A more typical October pattern

Filed in Uncategorized by on October 18, 2009 45 Comments

After a very impressive and record-breaking storm earlier this week, the weather has quieted down considerably over CA. The major exception to that statement is a very localized region near Redding over the past several hours. Some unexpected thunderstorms developed over parts of the Sacramento Valley and foothills today, but one particular (though very isolated) line of cells near Lake Shasta has apparently caused some damaging flash flooding and even evacuations in that region this evening. Storms and locally heavy rainfall continue at this hour, but are expected to diminish by midnight.

The powerful Tuesday storm brought extremely impressive rainfall totals to some parts of the state. Many of these totals would be impressive at any time of year, let alone in early October. The western Sacramento Valley smashed most of its all-time monthly rainfall records for October over the course of less than 24 hours (here in Davis, I recorded 4.35 inches; Fairfield recorded over 5 inches). These amounts represent a significant fraction of average annual rainfall in these areas. Fortunately, there was no major flooding as a result of these record-breaking rainfall totals, though widespread and noticeable flooding did occur (see pictures above). The eyebrow-raising 20+ inch 24 hour rainfall total in the Monterey County mountains is not an error; it did indeed occur. This system was phenomenally moist–with PWs as much as 4-5 standard deviations above the norm. There was so much residual low-level moisture in NorCal that, for much of the past week, dewpoints never dropped below 60 degrees and occasionally made it into the upper 60s–levels that I have never before seen in this part of the world. Fog at 67 degrees is a novelty up here, that’s for sure. Had this system occurred later in the winter, there would have been dangerous flooding (especially if such precipitation had fallen on top of a substantial snowpack). We did get lucky with this one, and it appears that its effects will be largely beneficial to the state.

A much weaker system will move into NorCal tomorrow, bringing mostly light precipitation. SoCal will stay dry. After that, the weather looks to remain dry for the foreseeable future.

An interesting note: Hurricane Rick yesterday became the second strongest hurricane since records began in the Eastern Pacific, with sustained winds of 180 mph. This hurricane is expected to weaken significant over the next 24 hours but still strike southern Baja California as a substantial hurricane. Remnant moisture is unlikely to affect the Southwestern United States.

Technical note: Weather West is currently undergoing significant upgrades. Upgrades to this blog have already taken place, so this page will not become unavailable. Other pages may temporarily disappear while new templates are uploaded this week. Hopefully the site will load more quickly and will be better navigable…