530 PM CDT

Tue Apr 19 2022

INCLUDES STUTSMAN COUNTY

…HYDROLOGIC OUTLOOK FOR SNOWMELT AND UPCOMING WEATHER…

An unusually strong April storm has left most of North Dakota with
an above normal amount of snow, and more importantly…water
equivalent in that snow for this time of year. Something unusual for
having this much snow in the spring snowmelt season is that the
snowpack is sitting on relatively warm soils. Additionally, there is
yet another multi-day rain and snow event expected to arrive in the
area during the latter half of this week.

The current heaviest snowpack up in the Souris River basin is also
favored for some of the strongest impacts from the upcoming rain and
snow event. In that sense, the biggest threat is from rain on top of
a melting snowpack, and there is a distinct risk of this taking
place Thursday into Friday, before turning into snow late on Friday
on into Saturday. The net effect of rain on a snowpack that is
beginning to melt is the enhancement of melt rates and the
magnification of the amount of liquid water that will be split
between infiltration and attempted runoff. The reason this will be
called attempted runoff is because ditches and natural drains are
largely filled with the deeper snowpack and the pathways for runoff
are not established. This will likely cause a ponding of water in
ditches and low-lying areas with little movement of that water into
the nearby rivers and streams.

Later on in the weekend, more snow and lower temperatures will again reach the area and try to again block any pathways for runoff that were established. In short, this will be a very dynamic period of rain, ponding of water, perhaps some runoff getting to streams, all before cooler temperatures and snow try to put the breaks on any runoff. Working in favor of flood risk mitigation is the generally thawed and permeable soils which will largely temper runoff as it`s being generated.

Central North Dakota in the Prairie Pothole Region, plenty of snow
and its associated water equivalent have already seen a browning of
the hilltops and windblown areas that had the lower overall snow
cover. This browning of the countryside is due to a slow melt of the
snowpack and infiltration of the meltwater into the underlying
permeable soils. Just like in the Souris River Basin, much of the
Prairie Pothole Region, including the James River Basin, has many of
the ditches and natural drains filled with drifted in snow. This
will again delay any runoff of rain and melting snow from getting
into the rivers and streams in the area. Overall, the James River
basin below Jamestown is less favored for the higher precipitation totals during the latter half of the week and this is also reflected in having an overall lower risk of flooding, although ponding of water should still be considered a reasonable outcome which can impact rural roads.

In the western part of North Dakota, near the Montana border and on
over to the Missouri River, drifted-in drainages are also expected
to hinder initial conveyance of any potential rain or snowmelt
runoff from easily getting to the rivers and streams of the area.
Also, this area of the state is favored to see more precipitation in
the form of snow than rain. Nonetheless, this is also the area of
the state currently favored for some of the higher precipitation
totals and this will eventually have to melt, but once again warm
and permeable soils are expected to minimize runoff at least well
into the weekend.

Lastly, basins such as Painted Woods, Apple and Beaver creeks that
drain portions of the state east of the Missouri River are currently
seeing a gentle melt of existing snow. Little to none of this melt
has been showing up in the ditches and natural drains thus far, and
that trend is expected to continue until such time as the snow and
ice blocking them are thawed and the melt rate or combined rain and
snowmelt runoff exceed the infiltration capacity of the underlying
soil.

All that being said, as rain enters the region over the coming days,
one should keep in mind that rain on top of snow can significantly
enhance overall liquid water available for creating runoff. Most of
the natural drains and road ditches will take time to clear enough
to allow conveyance of any runoff, so ponding of water is a very
distinct risk going forward. Overland flooding is not out of the
question, and the probability of minor flooding of streams going
forward is certainly not zero.