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009-011-013-015-017-019-121800-



Winter/Spring Flood Potential Outlook

National Weather Service Gray ME

148 PM EDT Thu Apr 11 2024



...SPRING FLOOD POTENTIAL OUTLOOK FOR NEW HAMPSHIRE AND 

WESTERN MAINE...



The flood potential outlook for New Hampshire and Western Maine 

is above normal. Ground conditions are exceptionally wet across 

the region with limited runoff storage. Melt combined with 

saturated antecedent conditions sets up ideal conditions for 

flooding, particularly in the mountains. The risk will remain 

elevated until the remaining snow has melted and spring green-up 

has begun. 



This is the eighth in a series of regularly scheduled flood potential

outlooks that are issued during the winter and spring seasons 

highlighting the flood potential during the next two-week period. 

This issuance represents the flood risk between April 11 through 

April 25th for New Hampshire and western Maine.



...OBSERVED SNOW DEPTH AND WATER EQUIVALENT...



The snow depth and snow water equivalents were well below normal 

for all but the higher elevations and wooded areas north of the 

foothills. Elsewhere, the ground was mostly bare. Snow depths of 6

to 12+ inches above 1500 feet with snow water values ranged from 

1.00 to 3.00+ inches...locally 4.00 to 7.00+ inches at high 

elevation regions of the White Mountains. 



The snowpack was nearing isothermal conditions, indicative of a 

ripe snowpack. An ongoing rain on snow event is expected to ripen 

and melt a significant amount of remaining snow. Looking ahead the

forecasts favors gradual melt the next two weeks with limited 

opportunities for growth.

 

...SOIL MOISTURE AND WATER SUPPLY CONDITIONS...



Exceptionally moist ground conditions, high streamflows, and high

reservoir and lake levels suggest very limited storage for storm 

runoff. Soils in areas without snow have thawed with water release

showing up in groundwater wells. The groundwater levels remain 

much above normal with additional recharge over the last few weeks

as thawing increased. Streamflow levels courtesy of the USGS were

running above to well above normal due to a recent rain on snow 

event. 



Runoff storage capacity remained below normal for the time of 

year with high lake levels for most of the region. Kennebec River 

Basin storage in Maine was 84 percent full which was 110 percent 

above normal. The nearby Androscoggin River storage was 72.5 

percent full which was 116 percent above normal. Lake 

Winnipesaukee...New Hampshire's largest lake...increased to 0.8 

feet above normal as of 09 April 2024. The lake is at its full 

level despite almost continuous releases during February. 



...RIVER AND ICE CONDITIONS...



The ice threat has ended for the season.



...CLIMATOLOGY AND TEMPERATURE AND PRECIPITATION OUTLOOKS...



El Nino has continued to weaken, although its influence has 

remained. The active subtropical jet stream has continued to 

advance moisture laden low systems into the Northeast. The result 

has been a winter with well below normal snowfall and well above 

normal temperatures and precipitation. This active trend looks to 

continue for a while longer, but with some shifting in the low 

track pattern. 



The Northern Atlantic Oscillation (NAO) which has been negative 

and has been promoting blocking and troughing is forecast to turn 

more neutral along with the Arctic Oscillation (AO). Meanwhile the

Pacific North American (PNA) is forecast to become more negative 

which would promote more troughing in the western CONUS. This 

setup would tend to favor weak ridging across the southeastern 

U.S. and mean troughing from the central into the western CONUS. 

Overall, this setup favors a southwesterly flow of milder air into

the Northeast with a low track generally favored to across the 

Great Lakes. The official National Weather Service 6 to 14 day 

Outlook for 16-24 April 2024 leans likely above normal 

temperatures and near normal to above normal precipitation.



...IN CONCLUSION...



Based on the above meteorological and hydrological information, 

the short term flood risk above normal. Groundwater levels are 

well above normal and storage capacity for runoff is limited. The 

potential for rapid runoff remains elevated until the seasonal 

green-up is underway. The weather pattern over the next couple of 

weeks looks to transition into more spring-like conditions with 

above average temperatures and increased precipitation 

opportunities. The addition of snowmelt and presence of ground 

frost in the mountains makes the risk higher in those areas. 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. 



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. The next Spring Flood Outlook will 

be issued on Thursday, April 25th. 



$$



Jamison