Bismarck  (National Weather Service 3-7-19) This Spring Flood and Water Resources Outlook is for the Missouri and James River basins of North Dakota and covers the period from mid-March through the middle of June. This outlook is the last in the Spring Flood and Water Resources Outlook series and we will revert back to the regular monthly issuance on the fourth Thursday of each month.

…Flood Outlook Highlights…

The probability of flooding across western and central North Dakota

has generally trended upward over the past few weeks. Received

snowfall, and that in the near-term weather forecast, have

increased the SWE (snow-water equivalent) that will be available

for the eventual springmelt season. This is particularly true

south of I-94.

 

In eastern North Dakota including the James River Basin, the headwaters

area down to Jamestown and Pipestem dams continue to have below

normal to near normal risk of at least some Minor flooding.

Downstream of Jamestown though is a different story. Wet, frozen

soils and an ever growing SWE ranging from 3 to well above 4 inches

across large areas are responsible for a now above normal risk of

Minor flooding on the James River near Lamoure. The risk of

overland flooding and high water on the smaller creeks and streams

across the area are also greater than normal. Were it not for the

protection afforded by Jamestown and Pipestem dams, flood risk

along the James south of Jamestown would be considerably higher.

 

The Prairie Pothole region, including at least parts of Sheridan,

Wells, Kidder, Stutsman, Logan, McIntosh and Dickey counties

suggests overland flooding will be a concern going

into spring.

 

Importantly, the probabilities do not include the risks associated with icejam related flooding. Icejams defy mathematical predictions, but are known to increase during early and rapid spring runoffs where the ice becomes mobilized, only to get stuck at some downstream constriction such as bridges and bends in the river

…Current Conditions…

The general consensus is that western and central North Dakota`s

snowpack sits atop a crust of fairly wet and frozen soil. This

creates a nearly impermeable surface and can enhance runoff from

a given snowpack. Rivers and streams are holding their full ice

cover well into March, this suggests a strong possibility that they

will still be at their respective maximum ice cover and thickness

for the year as spring runoff commences. This tends to increase

the risk of icejam related flooding IF a sudden change in

temperature brings on a rapid melt in March.

 

In general, the vast majority of the snow was received during the

especially cold temperatures of late January and February. Snow

during those cold temperatures tends to hold much less water

than snow received at more moderate temperatures. This kind of

snow can also be quick to melt given a sudden change in weather,

and that creates an increased risk of a fast melt. One plus this

year when compared to the floods of 2009, is that there`s

considerably less volume of water on the countryside. This would

suggest the flood season may be of a shorter duration than the

weeks long high water observed in past years.

 

…Weather Outlook…

The near term 6-10 and 8-14 day outlooks favor cooler than normal

and near normal to above normal precipitation. Looking farther

into the future, the week 3-4 outlooks suggest the cooler and

wetter than normal pattern the region has been in will begin to

moderate. And lastly, the three-month outlooks reflect an equal

chance for above normal, near normal, and below normal

temperature and precipitation.

The forecast may also be updated due to the weekend and next week’s snow storms containing a good amount of moisture.