Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
373 FXUS66 KSTO 022118 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 218 PM PDT Sun Jun 2 2024 .SYNOPSIS... Onshore flow and near normal temperatures persist today and Monday, with isolated showers possible overnight into Monday across the northern Sacramento Valley and along the northern Sierra. Hot weather and moderate to major HeatRisk then arrives Tuesday through the end of the week with periods of breezy to gusty winds. && .DISCUSSION... Discussion at a Glance - Cooler through Monday with periods of increased onshore flow and Delta Breeze. - An Excessive Heat Warning goes into effect from Tuesday morning through Thursday evening across the Valley and adjacent foothills. - Areas of Major HeatRisk Tuesday for the Valley, become widespread Wednesday for the Valley & Foothills with widespread triple digit high temperatures. Prepare now for elevated daytime highs and overnight lows and reconsider outdoor activities during the hottest part of the day (3:00-7:00 PM). - Areas of Major HeatRisk continue on Thursday, with primarily Moderate HeatRisk by Friday; Triple digits in the Northern and Central Sacramento Valley and adjacent Valley foothills with mid to upper 90s in the Delta and Sacramento metro area. Short-Term Discussion (Today THROUGH Wednesday)... As of early this afternoon, mostly sunny skies are evident across interior NorCal with only some high cirrus over Shasta and Tehama counties. Onshore south to west winds will persist through the afternoon and evening, with some gusts of 20 to 25 kts throughout the Delta and the vicinity. Otherwise, Valley high temperatures today look to reach the upper 80s to low 90s, with 70s to 80s at higher elevations. Before upper level ridging begins to dictate the background weather pattern, a trough looks to eject from the Pacific Northwest toward the Intermountain West late tonight into the early week ahead. As this wave moves within the vicinity of interior NorCal, there will be some potential (20% to 40% chance) of isolated showers across the northern Sacramento Valley and along the northern Sierra overnight tonight into Monday. Latest probabilities of exceeding 0.1" of QPF are around 10% to 25% at this time and as a result, minor impacts at most are anticipated. Otherwise, this system looks to bring a very brief reprieve from the heat on Monday, with Valley high temperatures in the low to mid 80s and 60s to 70s at higher elevations. As the trough exits the region late Monday, heights aloft are expected to rise as upper level ridging looks to build in over the western CONUS through midweek. This will result in a rapid warm up to well above normal temperatures from Tuesday through the end of the week. Resultant Valley high temperatures look to rise firmly into the upper 90s to low triple digits on Tuesday, with widespread triple digits in the Valley anticipated on Wednesday. Even at higher elevations, high temperatures into the 80s to 90s are expected. Overnight low temperature recovery will remain limited as well, with 60s to low 70s in the Valley and foothills and 50s to 60s across the mountains. This will lead to areas of major HeatRisk throughout much of the Valley and foothills, with moderate HeatRisk elsewhere. As a result, an Excessive Heat Warning goes into effect for much of the Valley and foothills at 11 am PDT Tuesday, June 4 and continues through 8 pm PDT Thursday June 6. Additionally, as the ridge builds in on Tuesday and Wednesday, surface winds are expected to shift to a north-northwesterly direction. Strongest winds are expected to occur Tuesday afternoon and evening throughout the Sacramento and northern San Joaquin Valleys, with gusts of 20 to 25 mph possible at times. This dry northerly wind combined with hot temperatures and forecast relative humidities into the upper teens to low 20s will likely result in some elevated fire weather conditions on Tuesday as well. Remember, area waterways continue to run fast and cold from snowmelt, creating dangerous conditions for those seeking relief in rivers and lakes next week. Stay tuned for updates as we get closer and plan ahead now to practice heat and cold water safety! To view the latest HeatRisk, please visit www.wpc.ncep.noaa.gov/heatrisk/ To view current water temperatures, please visit www.cnrfc.noaa.gov && .EXTENDED DISCUSSION (Thursday THROUGH Sunday)... Ensemble guidance is in good agreement on the ridge axis shifting eastward toward the Intermountain West across the late week period as a trough churns over the eastern Pacific. This will set up southwesterly flow aloft for interior NorCal and reintroduce south to west, onshore surface flow to the region as well. This should result in a gradual cooling trend from Thursday into the weekend, with an emphasis on "gradual". Valley high temperatures still look to remain in the upper 90s to triple digits on Thursday and Friday, with widespread moderate and areas of major HeatRisk Thursday becoming primarily widespread moderate HeatRisk on Friday. Comparatively cooler temperatures of Valley highs in the low to mid 90s and 70s to 80s at higher elevations, are then anticipated into the weekend. Periodically breezy to gusty late day winds are expected, with a slight (5% to 15%) chance for late day mountain thunderstorms from Thursday into the weekend as well. Additionally, area waterways continue to run fast and cold from snowmelt, creating dangerous conditions for those seeking relief in rivers and lakes next week. Stay tuned for updates as we get closer and plan ahead now to practice heat and cold water safety! To view the latest HeatRisk, please visit www.wpc.ncep.noaa.gov/heatrisk/ To view current water temperatures, please visit www.cnrfc.noaa.gov && .AVIATION... Generally VFR conditions prevail through the remainder of today across interior NorCal. Breezy to locally gusty south to west winds persist, with strongest gusts 20 to 25 kts in the Delta and vicinity late afternoon into the evening. Otherwise, some isolated rain shower potential after 06z at RBL and RDD (15-25% chance), and also along the northern Sierra (20-40% chance). Chance of MVFR in these areas as well after 12z. && .STO WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning from 11 AM Tuesday to 8 PM PDT Thursday for Carquinez Strait and Delta-Central Sacramento Valley- Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley. && $$