textproduct: San Diego

SYNOPSIS

Periods of rain, wind, and mountain snow are expected through Thursday. The final two rounds of widespread rain, snow, and gusty winds will be tonight into Wednesday morning and Thursday afternoon and evening. Strong westerly winds and heavy mountain snow can be expected tonight into Wednesday. There is a slight chance of isolated thunderstorms overnight. Periods of dry conditions expected Wednesday mid-morning into Thursday morning. Chances for showers decrease into Friday, with dry conditions looking like they will prevail through the weekend. Chances of precipitation increase again into early next week.

..New Aviation Discussion For the 00z TAF Package

Key Points: *A winter storm will bring widespread heavy snow to the mountains above 5000 ft creating hazardous travel conditions through Thursday evening. Snow levels as low as 3500 to 4000 ft Wednesday night and again on Thursday may result in light accumulations through the Cajon Pass.

*Gusty and potentially damaging west winds along the mountain crests and adjacent desert slopes this afternoon through Wednesday. Gusty westerly winds expected for the coast and valleys will peak Wednesday morning.

*Light to moderate rain is expected below the snow level at times through Thursday night. Ponding of water on roads and minor street flooding in urban areas possible. Increased flows on rivers, especially the San Diego and Santa Margarita.

At 1 PM, scattered light showers are moving west to east across the coastal basin. Areas of showers will become more widespread overnight. Mountain snow is expected to continue through Wednesday morning, with periods of heavy snow possible overnight. Snow levels at 1 PM were 5500 ft and are expected to drop to 3500-4000 ft by Wednesday morning. More details on expected rain and snow can be found in the Hydrology section below.

Winds will continue to increase over the mountains and into the deserts through the afternoon. Winds are expected to peak late tonight into Wednesday morning. Locally damaging wind gusts are possible for the desert mountain slopes. For the mountain ridges and desert mountain slopes peak gusts of 60 to 70 mph, potentially up to 75 mph in wind prone locations are expected. Wind gusts in the deserts will be 45 to 65 mph with the strongest winds near the mountain foothills. For the coast and valleys, peak gusts of 30 to 45 mph are expected, with local gusts up to 55 mph possible. Winds for the coast and valleys will peak in strength early Wednesday morning.

There will be decreasing chances for showers into Friday morning. Much of Friday through Sunday is trending drier than previous forecasts. High temperatures will warm each day for Friday through Monday with high temperatures on Monday around 5 degrees above average, ranging from the mid to upper 60s near the coast to the lower to mid 70s for the valleys with the lower deserts around 80. Shower chances begin to increase again early next week, with NBM showing chances of precipitation as early as Monday. The NBM is a bit of an outlier with individual ensemble members of the GEFS and ECMWF beginning to cluster around the middle of the week for the onset of the next round of precipitation.

AVIATION

180045Z...Coast/Valleys...SCT/BKN low clouds based 3000-5000 ft MSL currently through the coastal basin with isolated -SHRA. Conditions slowly deteriorate from north to south after 03Z Wed with SCT SRHA developing and bases lowering to 2000-3000 ft MSL through the early morning. Strengthening southwest to south winds will gust 25-35 kts through the basin (isolated gusts over 40 kts at the coastline) after 06Z ahead of a main band of moderate to heavy precipitation. This band is expected to sweep through from northwest to southeast from 09-15Z bringing widespread MVFR cigs/vis with intermittent IFR conditions expected in heavier showers. Slight chance (10-20%) for TSRA within the main band. Winds turn west and slowly weaken, thereafter, with generally VFR conditions expected. ISO-SCT -SHRA may briefly create MVFR cigs/vis through the day, especially in San Diego County.

Mountains/Deserts...Isolated SHRA/SHSN currently in the mtns will increase in coverage and intensity this evening/overnight as another line of moderate to heavy precip moves through the area. Mountains shrouded in FG through Wednesday morning. Additionally, strong south to southwest winds will continue to strengthen this evening with widespread gusts up to 35-45 kts after 06Z. Gusts to 55 kts along desert slopes of the mtns with isolated gusts exceeding 60 kts along the slopes in San Diego County. Precip will slowly come to an end from north to south from 12-18Z (except for persistent -SHRA/SHSN along coastal slopes) with winds turning westerly, but remaining elevated (strong along eastern facing slopes) through 00Z Thu. Mountain waves may surface at times along the desert floor.

MARINE

Gales will redevelop this evening and continue through Wednesday, generating hazardous boating conditions with steep seas building to 11-13 feet. Check the Gale Warning for more details. After another lull, strong winds will redevelop Thursday, likely producing hazardous conditions once again. Conditions will improve by Friday.

BEACHES

High surf of 4 to 9 feet is expected, with sets as high as 11 feet, highest in San Diego County on Wednesday. Dangerous swimming and surfing conditions and localized beach erosion can be expected. A High Surf Advisory is in effect through Friday and contains more details.

HYDROLOGY

Another round of widespread rain and mountain snow is expected tonight into Wednesday. Hourly rainfall rates are expected to be 0.20-0.30" per hour. Forecast rainfall totals for Tuesday into Wednesday are 0.20-0.60" for the coast and valleys, 0.20-0.30" for the High Desert, and 0.10-0.25" for the low deserts. 1-2" of rain are expected below the snow level.

The San Diego River at Fashion Valley and the Santa Margarita river are expected to reach monitor stage on Wednesday. Santa Margarita river is expected to peak at 11 AM at 10.9 feet and the San Diego River is expected to peak at 10 AM at 8.3 feet. Interested parties should continue to monitor river forecast and observed river levels. Current forecast indicates minor flood impacts to Avenida del Rio and Fashion Valley Mall Road may occur. Do not drive through flooded areas or around barricades. Please see the latest River Statement or CNRFC website for more information. There may be impacts to Whitewater River although with significant snow forecast to impact the higher elevations of the mountains, flood impacts may be limited.

Snow levels currently around 5500 ft and are expected to drop to 4000-3500 ft by Wednesday morning. Through Wednesday snow forecast has an additional 6 to 12" from 5000 to 6000 feet, 12 to 20" from 6000 to 7000 feet, locally exceeding 24" above 7500 feet. The San Diego County mountains are expected to see 3 to 6" below 5500 feet, and up to 9" above 5500 feet. For early Wednesday morning and again Thursday, there is a chance of accumulating snow on I-15 at the summit of the Cajon Pass.

Scattered light rain and snow showers are possible through Wednesday before another round of more widespread showers Thursday as a third shortwave moves north of the area. Snow levels for Wednesday and Thursday are expected to be 3500-5000 ft with an additional 2 to 6 inches of snow expected across area mountains. For the coast and valleys and additional 0.25 to 0.50" of rain are possible with 0.10" or less in the deserts.

There remains slight chances of precipitation Friday morning with conditions trending drier for the weekend. Additional shower chances are in the forecast for early to mid-next week with low confidence in details.

SKYWARN

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

SGX WATCHES/WARNINGS/ADVISORIES

CA...High Surf Advisory until 10 PM PST Friday for Orange County Coastal Areas-San Diego County Coastal Areas.

Wind Advisory from 8 PM this evening to 8 AM PST Wednesday for Orange County Coastal Areas-Orange County Inland Areas-San Bernardino and Riverside County Valleys-The Inland Empire- San Diego County Coastal Areas-San Diego County Valleys- Santa Ana Mountains and Foothills.

Winter Storm Warning until 10 PM PST Thursday for Riverside County Mountains-San Bernardino County Mountains.

Winter Weather Advisory until 10 PM PST Thursday for San Diego County Mountains.

Wind Advisory until 4 PM PST Wednesday for Apple and Lucerne Valleys-San Diego County Deserts-San Gorgonio Pass near Banning.

Wind Advisory from 10 PM this evening to 4 PM PST Wednesday for Coachella Valley.

PZ...Gale Warning from 8 PM this evening to 1 PM PST Wednesday for Coastal Waters from San Mateo Point to the Mexican Border and out to 10 nm-Waters from San Mateo Point to the Mexican Border Extending 10 to 60 nm out including San Clemente Island.