Henry Reges the CoCoRaHS National Coordinator has graciously given me permission to post his notes from yesterday’s webinar:
More precipitation fell last week in the north central mountains of Colorado and throughout western Wyoming and northern Utah, while dry conditions continued to prevail over southwestern Colorado. Very little changes were seen in the water-year-to-date precipitation percent of average from last week, with western Wyoming seeing the biggest improvements and northeast Utah and southwest Colorado showing the largest decreases. With the warmer than average temperatures this past week in Colorado, and very low peak snowpacks in Utah and Wyoming, the majority of the lower elevation snotels in the tri-state area have nearly melted out for the season. Cooler temperatures over the past month and late season storms have kept the higher elevation stations near their current average snowpacks, with little mid-May melting, though few of those stations actually reached their normal peak snowpack values. The warmer temperatures in Colorado also meant an increase in streamflows this past week, with runoff now following along with the seasonal trend in many locations, though many sites in Wyoming and Utah still show low flows due to cooler temperatures coupled with below average snowpack. Despite recent precipitation many of southwestern Wyoming’s stations in the Green River basin continue to show below average snowpack, precipitation, and streamflows consistent with moderate to locally severe drought categories. Just over 50% of all the gages in the UCRB are reporting below normal 7-day average streamflows (less than 25th percentile).
Not much precipitation is expected in the coming week. Northwestern Wyoming and eastern Colorado have the best chance of precipitation over the next 5 days. West of the divide, no large scale features are likely to bring moisture to the area, though there is the chance for convective precipitation. Today’s GFS 12Z run shows precipitation for much of the state over the weekend, but this is a major change from the 0Z run, so confidence in this forecast is low. Warmer than average temperatures will prevail over the area throughout the rest of this week. After this, there is a transition to a more zonal flow with reduced chances for precipitation and near normal temperatures next week.
Draft 1 of the U.S. Drought Monitor removed the small D1 from the headwaters region of the Colorado River and a trimming of the D0 in Jackson county. The general consensus was that this was a good call. There were also suggestions to further trim the D0 out of Jackson and northern Routt county in Colorado as this area has also been receiving a lot of moisture recently. Changes in Wyoming and Utah were coordinated with their state experts. Other suggestions were to add D0 to a small area on the south facing slopes of the San Juan Mountains in southwest Colorado. Even though the region is entering its climatological dry period, the area has been drying out for nearly two months and the majority of the snowpack there has already melted.