Area Forecast Discussion
Issued by NWS San Diego, CA

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000 FXUS66 KSGX 260436 AFDSGX AREA FORECAST DISCUSSION National Weather Service San Diego CA 930 PM PDT SUN SEP 25 2016 .SYNOPSIS... Strong high pressure aloft off the California coast, and surface high pressure over the Great Basin, will keep dry and warm Santa Ana conditions over the southwest California through Monday with periods of gusty northeast winds near the coastal foothills. Upper level low pressure over the Baja Peninsula will bring increasing moisture and slow cooling beginning Tuesday as it drifts northward bringing with clouds, and a small chance for sprinkles or scattered, light showers at times. Onshore flow and seasonal temperatures return for the latter half of the week as a developing trough of low pressure moves inland across the West. && .DISCUSSION...FOR EXTREME SOUTHWESTERN CALIFORNIA INCLUDING ORANGE... SAN DIEGO...WESTERN RIVERSIDE AND SOUTHWESTERN SAN BERNARDINO COUNTIES... ...evening update... Today was as expected quite hot west of the mountains. Record high temps were set today at Chula Vista and El Cajon. Monday will be even a bit hotter yet than what we saw today, for most locations west of the mountains. A heat advisory remains in place there due to the excessively hot conditions. Meanwhile, locations in the mountains and deserts are actually quite nice, with the high deserts enjoying relatively cool weather with highs in the lower to mid 80s! Gradients this evening continue to hover around 10 mb offshore from the Socal coast to the Great Basin. Don`t think we`ll get much stronger than this. By late Monday the high over the great Basin begins to break down so relief is in site. Gusty offshore winds will continue into Monday, but don`t think we`ll get much stronger than what we`ve already seen today. A strong wind gust report was just sent for updated max wind speeds. No other changes were made this evening. A slight chance of thunderstorms remains in the forecast for Wednesday and Thursday afternoons as we see some return moisture working in from the SE. ...Remainder of Monday afternoon forecast discussion... A strong 596 DM Ridge off the California coast and low pressure digging southwest across northwest Mexico will keep E-NE winds and Santa Ana conditions across southern California through Monday. Strongest winds/gusts will be along the coastal mountain foothills and especially San Diego County. Temperatures will be well above average again on Monday with highs well into the 90s to 105 west of the mountains. A Heat Advisory and Wind Advisory has been posted. Please see LAXNPWSGX or check our web page for details. The windy, warm and dry weather has increased the wildfire danger. See the Fire Weather discussion below for details. The digging trough will cut-off a low tonight over the central Baja Peninsula, then drift slowly northward and become centered over the Lower Colorado River Valley Wed morning. This will bring increasing clouds and moisture from the SE, and gradually decrease the offshore flow. Cooling aloft and increased mid-level moisture will bring a small chance of shwrs/tstms, especially over the mts mid week. The low will be absorbed by the westerly winds to the north by Thu as a longwave trough amplifies southward along the West Coast. This will bring increasing onshore flow, a return of the marine layer, and cooler weather into next weekend. The Models/Confidence...The 12Z ECMWF/GFS runs are in fair agreement through 240 hours, so there is moderate to high confidence out into the extended period. A few sprinkles are possible on Tue with a slight chance of shwrs/tstms over the mts midweek. Any precip that manages to develop looks light and scattered at this point. && .AVIATION... 260330Z...Most wind gusts will be 15-30 kt through 09Z tonight, but winds will increase 09Z through 22Z Mon from the E with gusts 25-35 kt, strongest over San Diego County. STG LLWS will prevail in many areas west of the mountains when NE/E winds do not reach the surface through Monday. Mdt to strong up/down drafts will also affect much of the region over and west of the mtns through Mon. Expect LLWS returning tonight to KONT, while KSNA will only have a few hours of NE surface winds, with LLWS at other times. Otherwise mostly clear with unrestricted vis through Monday. && .MARINE... No hazardous marine weather is expected through Friday. && .BEACHES... Swell and surf will subside tonight into Monday. && .FIRE WEATHER... Critical fire weather conditions will continue today along the coastal mountain slopes and adjacent foothill areas, with RH at or below 15 percent, and northeast winds of at least 25 MPH. The most critical combination of heat...lowest humidity...and strongest winds is expected today. Still quite hot on Monday, but winds look weaker and may not sustain critical thresholds in many areas north of San Diego County, but minimum RH in these areas will remain near ten percent. For San Diego County...some increase in RH is likely from the mountains eastward, possibly holding the coastal slopes just below critical Red Flag criteria, however winds will sustain 25 MPH or better in many areas. The offshore flow may remain strong over San Diego County on Tuesday, but the trend will be for weakening most areas. Tuesday into Wednesday there will be a moderation in the heat, and significant RH recovery. There will even be a chance of sprinkles on Tuesday, and a few showers over the mountains, mainly Wed/Thu. && .SKYWARN... Skywarn activation is not requested. However weather spotters are encouraged to report significant weather conditions. && .SGX Watches/Warnings/Advisories... CA...Red Flag Warning until 3 PM PDT Monday 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-San Gorgonio Pass Near Banning-Santa Ana Mountains-Including The Trabuco Ranger District of the Cleveland National Forest. Wind Advisory until 5 PM PDT Monday for San Diego County Mountains-San Diego County Valleys. Wind Advisory until 4 PM PDT this afternoon for Orange County Inland Areas-Riverside County Mountains-San Bernardino County Mountains-San Bernardino and Riverside County Valleys-The Inland Empire-Santa Ana Mountains and Foothills. Heat Advisory from 11 AM this morning to 8 PM PDT Monday 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. Beach Hazards Statement through this evening for Orange County Coastal Areas-San Diego County Coastal Areas. PZ...None. && $$ PUBLIC/FIRE WEATHER...JAD/17/JMB AVIATION/MARINE/BEACHES...PG

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