Area Forecast Discussion
Issued by NWS San Diego, CA

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000 FXUS66 KSGX 172342 AFDSGX Area Forecast Discussion National Weather Service San Diego CA 342 PM PST Tue Jan 17 2017 .SYNOPSIS... The focus of the forecast remains on the series of storms expected to impact California Thursday into Tuesday of next week. For our region, heavy mountain snowfall and heavy rain leading to urban and possible river flooding look to be the main impacts. However there could be periods of gusty winds and thunderstorms as well. As the event progresses flooding will become and increasing concern as soils in the region saturate. A break in the stormy pattern is expected by the middle of next week. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... The focus of the forecast remains the upcoming series of storms, slated to impact our region between Thursday and Tuesday of next week. Prior to these systems, weather will remain quiet in SoCal. The first storm system is slated to arrive on Thursday, bringing moderate to heavy rainfall, with snow at elevations above 5000 ft. With this system, light showers will be possible early Thursday morning, however the bulk of the rain/snow should arrive between 6 AM and 3 PM. Instability appears sufficient with this system for scattered thunderstorms Thursday morning and afternoon. The primary impacts should be mountain snowfall and locally heavy rain leading to urban flooding. The river flood threat with this first storm appears to be low. Activity should become more showery in nature Thursday night, with the best precipitation potential focused over the mountains and valleys. Storm two will impact the region Friday, with the best rainfall chances being Friday morning and afternoon. The primary threats with this system look to be winds, mountain snow and heavy rain. The strongest winds are expected in SD County, with gusty southerly winds along the coast in the morning transitioning to gusty northwesterly winds for all areas by Friday evening. There is some potential for thunderstorms friday afternoon, and this will have to be watched closely over the coming days with current model projections suggesting 35-50 kt 900-700 mb winds that could be easily be mixed to the surface resulting in strong gusts over the over the coast and valleys. Snow levels with this system may be as low as 4500 ft in the San Bernardino County Mountains, with levels closer to 5500 ft in the SD County Mountains. Therefore the most significant snow accumulations are expected at elevations above 6000 ft in the San Bernardino and Riverside County Mountains. Urban flooding will also be a concern with high rainfalls rates possible during the day on Friday. With the ground increasing in saturation, flash flooding and debris flows near burn scars will be a concern. Some River flooding, particularly involving the San Diego River, is possible during this period. A relative lull in activity is expected Saturday in Sunday, with scattered light to moderate rain/mountain snow showers Saturday and mostly cloudy conditions for most areas during the day on Sunday. Strong winds will remain a concern in the mountains and along the desert slopes, with mountain wave activity continuing through the day in Saturday. The third storm system is expected to arrive Sunday night and Monday. Currently the intensity of this system looks similar to Friday`s forecast storm. Thus heavy rain/mountain snow, winds and flooding may again be concerns with this system. At this time however, global models continue to show inconsistencies with the timing and evolution of the system. && .AVIATION... 172130Z...Mostly clear through this evening. Patchy low clouds along the coast tonight, with bases 800-1000 ft MSL and tops near 1200 ft MSL. VIS could lower to 1-3 SM BR where low clouds develop along the coast, or where fog forms in the valleys due to radiational cooling. Conditions will improve by late Wed morning. && .MARINE... A series of Pacific storms will create strong winds, rain and rough seas Thursday through Tuesday. Conditions hazardous to small craft are likely Thursday, then gale force wind gusts to 35 kt and very large combined seas of 14-18 ft are likely Friday and Saturday. Winds and seas will diminish Sunday, then gale force conditions developing again late Sunday through Monday as another system moves across the area. && .BEACHES... Swell will gradually increase Thursday into Saturday with high surf resulting. The highest surf will occur Saturday when surf could be large enough to cause coastal damage, coastal flooding and beach erosion. Swell and surf will decrease Sunday before increasing again Monday. A High Surf advisory will likely be needed through the period. && .HYDROLOGY... A Hydrologic Outlook has been issued to discuss precipitation potential, flooding issues, and runoff, including potential river flooding issues. Please see the Hydrologic Outlook, located on our home page: && .SKYWARN... Skywarn activation will not be needed today. && .SGX WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ PUBLIC...BA AVIATION/MARINE/BEACHES...JJT is the U.S. government's official web portal to all federal, state and local government web resources and services.