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Flood Potential Outlook
Issued by NWS Portland, ME
Issued by NWS Portland, ME
801 FGUS71 KGYX 141200 ESFGYX MEC001-005-007-011-013-015-017-023-025-027-031-NHC001-003-005-007- 009-011-013-015-017-019-151200- Winter/Spring Flood Potential Outlook National Weather Service Gray ME 800 AM EDT Thu Mar 14 2024 ...SPRING FLOOD POTENTIAL OUTLOOK FOR NEW HAMPSHIRE AND WESTERN MAINE... The flood potential outlook for New Hampshire and Western Maine is above normal in the mountains. Elsewhere, the flood risk is normal as meager snowpack is counterbalanced by limited runoff storage. The potential for flooding due to ice jams is done for the season. This is the sixth 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 14 through March 28th for New Hampshire and western Maine. ...OBSERVED SNOW DEPTH AND WATER EQUIVALENT The snow depth and snow water equivalents were well below normal for the time of year. The two-week change in snow conditions has been a loss for all but the mountains where repeated snow showers added depth. Elsewhere, the snowpack has shown compression and melt. In New Hampshire the snow depths ranged no snow in the southern and coastal locations, up to 6 inches north of the Lakes Region. Snow cover and deeper snow depths are mainly concentrated across the White Mountain region in northern parts of the state. Snow water equivalents are below normal across most of the state except closer to normal across the peaks of the White Mountains.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 8 inches above 2000 feet. In Western Maine the snowpack was limited to the foothills northward. Below normal snow water equivalents are found across the state except slightly closer to normal across western portions approaching the White Mountain region of New Hampshire. In the foothills and valleys the snow is 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. The snow condition was compressed with high densities. A 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 forecasts favors gradual melt the next two weeks 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 with water release. The groundwater remains well 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. The Androscoggin and Kennebec reservoirs have approximately 15-36% less capacity than normal. Storage remains high in the Connecticut and Merrimack watersheds where USACE reservoirs had only used 0-3% capacity. Lake Winnipesaukee...New Hampshire`s largest lakerecently dropped from maximum recorded levels to near seasonal normals due to continued drawdowns in February. ...RIVER AND ICE CONDITIONS... The ice threat has ended for the season. 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 running 4 to 8 degrees above normal. March began unseasonably mild and wetter than normal across most of the area with average temperature departures through the 10th ranged from +7 to +10F above normal. The precipitation departures through the 10th generally ranged from 2.00 to 4.00+ inches above normal thanks to successive low systems which arrived on the 2nd-3rd...5th-7th and 9th-10th. 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, lessened in February, and rebounded in March. By mid March the snowpack was running well below normal with little to no snow south of the foothills. A moderate El Nino remains with observed sea surface temperature (SST) anomalies +1.4C in the Nino 3.4 region. The El Nino has gradually weakened with the most recent three month average Oceanic Nino Index (ONI) +1.8C from December 2023 through February 2024. The El Nino is forecast to remain through March-May 2024 and then transition to ENSO-neutral conditions during April-June 2024. Late this summer a transition to La Nina conditions is forecast. The CPC 6-10 and 8-14 day outlooks March 19-26 generally agree with average temperatures leaning normal short term to above normal long term and precipitation near normal short term leaning wetter than normal long term. ...IN CONCLUSION... Based on the above meteorological and hydrological information, short term flood risk above normal in the mountains and near normal elsewhere. 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 addition of snowmelt 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, March 28th. $$ ...OBSERVED SNOW DEPTH AND WATER EQUIVALENT The snow depth and snow water equivalent was well below normal for the time of year. The two-week change in snow conditions has been a loss for all but the mountains where repeated snow showers added depth. Elsewhere the snowpack has shown compression and melt. 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 is 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. The snow condition was compressed with high densities. A 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 forecasts favors gradual melt the next two weeks 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 with water release. The groundwater remains well 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. The Androscoggin and Kennebec reservoirs have approximately 15-36% less capacity than normal. Storage remains high in the Connecticut and Merrimack watersheds where USACE reservoirs had only used 0-3% capacity. Lake Winnipesaukee...New Hampshire`s largest lakerecently dropped from maximum recorded levels to near seasonal normals due to continued drawdowns in February. ...RIVER AND ICE CONDITIONS... The ice threat has ended for the season. 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 running 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, lessened in February, and rebounded in March. By mid 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 looks to transition into more spring-like conditions with above average temperatures and increased precipitation opportunities. The time of year makes it more than likely that the precipitation type will be a rain- snow mix or rain. Temperatures are expected to continue above normal into the spring thaw as El Nino remains dominant. ...IN CONCLUSION... Based on the above meteorological and hydrological information, the short term flood risk is above normal in the mountains and near normal elsewhere. 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 addition of snowmelt 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, March 28th. $$