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Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
373 FXUS66 KEKA 012159 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 259 PM PDT Mon Jul 1 2024 .SYNOPSIS...A very strong heatwave remains on track to bring Major to Extreme HeatRisk and near record breaking temperatures across the interior Wednesday through the end of the week. Heat and very low humidity will also enhance fire weather concerns, especially Tuesday and Wednesday. && .DISCUSSION...Temperatures will begin increasing today, with interior temperatures currently running 5 to 10 degrees hotter than yesterday, especially in Lake and Mendocino Counties. Rapid warming and drying will persist 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 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. 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 impact on the heat. Though it may slighlty weaken heat for the southern half of the area, it is more likely that it will just shift the focus of heat further north into Trinity and Humboldt. 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 suggests 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. 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 sea breeze will 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 Crescent City. The vast majority of cluster ensemble members show the ridge persisting and only very slowly beginning to break down 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 around, albeit slightly weakened. All that is to say, all indicators point to strongly above average temperatures being here to stay for the foreseeable future. /JHW && .AVIATION...LIFR at the coast has been primarily replaced with VFR as of this time. Northwesterly winds will continue to increase with gusty winds at the coastal terminals today. Stratus will likely return tonight once temperatures cool and clouds off the coast push back inland. At KUKI, VFR conditions are persisting with gusty northwesterlies this afternoon. Mild winds should eventually return this evening with variable speeds after sunset. && .MARINE...Northerly winds will accelerate rapidly this afternoon/evening, with strongest winds leeward of Cape Mendocino as a high pressure begin to builds in and a thermal trough (in correlation with the incoming execessive heat inland) develops. These dynamics will favor moderate to strong pressure gradient. The pressure gradient will drive counterclockwise flow around the West with our coastal waters being where the winds blow from the north along the coast. Winds over the waters accelerate due to minimal friction between the land-sea interface. Winds will steadily increase from this afternoon through Tuesday, with widespread sustained strong to gale force winds and very steep seas through Wednesday. That all said, A Gale Warning is in effect for the outer waters this afternoon. These gales will propagate in a burst of very steep seas into the northern inner waters Tuesday evening through late Wednesday afternoon, and thus we have published a Hazardous Seas Warning for zone 450 as result. 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 (as of right now it does not pass the Cape) and relax the pressure gradient on Thursday. Seas will gradually subside Wednesday evening and Thursday. However, steep seas will persist across the waters into the weekend. && .FIRE WEATHER...The building heatwave will bring enhanced fire danger through the week, but especially Tuesday 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. Though restricted to ridgetops at night, such winds will mix down more broadly early each afternoon. For the forecast area, afternoon mixing will promotes widespread critical conditions in southeast Lake County Tuesday 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 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 Tuesday to 11 AM PDT Wednesday for CAZ107-108-110-111. Heat Advisory from 11 AM Tuesday to 8 PM PDT Wednesday for CAZ112. Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT Saturday for CAZ113>115. Red Flag Warning from 2 AM Tuesday to 8 PM PDT Wednesday for CAZ264. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 5 PM PDT Tuesday for PZZ450. Hazardous Seas Warning from 5 PM Tuesday to 5 PM PDT Wednesday for PZZ450. Small Craft Advisory until 3 AM PDT Wednesday for PZZ455. Small Craft Advisory until 5 PM PDT this afternoon for PZZ470. Gale Warning until 2 AM PDT Thursday for PZZ470. Gale Warning until 3 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