Flood Potential Outlook
Issued by NWS Portland, ME

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000 FGUS71 KGYX 121940 ESFGYX MEC001-005-007-011-013-015-017-023-025-027-031-NHC001-003-005-007- 009-011-013-015-017-019-141945- Winter/Spring Flood Potential Outlook National Weather Service Gray ME 340 PM EDT Thu Apr 12 2018 ...WINTER/SPRING FLOOD POTENTIAL OUTLOOK... The flood potential is above normal for western Maine with the exception of southwest Maine where it is normal. The flood potential is above normal for northern New Hampshire and near normal for southern New Hampshire. There is no longer a threat for ice jam flooding this season. This is the eighth in a series of regularly scheduled flood potential outlooks that are issued during the winter and spring seasons. These outlooks will be issued every two weeks until the end of the snow melt season, and will assess the potential for flooding based on a number of factors. ...CLIMATOLOGICAL GUIDANCE... March ended with near to somewhat above normal temperatures and precipitation that was below normal. Temperatures for April are averaging 4 to 6 degrees below normal with below normal precipitation. Medium to long range models are indicating a continuation of colder temperatures. Although it has been fairly dry for the last few weeks it does appear that the dry trend will end. The official National Weather Service 6 to 10 day forecast calls for below normal temperatures and about normal precipitation. The 8 to 14 day forecast calls for below normal temperatures with above normal precipitation. Strong low pressure will move into Maine and New Hampshire early next week. This storm has the potential to produce 2 to 4 inches of rain and strong winds. ...OBSERVED SNOW DEPTH AND WATER EQUIVALENT... ...NEW HAMPSHIRE... The ground is now bare in southern New Hampshire for the most part. The only exception to this is in Monadnock region where snow depth of 1 to 6 inches exist above 1000 feet in elevation. Farther north in the Pemigewasset and Saco River basins snow depth ranges from little if any in the valleys up to 1 to 2 feet above 1500 feet. A snow measurement taken by the Corps of Engineers near Cannon Mountain at an elevation of 1950 feet had a snow depth of 23 inches. From the white Mountains north to the Canadian border snow depth ranges from little if any in the lower elevations up to 2 to 3 feet near the Canadian border. A snow measurement taken by Great River Hydro at Moose Falls had a snow depth of 31 inches. Snow water equivalent of 1 to 1.5 inches exist in the higher terrain of the Monadnocks. From the Upper Pemigewasset and Saco River basin north to the canadian border snow water equivalent of less than 1 inch exist in the lower elevations up to 4 to 8 inches in the higher elevations. Near Cannon Mountain snow water equivalent was 8.4 inches and at Moose falls 8.7 inches. Snow water equivalent is below normal in southern New Hampshire but increases to near normal in the upper Pemigewasset and Saco River basins to a bit above normal near the Canadian border. ...WESTERN MAINE... The ground is bare within about 20 miles of the coast. Snow depth of 1 to 12 inches exist north of a line from Fryeburg to Augusta. From the foothills north to the Canadian border snow depth ranges from 12 to 30 inches. Snow water equivalent ranges from little if any within 20 miles of the coast up to 3 inches in the foothills. North of the foothills to the Canadian border snow water equivalent ranges from 3 to 8 inches. A measurement taken by Brookfield Snow water equivalent is below normal in southern and coastal locations and near normal from the foothills to the Canadian border ...SOIL MOISTURE AND WATER SUPPLY CONDITIONS... Soil moisture anomaly maps from April 11 indicate normal moisture conditions in western Maine and New Hampshire. The long term Palmer Drought Severity Index from April 7 indicates normal moisture conditions across New Hampshire and Maine. Reservoirs in the Androscoggin River basin are 45.9 percent full which is 6.9 percent above normal. All reservoirs in the Kennebec River basin are above normal for the time of year. Groundwater levels courtesy of the USGS show that monitoring wells in western Maine are below normal in southern areas and near normal in northern locations. In New Hampshire groundwater is mostly below normal for the time of year. Since the snow has melted away in southern areas, groundwater will likely continue to drop unless we get increased precipitation. ...RIVER AND ICE CONDITIONS... River flows are now mostly below normal due to the below normal precipitation over the last few weeks. In addition the snow in southern areas is now gone. The mountain snowpack will help to increase mainstem river flows as it melts over the next 2 to 4 weeks. There is no longer any ice cover on rivers in western Maine and New Hampshire. The threat of ice jam flooding has ended for the season. ...IN CONCLUSION... Based on the above information the flood potential is above normal for all of western Maine and central and northern New Hampshire. This is due mainly to a normal snowpack in the headwaters that has not yet begun to melt. Normally we would be seeing a steady increase in river flow this time of year as the mountain snowpack melts. However rivers continue to fall due to colder than normal temperatures and below normal precipitation. However heavy rain is expected early next week and this should start the spring melt. The farther we proceed into the spring season the greater the risk for a rapid warm-up combined with heavy rain. The threat for ice jam flooding is over for the season. It is important to note that major flooding does not occur from snowmelt alone. Rainfall, how much and in how short a period of time is the most important factor in determining the severity of flooding. Another Winter/Spring Flood Potential Outlook will be issued April 26. $$ TFH

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