Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
699 FXUS66 KEKA 021216 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 516 AM PDT Tue Jul 2 2024 .SYNOPSIS...A very strong heatwave will build in force today bringing Major to Extreme HeatRisk and near record breaking temperatures across the interior Wednesday through the weekend. Heat and very dry humidity will also enhance fire weather concerns, especially Tuesday and Wednesday. && .DISCUSSION...Satellite imagery continues to show extremely dry air settling across NW California under the influence of a building upper level ridge. Even the marine layer, bolstered by a strengthened inversion, is ragged at best and isolated to only the most protected parts of the Humboldt Coast. Temperatures will continue increasing today with interior temperatures reaching above 100 throughout the interior, but especially in Lake and Mendocino Counties. Rapid warming and drying will continue through Wednesday. The southern half of the area will see temperatures peak on Wednesday. Major to isolated Extreme HeatRisk is expected throughout interior valleys, but especially around Clear Lake and within the Russian River Valley. In both areas, NBM shows a 60 to 80% chance of highs in excess of 110. Such temperatures are either record breaking or very nearly so all across the southern half of the area. HeatRisk is bolstered by the fact that overnight conditions will bring very little relief. On valley bottoms, most likely lows are around 70 with strong thermal belts creating midslope lows closer to 80 by Wednesday morning. Model ensembles have come to better agreement on the development of the ridge through the week. While most models still show a weak surface low forming off the coast of Central California, few models show it having much impact on the heat. Though it may slighlty weaken heat for the southern half of the area, it will mostly just shift the focus of heat further north into Trinity and Humboldt by Thursday. Regardless, near record breaking heat will continue for the entire interior through through the week. Though conditions will be dangerously hot along the Trinity River by Wednesday, NBM suggest the peak heat further north around Friday. By this point, NBM shows a 70 to 90% chance of highs above 110 all along the Trinity River Valley. For Hoopa in particular, this could easily approach the all time high temperature record of 111. HeatRisk is only slightly diminished in the north thanks to lower nighttime temperatures closer to 60 through the week. Heat will even begin to move towards the coast as the week wears on and onshore flow continues to weaken. High pressure settling through the week will help create an increasingly shallow marine inversion which may, at times, be totally pushed offshore by easterly nighttime winds. While a triumphant sea breeze will certainly cool off coastal areas each afternoon, increasingly clear and hot mornings may allow high to approach 80 by late in the week. By Thursday and Friday, NBM shows a 50 to 70% chance of brief highs over 80 as close to shore as Arcata and downtown Crescent City. The vast majority of cluster ensemble members show the ridge persisting and only very slowly beginning to break down late this weekend. By Sunday, only 10% of members show the ridge pushing east. Even by next Tuesday, 50% of ensemble members still have the ridge sticking ridge sticking around, albeit slightly weakened. All that is to say, all indicator point to strongly above average temperatures being here to stay for the foreseeable future. /JHW && .AVIATION...LIFR conditions have been impacting KACV with OVC layer at FL003, while VFR conditions prevail at KCEC and KUKI. Pics from the sky shows stratus advecting northward and attempting to approaches KCEC. However, gusty N winds continues precluding any low clouds reaching this terminal. Otherwise, low clouds and patchy fog are expected to clear out with the diurnal heating late in the morning. Thereafter, expect prevailing VFR conditions for all aerodromes through at least Thursday. A period of visibility reduction with haze will be possible at KCEC in the afternoon due to the sea spray as the winds over the waters increase. Surface gusty northerly winds continues at KCEC early this morning, while calm winds at KACV and KUKI. After 19Z, winds becoming breezy N winds at 15-25 kt along the coast, with strongest gusts from 25-35 kt in the afternoon. Dry E-NE flow is expected to increase tonight as a high pressure continue building into the region. This will inhibited stratus develop for the coastal terminals. LLWS will be likely (60-75%)at CEC late tonight through Wednesday morning with a stronger component wind aloft. && .MARINE...Gale force northerly winds over the outer waters will continue through Wednesday, with advisory criteria for the inner waters. Locally gale force around Pt St George and downwind of Cape Mendocino as well. Winds will continue to strengthen through this evening, resulting in sustained winds around 35 kts with gusts to around 45 kts. Very steep and hazardous seas of 15-17 feet @ 11 seconds are expected for the outer waters tonight. A Gale Warning remains in effect for the outer waters through Wednesday evening. This gales will propagate in a burst of very steep seas into the northern inner waters this evening through late Wednesday afternoon. A Hazardous Seas Warning will be in effect late this afternoon for zone 450. These winds will gradually ease from south to north throughout the second half of the day on Wednesday. A southerly wind reversal will move north along the Mendocino Coast and relax the pressure gradient on Thursday. Seas will gradually subside Wednesday evening and Thursday, but steep seas will persist across the waters into the weekend. Followed by sub-Advisory conditions likely over the weekend with light to moderate winds and seas generally around 5-6 feet @ 8 s. && .FIRE WEATHER...The building heatwave will bring enhanced fire danger through the week, but especially today and Wednesday. As highs climb well above 100, RH will crater with most interior valleys very likely (80% chance) to see minimum RH between 5 and 10%. Overnight conditions will bring little relief with very poor RH recoveries of 30 to 40%. Even with only gentle terrain winds, such dry conditions will promote critical fire weather conditions each afternoon. There are several areas where enhanced winds will generate more widespread and long lasting critical conditions. First, as the high first builds across the area, a building pressure gradient aligned with the Sacramento Valley will promote gusty northeast winds along the Sacramento foothills with sustained winds of 12 to 18 mph. Such winds have already been observed early this morning with very poor RH recoveries barely above 20 percent. Though restricted to ridgetops at night, such winds will mix down more broadly early each afternoon. For the forecast area, afternoon mixing will promote widespread critical conditions in southeast Lake County today and Wednesday, prompting a Red Flag Warning in the area. Elsewhere, periods of critical fire weather are expected during the afternoon where terrain winds are enhanced, such as along the Trinity River Valley. Strong thermal belts will help promote critical conditions even on night, especially with moderate, dry northeast winds building each night on high ridges, especially in the Klamath Mountains. Fire Weather conditions will only slightly begin to ease by this weekend. /JHW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Heat Advisory from 11 AM Thursday to 8 PM PDT Saturday for CAZ102. Heat Advisory from 11 AM to 8 PM PDT Wednesday for CAZ104- 106. Excessive Heat Warning from 11 AM Wednesday to 8 PM PDT Saturday for CAZ105-107-108-110-111. Heat Advisory from 11 AM this morning to 11 AM PDT Wednesday for CAZ107-108-110-111. Heat Advisory from 11 AM this morning to 8 PM PDT Wednesday for CAZ112. Excessive Heat Warning from 11 AM this morning to 8 PM PDT Saturday for CAZ113>115. Red Flag Warning until 8 PM PDT Wednesday for CAZ264. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 PM PDT this afternoon for PZZ450. Hazardous Seas Warning from 5 PM this afternoon to 3 AM PDT Thursday for PZZ450. Small Craft Advisory until 9 AM PDT Wednesday for PZZ455. Gale Warning until 2 AM PDT Thursday for PZZ470. Gale Warning until 9 PM PDT Wednesday 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