Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
513 FXUS66 KSTO 120908 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 208 AM PDT Fri Jul 12 2024 .SYNOPSIS... Hot and dry weather will continue this week with Moderate to Extreme HeatRisk persisting across much of the region. Elevated fire weather concerns will also continue. Cooler temperatures on Sunday and into next week. && Key Points - Long-duration, dangerous heat event persists this week. - Very hot through Saturday, followed by some cooling over the weekend into next week. -Chances of showers/isolated T-storms along the Sierra Crest this weekend. .Discussion... Hot and dry conditions persist across interior NorCal this afternoon, with areas of Major and Extreme HeatRisk across the Sacramento Valley and adjacent Foothills. Upper level ridging persists near the Four Corners region and is expected to meander in that area for the next few days, which will keep our area very hot with widespread triple-digit high temperatures are expected to persist through Saturday. Right now National Blend of Models (NBM) probabilities remain ~100% for reaching 100 degrees F today through Saturday across the Valley and Foothills, with around 70-85% chances of exceeding 110 degrees F in the Northern Sacramento Valley today through Saturday. With the hot temperatures and areas of Major to Extreme HeatRisk, the Heat Advisories for the Delta, Sierra, southern Cascades, and Burney Basin and the Excessive Heat Warnings for the Valley and Foothills have been extended to last until Saturday evening. As the high pressure sits over the Four Corners region on Saturday, it will attempt to tap into some monsoonal/sub-tropical moisture, which will follow the upper level steering winds in a south-to-north orientation and move over the Sierra. Coupled with an area of low pressure off the California Coast that ensembles continue to project to develop, which will increase onshore flow, there is around a 15-35% chance of thunderstorms over the Sierra on Saturday afternoon/evening and around a 10-30% chance on Sunday afternoon/evening. Forecast soundings at the mid-levels show some elevated CAPE and some moisture, but a lack of synoptic forcing may inhibit growth. Models attempt to push some elevated convection through the Valley and over the Coastal Range but there is even less confidence in that versus the Sierra Crest. Chances for thunderstorm development on Sunday for northwestern Shasta County is 10-20%, peaking in the late afternoon and evening hours. No matter what, any storms that develop could be capable of gusty winds and possible fire starts from lightning strikes. If you are out and about in the mountains this weekend, remember when thunder roars, head indoors! Thanks to the aforementioned onshore flow and low pressure that is projected to develop this weekend, a slight relief in high temperatures is anticipated around the Central/Southern Sacramento Valleys, Delta, and mountains. Saturday high temperatures are forecast to be in mid 90s to around 105 in the previously mentioned areas, while the northern Sacramento Valley will remain the in the 105-113 range. Sunday, our upper level heights transition into a westerly component, which will spread some more relief to high temperatures around the entire area. The northern Sacramento Valley will see temperatures drop to around 100-104, with low 90s to 101 for the rest of the area. We will continue to see temperatures and HeatRisk decline as we move into next week. Latest HeatRisk: wpc.ncep.noaa.gov/heatrisk/ Heat Safety Tips: weather.gov/safety/heat && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... As we move into the next work week, upper level flow pattern with onshore flow will allow better relief from the heat we have been experiencing. HeatRisk will fall into the Minor to Moderate categories Tuesday through Wednesday. Temperatures will be close to climatological normal until Thursday, where we could climb to around 3-5 degrees above normal. Forecast high temperatures are around 90 to the low 100s for the Valley and Foothills, with low to mid 80s for the mountains Thursday and Friday with Friday being the hotter of the two days. Clusters show a ridge developing once again over the Four Corners region, which will increase our heights aloft and slightly increase our afternoon high temperatures, where triple digits are forecast for the area except in the Delta. By Friday, Valley locations can expect to be under Moderate HeatRisk throughout the Valley with Minor to Moderate over the foothills/mountains. && .AVIATION... VFR conditions next 24 hrs, except local MVFR possible vicinity isolated thunderstorms northern Sierra 22Z until about 02Z Saturday. Surface wind gusts generally below 12 knots except southwest wind gusts 15-20 knots vicinity west Delta after 00Z Saturday. && .STO WATCHES/WARNINGS/ADVISORIES... Excessive Heat Warning until 9 PM PDT Saturday for 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. Heat Advisory until 9 PM PDT Saturday for Burney Basin / Eastern Shasta County-Carquinez Strait and Delta-West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$