####018007307#### FXUS66 KEKA 031310 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 551 AM PDT Fri May 3 2024 .SYNOPSIS...A cold front will move across the area this evening through early Saturday morning bringing a period of heavy rain. Brief heavy wet snow is also expected above 2500 feet early Saturday morning. Colder air will settle over the area for the remainder of the weekend with frost and freezing temperatures expected for the interior valleys during early morning hours. && .DISCUSSION...Prefrontal light rain is expected to begin over Del Norte County late this afternoon. Heavy rain will develop this evening for Del Norte and northern Humboldt as a surface cold front moves southward by midnight or shortly after. Heavy rain rates >0.30in/hr are probable (>70% chance). Chance for hourly rates >0.50in/hr are 10-20% for the interior mountains Del Norte and Humboldt, except for the King Range where it is 40%. These heavy rates (>0.50in/hr) per the HREF are not expected to sustain over a large area (an entire basin) for more than hour or two and thus will hold off on hoisting a flood watch. Minor nuisance flooding of low-lying areas with poor drainage and ponding water on roads are certainly possible with these heavy rates. It is quite anomalous for early May and will continue to highlight the heavy rain in a weather story graphic and social media post. Flows on the rivers are low and April was not exactly wet with above normal precip, so soils are not saturated as earlier this winter. There will be run-off concerns and advisories may be necessary once the heavy rain commences by late this evening. The cold front will move SE by early Saturday and southern Mendocino and southern Lake Counties will also get a good soaking of rain, 0.50-0.75in over 6-12 hours, mostly Saturday morning. Threat of widespread heavy rain will diminish rapidly by midday Saturday after the brief influx of moisture shifts southward and an unseasonably cold airmass settles over the area. Looking at the HREF, snow levels are forecast to rapidly fall early Saturday with probabilities >70% for hourly snow rates > 1in/hr. This warrants at least a winter weather advisory for elevations above 2500 feet. Greatest uncertainty is with snow levels. Levels could vary to as low as 2000 feet to as high as 3500 feet. Leaned toward lower snow levels, 2500 ft, due to heavy precip rates driving the freezing levels lower. Impacts over the major highway passes will be offset the high May sun angle and relatively warm road surface. Reduced visibilities from heavy snow and slick roads will have impacts and a winter weather advisory has been hoisted til 11 AM Saturday. Shower activity will continue during the day on Saturday as the cold core aloft moves overhead and onshore westerlies bring open cellular shallow convection onto the coast. Not all that confident in the potential for low topped thunderstorms with surface temperatures cooling down drastically in the interior and 850mb temps dropping to -3C. High temps for the warmest valleys will struggle to reach 60F. After the precip winds down or diminishing subfreezing temperatures will be primary concern for the interior Sunday morning. It is certain (100%) for the mountains. Valleys will most likely freeze too (>70% chance), mostly in Trinity County. Spreads are much wider with probabilities from 30% to 70% for valleys in Del Norte, Humboldt, Mendocino and Lake. Frost or mid 30's are much more certain, even for coastal areas. Fog and low clouds will probably form and hinder the longwave cooling in some valleys, especially after 1 to 3 inches of rain. Another shortwave trough in NW flow will probably generate more showers Monday (highest chances Del Norte and northern Humboldt). This trough will not be as cold and moisture will be limited. Surface northerlies will begin to strengthen after passage of this shortwave trough and dry conditions are most likely into mid week (>80% chance). Majority of the 500mb ensemble cluster means (>80%) leads to more confidence in dry weather with slow warming of daytime temperatures. The one caveat to the "warming" will be potential for freezing early morning temps in the interior valleys under clearer skies and calm or light winds, assuming absolutely no fog and low clouds. Also, the strength of E-NE winds will factor into "how warm" and the eventual return of coastal stratus. High temps in the low 90's for warmest valley are not completely out of the realm of possibilities either, increasing to 20-40% on Friday. Interior valley high temps in the 80's are much more probable (>60%) by Friday. DB && .AVIATION...VFR prevailed at all terminals this morning. Nighttime fog product showed extensive low clouds and fog in the interior valleys. The LIFR conditions (1/4SM VV002 at FOT for example) will most likely not have long duration impacts at any of the terminals this morning. It may spill out from the valleys around daybreak and get close to KACV resulting in brief LIFR. Otherwise, VFR is forecast to prevail today as multi-layered clouds with an approaching front increase through the day. Conditions are forecast to deteriorate to IFR in moderate to heavy rain this evening at KCEC and KACV. IFR conditions will take longer to envelope UKI where LLWS should return with frontal passage by 12Z Sat. DB && .MARINE...Northerly winds have diminished in response to an approaching front. Southerlies are expected to develop this morning and slowly increase through the day today ahead of the cold front. Southerly gusts up to 30 kts are forecast with the passage of the front, particularly in the northern inners this evening, then sharply shift to west behind it's passage. Gusts up to 25 kts are expected with passing convective showers into Saturday morning, slowly becoming restricted to the southern outers by Saturday afternoon. Winds weaken Saturday night and turn westerly Sunday. Another weak frontal passage may pass early next week, then more robust northerlies are possible by midweek. Seas remain low and locally generated through this weekend, and a series of NW swells are expected to fill in early next week. DB/TDJ && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Winter Weather Advisory from 4 AM to 11 AM PDT Saturday for CAZ102-105>108-111. Frost Advisory until 8 AM PDT this morning for CAZ107-108. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory from 9 PM this evening to 3 AM PDT Saturday for PZZ450. Small Craft Advisory from 9 PM this evening to 9 AM PDT Saturday for PZZ470. Small Craft Advisory from 3 AM to 9 PM PDT Saturday for PZZ475. && $$ Visit us at https://www.weather.gov/eureka Follow us on Facebook and Twitter at: https://www.facebook.com/NWSEureka https://www.twitter.com/NWSEureka For forecast zone information see the forecast zone map online: https://www.weather.gov/images/eka/zonemap.png ####018008202#### FXUS66 KLOX 031311 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 601 AM PDT Fri May 3 2024 .SYNOPSIS...03/327 AM. A dry weather will continue through early Saturday morning, then an unseasonably cold storm system will brush the area to the north this weekend with a chance for light precipitation later Saturday into Sunday. Increasing onshore flow ahead of the storm will bring a cooling trend through Sunday. Night and morning low clouds and fog will struggle to clear at the coast today, then spread back inland tonight. A warming and drying trend will develop next week. && .SHORT TERM (TDY-SUN)...03/420 AM. The latest fog product imagery shows low clouds and fog becoming more entrenched across the region, extending well into the Southland valleys and touching the foothills. Clouds are little less extensive north of Point Conception, but clouds will likely continue to fill in later this morning across much of the coastal and valley areas. Cooling is set up to continue today as strengthening onshore flow out ahead of an unseasonably cold storm system will bring a deeper marine intrusion. The low cloud field will push well into the coastal slopes tonight and reach into the portions of the interior valleys north of Point Conception. The stronger onshore flow and the tightening pressure gradient out ahead of the storm's cold front will bring increasing southwesterly winds across the interior portions of the area through Saturday night. Winds should remain below advisory levels this afternoon and evening, but a wind advisory will likely be needed for the Antelope Valley and adjacent foothills on Saturday afternoon and night as the gradient tightens further. The storm system, over the Gulf of Alaska this morning, will dig south into northern California through Saturday night, brushing the area to the north. A cold frontal boundary will drop south into the region on Saturday, bringing rain to much of the area. PoPs have been nudged higher in the latest forecast, going higher than NBM solutions. All of the ensemble members have light precipitation developing for areas north of Point Conception, along the northern slopes of the mountains, and across eastern Los Angeles County. The forecast is little more questionable for southern Santa Barbara County, Ventura County, and western Los Angeles County. The forecast trends wetter as deterministic solutions are starting to trend more southwest to west with the low-level flow pattern. The forecast trends more toward the deterministic solutions south of Point Conception, buying into the model trends. Model tabular forecast output suggests a high- to-likely chance of rain for areas north of Point Conception, and moderate-to-high chance for areas southwest of Point Conception. There is a moderate chance that southern Santa Barbara County, Ventura County, and western Los Angeles County could end up being in a rain shadow effect as downsloping occurs from the Transverse Ranges. Rainfall amounts will likely range from a quarter inch or less, except a quarter to half inch across northwestern San Luis Obispo County. Amounts will be highest for the northern portion of the area and along the northern slopes of the mountains. Rainfall will only amount to a few hundredths at most for most coastal and valley areas south of Point Conception. Gusty west to northwest winds will develop across many coastal areas, into the Santa Ynez Valley, across southern Santa Barbara, up into the Interstate 5 Corridor, and down into the Antelope Valley. EPS solutions indicate good agreement across the area for the potential for wind advisory, but a handful of solutions indicate a gust potential over 55 mph at KSDB. This will need to be monitored as we get closer as wind gusts have been trending generally higher with each run. A colder air mass will spread into the area between Saturday and Sunday night with the cold front. Temperatures during this stretch trend colder than NBM values, and Sunday could be a cold day for May, similar to a February or March with 60s being common across the coastal and valley areas. .LONG TERM (MON-THU)...03/415 AM. A warming and drying trend will develop for the work week next week as high pressure aloft reestablishes. The forecast ensembles agree with a warming trend extending through at least Thursday. EPS solutions tend to hold onto the warming trend extending into next weekend. EPS cloud cover means point to the marine layer depth being kept in check, but confidence is moderate at best in this solution as we are in May. The latest forecast keeps some marine layer induced low clouds and clouds returning to coastal areas by mid week. && .AVIATION...03/1300Z. At 12Z at KLAX, the marine layer was 2800 ft deep with an inversion top at 4500 ft and a temperature of 14 C. Low clouds and fog were widespread in all coastal and valley areas, with clouds moving into the lower coastal slopes. Cigs were mostly high IFR to low MVFR, except LIFR to VLIFR north of Pt Conception, and in the valleys and foothills. Skies should clear by mid to late morning in the valleys and by noon on the coastal plain, but may linger all day at some beaches. Expect similar conditions tonight, with widespread low clouds in coastal and most valley areas, and low MVFR to high IFR conds, except LIFR to VLIFR conds in the foothills. KLAX...Low to moderate confidence in the 12Z TAF. There is a 20-30% chance that cigs will not scatter out at all today. There is only a 20% chance of an E wind component of 7-8 kt from thru 17Z and from 09Z-15Z Sat. KBUR...Low to moderate confidence in the 12Z TAF. There is a 30% chance of cigs lingering until 20-21Z. There is a 30% chance of cigs will arrive as early as 03Z tonight. && .MARINE...03/421 AM. In the outer waters, Small Craft Advisory (SCA) level winds are expected to increase to Gales (70% chance) this afternoon, with the strongest winds off the coast. Gales will continue thru late tonight, then drop to SCA levels. Winds may even drop below SCA level for a while Sat morning, but seas will remain above SCA levels. SCA level winds are expected (80% chance) Sat afternoon, then continue much of the time thru Tue. There is a 50% chance of Gale force winds Sun afternoon/evening, then a 30-40% chance during the afternoon/eve hours Mon thru Tue. In the inner waters N of Pt. Sal, SCA level winds will develop today, then continue thru late tonight. There is a 40-50% chance of SCA level winds/seas during the afternoon/eve hours Sat, then SCA winds are likely (70% chance) during the afternoon/eve hours Sun thru Tue. There is a 30% chance of gales Sun afternoon/eve. In the SBA Channel, there is a 40% chance of SCA level winds in western portions of the channel this afternoon thru late tonight, then Sat afternoon/eve. SCA level W-NW winds are expected Sat night thru late Sun night (80% chance), and are likely (60-70% chance) during the late afternoon thru late night hours Mon thru Tue. There is a 30% chance of gales Sun afternoon/eve. In the southern inner waters, there is a 30% chance of SCA level winds from Anacapa Island to Malibu during the late afternoon/eve hours Sat. SCA level winds are likely (70% chance) Sat night thru late Sun night. There is a 40% chance of SCA level winds during the late afternoon thru late evening hours Mon thru Tue. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for zone 645. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Saturday for zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Hall AVIATION...DB MARINE...DB SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox ####018008194#### FXUS66 KLOX 031312 AFDLOX Area Forecast Discussion National Weather Service Los Angeles/Oxnard CA 601 AM PDT Fri May 3 2024 .SYNOPSIS...03/327 AM. A dry weather will continue through early Saturday morning, then an unseasonably cold storm system will brush the area to the north this weekend with a chance for light precipitation later Saturday into Sunday. Increasing onshore flow ahead of the storm will bring a cooling trend through Sunday. Night and morning low clouds and fog will struggle to clear at the coast today, then spread back inland tonight. A warming and drying trend will develop next week. && .SHORT TERM (TDY-SUN)...03/420 AM. The latest fog product imagery shows low clouds and fog becoming more entrenched across the region, extending well into the Southland valleys and touching the foothills. Clouds are little less extensive north of Point Conception, but clouds will likely continue to fill in later this morning across much of the coastal and valley areas. Cooling is set up to continue today as strengthening onshore flow out ahead of an unseasonably cold storm system will bring a deeper marine intrusion. The low cloud field will push well into the coastal slopes tonight and reach into the portions of the interior valleys north of Point Conception. The stronger onshore flow and the tightening pressure gradient out ahead of the storm's cold front will bring increasing southwesterly winds across the interior portions of the area through Saturday night. Winds should remain below advisory levels this afternoon and evening, but a wind advisory will likely be needed for the Antelope Valley and adjacent foothills on Saturday afternoon and night as the gradient tightens further. The storm system, over the Gulf of Alaska this morning, will dig south into northern California through Saturday night, brushing the area to the north. A cold frontal boundary will drop south into the region on Saturday, bringing rain to much of the area. PoPs have been nudged higher in the latest forecast, going higher than NBM solutions. All of the ensemble members have light precipitation developing for areas north of Point Conception, along the northern slopes of the mountains, and across eastern Los Angeles County. The forecast is little more questionable for southern Santa Barbara County, Ventura County, and western Los Angeles County. The forecast trends wetter as deterministic solutions are starting to trend more southwest to west with the low-level flow pattern. The forecast trends more toward the deterministic solutions south of Point Conception, buying into the model trends. Model tabular forecast output suggests a high- to-likely chance of rain for areas north of Point Conception, and moderate-to-high chance for areas southwest of Point Conception. There is a moderate chance that southern Santa Barbara County, Ventura County, and western Los Angeles County could end up being in a rain shadow effect as downsloping occurs from the Transverse Ranges. Rainfall amounts will likely range from a quarter inch or less, except a quarter to half inch across northwestern San Luis Obispo County. Amounts will be highest for the northern portion of the area and along the northern slopes of the mountains. Rainfall will only amount to a few hundredths at most for most coastal and valley areas south of Point Conception. Gusty west to northwest winds will develop across many coastal areas, into the Santa Ynez Valley, across southern Santa Barbara, up into the Interstate 5 Corridor, and down into the Antelope Valley. EPS solutions indicate good agreement across the area for the potential for wind advisory, but a handful of solutions indicate a gust potential over 55 mph at KSDB. This will need to be monitored as we get closer as wind gusts have been trending generally higher with each run. A colder air mass will spread into the area between Saturday and Sunday night with the cold front. Temperatures during this stretch trend colder than NBM values, and Sunday could be a cold day for May, similar to a February or March with 60s being common across the coastal and valley areas. .LONG TERM (MON-THU)...03/415 AM. A warming and drying trend will develop for the work week next week as high pressure aloft reestablishes. The forecast ensembles agree with a warming trend extending through at least Thursday. EPS solutions tend to hold onto the warming trend extending into next weekend. EPS cloud cover means point to the marine layer depth being kept in check, but confidence is moderate at best in this solution as we are in May. The latest forecast keeps some marine layer induced low clouds and clouds returning to coastal areas by mid week. && .AVIATION...03/1300Z. At 12Z at KLAX, the marine layer was 2800 ft deep with an inversion top at 4500 ft and a temperature of 14 C. Low clouds and fog were widespread in all coastal and valley areas, with clouds moving into the lower coastal slopes. Cigs were mostly high IFR to low MVFR, except LIFR to VLIFR north of Pt Conception, and in the valleys and foothills. Skies should clear by mid to late morning in the valleys and by noon on the coastal plain, but may linger all day at some beaches. Expect similar conditions tonight, with widespread low clouds in coastal and most valley areas, and low MVFR to high IFR conds, except LIFR to VLIFR conds in the foothills. KLAX...Low to moderate confidence in the 12Z TAF. There is a 30-40% chance that cigs will not scatter out at all today. There is a 20% chance of an E wind component of 7-8 kt thru 17Z and from 09Z-15Z Sat. KBUR...Low to moderate confidence in the 12Z TAF. There is a 30% chance of cigs lingering until 20-21Z. There is a 30% chance of cigs will arrive as early as 03Z tonight. && .MARINE...03/421 AM. In the outer waters, Small Craft Advisory (SCA) level winds are expected to increase to Gales (70% chance) this afternoon, with the strongest winds off the coast. Gales will continue thru late tonight, then drop to SCA levels. Winds may even drop below SCA level for a while Sat morning, but seas will remain above SCA levels. SCA level winds are expected (80% chance) Sat afternoon, then continue much of the time thru Tue. There is a 50% chance of Gale force winds Sun afternoon/evening, then a 30-40% chance during the afternoon/eve hours Mon thru Tue. In the inner waters N of Pt. Sal, SCA level winds will develop today, then continue thru late tonight. There is a 40-50% chance of SCA level winds/seas during the afternoon/eve hours Sat, then SCA winds are likely (70% chance) during the afternoon/eve hours Sun thru Tue. There is a 30% chance of gales Sun afternoon/eve. In the SBA Channel, there is a 40% chance of SCA level winds in western portions of the channel this afternoon thru late tonight, then Sat afternoon/eve. SCA level W-NW winds are expected Sat night thru late Sun night (80% chance), and are likely (60-70% chance) during the late afternoon thru late night hours Mon thru Tue. There is a 30% chance of gales Sun afternoon/eve. In the southern inner waters, there is a 30% chance of SCA level winds from Anacapa Island to Malibu during the late afternoon/eve hours Sat. SCA level winds are likely (70% chance) Sat night thru late Sun night. There is a 40% chance of SCA level winds during the late afternoon thru late evening hours Mon thru Tue. && .LOX WATCHES/WARNINGS/ADVISORIES... CA...NONE. PZ...Small Craft Advisory in effect until 3 AM PDT Saturday for zone 645. (See LAXMWWLOX). Gale Warning in effect until 3 AM PDT Saturday for zones 670-673-676. (See LAXMWWLOX). && $$ PUBLIC...Hall AVIATION...DB MARINE...DB SYNOPSIS...Hall weather.gov/losangeles Experimental Graphical Hazardous Weather Outlook at: https://www.weather.gov/erh/ghwo?wfo=lox