When will wet weather return to the west?

It’s been said that if you don’t like the weather, just wait a bit. 2023 has started off wet and windy in the west, and warm in the east… but that’s all about to change.

California seems to always need rain, but this is getting ridiculous. In the first two and a half weeks of January, downtown San Francisco has picked up nearly 9″ of rain. That’s over 3 times the normal amount! This is now their second wettest January in the past 23 years… and February is still more than a week away. It’s a similar situation in downtown Sacramento, as they have picked up over 7 inches of rain so far this month… which is also over three times their normal amount.

Southern California has been just as wet. In downtown Los Angeles, over 8 inches of rain has already fallen this month, which is 4 times the normal amount. Santa Barbara has picked up nearly 8 inches of rain as well, while San Diego has received four times their normal rainfall so far.

All of this rain has been great news for the state’s reservoirs, which were exceptionally low just a few months ago. Lake Oroville is California’s second largest reservoir, and has risen over 130 feet since Thanksgiving. The state’s largest reservoir, Shasta Lake, is up more than 60 feet since November.

While it’s been wet in the west lately, it’s been warm in the east. Boston, Massachusetts and Portland, Maine have both had only about one-third of their normal snowfall to date. And the folks in New York City are still waiting for their first few flakes of the season! The parade of Pacific storms has flooded the eastern half of the country with relatively mild temperatures since Christmas. There was a major arctic outbreak in the middle of December, but high pressure over eastern Canada has prevented any additional cold blasts in the U.S. recently.

But as Bob Dylan once said: the times, they are a changin’. Long range computer models, like the GFS, are forecasting a large ridge of high pressure to develop over the west coast, and dry them out through the end of January. And while the west will dry out, the higher amplitude flow will continue to keep much of the northeast mild. The Ohio Valley should be wet.

500mb GFS model forecast for Wednesday, 1/25, showing high pressure over the west, and a strong upper level low over Kansas.

This is a wintertime pattern that the west coast has seen all too often lately; high pressure sends the storm track northward, and the drought continues. But long range models are offering some hope this time around.

There is nice agreement among the models that the developing west coast ridge of high pressure will retrograde westward into the central Pacific by the end of the month, allowing stormy weather to return to the west coast by early February. The Madden-Julian Oscillation will move into Phase 3, which can be wet for California… except the circulation pattern in the Pacific won’t support that this time around.

For the past three weeks, the jet stream has been very zonal across the Pacific: no major north or south oscillations, which has lead to atmospheric river after atmospheric river pounding California. With strong high pressure developing in the eastern Pacific, the wet zonal flow across the entire Pacific shouldn’t return. So, while the west will break out of the dry weather and see a return of soggy conditions by early February… it shouldn’t be the deluge of rain and snow that they’ve had to begin the year.

via Watts Up With That?

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January 20, 2023 at 08:09PM

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