textproduct: San Diego

SYNOPSIS

Cooler with breezy west winds can be expected through this evening. Winds turn offshore by Thursday, becoming stronger for the coastal slopes into the western valleys. The winds will bring cooler conditions across the mountains and deserts with slightly warmer conditions west of the mountains. Offshore winds will continue through the weekend with a chance of precipitation for some areas by Sunday into next Monday. A weak ridge will move over the region by early next week, bringing drier weather.

DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE

SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES...

A trough continues to push over Northern California today. This has contributed to a deeper marine layer that is taking its time clearing out this afternoon. Some areas near the beaches will be partially cloudy into the afternoon, but clouds will be expected to move back into the coastal areas and further into the inland valleys overnight into Thursday morning. If any fog forms, it will be over higher terrain. The troughing pattern will also bring elevated west winds across the mountains and deserts through this evening. Highest winds can be expected over the northern portion of our forecast area with mountain winds gusting near 35-50 MPH, while desert areas see winds closer to 25-40 MPH.

The trough will move inland over the Great Basin, stalling Thursday into Friday. This will bring northerly flow aloft, where winds will change to an offshore pattern by Thursday morning. North winds will funnel into the valleys and portions of the coast. NBM 75th percentile winds show gusts primarily near 20-40 MPH across much of this region. Areas near the foothills show winds closer to 40-50 MPH, locally higher below the Cajon Pass. Winds look to weaken some by Thursday night, then ramp up again Friday morning.

The low pressure system associated with the longwave trough will become cut off from the system, and meander southwestward, eventually over northern Baja California. Since we will remain on the west and north side of the low, offshore winds will continue over the region through the weekend , potentially into early next week. Strongest and most widespread winds look to occur sometime around Saturday, when the pressure gradient is strongest. The low will be able to pull in some moisture from Mexico, potentially some light precipitation for the lower deserts into the mountains. The position of the low is still unresolved in the models, where a track too far to the south would bring mostly dry weather. NBM chances increase near 15-30% by late Saturday night through Monday afternoon across these regions, even west of the mountains. Model ensembles do show light precip amounts, but these will be subject to change as we get closer in time. After the low departs, high pressure off the coast will begin to move over the area, with sunnier and drier weather.

AVIATION

042345Z....Coast/Valleys...Low clouds currently along the coast will become more widespread through 05Z Thu. Low clouds are expected to reach into the valleys and portions of the Inland Empire by 08Z Thu. Bases will be 800-1800 ft overnight with some vis reductions for elevated inland valleys. Low clouds/vis restrictions will clear 13- 16Z Thu. Gusts 20-30 kt possible below passes into portions of the valleys through the day. Areas of LLWS shear and mod up/down drafts expected.

Mountains/Deserts...VFR conditions will prevail through the period. Westerly wind gusts 25-40 kts through mountain passes, along desert slopes, and into the deserts through 12Z Thu. Isolated gusts to 55 kts through wind-prone passes and canyons. Winds will turn northerly around 12Z Thu. Strongest winds Thu will be on the coastal slopes of the San Bernardino mountains, High Desert, and in the Coachella Valley. Northerly gusts 30-45 kt, locally up to 55 kt expected. There will be areas of LLWS and mod up/down drafts.

MARINE

Northwest winds will develop on Thursday generating choppy and hazardous conditions. Gusts of 20 to 25 kt are expected with seas of 5 to 8 feet. A Small Craft Advisory is in effect from 7 AM to 10 PM Thursday. No additional hazardous marine conditions are expected through Sunday.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...Wind Advisory until 4 AM PST Thursday for Apple and Lucerne Valleys-Riverside County Mountains-San Bernardino County Mountains-San Diego County Deserts-San Diego County Mountains-San Gorgonio Pass near Banning.

PZ...Small Craft Advisory from 1 PM to 10 PM PST Thursday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm.

Small Craft Advisory from 7 AM to 10 PM PST Thursday for Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.