Last Hydrology Report: June 18th 2022

Here is an update on conditions in the Upper Yellowstone as of 9:00 AM Saturday, 6/18/2022.

Snowpack:

• Warm weather in the past couple days has melted a fair amount of snowpack. Snow water equivalent has dropped over 2 inches in the Yellowstone headwaters since the update on Thursday.

Streamflows:

• As expected streamflows have responded to snowmelt with delayed pulses of around 1.0 feet in stage. However flows overall have trended down drastically from Monday.

Weather:

• Forecasts show colder temperatures and small amounts of rain fall through Monday and then warmer temperatures Wednesday onward. No significant amount of rainfall is forecasted at this point in time.

What this all means:

• At this point there is little concern of any further flooding. Streamflows will continue to respond to snowpack melting however with no rain forecasted and considering the amount of snowpack lost in the past couple days, it is highly unlikely we will see flood stage again this spring. Flows will bounce up and down as melt continues but ultimately trend downward. Nonetheless, these slightly increased flows can impact banks that have been destabilized.

The state hydrologist will continue to monitor conditions and give warning if anything comes up. Otherwise, folks can fully focus on damage assessment and recovery and re-opening businesses where possible at this point in time rather than worrying about anymore incoming flood conditions.

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Most Recent Hydrology Report: June 16th 2022

Here is an update on conditions and anticipated conditions as of 6:00 AM on Thursday, 6/16/2022. 

 

Snowpack: 

• The rain on snow event that led to the flooding was predominantly snowpack above 8,000 feet. Little to no snowpack below 8,000 feet was present before the event started. Using the limited SNOTEL snowpack monitoring sites in the basin, on average 7.1 inches of snow water equivalent (SWE) came from 8,000 – 9,000 feet and 5.9 inches of SWE came from above 9,000 feet during the event. Currently on average 12.3 inches of SWE is present between 8,000 – 9,000 feet and 23.1 inches of SWE is present above 9,000 feet. Little or no snow is currently present below 8,000 feet other than recent snowfall. Little is currently known about the quality of the snowpack. 

 

Streamflow: 

• The United States Geological Survey has been able to visit nearly all the stream gage sites in the basin. Corwin Springs, Gardner River and Lamar River stream gages are currently all active. Carter’s Bridge is still having issues. Subject to change with more data and corrections, the flood peak at the Carter’s Bridge gage was 54,500 cubic feet per second (cfs) at around 10:00 PM on Monday 6/13/2022. Last reported flow at Carter’s Bridge was 24,000 cfs at 3:15 PM yesterday 6/15/2022. Other gages show a similar downward trend since Monday and are currently sitting fairly level. 

 

Forecast: 

• The forecast calls for warm temperatures today through Saturday and then cooler temperatures Sunday through Tuesday with some precipitation expected. Currently the amount of precipitation forecasted is very low, likely under 0.2 inches. Keep in mind that is simply a forecast and what to expect will be much more reliable on Saturday. 

 

What this all means:  

• Currently there is a fair amount of snowpack left in the basin however most of this is above 9,000 feet in elevation which protects the snowpack from rain on snow events given the elevation. Warm temperatures over the next couple days will likely increase streamflow in the basin however this rise should be below flood stage and likely in the range of 1.0 to 1.5 feet in stage at Carter’s Bridge. Monday flows should begin to recede again with the cold weather. Warm temperatures will not cause runoff as significant as what was seen from the higher elevation rain on snow event.  

Another update will be given Friday or Saturday when the incoming precipitation forecast is more reliable. 

 

 

Hydrology Report: June 14th 2022

Here is a summary of conditions in the Upper Yellowstone as of 5:30 AM this morning.

 

Rain forecast:

• Over the next six hours the National Weather Service (NWS) is forecasting 0.03 to 0.16 inches throughout the Upper Yellowstone with 0.16 inches expected in the National Park. Not much more is anticipated after that. Keep in mind this is only a NWS forecast.

• Interactive Radar Tool

 

Temperature:

• The National Park and Paradise Valley are expected to remain colder today (highs of 38 and 55 respectively). Then a warm wave will roll in starting with slightly increased highs Wednesday and significantly warmer conditions Thursday thru Saturday.

 

Snowpack:

• Rain on snow played a significant role in the current flooding. Between June 7 and June 13, 5.5 inches of snow water equivalent (SWE) was melted and subsequently became runoff. This was due to the 2 to 3 inches of rainfall rapidly increasing snowmelt rates. This is tremendous amount of snowpack to lose in a short period of time. That being said, the current SWE for the Upper Yellowstone is 11.8 inches. The median for this day is 7.7 inches. So significant snowpack still remains in the mountains.

 

Streamflow:

• Both of Corwin Springs and Gardiner River gages show a peak yesterday and decline since then. The Gardiner River gage will be the best indicator at this point of what is headed north if we do get more runoff.

 

What this all means:

• The next couple days flows will likely recede due to the lack of significant precipitation and cooler temperatures.

• Given no significant precipitation Thursday through Saturday, the warmer temperatures should not produce as much of an increase in runoff as the rain on snow event we just saw.

• Any significant rain events after Thursday will result in significant runoff (none is currently forecasted until Sunday)

• There is still a significant amount of snowpack remaining so keep an eye on rain forecasts over the next couple days and weeks.

 

Keep in mind weather forecasts are simply forecasts so focus most on the next two days rather than a week ahead. I will send these updates when conditions or forecasts change significantly.

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We will post another update by Friday as the latest especially to factor in what looks like will be warmer temps AND the potential for rain on Sunday. It will be important to keep an eye on that report in order to prepare accordingly.

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Corwin Springs Gage: National Weather Service Advanced Hydrologic Prediction Service

Gardiner Gage: National Weather Service Advanced Hydrologic Prediction Service

Lamar Gage: National Weather Service Advanced Hydrologic Prediction Service