####018006720#### FGUS71 KGYX 291249 ESFGYX MEC001-005-007-011-013-015-017-023-025-027-031-NHC001-003-005-007- 009-011-013-015-017-019-020100- Winter/Spring Flood Potential Outlook National Weather Service Gray ME 749 AM EST Thu Feb 29 2024 ...SPRING FLOOD POTENTIAL OUTLOOK FOR NEW HAMPSHIRE AND WESTERN MAINE... The flood potential outlook for New Hampshire and Western Maine is Below Normal. The potential for flooding due to ice jams is also below normal. This is the fifth 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 March 1 through March 14th for New Hampshire and western Maine. The short term flood risk through March is normal in the mountains given some remaining snow and continuous melt. The ice movement and above normal flows increases the risk of ice jams flooding over the next two weeks. From the foothills southward the risk is below normal given meager snowpack combined with limited opportunities for significant runoff events over the next two weeks. The long term flood risk is below normal. Runoff storage is low given high streamflows and saturated soils. However, the meager snowpack would need to show growth in March to increase the overall spring thaw flood risk to above normal levels. ...OBSERVED SNOW DEPTH AND WATER EQUIVALENT… The snow depth and snow water equivalent was well below normal for late February. The two-week change in snow conditions has been nondescript apart from the mountains where on and off snow showers accumulated several inches. Elsewhere, the snowpack compressed and melted. In New Hampshire the snow depths ranged from little if any snow in the southern and coastal locations, up to 6 inches north of the Lakes Region. From the White Mountains to the Canadian border the snow was more robust averaging 1 to 2 feet, upwards of 3 feet in the mountains. The stored water in the snowpack was generally less than 1 inch in the lower elevations, and 2 to 4 inches in the north country, and upwards of 6 inches above 2000 feet. In Western Maine the snowpack was limited to the foothills northward. In the foothills and valleys the snow was mainly prevalent in the wooded areas and up to 12 inches deep. The stored water ranged form 0.5 to 3 inches. From the Mountains to the Canadian Border the snow was more continuous and ranged from 1 to 2 feet deep, highest above 2000 feet. The stored water ranged from 3 to 6 inches with locally higher amounts. Recent rain on snow event caused melt and ripening even in the mountains with densities around 30% or higher. The snow temperatures were warming and primed to melt over the next two weeks. Looking ahead the forecast favors gradual melt with limited opportunities for growth. ...SOIL MOISTURE AND WATER SUPPLY CONDITIONS... Frost Depth ranged from 5 inches in the mountains to 12 inches across the region. Areas without a snowpack observed topsoil thawing. Given the deep frost depth this period of topsoil thawing will only result in limited amounts of water release. The groundwater remains well above normal for the region with the expectation that southern areas will start to see additional recharge over the next few weeks as thawing increases. Streamflow levels courtesy of the USGS were running 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. The Androscoggin and Kennebec reservoirs have approximately 15-36% less capacity than normal, but are nearing guide curves. Storage remains high in the Connecticut and Merrimack watersheds where USACE reservoirs had only used 0-3% capacity. Lake Winnipesaukee...New Hampshire's largest lake…recently dropped from maximum recorded levels to near seasonal normals due to continued drawdowns in February. Sebago Lake in Maine likewise dropped to seasonal normal levels following high levels much of winter. ...RIVER AND ICE CONDITIONS... River ice coverage was below normal for the time of year. Recent rain and melting snow event increased river flows to above normal, breaking up some river ice and moving it downstream. The temperature forecast favors thermal melt over the next two weeks as streamflow remains high due to melting snow. …CLIMATOLOGY AND TEMPERATURE AND PRECIPITATION OUTLOOKS… Very warm conditions have existed since December. By the end of February, the winter-to-date temperatures were running in the top 5 warmest with temperatures 4 to 8 degrees above normal. The winter was defined by the limited number of cold Arctic air intrusion events resulting in a paltry snowpack. Precipitation was heavy in December and the first half of January, but lessened in February. The dry conditions at a key period in winter resulted in limited snow growth. By the beginning of March the snowpack was running well below normal with little to no snow south of the foothills. The weather pattern over the next couple of weeks offers only limited precipitation chances. Temperatures over the weekend will start a warming trend which will favor a gradual melt over the next 7 to 14 days. Looking ahead the Climate Prediction Center continues favoring above normal temperatures and above normal precipitation through late March. The North Atlantic Oscillation is expected to turn negative mid-month, which could favor another cool down keeping some opportunities for snow. ...IN CONCLUSION... Based on the above meteorological and hydrological information, short term flood risk is normal across western Maine and New Hampshire mountains, and below normal elsewhere. The long term flood risk is below normal due to a lack of deep snowpack or significant river ice. The meager snowpack, increased sun angle, and above normal temperatures favor an early spring thaw. 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, March 14th. $$ $$