Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
182 FXUS66 KSTO 260907 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 207 AM PDT Sun May 26 2024 .SYNOPSIS... Warmer weather returns to the region today, with generally above normal temperatures and primarily minor HeatRisk expected through the week ahead. Weak onshore flow also persists through Tuesday, before dry, northerly flow arrives from Wednesday through the end of the week. && .DISCUSSION... Much calmer weather is being observed across interior NorCal as of early this morning, with generally light winds across the region and only a handful of lingering clouds across far northern Shasta County. These mostly clear skies and calm winds will allow for early morning low temperatures to dip a few degrees cooler than previous nights. As a result, most areas should settle in the upper 40s to mid 50s by sunrise, with a few higher elevation locations into the upper 30s to low 40s. Broad troughing aloft is already progressing eastward and rising heights look to fill in behind it, with upper level ridging amplifying across the Great Basin and Intermountain West. Despite this, broad troughing aloft will continue to influence interior NorCal as another trough builds in from the Gulf of Alaska toward the Pacific Northwest by the early week period. As this occurs, a few isolated, late day showers will be possible along the Sierra crest on Monday, generally south of the Highway 50 corridor. Otherwise, this pattern will lead to warming temperatures today into the early week ahead, with afternoon high temperatures in the mid 80s to low 90s. Onshore, south to west winds are also expected to continue, but overall remain breezy at most, with late day gusts 20 to 25 mph through the Delta and its vicinity. Ensemble guidance is trending toward a consensus of the trough ejecting eastward from the Pacific Northwest across the mid to late week time frame. While initial impacts for interior NorCal will be limited on Wednesday, the surface flow pattern is expected to at least begin transitioning to a northerly direction. This looks to result in somewhat split flow on Wednesday, with northerly winds from roughly the I-80 corridor northward, while onshore flow persists further southward. Temperatures overall still look to remain slightly above normal, Valley high temperatures in the mid 80s to low 90s, and 70s to 80s at higher elevations, today through Wednesday. Minor HeatRisk is expected to accompany these temperatures as well. && .EXTENDED DISCUSSION (Thursday THROUGH Sunday)... Ensemble guidance is in generally good agreement on the trough finally ejecting eastward on Thursday while transient ridging builds in behind it. With this upper level transitional period on Thursday, dry, northerly surface flow should overtake most areas, with some gusty winds possible throughout the day on Thursday as well. While ensemble means are still working to incorporate the increasing trend in winds for Thursday, current NBM 50th percentile forecasts indicate some gusts nearing 40 mph along wind prone portions of the Sacramento Valley (namely the central and western Valley along the I- 5 corridor). Resultant probabilities of wind gusts reaching 40 mph are in the 40% to 60% range as well. These breezy to gusty winds, combined with dry antecedent conditions could see afternoon humidities dropping into the low to mid teens for much of the region on Thursday and Friday, with a few localized instances of single digit humidities certainly possible also (primarily within the northern Sacramento Valley). While the ridging aloft should remain fairly transient, the ridge axis does look to position itself over interior NorCal on Friday. As a result, firmly above normal temperatures are anticipated from Thursday into the early weekend, with Valley high temperatures in the 90s and 70s to 80s at higher elevations. Even with the warming trend, probabilities of reaching triple digits remain fairly low at this time, around 15% to 30%, with highest probabilities on Friday across the central and northern Sacramento Valley. Current forecasts do depict some scattered moderate HeatRisk in these areas as well. Ensemble guidance is then indicating the return of broad troughing aloft amidst high heights, signaling a trend toward above normal temperatures persisting, but onshore flow returning and limiting the upper bounds of the high temperature forecast next weekend. && .AVIATION... VFR conditions next 24 hours, except for local southwest wind gusts to 20 kts near the Delta. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$