Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
430 FXUS66 KSTO 212101 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 201 PM PDT Fri Jun 21 2024 .SYNOPSIS... Dry weather continues. The hottest temperatures of the week are expected tomorrow with widespread triple digits, moderate HeatRisk, with areas of Major HeatRisk. Begining Sunday, temperatures will cool off slightly next week, but will remain above-normal. && Key Points: - Widespread Moderate HeatRisk is expected today through Monday, with areas of Major HeatRisk today-Saturday - A Heat Advisory is in effect from 11 am to 8 pm Saturday with Widespread Moderate HeatRisk and areas of Major HeatRisk in the Valley and foothills on Saturday; Highs in the triple digits. Short-Term Discussion (Today THROUGH Monday)... Ensembles and clusters remain in good agreement that we will transition to upper level ridge will begin over NorCal today resulting in warmer high temperature. The ridge will amplify over the weekend, as an upper high strengthens over the Desert Southwest. This will cause temperatures to heat up to well above normal levels from the upper 90`s to low 100`s today. Widespread triple digit heat is expected Saturday with Central Valley and lower foothill highs 100-106. Cooler Delta air will modify the late afternoon high temperatures over the Delta, and portions of the southern Sacramento Valley keeping most of these areas in moderate HeatRisk versus major to the north and over the foothills. Increasing southwest flow is expected over NorCal Sunday, as a trough moves through the Pacific Northwest. This will likely initiate an afternoon Delta breeze with high temps a few degrees cooler in the upper 90`s and low 100`s. Widespread Moderate HeatRisk expected through Monday, with areas of Major HeatRisk today and Saturday mainly over the Sierra foothills & northern Sacramento Valley. The National Blend of Models (NBM) is indicating a 80-100% chance of temperatures greater than 100 degrees F throughout most of the Valley on Saturday. By Sunday, a trough is expected to move through the Pacific Northwest resulting in increased southwesterly flow. This will translate into a more robust Delta breeze on Sunday with gusts 15-25 mph through the Valley. Slightly cooler temperatures will follow, but Moderate HeatRisk is expected to continue across most of the Valley and foothills through Monday. && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... Ensemble guidance favors a continuation of broad troughing and anomalously high heights aloft across interior NorCal through midweek. This will keep high temperatures slightly above normal for Tuesday and Wednesday, with 90s to low triple digits throughout the Valley and foothills and 80s to 90s at higher elevations. Despite this, onshore flow is expected to persist, with breezy to gusty late day south to west winds. Moving toward the latter half of the week, cluster analysis is in good agreement on an upper level trough progressing through the Pacific Northwest. There is some uncertainty with respect to the exact details on how this trough will evolve, but there is increasing confidence that a slight cool down to near normal temperatures will accompany this feature for Thursday and Friday. && .AVIATION... VFR conditions across interior NorCal over the next 24 hours. Sustained wind will generally be below 12 kts, with the exception being the Vicinity Delta where sustained southwesterly winds up to 15kts with gusts 15-20 kts are expected between 22z Friday-08z Saturday. Additionally, there is a 20-40% chance of marine low stratus intrusion west of Fairfield. && .STO WATCHES/WARNINGS/ADVISORIES... Heat Advisory from 11 AM to 8 PM PDT Saturday for Central Sacramento Valley-Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northern Sacramento Valley- Northern San Joaquin Valley-Southern Sacramento Valley. && $$