursday and Friday if this scenario plays out, though the chances for any precipitation are close to zero. Most ensemble clusters then agree that the ridge will re-intensify to a certain extent into next weekend, bringing temperatures back above average.

Weak offshore winds continue through the end of the week if the trough referenced earlier doesn't form, keeping relative humidity low for inland areas, while the coast experiences weak onshore flow.

Mountains/Deserts

SCT-BKN clouds around 10,000ft MSL and VFR conditions expected through the period with clouds clearing overnight. Local areas BLDU possible late tonight into Sunday morning with gustier easterly winds, and local wind gusts 30-45 kts through mtn passes. Mod up/downdrafts near the mountains 03Z-18Z Sun.

MARINE

No hazardous marine conditions are expected through Wednesday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Wind Advisory from 7 PM this evening to 1 PM PST Sunday for San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-Santa Ana Mountains and Foothills.

PZ...None.