Plenty of rainfall is expected across the Northern Plains as a low pressure system ejects off the Rockies. At the same time, the aforementioned low pressure system’s attendant warm front moves north from the Central Plains and into southern sections of the Northern Plains by dawn Sunday. It then becomes stalled out as disturbances move along it especially over northwestern section of the Great Lakes region. Anywhere from 1.5 to 2.5 inches of precipitation is expected especially across the Upper Great Lakes region with the most of the precipitation expected within a 24 hour period from dawn Sunday through dawn Monday.
During this time period, winds with a strong southerly wind component on the order of 2 to 3 standard deviations above normal will be able to bring in ample warmth and moisture to be able to create this precipitation. One way to get an estimate on the intensity of water that could fall from the atmosphere is to look at the precipitable waters index. Precipitable waters are around an inch according to an ensemble model, which is around 2 to 3 standard deviations above normal for this time of year. In addition, large scale lift is also favorable over the region where the most amount of precipitation is forecast. The other consideration for this time period will be that the warm front will tend to meander and that may allow some mixing with snow, sleet and possibly some freezing rain. This best chance for this will be overnight Saturday night and for latter portions of Sunday into the overnight hours as the front sags south and north winds bring cooler air in.
Any additional rainfall is welcome news for the area as April has been rather dry for the bulk of the United States aside from the Southern Plains as well as western sections of the Plains. In fact, the region has been close to an inch below normal so far for the month of April through the 21st on average, but there are some observation stations that are as much as 2 inches below normal. Of course with any precipitation, in order to keep flooding down, it’s better to have precipitation spread out overtime rather a one-time occurrence of a large quantity of precipitation. With this occurrence of a large quantity of precipitation, flooding is possible, but signs of a drought have not shown up in the drought monitor so ground soil should be able to soak up any standing water and flash flood guidance is well above the total amount of precipitation for this event. As a result, any major flooding is not forecast. Minor, poor drainage area flooding is possible however, and watch out for possible ponding on roadways during this time frame.