UPDATE: 9/15/2021, 1:35pm
Area Forecast Discussion National Weather Service Sacramento CA 134 PM PDT Wed Sep 15 2021 .SYNOPSIS... Chances of moisture (not a bunch) increasing with best chances on Sunday. Cooling definitely on track with coolest day Sunday. Some gusty winds possible early next with temperatures slowly rising. && .DISCUSSION... The cooling trend has started today as a weak upper wave has driven down the upper ridge that has been in place for a few days. Not too much change in weather tomorrow as next precipitation bringing system drops into Pacific Northwest coastal areas. Expect a dry and mild day Thursday. Friday...mid level winds will start to increase as the next system advances further onshore in Pacific Northwest. This will case a brief period of localized elevated fire weather concerns...but areas that reach that criteria in the Sierra is short lived and spotty thus we aren't going with any fire weather highlights. Onshore flow will bring delta breeze and in general more moist air into the area. Saturday...a lot like Saturday but mid level wester to southwest winds increase. This will continue to bring up relative humidity levels. Wind criteria would be a possible issue for fire weather but looks like relative humidity should keep us out of anything too bad. Saturday night chances of precipitation will start in the north and push south through Sunday. Confidence in areas north of I-80 getting some measurable rain is increasing. Looking at NBM, GFS and ECMWF ensemble data good to see they are all in line in places like Redding, Blue Canyon and Sacramento. Probabilities from NBM of 0.10 or more around the 50% mark in the higher elevations and foothills and northern Sacramento Valley. So system not super wet but wouldn't be surprised a few half in reports in some areas. Hopefully this consistency continues as the system get closer.
Here is some weather discussion from the National Weather Service and Predictive Services at NorthOps in Redding.
Strong winds are forecast for the Dixie Fire area on Friday. Firefighters have had a week to work on taking the heat out of the active northern edge of Dixie, so hopefully she stays in the box through these forecast winds.
329 AM PDT Wed Sep 15 2021 Dry and warm conditions remain through the week. More typical late-day breezes return today through Friday. Low pressure system coming in off the Pacific will bring stronger winds, cooler temperatures, and even some light showers this weekend. Drier conditions along with some locally gusty north to east winds will be possible early next week.
Energy Release Component
Fire scientists and firefighters use a data product called the Energy Release Component (ERC) to evaluate the relative dryness and flammability of forest vegetation. ERCs are calculated using historic and current weather trends and measurements of the moisture in sticks. Earlier in the year, we were experiencing record ERC levels, which were a warning we could expect extreme fire behavior for any new fires. Following last week’s rain, the ERCs in the ‘Far Eastside’ and ‘NE California’ zones (Dixie Fire) dropped down well below average levels for this time of year, but they are climbing steadily back up toward record levels with the current warm weather. Data from https://gacc.nifc.gov/oncc/fuelsFireDanger.php