Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
789 FXUS66 KSTO 042021 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 121 PM PDT Sat May 4 2024 .SYNOPSIS... A weather system moves through the area today bringing showers, mountain snow, isolated thunderstorms, gusty winds and cooler temperatures. Drier, warmer conditions return next week with gusty north to east winds mid-week. && .DISCUSSION... The late-season system is upon us bringing with a variety of impacts including Valley rain, mountain snow, and breezy winds. Radar earlier this morning presented with a classic narrow cold- frontal rain band (NCFR) aligned north-south that passed through the Sacramento Valley. Surface observations reported periods of gusty winds with the NCFR -- upwards of 40 to 46 mph in the northern Sacramento Valley around Redding, Red Bluff, and Chico. In the wake of the frontal passage, winds have subsided considerably. Can`t rule out some isolated thunderstorms developing in the afternoon in the Valley; the National Blend of Models (NBM) advertises roughly a 15-30% north of Sacramento. Up in the mountains, snow levels started this morning in the 6000 to 7000 foot range. As the cold air ushers in, expect snow levels to plummet to less than 5000 feet by mid-afternoon, and further drops to below 4000 feet by the evening. Snow levels will drop even more overnight as precipitation begins to taper off. This will result in a rain-to-snow transition for a handful of mountain communities through the rest of the day. A period of heavy snow will impact travel corridors such as Interstate 80 and Highway 50 this afternoon and evening with the HREF advertising peak afternoon/evening snowfall rates between 1-2.5 inch per hour. The Winter Storm Warning remains in effect for elevations 4000 ft and above through 8 AM Sunday. For a probabilistic sense, the National Blend of Models gives locations above 5000 feet a 50-90% chance of >= 12 inches of snow. Minor accumulations of up to an inch are expected between 3000 to 4000 ft. Precipitation ends in the late afternoon for the Valley and overnight in the mountains. Aside a few lingering snow showers at along/south of Interstate 80 day break Sunday, dry conditions are forecast to return to interior northern California. Despite the drier conditions, temperatures won`t be quick to rebound as Valley highs will remain in the 60s. For comparison, normal highs for the Sacramento Valley are in the upper 70s. That said -- this will be the start of day-to-day warming through the week as high pressure rebuilds over the eastern Pacific. // Rowe && .EXTENDED DISCUSSION (Wednesday THROUGH Saturday)... Warming temperatures are expected for the second half of next week as an upper-level ridge builds west of California and short- wave drops from the Pacific Northwest to the Great Basin. This synoptic pattern does favor dry, northerly winds for northern California: both the Extreme Forecast Index (EFI) and NBM are picking up on these increasing winds in the Wednesday-Thursday timeframe. During this same time, the day-to-day warming will see afternoon highs return to near-normal by Wednesday, and above normal for Thursday and into next weekend. While today may not seem very May-like, next weekend certainly will: the NBM gives roughly a 50-80% chance of exceeding 90 deg F for Saturday for many Valley communities. (That`s not a typo -- yes, I mean ninety!) // Rowe && .AVIATION... Quick moving late season storm system moves across interior NorCal today into Sunday. Gusty south-southwesterly winds and Valley rain showers through the afternoon. Isolated thunderstorms with MVFR/IFR conditions also possible between 20z and 03z from Sacramento northward. VFR conditions then expected in the Valley late this evening into Sunday. In the Sierra, widespread IFR/LIFR with moderate snow expected and periods of heavy snow possible through this evening and into the overnight hours. Snow levels 4000-5000 feet this afternoon, fall to 3000-4000 feet this evening. Southwesterly Sierra winds gusting 40-45 kts at times this afternoon, decreasing after 00z Sunday. && .STO WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 8 AM PDT Sunday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$