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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
$$


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