Area Forecast Discussion
Issued by NWS Eureka, CA
Issued by NWS Eureka, CA
966 FXUS66 KEKA 250234 AFDEKA AREA FORECAST DISCUSSION National Weather Service Eureka CA 734 PM PDT Mon Jun 24 2024 .SYNOPSIS...Interior warm and dry conditions continue through Tuesday while marine stratus dampens coastal temperatures. An upper level disturbance mid-week will allow for relatively cooler temperatures through Thursday. Warming temperatures will develop at the end of the week. && .UPDATE...This afternoon thunderstorms developed in the San Joaquin valley and made is as far north as Stockton. The Satellite shows convective clouds as far north as Napa county. IR Satellite also shows widespread convective off the central CA coast. The CAMS are showing some light returns in the modeled reflectivity over Mendocino and Lake counties. The low levels look to be dry so there may be some gusty winds associated with the showers. So have added thunderstorms to the forecast for Tuesday in southern Mendocino and Lake counties. These areas look like they have the highest probabilities of seeing a few lightning strikes, but it is possible these storms could make it farther north. This will need to be monitored as it gets closer. MKK && .PREV DISCUSSION... /issued 256 PM PDT Mon Jun 24 2024/ DISCUSSION...The afternoon visible satellite reveals mostly blue skies and stubborn stratus along the very immediate Humboldt and Del Norte coast. Mid to high level clouds are also observed streaming into S and CENT CA this afternoon from a sub-tropical moisture plume being guided in ahead of an approaching NE Pacific trough. Occasional lightning strikes are being observed along the CENT CA coast and over the ocean well offshore. Mid-level moisture will arrive in Lake and Southern Mendocino counties after midnight. Regarding potential impacts, model guidance is struggling to resolve instability with the mid to upper moisture. Soundings show very dry low-levels, so if a thunderstorm were to form, it would be mostly dry at the surface. The NAM model suite continues to bring in a fair amount of MU CAPE, but the model may be underestimating cloudcover. The question will be if the anomalous moisture, with PWAT values up to 1 to perhaps 1.16 inches will be sufficient for isolated high- based thunderstorm development during peak heating with forcing from terrain influence and a subtle shortwave/PVA band. Confidence is low on this solution, and the zones to continue to watch will be in the far southern Mendocino and Lake County. Any convective showers that do form will create gusty, erratic winds. The jet stream continues to remain unusually active for the season, with the oscillating progressive ridge to trough pattern to continue. The next trough is due Wednesday, and it will knock inland temperatures back to near or below seasonal norms. The trough will enhance westerly winds on Wednesday and to a lesser extent Thursday, particularly in Lake County where gusts to 30 mph will be possible through and over the favored terrain. /JJW AVIATION...Coastal stratus from overnight and this morning will continue to erode away to the immediate coast. Coastal terminals are forecast to stay at VFR into mid to late this evening. Westerly to north-westerly winds to 10 knots are expected throughout the region through the day. Mid to late this evening a reversal in winds along the Del Norte Coast will bring up to 10 knot southerly winds ushering in more coastal stratus. Coastal stratus is expected to envelop the usual areas along the coast with MVFR to IFR ceilings most likely overnight. Winds will die down at Ukiah late this evening with the terminal remaining in VFR throughout the current TAF period. MARINE...In general, northerly winds will weaken throughout the marine zones despite a slight uptick in winds in the lee of Cape Mendocino. Throughout tonight and into early tomorrow morning, the outer waters and southern inner waters are forecasted to support marginal steep, short period seas that meet small craft criteria. By mid morning tomorrow, seas are forecast to drop below small craft advisory conditions in the waters. Meanwhile a minor northwest swell of 5 feet at 11 seconds will persist through the day today and then decay through tomorrow. Northerlies are forecast to remain below 15 kt for most zones tomorrow through Thursday morning, aside from the persistent 15-20 kt northerlies expected directly downwind of Cape Mendocino. Winds may strengthen again Thursday afternoon and into this weekend. FIRE WEATHER...A plume of subtropical moisture will begin to arrive after midnight tonight. Though lacking instability, the moisture may trigger some gusty showers or an isolated dry thunderstorm through terrain enhancement in South Mendocino and Lake County. Though chances are very low (less than 10%), if strikes do occur, any grass fire starts would be capable of rapid spreading on Wednesday when an upper trough passage enhances westerly winds. Winds gusting to 30 mph and low RH values to the upper teens can be expected Wednesday. The onshore flow will be gusty on Thursday to a lesser extent, and RH values will tick up to the low 20s. /JJW && .EKA WATCHES/WARNINGS/ADVISORIES... CA... None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 3 AM PDT Tuesday for PZZ455. Small Craft Advisory until 9 AM PDT Tuesday 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