Mid-Week Rain, & Stormier Mid-November Pattern Change on the Way?

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So far this November has been quiet… but then again we’re only 10 days in (I’m probably impatient when it comes to awaiting storms). Even over the last several weeks, most storms have been relatively weak, though the last one towards the end of October was decent. At the moment, a ridge axis was located offshore of California, blocking a closed low… for now. By Wednesday, the low will have pushed northeastward off the Pacific Northwest coast, sending inland a healthy cold front. A moderate-strength westerly upper-level jet in excess of 100 knots will blast northern California as the front swings through, which will transport inland some decent precipitable water values – in excess of an inch.

0z NAM's forecast 300mb wind, valid early Thursday morning.

0z NAM’s forecast 300mb wind, valid early Thursday morning.

Currently, timing is still an issue with models, but appears the front will begin spreading precipitation across northern California late/overnight Wednesday, lingering into Thursday morning. Snow levels look like they’ll hold up above 7000ft given the warm nature of this closed low and the moisture it draws into the region. Anywhere from a quarter to a half inch of rain currently looks to be a good bet for most of northern California from San Francisco northward, with a half inch to an inch in parts of the northern sierra that are influenced by orographics (slightly to moderately in this case). Amounts have fluxuated a bit model wise, so basically blended model output in the aforementioned amounts.

November 10th

Ridging takes over behind this system as we’ve come to expect, but it appears it may not last longer than a week. In fact, another clipper front may try to slide into northern California over the weekend as a weakening storm rotates into the Pacific Northwest/British Columbia, but models are all over the place regarding this. Things could become more interesting next week – with both the GFS & ECMWF indicating potential for a more significant pattern change to occur and allow stronger storms to affect the western U.S. (including California). Timing is well off model-to-model, and in fact model solutions are quite different from one-another, but both deliver some hefty precipitation to the region some time next week. The GEM is completely opposite, with strong ridging taking over a good chunk of the west, so there isn’t total agreement just yet.

18z GFS ensembles, each panel showing an ensemble member's forecast precipitatiom from the 17th through the 24th of this month (November).

18z GFS ensembles, each panel showing an ensemble member’s forecast precipitatiom from the 17th through the 24th of this month (November).

A fair amount of GFS ensembles are moderately to very wet, while others have the bulk of the rain from the Bay Area northward – though most of interior northern California still picks up a fair amount in those more northerly-tracked simulations. The ECMWF ensembles also seem to agree with the idea of a more active mid to possibly late November as well. I’ll post another update this weekend to bring an update on the potential (larger scale) pattern change looming next week and/or beyond. It’s important to note that model predictions as I’ve always urged are not exactly whats going to happen, especially once you’re looking out a week or more, so to cut to the point, don’t put a whole lot of expectations into next week just yet.

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