At this writing, Thursday, April 12, there are indications that some heavy precip, mainly rain (though starting as snow/freezing rain), is heading our way, with the bulk of it having fallen by the time you read these words on Wednesday the 18th. There is the potential for liquid equivalent of 1.5 to 2.5 inches, and with the snowpack now less able to absorb water (known as a ripening snowpack), significant rises on streams and rivers will occur, and that in turn could get the ice moving. And when that happens, ice jams are always a risk.
As I mentioned last time, there are two main types of flooding we contend with at this time of the year. There is ice jam flooding, as residents of Fort Fairfield and Perth-Andover know all too well. Then there is general river flooding, or, as I like to call it, all-river flooding. That term means that all communities along the river will flood, rather than only those near an ice jam.
Ice jams occur when meltwater flows into the rivers and the ice is lifted from below, and starts to move along with the current beneath it. But because the ice, when it gets to moving, is in huge hunks and chunks, the ice can move in such a way that the normal river channel becomes blocked, causing the water to seek a different route. This can cause rapid flooding of areas adjacent to, and just behind the ice jam. Also, when ice jams release, they can cause very rapid rises in water levels downstream of the jam.
It should be pointed out that ice jams are not limited to larger rivers. There is a video I show in my presentations where a little mountain stream, along which people are hiking, VERY suddenly becomes a roaring torrent, with the only clue having been the rumbling sound of the approaching water. These people knew what the sound was, and climbed to safety just in time. Here is the URL for the video of that event: https://www.youtube.com/watch?v=FSZsNSxnyzs. Have the sound up and you will hear a woman say, “Somethin’s comin’.” An ice jam had formed upstream, the water built up behind it, and eventually it burst through.
Now, in terms of “all-river” floods, our most recent example being the terrible flood on the St. John River in late April of 2008, they tend not to happen with such severity unless you get another ingredient added to the snowmelt: heavy rain. Even though the winter of 2007-2008 was the record winter for snowfall in Northern Maine, flooding of the magnitude we saw would not have occurred had not a heavy rainstorm dumped up to 3 inches of rain over a fairly wide area in late April.
So major river flooding, which affects all communities along a river, does not happen from snowmelt alone. But if you have a big rainstorm, over a large area, that is concurrent with snowmelt, look out.
And with the rain we just had, I’d be rather surprised if we don’t have some river issues by today, at the very least some significant ice movement. Should you observe any flooding whatsoever, please immediately post to the Aroostook County Flood Watch Facebook page, from which I, the NWS and AEMA can see your reports. We thank you in advance.
By the way, here is an excellent resource on the internet where you can keep track of river levels. Google: “Northeast River Forecast Center.” You will get the NE sector of the US, with many dots on it. The one in “mid-Crown” Maine is the Fort Kent gauge.
Click on it. You will see a graph displayed, showing past river levels and future river projections. Note, if you see a dropoff of the river level right at the point where the past ends and the forecast begins, that is because the forecast is showing you the actual level of the water, whereas the line to the left may actually be indicating the height of the top of the ice. They can sometimes be several feet apart, until the water starts to rise back up toward the bottom of the ice.
There is also some great additional flood information if you scroll all the way to the bottom, under the river chart (or hydrograph). This additional information is given for any dot you click on. Here is information for Fort Kent. It’s very useful, because it allows you to hear a forecast river height and immediately connect it to where the flooding would actually be.
29.7 Feet: Dike along Saint John river is overtopped, flooding downtown Fort Kent from James Street to Market Street.
27.7 Feet: Near record flooding. Water reaches level of the international bridge deck supports. Dike and levee system at full capacity. Many homes flooded on Meadow Lane and Blockhouse Road. Flooding of lower east Main Street inundating several structures in the center of town. Water flowing over Fish River bridge. Evacuations mandatory.
26.7 Feet: Widespread flooding of lower east Main Street, inundating several structures in the center of town. Water flowing over the top of the Fish River bridge. Evacuations probable.
25.7: Saint John river reaches the bottom of the international bridge, bridge closed. Fish River reaches the bottom of the Main Street (Fish River) bridge, bridge closed. Homes threatened on Meadow Lane, Blockhouse Road, Dufour Street and Church Street. Evacuations possible.
24.7: Water reaches top of bridge piers on international bridge. Flooding in low spots and brook crossings along state route 161 above Fort Kent. 22.7: Quigley Flats (Quigley building supply lumber yard) and the block house park begin to flood. An elderly housing project on Normanguy Drive is evacuated. Between 20 and 22 feet, basement flooding begins at the B+M apartments on East Main Street.
Ted Shapiro holds the Broadcast Seal of Approval from both the American Meteorological Society and the National Weather Association. An Alexandria, Va. native, he has been chief meteorologist at WAGM-TV since 2006. Email him at tshapiro@wagmtv.com.
