Summary: September 18, 2018
As Coastal Carolina is immersed in the wake of Hurricane Florence, the Intermountain West continues to bake under a late season high pressure ridge and heat wave. This dichotomy nicely illustrates for us the elusive nature of a healthy water balance, a balance which may be gradually becoming more difficult to achieve with time. Fort Collins, Colorado has seen more 90+ degree days in September-to-date than the entire month of August. 7-day averaged temperature anomalies for the Upper Colorado River Basin and eastern Colorado are largely 4-10 degrees above normal. The entire five-state Intermountain West region has been above average (save for a small corner of New Mexico).
Most of the Intermountain West was shutout on the precipitation front over the last seven days. A few monsoon-driven storms hit New Mexico on Monday. All other moisture was essentially negligible. 82% of reporting USGS stream gages in the Upper Colorado River Basin are now reporting below the 25th percentile. 28% of stream gages are reporting at record low values. It's also worth mentioning that flows along the Colorado River channel and Gunnison channel are artifically boosted by releases from major reservoirs that are required to meet environmental regulations. Unregulated flow on these channels would be even lower. Reservoirs have taken a major hit over this warm season. Blue Mesa Reservoirs, the largest in Colorado, is storing only 47% of average water for this time of year, a near record low level. McPhee is nearing dead storage only. Curtailments are being mandated for the first time in history on the Yampa River in Colorado despite a normal-range snowpack this winter.
Unsurprisingly, land surface models, and remote sensing products show Upper Colorado River Basin root zone soils as being abnormally dry, and the vegetation abnormally crispy. One early fall drought impact noted is foliage turning earlier than normal.
A frontal disturbance is forecast to tack across the region Thursday through Saturday. This will have a much needed cooling effect for the region, especially east of the Continental Divide, but only to the point of bringing temperatures back into the normal range for this time of year. It should bring some heavy showers to eastern Arizona, and New Mexico. Some heavy rain may clip New Mexico. The headwaters of the Green, Yampa, White, and Duchesne River Basins in the northern portion of the Upper Colorado River Basin are forecast to remain high and dry. A cool down with more substantial moisture is more likely in the 8-14 day time frame for the northern reaches of the basin.
Improvements are right out this week. It was wicked hot with almost no moisture.
UCRB: It is recommended that D4 be added to southeast and central Mesa County, and Delta County in western Colorado. Between the one-two punch of a record low snowpack this winter, and near-record high evaporative demand this summer, water supplies have plummeted.
It is recommended that D1 be added in central Sweetwater County, WY. Hot, dry conditions have prevailed through much of the warm season, and water year precipitation is below normal.
Eastern Colorado: It is recommended that D1 be extended into northern Elbert County. 100% of crops in Elbert County were rated very poor this year.
UCRB & Eastern CO: A long, narrow expansion of D0 is recommended for southern Wyoming and eastern Colorado. This line is being drawn primarily as a compromise between VegDRI, which is picking up on the short-term effect of high temperatures and dry conditions, and the water year to date AHAPS and COOP precipitation. With the expansion, all of Sublette County, southern Fremont County, central Carbon County, and central Albany County will be included in D0 in Wyoming. In Colorado, D0 will extend to include eastern Larimer County, southwest Weld County, Adams and Arapahoe County, southwest Washington County, northern Lincoln County, and western Kit Carson County.
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