Convection Possible This Afternoon

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We’ll remain in a unsettled pattern through the rest of today (Tuesday) as a strong jet stream in Oregon continues to direct deep tropical moisture and bands of increased lift into northern California before the jet stream lifts further northward through the day Wednesday, cutting off precipitation chances

A graphic indicating today's unusual weather for late June.

A graphic indicating today’s unusual weather for late June.

Today, on top of the mainly stratiform precipitation, there may be enough wind and moisture convergence in parts of the Sacramento valley and adjacent foothills this afternoon and evening to aid in the development of some convective activity… possibly including some thunderstorms.

Shear from Sacramento northward is quite strong given the 100kt+ jet blasting Oregon, with 50kt+ 300mb winds from Sacramento north. Because there’s an upper level low off the Pacific Northwest coast, there is decent veering with height in the jet streak/winds aloft… with 0 – 3km SRH in the 50 – 150 M2/S2 range… locally in excess of 200 M2/S2.

Instability will me meager… with SBCAPEs in the 200 – 300j/kg range, possibly up to 500j/kg locally, and lapse rates are poor… limiting potential for long duration thunderstorms. However… given strong moisture and wind convergence in pockets of the Sacramento valley, some thunderstorms may be able to develop despite the lack of decent instability. The area with the best chance of thunderstorms looks to generally be from Sacramento northward, with the strongest convergence in the north end of the valley up the Shasta drainage, meaning the Redding area as the best threat of some thunderstorms through the early to mid-evening.

Since there is a good bit of shear, can’t rule out a stronger thunderstorm (or a few) in the central/northern valley… mainly capable of extremely heavy rainfall given the 1.4 – 1.6″ precipitable water plume overhead, and some hail. If instability does become locally stronger, including CAPEs around 500j/kg for instance, couldn’t rule out a brief funnel cloud or weak tornado. Wouldn’t put much on that potential, though.

Things will dry out through Wednesday as the upper low and it’s associated jet stream lift northward.

By the weekend into next week, a potentially significant heatwave is possible. May have another blog specifically for this event in the next couple of days as models refine ridge placement and temperatures.

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