Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
996 FXUS66 KSTO 270818 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 118 AM PDT Mon May 27 2024 .SYNOPSIS... Warm weather continues, with minor HeatRisk through midweek, transitioning to moderate HeatRisk late week. Weak onshore flow through Tuesday then shifts to breezy, to occasionally gusty, northerly surface flow mid to late week, with onshore flow returning by the weekend. Elevated fire weather concerns for the northern and central Sacramento Valley Thursday. && .DISCUSSION... Another quiet overnight period is ongoing for interior NorCal as we move into Memorial Day. Cloud cover is currently nonexistent, but onshore flow is a bit stronger than last night, which should result in early morning low temperatures returning to the low to mid 50s, with a handful of 40s at higher elevations. Heights aloft are beginning to rise though as an upper level ridge begins to amplify across the Great Basin and Intermountain West through the early week period. Interior NorCal still looks to remain primarily influenced by broad troughing as an upper level trough tracks toward the Pacific Northwest Tuesday into Wednesday. The resultant appreciable weather pattern will remain warm and mostly dry for today and Tuesday, with some late day breeziness from the Delta breeze. High temperatures this afternoon look to reach the upper 80s to low 90s in the Valley, with 70s to low 80s at higher elevations. A few late day, isolated storms along the Sierra crest south of Highway 50 will also be possible (10-15% chance), but should move off of the crest relatively quickly. As the aforementioned trough moves toward the Pacific Northwest on Tuesday, onshore flow should be a little breezier, which will limit Valley high temperatures to the mid to upper 80s for Tuesday afternoon. The upper level trough then begins to eject eastward Wednesday into Thursday while ridging aloft amplifies offshore. This is expected to result in the return of dry, northerly flow to the region from Wednesday into the late week period. A warming and drying trend is anticipated, with Valley temperatures well into the 90s on Thursday and Friday. Friday looks to be the warmest day of the week, with some 20% to 40% probabilities of reaching the triple digits in the Sacramento Valley. This will result in some fairly widespread areas of moderate HeatRisk through the late week period. Additionally, Thursday could see some gusty northerly winds, particularly across the northern and central Sacramento Valley, with 35% to 55% probabilities of gusts exceeding 40 mph at this time. Afternoon minimum RH values into the low to mid teens, with a few localized instances of single digits, will likely result in a period of elevated fire weather concerns where the driest conditions and gustiest winds overlap on Thursday. && .EXTENDED DISCUSSION (Saturday THROUGH Monday)... Ensemble guidance continues to show fairly uniform agreement in the upper level pattern across the weekend and into early next week. The transient ridging aloft on Friday looks to flatten by Saturday, with broad troughing again building in across the west coast. This will result in continued warm temperatures, but a comparative cool down from firmly in the 90s in the Valley on Friday, to the upper 80s to mid 90s from Saturday into next week. Widespread moderate HeatRisk shrinks to scattered areas throughout the central and northern Sacramento Valley, with primarily minor HeatRisk then anticipated across the weekend for most. The return of onshore flow is expected to facilitate this relative cool down with periodically breezy late day south to west winds. && .AVIATION... VFR conditions next 24 hours. Local southwest surface wind gusts 15-25 kts vicinity west Delta, generally less than 12 kts elsewhere. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$