Hydrologic Outlook
Issued by NWS Denver/Boulder, CO
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532 FGUS75 KBOU 162325 CCA ESFBOU COC001-005-013-014-019-031-035-039-047-049-057-059-069-073-075-087- 093-095-115-117-121-123-031200- Probabilistic Hydrologic Outlook National Weather Service Denver/Boulder CO 400 PM MST Thu Feb 16 2017 ...Spring Flood and Water Resources Outlook... This outlook is for north central and northeast Colorado and includes the Colorado...North Platte and South Platte Rivers. ...Flood Outlook Highlights... * Near average risk of minor snowmelt flooding in the North and South Platte River basins. * Above average risk of minor snowmelt flooding in the headwaters of the Colorado River in north central Colorado. Areas prone to flooding in the past may experience issues again this year. * Significant flooding due to mountain snow runoff alone is not likely. However...it is still early in the snow accumulation season and conditions could change before the runoff begins. Above normal temperatures have melted the snowpack in the lower foothills and diminished frozen ground. Near normal subsurface soil moisture was observed in north central Colorado with low soil moisture in eastern Colorado. This has slightly decreased the risk of significant spring snowmelt flooding in the North and South Platte River basins. However...mountain snowpack is higher in the Colorado River basin leading to a higher than usual spring flood potential due to snowmelt west of the Continental Divide. Above normal future snow accumulations combined with heavy rains and rapid melt will increase the current flood potential while below normal future precipitation and gradual or intermittent freezing and thawing will decrease the magnitude of the current assessment. Near average risk suggests that locations which typically experience minor spring time flooding may flood again this year and those that typically don`t will not. ...Current Hydrologic Conditions... The Colorado River basin snowpack on February 16th was 144 percent of normal and had nearly reached the peak normal snowpack (99 percent of the peak). In a typical year the snowpack is only 69 percent of the peak snowpack at this time with April 10th being the normal peak date as reported by the Natural Resources Conservation Service. The mountain snowpack in the South Platte River basin was 138 percent of normal and 85 percent of the normal peak snowpack. In a typical year the mid-February snowpack is only 61 percent of the peak snowpack with the normal peak date being April 27th. Therefore...there is still plenty of time remaining for the snowpack to rise above the normal peak. The Laramie and North Platte River basin snowpack on February 16th was 130 percent of normal and 82 percent of the normal peak snowpack which typically occurs around April 11th. Liquid water in the mountain snowpack generally ranged form 8 to 40 inches. Basin reservoir storage continued to hold fairly steady at 105 percent of average and 73 percent of capacity at the end of January. 85 percent of the U.S. Geological Survey stream gages had normal to above normal flows in mid-February. Widespread Moderate Drought /D1/ or Abnormally Dry Conditions /D2/ continued to be observed east of the Continental Divide. There were no drought designations west of the divide on the February 14th U.S. Drought Monitor. ...Climate Summary... Precipitation since January 1st has been above normal in the mountains and near to below normal at lower elevations. 2017 temperatures have been near to above normal with the exception of the northeast Colorado corner. ...Weather and Drought Outlooks... The 30 and 90 day precipitation outlooks and 30 day temperature outlook have equal chances of being near...above or below normal. The 90 day temperature outlook has a tilt toward above normal temperatures. The U.S. Seasonal Drought Outlook valid February 16th through May 31st indicates drought conditions persisting east of the Continental Divide (D1 or greater on the U.S. Drought Monitor). ...Numerical River Outlooks... In Table 1 below, the current (CS) and historical (HS) or normal probabilities of exceeding minor...moderate...and major flood stage are listed for the valid time period. CS values indicate the probability of reaching a flood category based on current conditions. HS values indicate the probability of reaching a flood category based on historical or normal conditions. When the value of CS is greater than HS...the probability of exceeding that level is higher than normal. When the value of CS is less than HS...the probability of exceeding that level is lower than normal. ...Table 1--Probabilities for minor...moderate and major flooding... Valid Period: 2/18/2017 - 5/19/2017 : Current and Historical : Chances of Exceeding : Flood Categories : as a Percentage (%) Categorical : Flood Stages (FT) : Minor Moderate Major Location Minor Mod Major : CS HS CS HS CS HS -------- ----- ----- ----- : --- --- --- --- --- --- :South Platte River South Platte 7.0 9.0 11.0 : <5 <5 <5 <5 <5 <5 Denver 11.0 12.5 14.0 : <5 <5 <5 <5 <5 <5 Henderson 10.0 11.0 15.0 : 6 6 <5 <5 <5 <5 Kersey 10.0 11.5 13.0 : 8 9 5 6 <5 <5 Weldona 10.0 11.0 13.0 : 7 8 5 6 <5 <5 Balzac 10.0 11.0 13.0 : 8 8 5 6 <5 <5 Julesburg 10.0 11.0 12.0 : <5 5 <5 <5 <5 <5 :Plum Creek Sedalia 8.0 10.0 12.0 : <5 <5 <5 <5 <5 <5 :Bear Creek Morrison 9.0 10.0 11.0 : <5 <5 <5 <5 <5 <5 Sheridan 8.0 10.0 11.0 : <5 <5 <5 <5 <5 <5 :Clear Creek Golden 10.0 13.0 14.0 : <5 <5 <5 <5 <5 <5 Derby 9.0 10.5 11.5 : <5 <5 <5 <5 <5 <5 :N Fk Big Thompson River Drake 6.0 7.0 8.0 : <5 <5 <5 <5 <5 <5 :Cache la Poudre River Fort Collins 9NW 7.5 9.0 10.5 : <5 <5 <5 <5 <5 <5 Fort Collins 10.5 11.5 13.0 : <5 <5 <5 <5 <5 <5 Greeley 8.0 9.5 10.5 : <5 <5 <5 <5 <5 <5 :North Platte River Northgate 8.0 9.5 11.0 : 5 <5 <5 <5 <5 <5 Legend CS = Conditional Simulation (Current Outlook) HS = Historical Simulation FT = Feet In Table 2 below...the 95 through 5 percent columns indicate the probability of exceeding the listed stage levels (FT) for the valid time period. ...Table 2--Exceedance Probabilities... Chance of Exceeding Stages at Specific Locations Valid Period: 2/18/2017 - 5/19/2017 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :South Platte River South Platte 3.7 3.8 3.8 3.9 4.0 4.7 5.2 Denver 4.0 4.0 4.2 4.7 5.3 6.4 7.1 Henderson 5.2 5.5 5.7 6.6 7.2 9.0 10.2 Kersey 4.3 4.3 4.7 6.0 7.7 8.9 11.3 Weldona 2.9 3.0 3.1 4.2 6.1 7.3 10.8 Balzac 2.6 2.8 3.0 4.2 5.6 7.6 10.9 Julesburg 4.6 4.7 5.0 6.0 6.9 7.9 9.6 :Plum Creek Sedalia 4.0 4.1 4.2 4.4 4.6 5.3 6.9 :Bear Creek Morrison 6.0 6.1 6.3 6.5 6.8 7.2 7.7 Sheridan 2.6 2.7 2.8 3.1 3.6 4.5 4.8 :Clear Creek Golden 4.2 4.3 4.5 4.7 5.0 5.4 5.7 Derby 2.2 2.3 2.5 2.8 3.3 3.9 4.9 :N Fk Big Thompson River Drake 3.9 4.0 4.0 4.1 4.2 4.4 4.6 :Cache la Poudre River Fort Collins 9NW 3.3 3.4 3.5 3.8 4.1 4.8 5.7 Fort Collins 1.4 1.5 1.7 2.2 3.1 4.7 6.2 Greeley 2.2 2.2 2.5 3.2 4.8 6.8 7.8 :North Platte River Northgate 4.8 5.1 5.3 5.5 6.0 6.9 7.8 In Table 3 below...the 95 through 5 percent columns indicate the probability of falling below the listed stage levels (FT) for the valid time period. ...Table 3--Nonexceedance Probabilities... Chance of Falling Below Stages at Specific Locations Valid Period: 2/18/2017 - 5/19/2017 LOCATION 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :South Platte River South Platte 2.8 2.8 2.8 2.8 2.8 2.8 2.8 Denver 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Henderson 3.9 3.8 3.3 3.1 3.0 3.0 3.0 Kersey 3.6 3.3 3.0 2.9 2.8 2.7 2.7 Weldona 1.9 1.4 0.2 0.1 0.1 0.1 0.1 Balzac 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Julesburg 1.8 1.8 1.8 1.8 1.8 1.8 1.8 :Plum Creek Sedalia 3.7 3.7 3.7 3.7 3.6 3.6 3.6 :Bear Creek Morrison 5.6 5.5 5.5 5.5 5.5 5.5 5.5 Sheridan 2.2 2.2 2.1 2.1 2.1 2.1 2.1 :Clear Creek Golden 3.5 3.5 3.5 3.5 3.5 3.5 3.4 Derby 0.9 0.9 0.9 0.9 0.9 0.9 0.9 :N Fk Big Thompson River Drake 3.8 3.8 3.7 3.7 3.7 3.7 3.7 :Cache la Poudre River Fort Collins 9NW 2.8 2.8 2.8 2.8 2.8 2.8 2.8 Fort Collins 1.1 1.0 0.5 0.4 0.4 0.4 0.4 Greeley 1.4 1.3 1.3 1.3 1.3 1.3 1.3 :North Platte River Northgate 2.4 2.4 2.4 2.4 2.4 2.3 2.3 These long-range probabilistic outlooks contain forecast values that are calculated using multiple season scenarios from 30 or more years of climatological data...including current conditions of the river...soil moisture...snow cover and 30 to 90 day long-range outlooks of temperature and precipitation. By providing a range of probabilities...the level of risk associated with long-range planning decisions can be determined. These probabilistic forecasts are part of the National Weather Service`s Advanced Hydrologic Prediction Service. Spring flood outlooks are routinely issued in February and March to give advanced notice of possible flooding. The next scheduled spring flood outlook will be issued Thursday March 2nd. Visit our web site weather.gov/bou for more weather and water information. $$ th

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