August 7, 2013
Highlights
- Short-term drought conditions have eased considerably over the region after a wet July, with lesser improvements in long-term drought conditions.
- July precipitation was above average over most of the region; Colorado and Utah were wetter overall than Wyoming.
- Observed April through July runoff was boosted only marginally by the monsoon moisture, and still ended up well below average in most basins.
- At the end of July, reservoirs across the region were generally lower than at this time last year, and almost all were below the long-term average.
- The NOAA CPC seasonal climate outlooks show equal chances for wet or dry conditions for the region through November, except for a wet tilt for far northern Wyoming for August.
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July Precipitation and Temperatures, and Current Drought
July was a rare month for this water year: the majority of the region experienced above-average precipitation, as a timely and active monsoon consistently brought subtropical moisture into the region. Conditions were generally wetter across Utah and Colorado than Wyoming, with the largest wet anomalies in southwestern Utah and far western Colorado. Conversely, extreme north-central Utah, far northwestern Colorado, and parts of southwestern Wyoming were mostly skipped by the July rains. We are far enough along in the water year that one good month scarcely changed the HPRCC Water Year Precipitation map, which still shows only isolated areas with above-average precipitation since October 1.
Despite the moisture, July temperatures were warmer than average across most of the region, except in parts of eastern Colorado and far northeastern Wyoming. Most areas were 0-4°F above monthly average temperatures for July. The hot spot for the region was Salt Lake City, where July 2013 clocked in at an average of 84.1°F (5.4°F above average), the warmest July and warmest month since the official record began in 1928, just beating out July 2007.
After the July rains, the latest US Drought Monitor representing conditions as of July 30, shows multiple small areas of improvement by one category: along the Colorado Front Range (to D0), along the Wasatch Front (to D0), in southwestern Utah (to D0), far northeastern Colorado (to D1 and D2), and southeastern Colorado (to D3). There was also some expansion of D3 in south-central Wyoming, and east-central Colorado. Last year there was considerable expansion of drought area during July—which did not occur this year—so overall conditions are now somewhat better than at this time last year.
Current Streamflows
Once again, in the maps of current streamflows across Colorado, Utah, and Wyoming, there are more gages in the below-normal categories than the above-normal categories, but more gages are in the "normal" (green) category than one month ago. The July rains have had a positive effect on streamflows in many Colorado and Utah basins. For example, the Colorado River near the CO-UT state Line jumped from the 8th percentile on July 1 to the 46th percentile (95% of median flow) on August 4. This gain was not just relative to the median; streamflows actually increased from about 3000 cfs to 3600 cfs over this period.
However, this boost in July streamflows has been “too little, too late”, and has not substantially increased the overall low to very low April–July runoff across the region, especially in the Upper Colorado River Basin. The preliminary observed unregulated inflows to Lake Powell for April through July totaled 2.55 MAF (39% of median), well below the "most probable" June 1 forecast of 3.0 MAF. This was the 4th lowest spring-summer runoff since 1964, below 1981 but above 2012.
Reservoir Storage
After a second straight year of generally poor April–July inflows, the region’s reservoirs tended to reach their seasonal peak levels "early and low" this year. As of July 31, the vast majority of reservoirs were below the long-term average for the date, and generally below last year's level as well. On July 31, Lake Powell held 11.20 MAF (46% full), down from 14.68 MAF (60% full) on the same day last year.
Seasonal Climate and Drought Forecasts
The latest monthly Climate Outlooks released on July 31 by NOAA CPC show a wet tilt for precipitation for August in far northern Wyoming, but no tilt elsewhere. The seasonal outlooks released July 18 show no tilt towards wetter or drier conditions for the August–October and September–November periods. The CPC Climate Outlooks once again show enhanced odds for above-normal temperatures for the upcoming seasons, consistent with long-term warming trends. The latest CPC Seasonal Drought Outlook released July 18 projects that drought conditions will persist for most of our region through October, but further improvement is expected in southeastern Utah and southwestern and south-central Colorado over the next three months, reflecting the expected continuation of what has been a robust monsoon so far.
The latest PSD Precipitation Forecast Guidance ("SWcast") released July 12 for July–September 2013 conditions, shows a wet tilt for the period for eastern Colorado, and a stronger dry tilt for the northern Front Range, similar to the previous forecast for this period issued in May. Both of the regions showing tilt have shown modest positive forecast skill for the late-summer/early fall over the last decade. No tilt is forecasted for the rest of Colorado and Utah, indicating equal chances for wet, dry, and middle outcomes.
ENSO indicators still continue to show ENSO-neutral conditions, as they have since last fall. The models in IRI's mid-July ENSO Prediction Plume again indicate a consensus towards ENSO-neutral conditions continuing through the fall, with the dynamical models tending towards the warm side of neutral, and the statistical models tending to stay on the cool side. Several models call for a quick cooling into La Niña conditions by fall, but most of those do not continue the La Niña event through the winter. A few dynamic models forecast the development of weak El Niño conditions by late winter.