10/08/2025
Sacramento Weather Discussion For Wednesday, October 8, 2025 - 2141z (2:41 pm PDT)
……….Synopsis……….
After a warm last couple of days, cooler and unsettled weather returns for the rest of the work week into the weekend, with rain chances increasing yet again for early next week with well below average temperatures throughout.
……….DISCUSSION……….
Latest satellite imagery indicates a very deep Marine layer of around 5,000 ft, all thanks to Upstream troughing that is impinging on our area, allowing geopotential heights to fall with low-level temperatures, also cooling. Now with low-level temperatures cooling, there has been some decent cool air advection owing to onshore flow and low-level Stratus, which persisted this afternoon around the immediate Bay Area, with some Stratus trying to pour into the Carceniz Strait in the Rio Vista area, This and all has allowed at temperatures to stay quite cool compared to yesterday with many areas in the immediate Delta struggling to even climb out of the upper 60s. But of course, with the lower Sun angle compared to mid-summertime, temperatures this time of the year can't recover as quickly. Therefore, I still expect temperatures to be on track to reach the low 70s across much of the Sacramento Valley with mid to Upper 70s around the Stanislaus County area, such as Modesto, Turlock, and Manteca, which includes Tracy. But this is the beginning of a more pronounced pattern change that takes effect by tomorrow and Beyond, with today the transition day. For tonight, expect low-level cloud cover to increase as the air mass gradually begins to lift. Again, thanks to an approaching shortwave trough as mentioned earlier. Now, because there is enough lift and low-level instability, it wouldn't be entirely surprising to squeeze out some moderate to heavy drizzle in favored locations. Overnight tonight, primarily the closer you get to the bay and the coast. The low-level cloud cover should keep temperatures a little milder tonight, primarily in the mid to Upper 50s in many spots, with a few 60s squeezed in there. Now, where any clearing remains in some areas tonight, overnight lows could still dip into the upper 40s to lower 50s, but this is with low confidence.
……….Thursday-Friday……….
Now tomorrow is going to be an interesting day, skies should start off partly to mostly cloudy with widespread low Stratus blanketing much of the Bay Area into at least Solano County and the Rio Vista region, where some onshore push will help to usher some of that Stratus in these areas. Any fog will likely mix out by mid-morning; however will likely be replaced by a few mid-level clouds, part of that trough that is swinging through the region. This will lead to an even cooler day tomorrow with low 70s area-wide with onshore winds picking up by late morning into the afternoon hours with wind gusts in the valley up to about 25 miles an hour from the Westerly direction. Now, if going to the mountains ahead of Columbus Day weekend, strong upslope flow will lead to wind gusts and excess of 30 to 40 miles an hour, with peak gusts in the ridge tops exceeding 50 to 65 mph from the southwest direction. It is also worth noting due to the fact that the upper-level low will briefly become pinched off from the overall flow not much in the way of precipitation is expected with this first system; however, once it does become more progressive on Friday, some accumulating showers are anticipated primarily north of I-80 into Butte and Sutter counties. Now I just briefly mentioned Friday is going to be the day to watch for any showers to arrive from the northwest part of the same trough that again will become Progressive and will move overhead, especially Friday afternoon into Saturday morning. There is excellent agreement in the ensembles from the ECMWF and GEFS and of course, with clouds and some showers on Friday, temperatures will stay on the cooler side in the low 70s with a few upper 60s north of I-80 given not much sun will peak through. So make sure you Have your reindeer handy just in case if it showers on you.
……….Saturday-Sunday……….
Now, once cooler air arrives in the wake of the passage of a weakening cold front, surface-based instability as temperatures aloft are rather cool will lead to some pop-up showers and potentially a thunderstorm on Saturday Or right now chances of this occurring are less than 20% so confidence is low but if any storm were to pop up, brief downpours and gusty winds would be the main hazards given that these would be lower topped storms. Rainfall accumulations between Friday and Saturday look to be less than a tenth of an inch area-wide wide with up to perhaps a quarter of an inch across Butte and Sutter counties in the northern end of the Sacramento Valley.
Sunday is another transition day as the leading shortwave progresses eastward, followed by a re-amplification of another trough that will drop straight down from the Canadian Prairie, and this one looks to be much more dynamic than the first one and cooler as well. Temperatures could warm some on Sunday but still thinking low to mid 70s area wide, which still is below average for this time of the year by a safe margin of 5 to 10°. One thing that's noticeable, though, is with longer nights, shorter daylight, days being cooler, and overnight lows, especially Saturday night and Sunday night, look to be the first round of widespread upper 40s across the valley, which is also below average for this time of the year. For reference, the average low in Sacramento for October 15th is 52°, the low is forecasted to be 48°. So get used to getting the jackets out to keep you warm when commuting to work, especially on Monday morning.
……….Monday-Tuesaday……….
Most Ensemble members are highlighting the next arrival of another more Amplified trough digging straight down from Canada there are notable differences on how this evolves between that of the Canadian and Euro model indicating that the trough will drop down along our Coast and meander for a day then moves straight into Northern California whereas the GFS still has more of an inside slider setup with the trough digging down across the Great Basin with northerly flow This has resulted in a lot of uncertainty in the forecast but one thing's for sure with two different scenarios setting up, temperatures will be notably cooler by Monday and Tuesday with daytime highs in the low to mid 60s. Now the other scenario would bring light chances of showers across our area with southerly winds between 10 and 20 mph. And right now the best guess forecast here with rainfall totals are anywhere between about a tenth to a quarter of an inch in the Sacramento and San Joaquin Valley, with up to about a half an inch to 3/4 of an inch of rain for the Sierra Foothills. Snowfall totals with this one look to range between 6 to 12 in based on NBM model guidance. Will keep you updated as this gets closer
……….EXTENDED……October 15th-18th……….
Long-range model guidance suggests that unsettled weather will continue with additional chances of showers with below-average temperatures through most of the work week into the following weekend.
Forecaster……….David Schlotthauer