Much of our forecast area has experienced quite a shift in the weather pattern over the past month. This transition brought flooding to both Northern and Southern California and provided a much needed boost to the Sierra snowpack. The weather pattern has shifted once again this past week and given way to sunny skies and dry conditions across the region.
While the December and early January storms were beneficial to the California snowpack, they did little to improve conditions across the rest of the West. Figure 1 shows the minimum rank of snow water equivalent (SWE) for snow pillows across the west as of January 12th. The purple and light blue colors highlight sites that rank at or near the bottom of the to-date historical record for measured SWE. Prior to the onset of storms in mid-December, snow pillows in the Sierra were also measuring at or near record low snowpack. Those sites along the Sierra have recovered nicely and are now reporting near median conditions, as shown in Figure 1. The snowpack in the Trinity, Klamath, and the Humboldt basin in northern Nevada are still lagging well behind the historical median due to the warm storms that brought mostly rain to these watersheds.
Figure 1: Image from the NRCS showing the minimum to date ranking of SWE at snow pillow across the West. Source: NRCS
While much of the West is currently lacking for snow, water year precipitation totals across the region are near to above normal in most areas, as shown in Figure 2. Much of the CNRFC forecast area is well above normal, particularly across the southern third of California and Nevada. Drier conditions persist across far Northern California, Southern Oregon, and Northeastern Nevada.
Figure 2: Image from the Center for Western Weather and Water Extremes (CW3E) showing year-to-date precipitation anomalies. Data for this image is provided by PRISM. Source: CW3E and PRISM.
As one might expect with the recent precipitation, drought conditions have improved across the region. According to many observers who track this sort of thing, this is the first time in 25 years that California is 100% free of drought and abnormally dry conditions based on the U.S. Drought Monitor. So yes, no need to adjust your glasses; the white space you see in Figure 3 is as intended. Note that the U.S. Drought Monitor is created not only based on physical indicators such as precipitation, but also incorporates insight from local experts and reports on drought impacts. Thus, the map reflects more than just recent precipitation.
Figure 3: U.S. Drought Monitor showing no drought or abnormally dry conditions across all of California. Source: U.S Drought Monitor
While the recent storms have provided a nice boost to the snowpack, warmer storms throughout the last month have also brought precipitation in the form of rain to many locations, including the mountain regions. This has led to high rates of runoff across the region, with the vast majority of stream gages reporting well over 150% of the to-date median, as shown in Figure 4. The exceptions are the Humboldt River watershed, Southern Oregon, and along the Northern California coast. These regions have received near average precipitation thus far this water year, as shown in Figure 2.
Figure 4: Observed water year flow to date across the CNRFC forecast domain. Source: CNRFC
Rain in the mountain regions has led to a significant increase in soil moisture. As shown in Figure 5, SNOTEL (Snow Telemetry) sites in the Eastern Sierra are reporting record to near record levels of soil moisture for this time of year. High soil moisture, along with a healthy snowpack in place across the Sierra, should help facilitate more efficient runoff as we progress towards the melt season later this spring. Soil moisture is also quite high in the Humboldt basin due to periodic light rain events that have brought water year precipitation totals to near normal (Figure 2).
Figure 5: Image showing soil moisture at near record levels across the Eastern Sierra. Source: NRCS
Current water supply forecasts are running near to just above median for many locations, as shown in Figure 6. After big increases over the past month, forecasts have trended downwards in recent days as we enter a second week of dry weather. With abundant sunshine and well above normal temperatures forecast through the middle of next week, expect to see some of the low to mid elevation snow (roughly in the 5,000-7,000ft range) in exposed locations begin to melt.
Figure 6: Forecasted seasonal runoff volume expressed as a percent of median. Source: CNRFC
Warm and dry conditions are expected to persist through at least mid-week next week. Models are currently showing signs of a pattern change by the middle to end of next week. However, there is still a fair amount of uncertainty if any change will actually happen. There are numerous ensemble members across multiple models that continue to indicate a dry weather pattern for much of the area. Even the wetter ensemble solutions are on the drier end of the spectrum. Thus, chances are high that we will not see significant precipitation through the end of January. The precipitation outlook from the Climate Prediction Center (CPC) is shown in Figure 7.
Figure 7: 8-14 day precipitation forecast from the CPC favoring near normal to slightly above normal chances of precipitation across the area. Source: CPC
