Widespread Major HeatRisk and well above normal temperatures are expected today across interior NorCal. Moderate HeatRisk with broad areas of Major HeatRisk expected Thursday. Cooler, but still seasonably warm, weather expected heading into the weekend.

Excessive heat warning today through Thursday

Discussion

Key Points

  • An Excessive Heat Warning remains in effect through 8 PM PDT Thursday evening across the Valley and adjacent foothills.
  • Hottest day of the week today: Widespread MAJOR HeatRisk, triple digit temperatures, and elevated overnight lows. Reconsider outdoor activities during the hottest part of the day (3:00-7:00 PM).
  • Areas of Major HeatRisk continue on Thursday, with 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 Saturday)

The first heat event of the year is here and so are the elevated overnight temperatures! Just after midnight (as of 2:22 am), temperatures in the Delta & Valley are in the low 70s-low 80s, meanwhile in the foothills & mountains are in the upper 50s-mid 70s.

Major heatrisk today and tomorrow

These H-O-T, HOT(!) temperatures continue today, with widespread Major HeatRisk and triple digit daytime highs. Heights aloft continue to rise over the western CONUS as a strong high-pressure ridge sets up shop over Northern California. Major HeatRisk will cover the majority of the Sacramento Valley & foothills on Thursday, as a result, an Excessive Heat Warning remains in effect for the Valley and foothills through 8 PM PDT Thursday. Breezy north to west winds are expected to increase throughout the day today, but will not be as strong as yesterday's breezes.

As the ridge pushes eastward towards the Great Basin and Intermountain West throughout the rest of this week, more elongated troughing will work to replace it. Northern California will be under southwesterly flow aloft which means increasing onshore flow is expected late Thursday-Saturday. We'll begin to see the return of Moderate HeatRisk across the region by Friday as the Delta breeze fights valiantly against the heat. While the majority of the Valley & Delta will experience only-slightly elevated overnight lows, the northern Sacramento Valley and elevations generally above 2000 ft will see overnight temperatures 10-20 degrees above-normal (15-20 degrees in the mountains). Additionally, this flow pattern aloft will at least introduce some low end potential (5% to 15% chance) for isolated shower or thunderstorm activity along the Sierra crest south of the Highway 50 corridor with a 10-15% chance in far western Tehama and Shasta counties on Thursday.

Heat symptoms

Area waterways continue to run fast and cold from snowmelt, creating dangerous conditions for those seeking relief in rivers and lakes next week. Remember to practice heat and cold water safety this week!

HeatRisk categories

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 (Sunday through Wednesday)

Upper trough along the CA coast progged to form closed upper low Sunday as it digs offshore. Meanwhile EPAC upper ridge builds into the W Coast through early next week. Warming will result Sunday into Tuesday with above normal temperatures.

Major heat risk next Monday and Tuesday

Triple digit heat in the N Sac Valley Sunday, expands through much of the Sac Valley Mon/Tue. Weak Delta cooling expected to keep high temps below the century mark in the S Sac Valley. Offshore closed upper low nudges slightly closer to the CA coast midweek allowing for minor deepening of marine layer. This will result in additional slight cooling in Delta breeze influenced areas, but highs in S Sac Valley remain around 10 degrees above normal. Triple digit highs continue in the northern and central Sac Valley Wednesday with mostly 80s to lower 90s for the mountains and foothills.