FGUS61 KTAR 111123 CCA ESGTAR Winter/Spring Flood Potential Outlook National Weather Service Northeast River Forecast Center Norton MA 722 AM EDT Thu Apr 11 2024 WINTER/SPRING FLOOD POTENTIAL FOR THE NORTHEASTERN U.S. /8/ Based on the information available at this time...the Winter/Spring Flood Potential for the northeastern United States is above normal across extreme southeastern New York...southern New England...southern Vermont...most of New Hampshire including the White Mountains and most of Maine except far northwestern areas. The Winter/Spring Flood Potential for the northeastern United States is near normal across far northwestern Maine...far northern New Hampshire...northern Vermont extending into the Champlain region of New York and most of the Adirondacks. The Winter/Spring Flood Potential for the northeastern United States is below normal across western New York...parts of central New York including the Black River basin and far northern New York including the Saint Lawrence Valley region. The potential for flooding due to ice jams has passed for the season. ...CLIMATE GUIDANCE... March 2024 was summarized by above normal temperatures and above normal precipitation in most areas except drier than normal across western New York. The first week of April 2024 has generally featured wetter than normal conditions except drier than normal in far northern Maine. Average temperature departures have varied from +1 to +3F above normal in the northern and western basin areas and -1 to -3F below normal across the southeastern basins where cloudiness and onshore wind have maintained cooler than normal average temperatures. A slow moving low pressure system on the 3rd-5th brought 1-2+ feet of snow across portions of the northern New England high terrain into southern and western Maine with lower totals mostly varying from 3 to 12 inches across the eastern Adirondacks and northern Catskills of New York...lower terrain areas of eastern New York...lower terrain areas of northern New England outside of southern Maine and in northern Massachusetts. Extreme southeastern New York and far southern areas of New England observed significant rainfall totals of 1.00 to 3.00 inches from this event. April 2024 precipitation departures through the 8th ranged from +0.50 to +1.50 inch above normal except near normal to less than +0.50 inch above normal in portions of far northern New England and far northern New York into western New York. The 30 day precipitation departures were mostly ranging from +1.00 to +5.00 inches above normal highest across the eastern and southern New England basins. 30 day precipitation departures were near normal to up to -1.00 inch below normal in central and western New York and at Marthas Vineyard and Nantucket. El Nino has continued to weaken although its influence has remained as an active subtropical jet stream has continued to advance moisture laden low systems into the Northeast. This active trend looks to continue for awhile longer but with some shifting in the low track pattern. A moderate strength El Nino remained as of 08 April 2024 with a +1.2 Celsius Sea Surface Temperature (SST) anomaly observed in the Nino 3.4 region. The latest three month average from January-March 2024 was +1.5 Celsius. Sea Surface Temperature (SST) anomalies were cooling most notably in the far eastern Pacific and were expanding across the equatorial Pacific. The El Nino in progress is forecast to continue to weaken with ENSO Neutral conditions likely later this spring...then a transition to La Nina conditions late this summer into this autumn. The Northern Atlantic Oscillation (NAO) which has been negative and 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 be west of the NERFC area with the possibility of above normal precipitation across the western basins where it is needed. The details are somewhat uncertain however due timing and phasing of low systems with QPF focus areas. 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. ...OBSERVED SNOW DEPTHS AND WATER EQUIVALENTS... Significant snow cover leftover from late March into early April had decreased substantially in many areas due to melt...particularly across the lower elevations. Some significant snow remained along the White Mountain region of northern New Hampshire and the higher terrain areas of western Maine. ...NEW YORK STATE... The ground is bare across the majority of the state with the exception of some of the highest elevations above 1500 feet within the central and eastern Adirondacks with snow depths up to several inches mainly in wooded areas. The mesonet webcam at Whiteface Mountain was indicating some patchy snow cover. Snow water values were as high as 1.00-2.00+ inches across the high peaks. Elsewhere in the lower elevations along the Adirondack slopes NIL to less than one inch. The highest snow water values were found along the upper reaches of the East Branch of the Ausable River at Ausable Forks and the upper reaches of the Hudson River at Newcomb and North Creek. ...SOUTHERN NEW ENGLAND... The ground is now bare across most of the region after melt runoff from snow accumulation April 3-4 across northern and western Massachusetts and northern Connecticut. Some patchy light snow cover remained across deep wooded areas of the northern Berkshires into western Franklin county. Snow water values in this region were under an inch. ...VERMONT... Most of the area snow cover is limited in areal coverage and found within wooded areas and primarily to elevations above 1500 feet. The ground is bare across the majority of lower elevation areas. The ground is bare across most of the Champlain Valley region and along the Swanton River. A couple of inches of snow depth was reported at Jeffersonville and Greensboro heading east along wooded and high terrain areas. Snow water values are generally NIL to 0.50 inch in this region. Examining southern Vermont and portions of the middle Connecticut River valley...the ground is mostly bare in lower elevation areas with up to several inches observed in the highest terrain areas. Snow water values are near NIL across lower elevation areas and 1.00- 2.00 inches in high terrain areas. The highest snow water values were found along West Harriman Reservoir and the West River at Ball Mountain Lake. Observing central and northeastern Vermont along the Green Mountains and portions of the upper Connecticut River valley...the ground is mostly bare now along most of the immediate upper Connecticut River. Snow depths increase to 2 to 8+ inches approaching the slopes of the Green Mountains particularly in wooded and high terrain areas above 1500 feet. Groton reported a 24 inch snow depth on 10 April 2024. Snow water values range from NIL to up to an inch approaching the upper Connecticut...1.00 to 3.00+ inches on average across the high terrain with locally 4.00 to 7.00+ inches across the higher peaks. Mount Mansfield reported an 81 inch snow depth on 10 April 2024...11 inches above its long term average. The highest average snow water equivalents were found along the Little River in Waterbury...the upper reaches of the Connecticut River at North Stratford and Dalton...and the Black River at North Springfield. ...NEW HAMPSHIRE... Snow cover was becoming more confined across high terrain and wooded areas particularly along the White Mountain region. Elsewhere the ground is now mostly bare. The ground is mostly bare across southern parts of the state with a few inches observed in deep wooded areas of the Monadnocks. Snow water values vary from NIL to under 1.00 inch. In northern areas the ground is mostly bare across the lower terrain with a few to several inches found across deep wooded areas particularly nearing the slopes of the White Mountains. Snow depths increase to 6 to 12+ inches above 1500 feet in this region. Mount Washington reported a snow depth of 8 inches on 10 April 2024 and 24 inches at Crawford Notch. Snow water values mostly vary from 1.00 to 3.00+ inches...locally 4.00 to 7.00+ inches at high elevation regions of the White Mountains. The highest snow water equivalents were found along the upper reaches of the Pemigewasset River at Woodstock and Plymouth...Baker River at Rumney and the Ammonoosuc River at Bethlehem. ...MAINE... The ground is mostly bare along coastal plain areas with some patchy snow cover further inland and approaching the foothills. Snow depths range from NIL along the immediate coast and 2-4 inches across wooded areas. Snow water values ranged from NIL along the immediate coast increasing to 1.00 to 1.50 inches along portions of the foothills. Across western Maine Snow depths vary from 3 to 6+ inches primarily across wooded areas and 10 to 20+ inches above 1500 ft. The highest observed snow depths were found from Baxter to the Allagash in northwestern Maine. Snow water values vary from 1.50 to 3.50+ inches except 4.00-7.00+ inches at the high peaks. ...SOIL MOISTURE AND GROUNDWATER CONDITIONS... Excessive wetness for most in March continued into the beginning of April 2024. Above normal precipitation has been reported in many areas combined with snowmelt. The Palmer Drought Severity Index (PDSI) examines moisture states from weeks to months in the past. The latest PDSI from 06 April 2024...showed all of central and southern New England as well as all of east central and southeast New York State in the extremely moist category which is the wettest possible depiction in the Palmer Index. Only areas of northern and western New York State continue to observe near normal antecedent moisture states where precipitation departures have been mostly drier than normal along with less available snowpack for melt. Near surface soil moisture anomaly maps from 08 April 2024 continue to show wetter than normal conditions from eastern New York State into most of New England. In contrast...western New York State continues to see anomalously dry conditions remaining from the Genesee Valley west towards the shoreline of Lake Erie due to low precipitation and lack of snow this Winter. A stubborn area of moderate drought continues to be depicted in the United States Drought Monitor between Buffalo and Rochester New York. Taking a look at groundwater monitoring wells across the region courtesy of the United States Geological Survey ( USGS ) reveals groundwater levels generally similar to late March. Above to much above normal groundwater levels are prevalent throughout just about all of New England as well as across the Adirondack Mountain and lower Hudson Valley regions in New York State. USGS monitoring wells at record high levels for early April include: West Brookfield Massachusetts - 63 years of record Sheffield Massachusetts - 35 years of record Sandwich Massachusetts - 59 years of record Wenham Massachusetts - 57 years of record Richmond Rhode Island - 46 years of record Exeter Rhode Island - 35 years of record Wenham Massachusetts - 57 years of record Calais Maine - 42 years of record Kenduskeag Maine - 44 years of record Litchfield Maine - 46 years of record Hadley Lakes Maine - 37 years of record In contrast...groundwater levels across portions of western New York State remain very low for early April. The USGS groundwater monitoring well at Gainesville and Caledonia were near to slightly above its historical April minimums despite some beneficial precipitation to begin the month. These wells are located within the area of abnormally dry and moderate drought conditions indicated in the latest United States Drought Monitor map from 04 April 2024. We note that the large...deep aquifer across Long Island east of New York City...is near to below normal for early April. Moderate drought had remained across Nantucket Island in southeast Massachusetts. Groundwater is increasing on Nantucket but still remains below normal. ...RESERVOIR LEVELS AND WATER SUPPLY... Water supply reservoirs across most of New England continue to average above to well above normal in most areas. Across New York State...water supply reservoirs generally range from near to above normal to except below normal in western portions of the state. Across northern New York State...Indian Lake is running about 1.6 feet higher than normal for early April. Great Sacandaga Lake just to the south was more than 12 feet higher than its normal early April pool height. Hinckley Reservoir was about 4 feet below normal for early April. Just north of Hinckley...Stillwater Reservoir was about 0.8 feet above its normal early April level. Owasco Lake in central New York State is about 0.5 foot below normal for early April. And in northeast New York State...Lake Champlain is about 0.3 foot above its median level for early April at 98.4 ft. elevation. Across southeastern New York State...the New York City Water Supply System...comprised of 7 large reservoirs...was at 99.4 percent capacity as of 10 April 2024 which was 0.5 percent above normal. Five of the 7 large reservoirs comprising this system were above capacity and spilling water uncontrolled over their outlet works. In northern New England...Kennebec River Basin storage in Maine was 84 percent full as of 09 April 2024 which was 110 percent above normal. The nearby Androscoggin River storage was 72.5 percent full which was 116 percent above normal. The Penobscot storage is 70.7 percent full. Union River storage is 79.6 percent full which is 48.2 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. In far northern Vermont...Lake Memphremagog in Newport was running slightly above normal about 0.2 to 0.3 feet above its median level as of 08 April 2024. Across southern New England...Quabbin Reservoir...the main water supply reservoir for the Boston Metropolitan area...was spilling at 100.9 percent of capacity as of 08 April 2024. The smaller Wachusett Reservoir was also in the normal range for March...at 92.3 percent of capacity. Scituate Reservoir...the main water supply reservoir for northern Rhode Island including the city of Providence...was at 285.27 feet as of 09 April 2024. This was 105.0 percent of capacity. At this level...water was flowing over the spillway uncontrolled into the mainstem Pawtuxet River. In general...we do not anticipate large scale water supply issues heading into Spring. However...there are some areas of concern...particularly across western New York State in the Genesee Valley and Buffalo Creek regions where below normal groundwater levels and the current lack of snowcover for recharge may lead to supply issues unless we observe above normal precipitation amounts through Spring. In addition...portions of the Black River basin extending to near Lake Ontario and southern Saint Lawrence County New York may need to be monitored due to longer term precipitation deficits...near normal groundwater levels and lack of snow cover for recharge. Low groundwater levels and long term precipitation deficits primarily beyond 90 days have had some concern for water supply issues this spring on Nantucket Island in southeastern Massachusetts. However recent readings do confirm improvement to groundwater levels on Nantucket. ...RIVER AND ICE CONDITIONS... Streamflows are near to above normal across most of New England and New York State with the exception of far western New York State and the Black River basin of central New York where they are near to below normal. The highest flows are currently found across coastal Maine and coastal New Hampshire...southern New England and extreme southeastern New York State. High flows were observed in Washington County in east coastal Maine along the Saint Croix River and Grand Lake Stream. Above normal precipitation to begin April briefly helped alleviate low flows some across the Genesee River...Oatka Creek...Tonawanda Creek and Black Creek drainages in western New York State. However streamflows have now regressed to below normal compared to the 7 day averages in these areas. The Black River near Watertown and Boonville was reporting low streamflows as well as the Oswegatchie River near Oswegatchie NY. Current streamflows in these areas were similar to the 7 day averages. Steady and significant rainfall going forward will be necessary to keep these areas from dropping back to critically low levels as there is a lack of snow cover and developing greenup will add to increased absorption and evaporation of available moisture in the coming weeks. Regarding river ice...rivers are mostly open and flowing across the NERFC area. The general exception area is in portions of northern and western Maine...northern New Hampshire and far northeastern Vermont where there is some limited river ice observed mainly confined to lakes and reservoirs. River ice across these areas is generally thin. River ice has now flushed where it was most prevalent along the northern Maine rivers. The ice jam threat has otherwise passed for the season across the NERFC area. ...IN CONCLUSION... The Winter/Spring Flood Potential is above normal across central and parts of northern New Hampshire from the White Mountain region and points south...and most of Maine except far northwestern areas. Antecedent conditions remain extremely moist in this region. Groundwater levels are generally above normal and within the 90th percentile to maximum values for early April in downeast Maine. Streamflows remain above normal. Some snowpack of significance remains across the White Mountain region of New Hampshire extending into western Maine where it is still a bit above normal for the time of year. There is little room for runoff storage due to high groundwater levels. Low pressure and a cold front are forecast to bring 1.00 to 2.00+ inches of QPF 4/11-13 combined with additional modeled snowmelt runoff. MMEFS is indicating chance to likely probabilities for minor flooding in this region from 4/12-14. An active pattern is forecast to continue but with some pause in the above normal precipitation threat. Eventual greenup will aid in additional absorption and evapotranspiration of moisture. The Winter/Spring Flood Potential is above normal across extreme southeastern New York...southern New England...southern Vermont and southern New Hampshire primarily short term. Antecedent conditions are extremely moist in this region. Groundwater levels are generally above the 90th percentile to maximum values for early April. Streamflows remain above normal. Although there is little or no snowpack left there is also little additional room for runoff storage. Low pressure and a cold front are forecast to bring 0.75 to 2.00 inches of QPF 4/11-12. MMEFS is indicating chance to likely probabilities for minor flooding in this region from 4/12-14. An active pattern is forecast to continue but with some pause in the above normal precipitation threat. Developing greenup will assist in some additional absorption and evapotranspiration of available moisture. The Winter/Spring Flood Potential is near normal across far northern New Hampshire and far northwestern Maine. Antecedent conditions remain very moist in this region. Groundwater levels and streamflows are generally near normal for early April. There is some snowpack of significance remaining in high terrain areas. There is some room for runoff storage in this region. Low pressure and a cold front are forecast to bring 0.50 to 1.00+ inch of QPF 4/11-13 combined with additional modeled snowmelt runoff. River rises are forecast but the chance for river flooding in this region appears less likely according to MMEFS and long range data. An active pattern is forecast to continue but with some pause in the above normal precipitation threat beyond the short range. The Winter/Spring Flood Potential is near normal across northern Vermont into most of the Champlain region of New York and the Adirondacks. Antecedent conditions remain very moist to extremely moist in this region. Groundwater levels and streamflows are generally near to above normal for early April. There is some snowpack of significance remaining in high terrain areas but there is some room for runoff storage in this region. Low pressure and a cold front are forecast to bring 0.50 to 1.50+ inch of QPF 4/11-13 combined with some additional modeled snowmelt runoff. River rises are forecast but the chance for river flooding in this region appears less likely according to MMEFS and long range data. An active pattern is forecast to continue but with some pause in the above normal precipitation threat beyond the short range. Eventual greenup will aid in additional absorption and evapotranspiration of moisture. The Winter/Spring Flood Potential is below normal from western New York and parts of central New York including the Black River basin extending into the Saint Lawrence Valley region of northern New York. Antecedent conditions are drier than normal in western New York where there is also a lack of snow cover for any recharge. Abnormally dry to moderate drought conditions remain from Rochester to Buffalo New York where groundwater levels are near historical lows for early April. Streamflows were at below normal to near normal levels. Antecedent conditions are near normal to slightly wetter than normal from the Black River basin into the Saint Lawrence Valley region but there is also a lack of snow for recharge. Thus there is storage available for runoff and a lower risk for river flooding. Beneficial rainfall is forecast near term. The long range outlook favors near normal to above normal precipitation. Eventual greenup will aid in additional absorption and evapotranspiration of moisture. The potential for flooding due to ice jams has passed across the NERFC area. River ice coverage has diminished with some leftover thin and patchy ice remaining in parts of western and northern Maine into far northern New Hampshire in limited scope. River ice has flushed out in northern Maine. The increasing sun angle and warming temperatures will prevent additional development of river ice for the remainder of this season. It is important to remember that very heavy rainfall can result in flooding at any time of year...even in areas that have little or no snow on the ground. A graphic depicting the flood potential across the NERFC service area is available on the NERFC web site at *** www.weather.gov/nerfc/springfloodpotential *** The next Winter/Spring Flood Potential Outlook by the NERFC is scheduled on Thursday 25 April 2024. End/Strauss $$