####018016516#### FGUS75 KBOU 292238 ESFBOU COC001-005-013-014-019-031-035-039-047-049-057-059-069-073-075- 087-093-095-115-117-121-123-022245- Water Supply Outlook National Weather Service Denver CO 338 PM MST Thu Feb 29 2024 ...SPRING FLOOD AND WATER RESOURCES OUTLOOK FOR NORTH CENTRAL AND NORTHEAST COLORADO... ...Spring Flood and Water Resources Outlook for North Central and Northeast Colorado Issuance Number 2... This is the second 2024 spring runoff outlook for North Central and Northeast Colorado covering all or portions of the Upper North Platte...Upper South Platte and Upper Colorado River Basins. Flood and Water Supply Outlook Summary -------------------------------------- Spring flood potential is near to slightly below normal at this time for the South Platte River Basin, the Upper North Platte River Basin and the far Upper Colorado River Basin. Any widespread, significant flooding is not likely due to snowmelt alone. It should be emphasized that it is very early and snow typically accumulates into April, therefore conditions may change before the runoff begins. Water supply forecasts issued in mid-February by the National Weather Service project generally below average April through July runoff volumes for Upper Colorado and South Platte Basins. The one exception being the Upper North Platte basin, and the Fraser River Basin which are expected to produce a slightly above average runoff volume if current conditions persist. Appreciable mountain snowmelt runoff in a normal year starts in late April to early May. Mountain snowmelt generally peaks in mid-May to mid-June. It is still very early to make long range predictions on the magnitude of flooding from mountain snowmelt runoff. Heavy rainfall, a cold spring, or unseasonably warm temperatures during the snowmelt season can affect total runoff volume and peak flow, increasing the threat of flooding. Observed Precipitation...Snowpack and Temperatures -------------------------------------------------- The average higher elevation total water year precipitation for the Upper Colorado, Upper South Platte and the Upper North Platte Basins are near to slightly below normal with and Cache La Poudre Basin below normal. For the water year the percent of normal precipitation is still below normal for the central and northern part of the Denver metro area extending out into most of the northeastern plains. The exception with along the north Weld county border and most of Sedgwick and Phillips counties with near normal precipitation. Southern part of the Denver metro area into the Palmer Divide and adjacent foothills are near to slightly above normal. Precipitation in October through November was well below normal for most of Northeastern Colorado including the eastern plains, the urban corridor and mountains. In December the far eastern plains over to the Palmer Divide and into the foothills had above normal precipitation for the month. The northern part of the metro area east and north had much less than normal precipitation. Weld and Morgan counties had the least precipitation. January continued the dry trend over most of the eastern plains and Denver metro area. The Palmer Divide and portions of the mountains received some much needed moisture and spotty areas above normal for the month. The very end of January and into February brought much needed precipitation to the area. The eastern plains and into the foothills have received well over normal precipitation for the month of February so far. The mountains also received much needed snow and increased the snowpack to near to slightly below normal for the water year. Temperatures on average since the beginning of the water year through December have been well above normal. In January temperatures were below normal. So far in February temperatures have been above normal. The northern part of the Front Range mountains has had less snow and precipitation than normal including the St Vrain, Big Thompson, and Cache La Poudre Basins. Basin snowpack conditions for the period October 1 2023 to February 28 2024: --------------------------------- (Snow is percent of Median) (Total precipitation is percent of Average) Basin Snow Precip ----- ---- ------ Upper Colorado 99 100 South Platte 93 89 Upper North Platte 97 97 Subbasin Snow Precip -------- ---- ------ Colorado Headwaters 102 102 Blue 103 102 South Platte Headwaters 104 94 Clear Creek 100 102 St Vrain 88 86 Big Thompson 92 87 Cache La Poudre 88 83 North Platte Headwaters 93 94 Climate Outlook --------------- The current ENSO pattern is El Nino and is forecast to transition to the neutral phase later this spring. The chance of ENSO changing to neutral later this spring reaches 79 percent. The outlook for March favors equal chances of either above, below or normal temperatures with a better chance of above normal precipitation over the mountains and along the urban corridor with a slightly smaller chance of above normal precipitation on the eastern plains. Farther out, the March through May seasonal outlook favors equal chances of either above, below or normal temperatures and equal chances of either above, below or normal precipitation for Northeastern Colorado. 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: 03/02/2024 - 09/30/2024 : 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 8.5 9.5 : <5 5 <5 <5 <5 <5 Denver 11.0 13.0 15.0 : <5 <5 <5 <5 <5 <5 Henderson 11.0 13.0 15.0 : <5 <5 <5 <5 <5 <5 Fort Lupton 11.0 13.0 15.0 : 5 5 <5 <5 <5 <5 Kersey 10.0 11.5 13.5 : 15 15 11 8 <5 <5 Weldona 10.0 11.0 12.0 : 12 9 9 8 8 6 Fort Morgan 17.5 19.5 21.5 : 12 13 10 10 8 7 Balzac 10.0 11.0 12.5 : 12 12 11 11 9 9 Atwood 11.5 13.0 14.5 : 11 11 10 10 <5 <5 Julesburg 10.0 11.0 12.5 : 10 10 <5 <5 <5 <5 :Plum Creek Sedalia 8.0 10.0 12.0 : 6 <5 <5 <5 <5 <5 :Bear Creek Morrison 9.0 10.0 10.5 : <5 <5 <5 <5 <5 <5 Sheridan 8.0 10.0 10.5 : <5 <5 <5 <5 <5 <5 :Clear Creek Golden 8.5 9.5 10.5 : <5 <5 <5 <5 <5 <5 Derby 10.5 11.5 12.5 : <5 <5 <5 <5 <5 <5 :N Fk Big Thompson River Drake 5.5 6.0 7.0 : <5 <5 <5 <5 <5 <5 :Cache la Poudre River Fort Collins 9NW 7.5 9.0 10.5 : 5 10 <5 6 <5 <5 Fort Collins 10.5 11.5 13.0 : <5 <5 <5 <5 <5 <5 Greeley 8.0 9.5 10.5 : 14 17 7 12 5 7 :North Platte River Northgate 8.0 9.5 11.0 : 8 13 <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: 03/02/2024 - 09/30/2024 Location 95% 90% 75% 50% 25% 10% 5% -------- ------ ------ ------ ------ ------ ------ ------ :South Platte River South Platte 3.9 4.0 4.2 4.4 4.8 5.3 6.6 Denver 4.7 5.0 5.5 5.9 6.4 7.3 7.4 Henderson 5.5 5.8 6.6 7.1 7.8 8.5 9.0 Fort Lupton 5.3 5.6 6.9 7.8 8.9 9.6 11.1 Kersey 4.3 4.5 6.1 7.5 8.4 12.3 13.0 Weldona 3.6 3.6 5.2 6.2 7.5 10.3 13.3 Fort Morgan 10.3 10.4 11.8 13.4 14.9 19.5 22.5 Balzac 3.5 3.7 5.1 6.8 7.7 11.7 13.7 Atwood 4.5 4.6 5.9 7.7 8.4 12.6 14.2 Julesburg 6.2 6.2 7.1 8.1 8.5 10.0 10.6 :Plum Creek Sedalia 4.2 4.2 4.4 4.9 5.5 7.0 9.1 :Bear Creek Morrison 6.4 6.5 6.8 7.0 7.2 7.5 7.6 Sheridan 3.2 3.3 3.7 4.4 5.0 5.4 5.5 :Clear Creek Golden 4.7 5.1 5.7 6.0 6.5 6.8 7.3 Derby 4.9 5.0 5.4 6.1 6.6 7.0 7.5 :N Fk Big Thompson River Drake 2.9 3.0 3.1 3.3 3.8 4.0 4.6 :Cache la Poudre River Fort Collins 9NW 4.0 4.1 4.7 5.1 5.9 7.1 7.5 Fort Collins 2.3 2.4 3.4 4.7 5.4 7.2 9.0 Greeley 1.9 1.9 2.9 5.2 6.1 8.5 10.4 :North Platte River Northgate 4.4 4.7 5.7 6.3 7.2 7.7 8.5 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: 03/02/2024 - 09/30/2024 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 2.9 2.9 2.9 2.9 2.9 2.8 Henderson 3.6 3.5 3.5 3.5 3.5 3.5 3.5 Fort Lupton 3.5 3.3 3.3 3.2 3.2 3.2 3.2 Kersey 2.6 2.4 2.2 2.1 2.0 2.0 2.0 Weldona 2.2 2.2 2.2 2.1 2.1 2.0 2.0 Fort Morgan 9.2 8.9 8.5 8.4 8.4 8.4 8.4 Balzac 2.4 2.3 1.9 1.4 0.7 0.6 0.6 Atwood 3.1 2.8 2.2 2.0 1.8 1.6 1.6 Julesburg 3.3 3.3 3.3 3.3 3.3 3.3 3.3 :Plum Creek Sedalia 3.7 3.7 3.6 3.5 3.5 3.5 3.5 :Bear Creek Morrison 5.7 5.7 5.7 5.6 5.5 5.4 5.3 Sheridan 2.5 2.4 2.3 2.1 2.0 2.0 1.9 :Clear Creek Golden 3.4 3.3 3.3 3.3 3.3 3.3 3.2 Derby 2.9 2.7 2.7 2.7 2.7 2.7 2.7 :N Fk Big Thompson River Drake 2.4 2.4 2.4 2.4 2.4 2.4 2.4 :Cache la Poudre River Fort Collins 9NW 2.8 2.8 2.8 2.8 2.8 2.7 2.7 Fort Collins 0.1 0.0 0.0 0.0 0.0 0.0 0.0 Greeley 0.8 0.8 0.7 0.7 0.7 0.7 0.7 :North Platte River Northgate 2.4 2.4 2.4 2.4 2.4 2.4 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. Following are the forecasts for selected locations: Median Forecast Volume Percent Stream and Station Period 1000 AF of Avg __________________ ______ _______ _______ South Platte River Antero Reservoir inflow Apr-Sep 12 85 Spinney Mtn Res inflow Apr-Sep 36 80 11-Mile Canyon Res inflow Apr-Sep 40 79 Cheesman Lake inflow Apr-Sep 74 79 South Platte Apr-Sep 149 73 Bear Creek Morrison Apr-Sep 17 63 Clear Creek Golden Apr-Sep 98 75 South Boulder Creek Eldorado Springs Apr-Sep 34 85 Boulder Creek Orodell Apr-Sep 51 98 Saint Vrain Creek Lyons Apr-Sep 75 69 Cache La Poudre River Canyon Mouth Apr-Sep 184 88 North Platte River Northgate Apr-Sep 332 112 Colorado River Granby Apr-Jul 193 86 Willow Creek Willow Creek Res Apr-Jul 46 92 Fraser River Winter Park Apr-Jul 21 113 Williams Fork River Williams Fork Reservoir Apr-Jul 82 85 Blue River Dillon Res Apr-Jul 148 89 Green Mtn Res Apr-Jul 259 93 Muddy Creek Wolford Mtn Res Blw Apr-Jul 47 91 Colorado River Kremmling Apr-Jul 792 91 These forecasts reflect natural flow only. Actual observed flow will likely be affected by upstream water management. It should be emphasized that snow accumulation and snow pack conditions could change before the runoff begins. Changing hydrometeorological conditions can have a significant impact on water supply forecasts. Additional products will be issued as conditions evolve. Additional supportive information --------------------------------- - Visit the Missouri Basin RFC information webpage for water supply forecasts east of the divide at weather.gov/mbrfc/water. - Visit the Colorado Basin RFC for water supply forecasts west of the divide at cbrfc.noaa.gov/lmap/lmap.php?interface=wsup. - Visit our website at weather.gov/bou for additional local weather...climate and stream information. - Long range precipitation and temperature outlooks are available at www.cpc.ncep.noaa.gov/products/predictions/. - Snowpack and reservoir data are available from the Natural Resources Conservation Service at www.wcc.nrcs.usda.gov/snow/. $$ as