Summary: April 24, 2018
Last week's exciting weather pattern brought excessive winds and warm temperatures, followed by a large moisture-rich system that dumped rain and snow across many parts of the Intermountain West. Large areas of Wyoming and Colorado, along with some more isolated spots in Utah and New Mexico, received over half an inch of precipitation for the week. The biggest disappointment is that larger accumulations weren't observed over the worst drought areas in eastern CO and NM, and little to no precipitation fell over the Four Corners, where D4 (exceptional drought) was recently introduced on the U.S. Drought Monitor.
High winds, warm temperatures, and low relative humidities have dominated much of the plains areas. The result is that what little moisture is in the ground gets sucked up into the atmosphere, and fire danger has been extremely high. Fires have been an issue in CO, NM, and UT.
For most of the higher elevations in the IMW, snowpack accumulation has peaked and melting has commenced. For the northern basins, that meltoff is a bit more slow, with a few lingering snow events helping to delay it. But snowmelt has been rapid in the southern basins. Despite a better snow season in the northern basins, many areas still did not quite reach their average peak this year. Runoff is less than average, and it's forecasted that water supplies will be below average this summer. The Upper Green basin in WY remains the Upper Colorado River Basin's one area of good conditions. To the south, the situation is much more bleak. Dust is a major concern in the San Juan mountains. In addition to low snowpack peaks, runoff is in poor shape, melting will likely be completed a month earlier than normal, and water supply forecasts are much below average.
As we progress through spring, we enter the "wet" season for much of the eastern plains. For these areas, a soaking event like what we saw last week should be typical. Events that drop half an inch of moisture are expected this time of year, and while they may delay further deteriorating drought conditions, they are not beneficial enough to eliminate impacts or improve drought conditions. For areas around the Four Corners and the higher elevations currently in drought, they are now entering their "drier" time of year. The chances of chipping away at drought during the dry season are slim, and those who reside in those areas will likely have to wait till the kick-off to monsoon season to see large scale relief.
On a positive note, the Climate Prediction Center is showing that the Southern Plains drought area (which extends into eastern CO and NM) has a good chance of above average precipitation on the 3-4 week time scale. Unfortunately, with a summer seasonal outlook showing warmer than average conditions likely, summer water demands are likely to be high, putting stress on a vulnerable water supply and further stressing already struggling crops and rangelands.
Improvements: Areas outlined in blue are recommended to show 1-category improvements to their U.S. Drought Monitor categories. For all these areas, long-term SPIs are more marginal (on the edge of a specific D-category possibly), and they've received enought month-to-date moisture to justify improvements. In Utah, D3-to-D2 improvement areas have received 2 to 4 inches of moisture in April. In Colorado, D1 and D0 areas recommended for improvement are mostly showing near, to slightly below, normal SPIs any different timescales, and have received 2 inches or more of moisture since the beginning of April.
Deteriorations: Areas outlined in black are recommended for expansion to D3 drought conditions. All areas are reporting very strong and damaging winds sucking moisture out of the ground, many fires, wheat and grasses are struggling, and irrigated lands are struggling as well. Higher elevation areas are bare of snow or SNOTEL is reporting less than 5th percentile snowpack (with many showing 0 percentile precipitation water-year-to-date). The black striped areas outlined in gray have already been proposed for D4 expansion by the U.S. Drought Monitor author. These areas received little-to-no precipitation in the most recent storm event that passed over last weekend. While short-term SPIs aren't as bad, these proposed D3 and D4 expansion cover areas where longer-term SPIs (particularly at the 6-month time scale) are less than -2.
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