Area Forecast Discussion
Issued by NWS Sacramento, CA
Issued by NWS Sacramento, CA
185 FXUS66 KSTO 232126 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 226 PM PDT Mon Sep 23 2024 .Synopsis... Elevated fire weather conditions persist into tonight due to breezy northerly winds and low humidity. Hot weather with Moderate HeatRisk through Tuesday with temperatures cooling off midweek. Dry and warmer weather on Friday and through the weekend. && .Discussion... Breezy northerly surface winds gusting 10 to 15 mph are being observed along the I-5 corridor in the Sacramento Valley as of 2:22 pm this afternoon. Winds in the Valley will weaken through this evening with periodically breezy northeasterly winds across the adjacent Sierra foothills tonight gusting 15 to 20 mph. Alongside the locally gusty northerly winds, limited overnight humidity recovery and daytime minimum humidity values into the teens to single digits are anticipated as well. This will result in period of elevated fire weather conditions through this tonight where strongest winds and lowest humidity coincide (generally Interstate 5 westward in the central/northern Sacramento Valley). Broad ridging aloft will allow above normal temperatures to continue today and Tuesday, resulting in fairly widespread Moderate HeatRisk across the Delta, Valley, and foothills. Despite the favorable pattern, current probabilities of high temperatures exceeding 100F run around 20% to 35%, with highest probabilities in the northern Sacramento Valley today shifting to the southern Sacramento and northern San Joaquin Valleys on Tuesday. Heading into Wednesday, a deepening upper level trough offshore will promote cooler, near normal inland temperatures and breezy onshore flow. Winds are forecast to gust between 15-25 mph through the Valley during the afternoon and evening hours, with gusts up to 30 mph in the Delta. Humidity values are expected to increase slightly with shift in the flow pattern as well with daily RHs in the low 20s to low 30s and improved overnight recoveries. Temperatures begin to rise by Thursday continuing into late week, as broad ridging sets in over NorCal. && .EXTENDED DISCUSSION (Friday THROUGH Monday)... Latest ensembles and clusters continue to show warmer temperatures for Friday, with above normal temperatures continuing through the weekend. This is due to atmospheric heights rebounding in the wake of a departing upper level trough, with the main ridge centered over the 4 Corners area(desert Southwest). So while temperatures will be unseasonably warm, significant heat impacts are not expected. Friday highs are projected to be around 7-10 degrees above normal (90s for the Valley), with scattered Moderate HeatRisk across the area. The weekend has forecast highs 5-7 degrees above normal, with Pacific Northwest troughing projected to bring some lowering heights and slight cooling over the area. There is still quite a bit of uncertainty in the exact pattern Sunday into early next week, so NBM temperatures reflect this with a fairly large range of possibilities. Overall, temperatures suggest a gradual cooling trend. The primary concern with this pattern will be the shift from onshore surface flow to predominantly northerly/offshore surface flow. Potentially breezy north to east winds and daytime humidity into the teens to 20s with limited overnight recovery could bring some elevated fire weather concerns for early next week. There remains a lot of uncertainty in the exact pattern, so stay tuned for details. && .AVIATION... VFR conditions over interior NorCal next 24 hrs. Surface wind mainly below 12 kts except vicinity of the Delta, where there will be southwesterly surface wind up to 20 kts at times, and in mountains. && .STO WATCHES/WARNINGS/ADVISORIES... None. && $$