Following a buildup of ice this week, rain accompanying a thaw this weekend will bring the risk of sporadic flooding and additional ice jams to parts of the Northeast and Midwest.
Rain spreading from west to east into Saturday night will last less than 24 hours in most areas, but enough can fall in a short period of time to cause rises on streams and flooding in urban, poor drainage areas.
The single-digit and subzero cold earlier this week caused the amount of ice on streams and rivers to increase and become thicker in northern areas of the Midwest and Northeast.
During Wednesday, one area where ice became bottled up was along the Delaware River near Trenton, N.J., and the Lehigh River, near Easton, Pa.
An ice jam caused problems along the Niagara River Thursday and Friday, bordering New York state and Canada.
Portions of the Susquehanna River in Pennsylvania have also been clogged with ice during the latter part of this week.
Saturday morning, an emergency manager reported flooding in Silver Creek, N.Y., located south of Buffalo, on some roads and in homes due to an ice jam on Silver Creek.
Ice collects on the Delaware River in view of Philadelphia, Wednesday, Jan. 8, 2014. Temperatures across Pennsylvania are rising after a blast of arctic air set cold-weather records earlier this week from the Midwest to the East and South. (AP Photo/Matt Rourke)
With rain and warmer conditions on the way, the greatest risk for minor, sporadic flooding exists from northwestern Pennsylvania and western New York, eastward to central New England, and from northern and central Indiana to northwestern Ohio according to National Weather Service hydrologists.
According to Ronald Horwood, senior hazard hydrologist with the New England River Forecast Center, "There is the potential for flooding and ice jams this weekend, especially from near Buffalo, N.Y., through Massachusetts."
These areas have been very cold with locally heavy snow recently and will have the warmest weather with significant rain this weekend.
Farther west, there is a substantial amount of snow on the ground in much of Indiana and northwestern Ohio to neighboring Michigan. A fair amount of minor flooding is expected in the region with this weekend's mild air and rain coming in.
According to Joe Heim, senior hydrologist with the Ohio Valley River Forecast Center, "There is always the potential for very localized flooding due to ice jams and a thaw following a spell of cold weather, but ice jam flooding is dependent on the thickness of the ice, temperatures and rainfall that occurs, as well as the characteristics of each stream and river."
Meanwhile, in the mid-Atlantic region, the ice buildup on portions of the Susquehanna and Delaware rivers is being monitored.
"Fortunately, the ice is not very thick and the main channels appear to be open along most of the major rivers in the mid-Atlantic," Senior Hydrologist Charles Ross of the Mid-Atlantic River Forecast Center said Wednesday morning.
Ross cautioned that conditions along streams and rivers could change rapidly as rain falls on the area and more ice breaks up and moves downstream this weekend.
Most areas do not have a significant amount of snow on the ground to add to the runoff. However, a lack of snow cover and a frozen ground can lead to a more rapid runoff and sporadic problems where ice gets jammed up.
The duration of the cold spells has been short enough to keep ice formation to a minimum over all but the upper reaches of the Midwest, northern New York state and northern New England.
"The areas farther north, near the Canada border, will likely not get enough rain and high enough temperatures to cause rapid melting and widespread shifting of the ice with this weekend's event," Horwood said.
Communities that are protected by a levee system will not have problems with this event.
While ice has rebounded after last week's thaw, it is likely not thick enough to be venturing on in most areas.
"In my opinion, it is too dangerous to be on the ice due to the changeable conditions so far this winter keeping the ice too thin in much of the mid-Atlantic," Ross added.
The same conditions exist over much of the Ohio Valley.
In addition to the risk of urban, small stream and ice jam flooding this weekend, motorists should be on the lookout for potholes.
As the ground thaws and rain falls, traffic moving over weak areas of pavement can produce potholes.
A more serious concern for areas that received heavy lake-effect snow in recent days and were hit by the snowstorm in the Midwest last weekend is the potential for roof collapses.
Not enough rain may fall to wash away all of the snow on roofs. The added weight can stress some flat and shallow angle roofs to the point of failure, especially where there is a more than a foot of snow accumulation. Remove snow from your roof only if you can do so safely. If there is any doubt, consult a professional.
The 99th running of the Indianapolis 500 is set to take place on Sunday afternoon, but showers and thunderstorms may make an unwelcome appearance.
After a cooler and dry start to the holiday weekend, a surge of warmth will greet most Memorial Day cookouts and activities in the mid-Atlantic.
Memorial Day marks the unofficial start to summer, but the summer warmth set to dominate the Northeast next week will not be here to stay.
California farmers with century-old water rights in the San Joaquin River Watershed will no longer be able to draw water from the river as a result of the state's historic drought.
Dry weather will be the rule in Charlotte, North Carolina, this weekend, the site of this week's NASCAR race.
It might feel more like late October rather than late May in the Northeast on Friday night as temperatures dip well below normal.
San Antonio, TX (1998)
Very dry since April 1st - only 0.05 of rain.
Hallam, NE (2004)
The "Hallam" tornado touched on the ground for 2.5 miles and reached F4 status at it's peak intensity. 95% if the town of Hallan's buildings were damages or destroyed.
New Brunswick, NJ (1804)
Tornado destroyed 2 barns, 1 hotel and 3 houses. "The damage done in this village cannot be less than $1,500 or $2,000." New York Evening Post, June 5, 1904.