The following is an outlook of expected weather conditions over the course of the next 3 to 4 weeks of the critical 2011 spring melt period from the National Weather Service in Grand Forks
A large blocking weather pattern has developed in the wake of the March 23 storm. As a result, a large cold high pressure system has dominated the weather over the northern plains for the past week. This pattern will likely continue into the early part of April. As a result, near perfect melt conditions are forecast with daytime temperatures above freezing and night lows below freezing. No significant precipitation is forecast before April 3rd. What precipitation does fall will likely be less than one tenth of an inch and should fall as rain and snow mixed.
Despite this near perfect melt, rivers are responding as runoff efficiency is high due to relatively saturated soils. While some absorption / percolation is occurring, many areas - even areas with little frost - are too wet to absorb the runoff fully. This will continue, resulting in continued river responses.
8 to 14 day outlook:
Beyond the first few days of April, a gradual change in the weather pattern is forecast to develop which will will result in an increasing risk of additional precipitation. An event in the western Pacific, known as a Madden-Julian Oscillation (MJO), is forecast to push into the central Pacific and weaken. Based on information provided by the CPC, the MJO will be in a position to change the flow across the United States which will enhance the risk of above normal precipitation across the northern plains and Red River Valley region. The 8 to 14 day outlook, for April 5th through the 11th calls for above normal precipitation. Using guidance from the Global Forecast System (GFS) computer model, the overall pattern will be one of continued below normal temperatures for early April, with an increase in precipitation in the April 3rd - 5th time period, then again toward mid month.
Mid - Late April:
A decaying La Nina will continue to exert an influence on the regions weather. Based on data supplied by the CPC, the greatest impacts from a La Nina are in the March and April time period. Climatology also shows that April, as a transition month, has an increased risk for major mid-latitude storms to impact the northern plains. The CPC outlook calls for the likelihood of above normal precipitation and below normal temperatures through April.
Flood Risk Assessment:
See the bi-weekly NWS Grand Forks product BISESFFGF titled Spring Thaw Progress for the Red River of the North. This product will be issued on Mondays and Thursdays until the spring snowmelt flood begins in earnest.
At this time, minor flooding is expected to continue and grow in coverage, with the risk for local river variations of 1 to 3 feet due to ice jams. As indicated, below normal temperatures and below normal precipitation the next week will be in place, making for a near ideal melt cycle. Due to ice jams, frozen drainage systems and the existing runoff, there will be a continued threat for areas of overland flooding.
Beyond April 3rd, continued below normal temperatures would favor a mix of rain and snow as the primary precipitation threat. The overall climate/weather pattern suggests a series of storm systems will traverse the northern plains, maintaining an enhanced risk of above normal precipitation through the period. As is typical of the spring years with a weakening La Nina, increased storminess is very likely.
At this time it is impossible to make Quantified Precipitation Forecasts beyond about day 5, therefore we refer to the three categories of Below, Near Normal or Above to describe the precipitation threat. The overall precipitation pattern should be near to below normal through the first few days of April, transitioning to above normal precipitation during the first week of April as described above. It is important to remember that April is a transition period, when weather systems can develop and intensity rapidly. Due to the technological limitations, the NWS in Grand Forks is generally only able to describe trends of major storm systems beyond the 7 to 10 day period.
It is important to note that during this critical period, the flooding will be very sensitive to any precipitation greater than one quarter of an inch in any 24 hour period. Precipitation amounts of one half inch or more would result in even more significant runoff and resultant rises.
As the overall pattern transitions from relative quiet to a more stormy pattern, your NWS will update this Hazards Outlook.
Climate Services Focal Point NWS Grand Forks