Green and Yampa Rivers: Spring Forecast and Runoff Summary

June 23rd, 2016

Ashley Nielson-Senior Hydrologist Colorado Basin River Forecast Center National Weather Service/NOAA What is the Colorado Basin River Forecast Center?

Mission: To understand and predict changes in the Earth’s environment…to meet our Nation’s economic, social and environmental needs

Mission: The NWS provides, weather, hydrologic, and climate forecasts and warnings….for the protection of life and property and the enhancemnet of the national ecomony

The NWS has 13 river forecast centers defined by major river basins across the country that produce timely and accurate water forecasts to support the NWS/NOAA missions CBRFC: Who are we? CBRFC Water Supply Forecast Basins

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NOAA,NWS,CBRFC www.cbrfc.noaa.gov B.Bernard 2014 Today’s Presentation – Questions to Answer

1. Late season water supply forecasts increased significantly - What happened ?

2. How did the Yampa - Deerlodge daily streamflow forecasts perform?

3. What are the sources of uncertainty in the forecasts?

4. How is the flood stage at Jensen determined? - Aldis Strautins – Service Hydrologist Grand Junction

Looking Back – Snapshot on April 1st 2016

Water Year Precipitation Snow Conditions October 2015 – March 2016 SNOTELS: % Median SWE Upper Colorado significant runoff contributing areas

98%

Flaming Gorge Flaming Gorge

Yampa River 98% Yampa River Looking Back – Snapshot on April 1st 2016 Water Supply Forecasts: April – July Volumes Most Probable Scenario (% of 1981-2010 average) • CBRFC model makes assumptions about long range future weather

• Official forecasts provide a range of possible outcomes based on “dry”, “average”, and “wet” weather scenarios

• “Average” scenario is most commonly

Flaming used forecast Gorge 76% Little Snake 81% April 1st Flaming Gorge Forecasts: Dry 520 KAF (53% average) Average 740 KAF (76% average) Yampa 91% Wet 1150 KAF (118% average)

White April 1st Yampa River Forecasts: 88% Green River Dry 825 KAF (66% average) 76% Average 1130 KAF (91% average) Wet 1450 KAF (117% average) What happened after April 1st? • Weather pattern shifted in late April and carried through May • Series of slow moving low pressure systems

Upper Atmospheric Air Pattern at ~18,000 ft

May 7 – May 12 May 15 – May 25 What happened after April 1st? • Storms brought significant rain and snow to Green and Yampa River basins • Much above average precipitation for April and May • Much below average temperatures for May

April 2016 Precipitation May 2016 Precipitation May Max Temperature How wet was it? Upper Green and Yampa April-May Precipitation Historical Ranking • April-May precipitation at many locations was in the top 3 of the historical record

Location April-May April-May % of Average Observed Average (in) (in) Farson 1.9 6.95 372% (47) Green 2.2 5.98 270% River (50) Hickerson 5.05 9.2 182% Park (31) Divide 7.3 13.1 180% Peak (36) What were the impacts? • Significant rises in streamflow from precipitation events

Rain Rain + Snowmelt

Upper Yampa Green

• Increase in snowpack and delay of melt and runoff

Upper Yampa Green What were the impacts? • Extended period of high flows

Fontenelle

Blacks Fork

Flaming Gorge Henry’s Fork

• Efficient runoff and higher peak flows when when melt started in early June • Reduced demands and irrigation What were the impacts? • Extended period of high flows

Fontenelle

Blacks Fork

Flaming Gorge Henry’s Fork

• Meeks Cabin and Stateline reservoirs spilled • Observed flows from this area were more than expected What were the impacts? • Extended period of high flows increased Flaming Gorge elevations

Fontenelle

Blacks Fork

Flaming Gorge Henry’s Fork

• A significant amount of inflow during May and early June was from the area below Fontenelle reservoir including Blacks Fork, Henry’s Fork, and other tributaries • Typically this area does not contribute significant flows What were the impacts? • April-July water supply forecasts increased on May 1st and June 1st

Most Probable Scenario (% of 1981-2010) average) Most Probable Scenario (% of 1981-2010) average)

76% 93%

81% 146%

91% 145%

88% 90% 76% 103%

April 1st June 1st What were the impacts?

• April-July water supply forecasts increased on May 1st and June 1st

Flaming Gorge Yampa-Deerlodge

10-Day Streamflow Forecasts: Yampa River –Deerlodge and Green River-Jensen

Flaming Gorge Releases

Yampa Deerlodge Forecasts 5/29-6/14

• Daily forecasts were higher )

cfs than observed values • Why? Flow (

5/28 5/30 6/1 6/3 6/5 6/7 6/9 6/11 6/13 6/15 What are the sources of uncertainty in the forecasts?

1. Future Weather • Uncertainty in temperature and precipitation forecasts

2. Model Snow States • Is the model’s representation (amount and extent) of the snowpack correct? • SNOTELS and satellite images used to verify model snow states • Wet cold springs are especially difficult to verify snow states • Many SNOTELS already melted out; not useful • Limited satellite images due to cloud cover; not useful

3. Observed Streamflow • USGS gage errors +- ~5-8%

4. Demands/Diversions Assumptions • Model makes assumptions about future diversions/demands • Typically less than assumptions in wet springs

Today’s Presentation – Questions to Answer 1. Late season water supply forecasts increased significantly - What happened ? • Change in weather pattern in late April through May • Near record or record April-May precipitation • Delayed melt and rain resulted in efficient runoff and a long period of elevated flows • Important to evaluate forecast range (dry, average, wet scenarios)

2. How did the Yampa - Deerlodge daily streamflow forecasts perform? • Forecasts were too high • Model mostly likely had to much snow

3. What are the sources of uncertainty in the forecasts? • Future Weather • Model Snow States • Observed Data • Demand/diversions assumptions

Questions? NWS Critical Levels Green River- Jensen National Weather Service River Critical Levels

Critical levels are defined by local NWS Service Hydrologists so flood watches and warnings can be issued.

• Bankfull Stage: established gage height at a given location above which a rise in water surface will cause the river to overflow the lowest natural stream bank

• Flood Stage: established gage height for a given location at which a rise in water surface level begins to impacts lives, property, or commerce.

• Minor Flooding: minimal or no property damage but possible public threat (roads, etc)

• Moderate Flooding: some inundation of structures and roads near stream. Some evacuations of people and/or transfer of property to higher elevations

• Major Flooding: extensive inundation of structures and roads. Significant evacuations/transfers.

National Weather Service River Critical Levels Green River near Jensen Current USGS Rating Table Bankfull Stage = 9.0 feet ~18,100 cfs

Flood Stage = 10.8 feet ~24,000 cfs Moderate = 12.0 feet ~28,400 cfs Major = 14.0 feet ~36,000 cfs

5.10 feet: 5490 cfs 10.0 feet : 21,200 cfs

Photo: USGS Photo: USGS National Weather Service River Critical Levels

Green River near Jensen Current USGS Bankfull Stage = 9.0 feet Rating Table ~18,100 cfs Flood Stage = 10.8 feet ~24,000 cfs

Years since 1980 > Flood Stage 1983 1984 1997 2011 Contact Us!

• Ashley Nielson-Green River Forecaster • [email protected] • 801-524-5130 x333

• Aldis Strautins-Service Hydrologist • [email protected] • 970-256-9463

www.cbrfc.noaa.gov

@nwscbrfc

facebook.com/nwscbrfc Extra Slides Why is the Flaming Gorge forecast only ~75 % of average when the snowpack is near normal? 1. Dry fall soil moisture conditions • Can impact spring runoff efficiency • Negative impact on the forecasts

2. High elevation snow conditions are not as good • Rain rather than snow in Fall, normally snow • SNOTELS don’t represent this area • Largest contributing area for water supply

3. Distribution of snow in contributing areas • Flaming Gorge Inflow = Green River + Local (Hams Fork, Uintas, Big Sandy) • Green River = ~80% Local = ~20% • Green River Breakdown Wind Rivers Below normal snow ~75-80% of inflow Wyoming Range Normal snow ~20-25% of inflow

Peak Flow Forecast: Yampa River-Deerlodge

Forecast: 10000 CFS Average: 13500 CFS Flood: 20700 CFS Last Year: 10100 CFS