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NIDIS Intermountain West
Drought Early Warning System
December 5, 2017


Current U.S. Drought Monitor Depiction


Recommended Changes

Summary: December 5, 2017

The majority of the Intermountain West is currently experiencing a warm and dry pattern, as a persistent ridge of high pressure has settled over the region.  Following a decent start to the water year and snowpack season in the northern mountains (for northern Colorado, and especially for western Wyoming), snowpack accumulations have stalled.  In addition to dry short-term SPIs throughout the lower elevations, both modeled soil moisture and the Evaporative Demand Drought Index show early signs of drought stress, particularly in the southern portion of the IMW.

Monthly averaged temperatures throughout the Upper Colorado River Basin were 6 to 10 degrees warmer than average for November.  Warm anomalies have continued, and while we can expect some cold snaps sprinkled in (it is after all winter!), it's likely that December will be warmer than average as well.  These warm temperatures (and lack of snowfall in the lower to middle elevation mountains) are limiting sufficient snowpack accumulations.  Many locations that normally show a widespread solid snow cover by this time of year are now reporting bare ground.

At this time, impacts are fairly minimal as vegetation has entered dormancy and water supplies are in good condition.  At the beginning of the new year, we begin a critical time period where impacts from lack of snowpack accumulation become an increasing certainty and deficits are harder to recoup and recover from.  If the warm and dry pattern continues, we could see increases in evaporative losses in the latter part of winter, further drying of soils, and an early onset to snowmelt and wildfire risk.  Due to a better start to the season for the northern basins, they may be spared; but areas around the Four Corners, southwest Colorado, and eastern Utah, and south into AZ and NM will be more vulnerable to severe drought impacts.

Recommendations

UCRB:  Due to widespread degradation to D1 last week, we recommend status quo this week.  With warm and dry persistent conditions, we will be anticipating expansion of D1 and possible introduction of D2 in the coming weeks.  But for now, the current depiction is sufficient.

Eastern Colorado:  Status quo is recommended.

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