Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
133 FXUS66 KSTO 181033 AAA AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 130 AM PDT Sat May 18 2024 .SYNOPSIS... Seasonable temperatures will continue through the weekend and into early next week. Mostly sunny and dry conditions with periods of breezy winds expected through the next 7 days. Isolated showers and thunderstorms over high Sierra south of Highway 50 today. && .DISCUSSION... Synoptically, west-southwest flow will continue to keep onshore winds through Saturday morning. Latest GOES-18 Nighttime Microphysics RGB indicates the marine low stratus deck is pushing inland into the Delta region. Hires guidance is not handling current trends well. Based on current 20-30 mph Delta winds and already apparent intrusion of stratus deck, continued eastward push of stratus looks probable with potentially similar coverage by sunrise to what was observed yesterday with areas around or just west of the Greater Sacramento Metro. Besides possible morning stratus, expect a mostly clear Saturday with continued breezy onshore winds through Saturday night, though not as strong as Friday night. Only other weather of note will be the isolated shower and thunderstorm chances along the Sierra crest mainly south of Highway 50 this afternoon- evening where NBM has 15-30% probabilities of thunderstorms. Best chances will be in southeastern Tuolumne County today where hires indicates decent instability will develop with little/minimal CIN. No significant forcing besides the mountains themselves, so main impacts expected with any thunderstorm will be brief heavy rain, locally gusty winds, lightning, and small hail with the stronger updrafts. Given west- southwesterly flow aloft and mean winds around 10 knots, thunderstorms will drift eastward after forming. Throughout the day today, a trough from the British Columbia will dig into the Great Basin region, which will shift a more westerly flow to a northwesterly flow overhead tonight-Sunday. As this trough phases with a closed upper-low in SoCal Monday, pressure gradients across NorCal will increase, producing another breezy north wind day. Currently the NBM has a 50-75% probability of gusts greater than 34 knots (~40 mph) in the usual north wind prone area in the western Sacramento Valley along the I-5 corridor. Current forecasts continue to keep gusts only to around 25-30 knots, but given the probabilities of higher winds, winds may increase as we get closer. Per usual with north wind days, minimum afternoon RH`s will decline, with widespread less than 15% RH values in the Sacramento Valley. Temperatures will be mild, but breezy winds and low RH`s will lead to locally elevated fire weather conditions Monday. Northerly flow will weaken Tuesday, allowing temperatures to increase but winds to decrease. Tuesday appears to be the warmest day in the next 7 days, with highs in the mid 80s to low 90s across the Valley/Delta and upper 60s to low 80s in the Foothills/Mountains. //Peters && .EXTENDED DISCUSSION (Wednesday THROUGH Saturday)... Series of upper lows progged to move through the PacNW during the extended forecast period. Associated upper troughing will extend into NorCal. Models differ with timing, track, and strength of lows leading to some forecast uncertainty with precipitation potential. NBM shows some showers chances over our northern and eastern foothills/mountains Friday and Saturday afternoon. High temperatures forecast to cool through the extended period, returning to near normal Friday, and slightly below normal Saturday. && .AVIATION... VFR conditions over interior NorCal next 24 hrs except areas MVFR/IFR in stratus vcnty of Delta til 18z and locally in Sac Vly til 17z. In Central Vly, sfc wind mainly at or below 12 kts til 00z Sat, then areas sfc wind up to 20 kts. Vcnty Delta SWly sfc wind 15- 25 kts with lcl gusts to 35 kts. Isolated -shra/-tsra possible over SierNev, S of Hwy 50 btwn 19z-02z. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$