Mar 4, 2011 4:09 PM by Meteorologist Mike Heard

Spring Flood Outlook - Update

This spring flood outlook is for Montana east of the divide from the Great Falls National Weather Service.

Significant snowpack covers much of north central and eastern Montana and temperatures continue to stay below normal. Snowmelt, coupled with above normal soil moisture conditions and climatological rainfall this spring, is likely to raise many rivers above flood stage during the next few months.

Based on current conditions there is a better than 90% chance for minor flooding for north central and north eastern Montana and there is a better than 90% chance for moderate to major flooding in areas near Harlem, Tampico, Glasgow and Nashua.

Based on the current snowpack conditions in south west Montana there is a better than 80% chance for minor flooding on the Big Hole river near Melrose. There is a better than 60% chance for minor flooding on the Gallatin River near Gallatin Gateway. Rivers in south west Montana have a less than 35% chance for moderate flooding due to snowmelt at this time.
Early March, Montana is over three quarters of the way through the main snowfall period. There are still four to six weeks remaining until the seasonal snowpack peak is reached.

La Nina continues to weaken in the equatorial pacific but until it reaches a neutral phase by late spring or early summer we will continue to see below normal temperatures and above normal precipitation through March, April and into May. This means that there is a high probability for snowpack conditions to remain above normal or well above normal in south west Montana by the end of the snow season.

The months of April through June are typically the wettest months of the year. If this spring season produces a good rainy pattern ontop of the healthy snowpack melt there is a risk for flooding if conditions are just right and they are: rapid warm up, heavy rain, above normal snowpack. We will keep a close watch on the longer range forecasts for that possible weather scenario.

Climate Prediction Center long range forecast for this summer has south west Montana under a hotter and drier than normal pattern.


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