First Half of October Looking Dry

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After a relatively active late September, the first half or third of October is looking quite dry, with dominant ridging taking over by this coming week. Over the last couple weeks, a couple of weak to moderate-strength Pacific storm systems impacting/affecting northern California delivering some measurable rainfall, thunderstorms, and even snow above about 8000ft Saturday. Certainly nothing that impacts the drought, but something.

Lightning photographed Friday night from here in Rocklin, looking east toward Auburn from a ridge.

Lightning photographed Friday night from here in Rocklin, looking east toward Auburn from a ridge.

The overall pattern changes pretty drastically by this coming week, though. Overall longwave trough sets up east of the Rockies through the week, with large-scale ridging taking over the eastern Pacific & most of the western U.S., with troughing in the central Pacific amplifying our ridge between the troughs/upper-lows. 850mb temperatures drastically rise through the week and beyond, from the single digits this weekend to the 18 – 24c range by mid to late-week as the strong upper-level ridge overhead draws northward increasing warm mid-level temperatures from the south. Valley temperatures return into the upper 80s to mid-90s by mid to late-week due to this strong ridging and rapidly warming mid-level temperatures (which is also in-part due to increasing surface temperatures, not just warmer mid-level temps being ushered northward by the upper-level ridge).


GFS’s forecast 2-meter temperatures for Wednesday afternoon, indicating low to mid-90s across much of the lower elevations of northern and central California.

Surface temperatures rocket well out of the normal range due to this, as seen below. Troughing settling into the middle part of the country brings their temperatures down drastically, with the opposing pattern here on our side of the lower-48. That little bit of snow that fell in the sierra won’t be lasting long. In addition to the heat (for the time of year), troughs passing to the north and east of California could also mean periods of gusty/increased offshore winds, drying out the ground after the bit of precipitation we’ve received and increasing fire danger.

GFS's forecast surface temperature anomalies for Saturday afternoon.

GFS’s forecast surface temperature anomalies for Saturday afternoon. Most of California sits in temperature 10 degrees above normal.

The GFS and ECMWF, along with most of their ensembles indicate this pattern continuing through at least mid-month. Now looking out 2 weeks plus is quite tricky, but this pattern has shown it’s persistence before, lasting months. We can hope for a better second half of the month, but long range models including the ECMWF-EPS weeklies and CFS indicate a below-normal month precipitation wise across California, along with above-normal temperatures. CFS wants to continue this dreaded pattern into November as well, but I don’t even trust most models more than a week typically, so we’ll see.

I’ll have a new post once the next storm shows up, which is hopefully sooner than what most long-range indications suggest.

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