Hot and dry weather will continue through Saturday with Moderate to Extreme HeatRisk persisting across much of the region. Elevated fire weather conditions will also continue. Isolated thunderstorm chances today-Sunday, mainly along the Sierra crest, best chances from US-50 southward. Cooler temperatures on Sunday and into next week.
Key Points
- Long-duration, dangerous heat event persists through Saturday, followed by some cooling over the weekend into next week.
- Chances of showers/isolated T-storms along the Sierra Crest today through the weekend.
- Red Flag Warning has been issued for Fire Zones 221 and 269 for elevations greater than 6000 feet.
Discussion
Another hot day in store for interior NorCal today. At the time of this writing, it is 106 F at our Downtown Sacramento weather observation site, and the temperature is forecast to climb to around 110 as we move into the peak heating hours. Tomorrow we expect a slight cooldown across the central Sacramento Valley, Delta, and northern San Joaquin Valley with highs in the 90s to 105, with the coolest temperatures in the Delta thanks to onshore flow. The Heat Advisory for the Delta and Sierra, as well as the Excessive Heat Warnings for the Valley and Foothills remain in effect until 9PM PDT tomorrow night.
We are still under the influence of a broad area of high pressure in the Four Corners region and will remain affected by the high pressure until at least Sunday night. Monsoonal moisture is embedded within the high pressure, and is beginning to move into our area this afternoon. Some flashes of lightning have been observed this afternoon, mainly in far southeastern Tuolumne County just east of Hetch Hetchy. This activity is moving off to the northeast and out of our coverage area, however an isolated shower or thunderstorm cannot be ruled out the remainder of the day in the far southeastern sections of the forecast area. Tomorrow, temperatures will cool as monsoonal moisture will advect into interior NorCal, bringing some high clouds and possible sprinkles across the Valley. Some HiRes Convective Allowing Models (CAMS) such as the NAM and HRRR reveal the potential for thunderstorms across the Sierra crest, with the best chances south of HWY 50 tomorrow and Sunday. Forecast soundings suggest a north-northeast steering current, so any storms that develop could drift along the Sierra crest.
Current National Blend of Models probabilities for thunderstorms are around a 15-30% chance for tomorrow and Sunday. With the elevated ERC values in the Sierra and the potential for dry thunderstorms, a Red Flag Warning has been issued for Fire Zones 221 and 269 for elevations above 6000 feet beginning tomorrow at 5AM PDT and lasting through Sunday at 8PM PDT.
Weak offshore troughing develops Sunday as well and will promote more onshore flow into the Delta and central Sacramento Valley, which will help lower temperatures across the region. Confidence has increased in relatively cooler temperatures as we move into the next work week, with the return to nearnormal highs. Moderate HeatRisk will persist across the region beginning Sunday. Upper level heights will remain in a westerly flow pattern, so the relative cool down is expected to persist as we move into the extended period.
Latest HeatRisk: wpc.ncep.noaa.gov/heatrisk/
Heat Safety Tips: weather.gov/safety/heat
Extended Discussion (Tuesday through Friday)
Tuesday and Wednesday, we will still have westerly flow aloft which will promote more onshore flow and help us remain near normal temperature wise.
Widespread Minor and isolated Moderate HeatRisk return, which will be a welcome relief after our record setting heat wave. Forecast high temperatures are currently 90100, with the warmest temperatures in the northern Sacramento Valley.
Thursday and Friday, a ridge of high pressure will once again try to build in over the Four Corners region, which will increase high temperatures around the area again, but at this time, will not compare to our latest heat event.
Minor to Moderate HeatRisk will remain in the forecast, and high temperatures are forecast to be in the low 90s to around 105, with the Delta being the coolest and the northern Sacramento Valley once again being the warmest.