Record to well-above normal snowpack primed to melt across the state of Montana.

FROM NRCS:  After a winter and spring that dropped seemingly non-stop snowfall across most of Montana, spring runoff is finally here. April started just like many of the other months so far this snow season, with abundant precipitation falling and continuing to build the mountain snowpack, according to snow survey data collected by the USDA Natural Resources Conservation Service.

Some areas in southwest Montana set new records for April precipitation (Gallatin and Madison valleys), and almost all areas except the Rocky Mountain Front and Hi-Line received near to above normal precipitation. “The crazy fact about this April was that average to well-above average precipitation fell during the first 18 days of the month; the latter half of the month was dominated by high pressure with abundant sunshine and well-above-average temperatures,” said Lucas Zukiewicz, NRCS water supply specialist for Montana.

Early April precipitation only continued to add to a snowpack that was well-above normal across the state, and the snowpack was record-setting in the Upper Clark Fork, Blackfoot and Clark’s Fork (Yellowstone) River basins. Peak snow water equivalent in these basins exceeded prior record years of 1975, 1997 and 2011, and occurred during the third week of the month. Many SNOTEL sites and snowcourses in these basins remain record for May 1 even though melt has already started at low to mid-elevations.

“Snowpack percentages are incredibly high for this date across the state, and in almost all river basins,” Zukiewicz said. “At some point in the spring, I stopped getting excited by the continued snowfall, and started worrying about it.”

The NRCS forecasts long-duration streamflows for water users across the state, and the May 1 – July 31 forecasts reflect the well-above normal snowpack across the state and are above to well-above average in almost all river basins. Even though the agency forecasts long-term volumes, it works closely with cooperators in the National Weather Service, Bureau of Reclamation, and Montana Department of Natural Resources and Conservation to provide information to them on current snowpack conditions and forecasted volumes in order to manage reservoirs and issue information to the public regarding the coming runoff.

Water managers in the state have been actively managing reservoirs in anticipation of the well-above-average runoff in some basins, and reservoirs in some systems had been dropped to near historic levels before runoff began in mid-to-late April. Since late January the Bureau of Reclamation has dropped Hungry Horse Reservoir in the Flathead River basin nearly 70 feet, and in the Sun River basin, Gibson Reservoir was dropped to close to a record low on April 1.

“Active management in the river systems with reservoirs this year has been great to see with the huge snowpack we have, but water users on non-controlled streams and rivers will be at the mercy of the weather this year with regards to snowmelt runoff,” Zukiewicz said.

Active snowmelt runoff began mid-month across the state, with low-elevation melt causing substantial increases in river and stream flows. “In many cases, the large increases in flows were from elevations below what we measure with our current monitoring network,” he said. “Valley and plains snow this year was abundant due to the below normal temperatures. When it and the low elevation mountain snowpack started to melt, it resulted in quick increases in flows in many rivers and streams.” Snowpack remains well-above normal for this date at almost all water yielding elevations, meaning that the bulk of the snow water remains to enter the rivers and streams.

The official National Weather Service flood potential forecasts across the state indicate there is significant potential for flooding along some rivers and streams this spring and summer, something that is already occurring. “Ultimately, we’ll have to wait and see how fast the snowpack comes out this year, but the potential is there for big flows to occur with the amount of snow still left in the mountains,” Zukiewicz said. “A long period of sunny days with above average temperatures or a rain-on-snow event would be a game changer. A close eye should be kept on the weather forecasts this spring and summer, especially if you live in a low-lying area near a river or stream.”

Current snowpack conditions and long-term streamflow forecasts can be found in this month’s NRCS Montana Water Supply Outlook Report, which can be found at the website below after the 5th business day of the month:

http://www.nrcs.usda.gov/wps/portal/nrcs/main/mt/snow/waterproducts/basin/

 

Current Snowpack and Coming Spring Weather Critical to Summer Water Supplies

Snowfall in some locations of Montana has been record-breaking during February, resulting in snowpack totals for March 1st that are well above normal for most river basins, according to snow survey data collected by the USDA Natural Resources Conservation Service (NRCS). Twenty-five SNOTEL (SNOwpack TELemetry) stations and manual measurement locations set new records for February totals, and 21 measurements at other locations were the second highest on record.

“Abundant mountain, valley and plains snowfall this winter have Montana under a blanket of snow at the beginning of March,” said Lucas Zukiewicz, NRCS water supply specialist for Montana. “While this is great news for long-term water supply, it’s been hard on a lot of families and businesses in the plains.”

Snowpack totals are above normal in all major river basins of the state of Montana for March 1, and some measurement locations are setting records for this date. Fifteen snowpack measurement locations have set a new record for March 1, and 12 are the second highest on record. Most of these records are being set in the headwaters of the Upper Clark Fork, mountains of the Missouri Mainstem around Helena and in the headwaters of the Upper Yellowstone and Clark’s Fork of the Yellowstone River basins. While not record-setting, most other river basins have seen consistent and above normal moisture this winter due to the favorable La Nina weather patterns this winter. Many snowpack measurement locations have already reached the normal “peak,” or maximum amount of snow water contained in the snowpack, on March 1st. Zukiewicz said only one area seems to be left out of this year, the Centennial range which serves as the headwaters for the Red Rock River in southwestern Montana. It has a snowpack that remains below normal for this date.

“As we approach spring, water users across the state start to plan for the coming growing season, water supply and allocations from spring runoff of the mountain snowpack,” Zukiewicz said. “This year looks to deliver above average flows in the rivers in most locations due to the deep mountain snowpack.”

On March 1, the NRCS Montana Snow Survey began to issue forecasts for the spring and summer runoff with many locations forecasted to be above to well above average. Some forecasted volumes for rivers in south-central Montana for the April 1 through July 31 period are approaching records. “The median forecast for the Clark’s Fork at Belfry, Mont., is above the record for that location,” Zukiewicz said. “There’s going to be a lot of water coming out of the Beartooth Range this spring and summer.”

While spring is always critical to the timing and volume of water supply, Zukiewicz said he will keep a close eye on the week-to-week weather patterns over the next few months. Climatologically, the months of March through May are some of the most significant months with regards to precipitation for river basins east of the Divide, and many basins already have an above-normal snowpack. Any continued snowfall will build on the above normal snowpack and will further increase the amount of water available for runoff.

“At this point, we have pretty close to assured adequate water supply in many areas due to heavy early season snowfall,” Zukiewicz said. “As much as it pains me to say it, a normal month or two would be the best case scenario from here on out.” The NRCS Montana Snow Survey will issue the next snowpack report and updated water supply forecasts for the state on April 1, 2018. “By then we should have a good idea if this pattern is going to break or keep going.”

Individual point forecasts for streams and rivers can be found in the monthly NRCS Water Supply Outlook Report and should be consulted as conditions vary from basin to basin, and even within the basins themselves.

Monthly Water Supply Outlook Reports can be found at the website below after the 5th business day of the month:http://www.nrcs.usda.gov/wps/portal/nrcs/main/mt/snow/waterproducts/basin/

Source: NRCS