Summary: April 25, 2017
Last week the Upper Colorado River Basin had a large area in eastern Utah and southwestern Colorado with little to no precipitation. Precipitation in the range of 0.25" to 1.00" fell over the weekend in northwestern Colorado and southwestern Wyoming. The higher amounts were in Moffat, Routt, Grand, Summit and parts of Eagle, Garfield and Rio Blanco counties. Not showing up on the map is precipitation that fell Monday after 7 AM into Tuesday. Much of northwestern Colorado received between 0.10 and 0.50" yesterday. Most of this precipitation was rain, however the higher elevations saw snow. April precipitation through the 24th at 7AM is in the 1-2" range along the Divide and less than 0.5" in eastern Utah.
SPIs in western Colorado are showing quite a bit of dryness, with 30-day SPIs in the 0 to -1 range with a few down to the -1.5 range. 90-days SPIs look even drier. The 6-month SPI is looking much better with many SPIs in the 0 to +1 range.
Eastern Colorado saw some very beneficial precipitation last week, with much of the area seeing at least 0.5" and Larimer, Weld, Morgan and Kit Carson counties receiving over 1 inch of new precipitation. Chaffee, Park, Douglas and part of Arapahoe counties saw less than 0.25" last week. Much of northeastern Colorado from Larimer to Philips and Sedgwick counties saw an additional 0.25 to 0.5" Monday afternoon and Tuesday morning.
SPIs in eastern Colorado are pretty mixed. Southeastern Colorado is showing 30-day SPIs in the +1 to +2 range and 0 to +1.5 for the 90-day. Farther north, SPIs are only in the 0 to +1.5 range. In the Denver Metro and northern Front Range, 3-day SPIs vary between the -1 to +1, but dry out to the 0 to -1.5 range for the 90-day SPI, showing the longer term dryness.
Despite the precipitation, temperature for April remain above normal for the entire area. This has been driving snowmelt in the mountains. Basins in Colorado are currently below normal for this time of year, meaning the snow is currently melting faster than normal. Streamflows are responding to the rapid snowmelt, with the majority of streamgages reporting at much above normal.
It should be noted, that while snowpack in the mountains was great this year, much of the snowpack was above 9,000 feet, the mountain valleys have not seen the same great snow and precipitation since February.
The outlook shows a good chance for precipitation coming to the area this week, with the main chunk hitting eastern Colorado, especially the Arkansas Valley. Temperatures with this pattern could be cold enough to bring snow and killing freeze into the plains of Colorado.
UCRB: Status quo is recommended for the UCRB. While the higher elevations have seen a great season, the mountain valleys have been dry for a few months now and SPIs are starting to show it. With the precipitation that fell over the last few days and the great water supply, we will continue with status quo, however keep a close eye on the valleys.
Eastern Colorado: The USDM author has proposed reduction of D0 in eastern Colorado and D1 in Weld and Larimer counties. The Climate Center endorses most of these changes with the exception of the D0/D1 reduction in Larimer County. Much of the county has missed out on many of the events and remained dry. 30 and 60-day SPIs are now positive, however the SPI quickly goes back to dry on the 90-day SPI.
In addition to the proposed improvements, reduction of D0 in northern Pueblo County is recommended. This area has seen the same beneficial precipitation that helped wipe out D0 from Huerfano County and SPIs are positive on all time scales.
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