Saturday, December 6, 2014

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Weekend Update and Look Ahead

Since Friday afternoon, the west slopes of the Sierra have seen variable amounts of precipitation mainly in the form of light rain (snow) below (above) 8000 ft with higher amounts north and west. Figure 1 provides a spatial overview with precipitation amounts ranging from a few hundreds to well over and inch across the area.

Figure 1. 24 hour precipitation totals (Friday-Saturday afternoon) from the CNRFC. 

Although residual moisture at mid levels lingered through most of Saturday, the upper-level continues to ridge out over northern-central CA and western NV with low-level drying. This will be the theme overnight through Sunday afternoon ahead of the next shortwave. Although associated with a decent subtropical moisture plume, the track of the next storm system continues to follow a more northward trajectory with time. Therefore, precipitation amounts will be higher for extreme northern CA and southwestern Oregon and reduced for the Tahoe area. More specifically, near and around the Tahoe Basin, we can expected:
  • A mix of sun/clouds on Sunday and mild
  • Weaker storm system overnight Sunday through Monday
  • More northward track keeping precipitation amounts reduced near Tahoe
  • Snow levels around 7500' and above with 1-4" possible
As noted in Nick's earlier post, the Pacific remains active through next week with a larger storm system anticipated Thursday-Friday. The MJO pattern remains favorable over the short term while El Nino teeters positive. Note the gradual positive progression in the surface temperature anomalies over the southern Pacific over the course of 2014 (Figure 2). A broad positive anomaly remains persistent since May from the 140E meridian eastward across the southern Pacific, with a slight decline in August (southern-central Pacific) and then a restoration through September and especially November. Typically, a wetter and more active pattern becomes favorable for central CA during slightly positive to near-neutral El Nino conditions. Monitoring these anomalies for the month of December and the associated atmospheric response will be important for our upcoming Winter season.
Figure 2. Sea surface temperature anomalies straddling the equator west to east across the Pacific Ocean (left to right) for January through November 2014 (top to bottom). Courtesy of CPC. 


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