National Drought Summary - April 1, 2008
The West:
Substantial changes were introduced across many of the dry areas across the western states this week, almost none of which were based on conditions observed during the prior week. Early April represents the approximate climatological peak in snowpack for much of the West, and conditions at this time of year provide substantial insight into how streamflows and reservoir stores will unfold as the snow melts and the warmer time of the year progresses. March 2008 was drier than normal for most areas in the West affected by dryness and drought. In fact, Phoenix, AZ recorded its first precipitation-free March since 1984. However, snowpack on April 1, 2008 was near to substantially above normal across a vast majority of the region (basin-averaged amounts below 90 percent of normal were restricted to the central Sierra Nevada, west-central and eastern sections of Nevada, south-central Idaho, and most of the higher elevations across the southernmost Rockies, where peak snowpack tends to occur earlier in the year). This bodes well for the forthcoming warm season, but must be considered along with the dry 2006-2007 winter across most of the region, and even longer-term dryness across Arizona, southern sections of California and Nevada, much of central and western Wyoming, and a few other areas scattered across the West. As of April 1, only Arizona reported above-normal statewide reservoir storage, and 6 states (WA, OR, NV, UT, NM, and WY) reported only 65 to 75 percent of normal, though this of course should be bolstered as the current substantial snowpack melts.
Given all of these factors, a significant reduction was made in the extent of D2 conditions, which are now limited to central Nevada, areas near the Nevada/Oregon/California triple point, part of southeastern Idaho, northern Utah, and southwestern Wyoming. In addition, smaller areas of improvement from former D0 and D1 conditions were introduced in southeastern Oregon, central and southern Idaho, western Wyoming, and southeastern Utah. On the other hand, this re-assessment led to a few areas of deterioration, with D1 conditions returning to the Sierra Nevada, and some expansion of D0 to D1 conditions in parts of southern Utah and northern Arizona.
It should be noted that substantial long-term deficits still exist across much of the Southwest despite near-normal precipitation for the last 12 months. Some of the southeastern California deserts have received less than half of normal rainfall since April 2005, and reports of 50 to 80 percent of normal are common across southern California, central and southern Nevada, and parts of Arizona.
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© 2008 National Drought Mitigation Center