Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
656 FXUS66 KSTO 310902 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 202 AM PDT Fri May 31 2024 .SYNOPSIS... Warm temperatures again today, with a chance to break triple digits in the Valley. Slight cooldown Saturday-Monday before the return of triple digits Tuesday through Friday. Slight chance of showers in Shasta County Monday afternoon. && .DISCUSSION... Discussion at a Glance - 20-40% chance of Sacramento Valley climbing into the triple digits today, followed by a slight cool down Saturday-Monday and increased onshore flow. - Major HeatRisk Wednesday & Thursday for the Valley & Foothills when there is the potential for widespread triple digit high temperatures. Prepare for elevated daytime highs and overnight lows, reconsider outdoor activities during the hottest part of the day (3:00-7:00 PM). - Moderate HeatRisk next Friday (June 7), with isolated Major HeatRisk across the Valley; triple digits in the northern Sacramento Valley (areas north of and including Chico) and cooler low to mid 90s in the Sacramento area as onshore flow cools temperatures. Short Term Discussion Mostly clear skies prevail across interior NorCal this morning with breezy northerly winds still observed in the northern Sacramento Valley. Winds should calm as we move into the morning/afternoon hours. High pressure is forecast to move inland today and build over the area, increasing daytime temperatures for the region. Warmest temperatures are forecast for the northern Sacramento Valley, where the better probabilities (20-40%) reside for breaking 100 exist. The Delta will remain in the low 90s, thanks to onshore flow reducing the highs slightly. Northern San Joaquin Valley and the Sacramento area will be in the mid to upper 90s as well. Tomorrow, weak upper level troughing moving through the PacNW will help reduce high temperatures, as the axis of the trough will slide through NorCal. High temps will be in low to mid 90s for the Valley, and cooler mid 80s for the Delta. Breezy winds will also be possible in the Delta, with speeds up to 20 mph possible. This "cool down" will last until Monday, when another PacNW trough will eject from a closed low in the Gulf of Alaska and will slide through the area, flattening our heights into a more westerly component. Sunday high temps will be similar to Saturday`s across the region. Monday, the trough axis slides through the area and will help lower temps into the 80s for the Valley and cooler 60s to low 80s for the foothills and mountains. A slight chance (20-40%) of showers Monday morning are possible in Shasta County, with the higher probabilities north of Redding. There is decent (100-200%) precipitable water with this trough, however the Valley will remain dry as the trough will stay well north of our area. The trough will quickly vacate the area, and upper level ridging will begin to develop in the eastern Pacific. Locally breezy conditions may exist for the Delta and Valley as the trough leaves the area, with wind gusts of 20-25 mph possible. && .EXTENDED DISCUSSION (Tuesday THROUGH Friday)... Tuesday, we will see upper level ridging moving inland, increasing our heights and also increasing our high temperatures around the region. Daytime high temperatures in the upper 90s for the Valley, with areas of Major HeatRisk in the central Sacramento Valley. National Blend of Models (NBM) probabilities of reaching 100 for the aforementioned area are around 50-75% on Tuesday. Wednesday the ridge will be firmly over the area, once again increasing daytime temperatures on both Wednesday and Thursday. Widespread triple digit temperatures are anticipated in the Valley on Wednesday and Thursday. High probabilities from the NBM of 70-100% exist for temperatures greater than 100 degrees, and there is a 20-40% chance that areas in the central and northern Sacramento Valley break 110. With the expected hot temperatures, widespread Major HeatRisk is expected across the Valley. Major HeatRisk affects everyone without effective cooling and/or adequate hydration. Consider canceling outdoor activities during the heat of the day. There is some discrepancies between ensembles regarding the strength and location of the ridge, as the ECMWF has the deep ridge stronger and located over NorCal while the GEFS has the ridge slightly weaker and further to our east. If the ECMWF where to verify, warmer temperatures could be experienced as to what is currently forecast. Regardless of which ensemble verifies, triple digits are very likely Wednesday and Thursday. Next Friday (June 7), there is a large spread on potential temperatures, as well as location/strength of the upper level ridge. Cluster Analysis reveals high confidence of the overall synoptic pattern still dominated by ridging, but a number of the clusters (11%) have our area in a more zonal pattern, which would help ease temperatures. The NBM reflects this disagreement on which pattern will occur, as the high temperature spread is currently 15 degrees (86-101 for Sacramento/KSAC). Regardless, upper 80s to low 100s will still be possible on Friday for the area, with widespread Moderate HeatRisk and isolated Major HeatRisk for the Valley/foothills. && .AVIATION... VFR conditions expected over the next 24 hours. Sustained surface winds under 12 kts except winds 15 to 25kts in the Delta after 00Z Saturday. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$