Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
974 FXUS66 KEKA 141124 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 424 AM PDT Sun Jul 14 2024 .SYNOPSIS...The prolonged heatwave breaks while the threat for thunderstorms and dry lighting increases as monsoonal moisture drives in from an offshore low pressure system. After lingering thunderstorm chances Monday, inland temperatures continue to trend down for the first half of next week before turning higher again. && .DISCUSSION...Attention is focused on a mid to upper low advancing alongside the CA coast. Guided between the Four Corners high and the low, a healthy plume of mid level monsoonal moisture is currently moving in from the south. This moisture will increase in the mid to upper levels, with a very dry surface layer. Model soundings hold the classic inverted V signature and present enough elevated instability (MUCAPE) for strong "dry" showers and thunderstorms over the interior regions, mainly in Lake, Eastern Mendocino, and Trinity counties. Interior Humboldt also looks probable to see some thunderstorms. Chances will increase through this evening (15 to 25%) as discrete areas of PVA rotate in off the low and the moisture within interacts with the higher terrain. Early morning convective activity began in coastal Mendocino and into Southern Humbodlt County. This coverage aligned with a modeled, focused area of forcing associated with PVA. A secondary similar feature will form later this morning, and will track over Humboldt and into Trinity County. Expanded forecast thunderstorm coverage (isolated) over most of Humboldt and Mendocino in anticipation of this, but confidence remains highest for farther east from Lake to Trinity County, especially this afternoon and evening over Trinity when scattered coverage is possible. See the Fire Weather section for more on this threat and the ongoing Red Flag Warning. There looks to be just enough lingering moisture on Monday for additional thunderstorms over Trinity County. A shortwave trough will clip N CA on Tuesday, but this system looks to be much drier. A few showers may attempt to form closer to the Del Norte area. SREF currently keeps a sliver of 5% chance for thunderstorms contained in Siskiyou County.The Four Corners region high will continue to weaken the first half of next week when most of the warmer interior valleys drop below 100. Thereafter, the Four Corners high will restrengthen and expand back west. NBM currently holds a moderate probability (40 - 50%) of temperatures to exceed 105 by next weekend for inland valleys such of Ukiah and Weaverville. /JJW && .AVIATION...LIFR/IFR conditions prevail at the coastal terminals early this morning. Some high-based convective clouds are moving through, with occasional lightning in areas. The terminals are unlikely to see thunder today, but it is not completely out of the question. Brief erratic wind gusts could accompany any thunder. Scattering of low ceilings today is uncertain as the near-surface conditions remain similar to yesterday, but VFR conditions in the afternoon are possible. Any clearing will be short lived as stratus is forecast to make a comeback in the evening bringing LIFR/IFR ceilings and visibilities back. UKI is forecast to remain VFR through the day. JB && .MARINE...Winds and steep seas will continue to gradually subside today. Seas are expected to fall below advisory criteria by the late morning in the inner waters, and the evening in the outer waters. Some thunderstorms are possible today nearshore and are already being observed early this morning. The best chances to see thunder would be this morning south of Cape Mendocino. Thunder will likely be dry and could see some brief erratic gusty winds and steep seas. A disturbance offshore Tuesday is forecast to bring in southerly breezes. High pressure sets back up midweek, bringing northerlies back. JB && .FIRE WEATHER...The dry thunderstorm event is underway. Early morning thunderstorm activity began near coastal Mendocino and into Southern Humboldt. The risk for dry lightning and gusty outflow winds has been expanded to include most of Humboldt and Mendocino counties. A shower or thunderstorm cannot be ruled out for eastern Del Norte this afternoon given what has been verifying. The highest concern remains in zones 277 and 283 where the Red Flag Warning remains. These zones have the best coverage of this activity and live fuels are more receptive to burning. Zone 263 in South Lake County may see good coverage of dry lightning this morning before activity moves north. Additional isolated thunderstorms are forecast for East and Northeast Trinity County on Monday before the moisture exits. A shortwave trough will clip the region on Tuesday and will increase southerly winds in the interior, particularly in Trinity County where locally critical fire weather conditions are forecast as a result. && .EKA WATCHES/WARNINGS/ADVISORIES... CA... Red Flag Warning until 10 PM PDT this evening for CAZ277- 283. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM PDT this morning for PZZ450. Small Craft Advisory until 3 PM PDT this afternoon for PZZ470-475. && $$ 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