Extended Streamflow Guidance
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Winter/Spring Flood Potential Outlook
National Weather Service
Northeast River Forecast Center Norton MA
743 PM EDT Wed Mar 27 2024

WINTER/SPRING FLOOD POTENTIAL FOR THE NORTHEASTERN U.S. /7/

Based on the information available at this time...the Winter/Spring
Flood Potential for the northeastern United States is above normal
across most of southern and eastern New England extending into
portions of southeastern New York State. The Winter/Spring Flood
Potential is near normal from portions of northern Maine southwest
into northern New Hampshire...most of Vermont and a large portion of
eastern New York State. The Winter/Spring Flood Potential is below
normal from the Saint Lawrence Valley in northern New York State
southwest into most of central and all of western New York State.

The potential for flooding due to ice jams is near to slightly above
normal across the Saint John...Big Black...Allagash and Fish River
basins in far northern Maine. Elsewhere across New England and New
York State...the potential for flooding due to ice jams has passed
for the season.

...CLIMATE GUIDANCE...

After a very dry February across New England and New York
State...March 2024 reverted back to a pattern this Winter will
likely be remembered for...warm throughout with extremely wet
conditions centered on coastal New England and southeastern New York
State. Temperatures through 25 March have averaged 4 to 8 degrees F
above normal with the warmest departures centered on central and
western New York State where Buffalo and Syracuse have averaged 7.5
and 7.3 degrees above normal respectively through the 25th.

6 to 10 inches of melted equivalent precipitation has occurred in
most areas of New England south and east of the Appalachian Mountain
chain stretching into east central and southeast New York State.
Through the 25th of March...melted equivalent precipitation totals
were as follows:

STATION              TOTAL         DEPARTURE

Providence RI        9.72            +5.80
Portland ME          8.89            +5.60
New York City        8.24            +4.76
Hartford CT          7.04            +3.93
Concord NH           6.85            +4.21

The only areas seeing near to slightly below normal rainfall this
month come from western New York State where Buffalo and Rochester
have failed to reach 2 inches for the month through 25 March 2024.

With the warm temperatures during March 2024...most long term
climate sites have reported below normal snowfall. New York
City...Hartford CT...Providence RI and Boston MA have not reported
measurable snow so far this month. Far northern Maine has managed to
eek out above normal snowfall. Through 25 March 2024...Caribou Maine
had reported 25 inches of snowfall which was 6.8 inches above
normal. A recent storm also dropped 1 to 2 feet of snow from the
southern Adirondack Mountains in northern New York State northeast
into interior Maine which also pushed local snowfall amounts above
normal in those areas.

Although El Nino has begun to weaken...we are still seeing its
influence manifested in very intense southern stream storm systems
that gather Gulf of Mexico moisture and then try to head up the east
coast. Another in this seemingly endless pattern of El Nino driven
storms is poised to ride northeast just east of Cape Cod over the
next few days...potentially bringing 2 to 4 inches of rainfall to
far southeast Massachusetts and downeast Maine which may exacerbate
flooding in those areas.

After that...it looks like early April 2024 will be characterized by
a negative North Atlantic Oscillation ( NAO ) Index. This should
promote a lot of upper level blocking downstream of New England in
the North Atlantic which will likely deflect cold air from Canada
southward into New England and New York State. At the same
time...medium range climate indices call for the Pacific North
America ( PNA ) Index to remain neutral to slightly positive. A
positive PNA favors upper-level troughing across the southeastern
United States. The combination of a negative NAO and somewhat
positive PNA does increase the odds of east coast storminess. It
remains to be seen where exactly the upper level blocking sets up
and whether it will keep the coastal systems south and east of New
England or allow them far enough north to impact the southern and
eastern portions of the NERFC service area. Also...with near to
below normal temperatures expected in early April...we may not be
done with snow for this Winter...especially across northern New York
State and interior sections of New England.

The official National Weather Service 6 to 10 day Outlook for 1-5
April 2024 seems to agree with this overall theme as it leans
towards below normal temperatures across New York State and all of
New England except central and northern Maine where temperatures
could be near to perhaps a tad above normal. Precipitation during
the same time period is leaning above normal across all of New
England and New York State.

So...it does seem active weather will continue as we transition from
March into early April 2024.

...OBSERVED SNOW DEPTHS AND WATER EQUIVALENTS...

A 1 to 2 foot snowstorm last week did boost snow depths and water
equivalents from the Adirondack Mountains in northern New York State
into the Green and White Mountains of Vermont and New Hampshire
respectively into much of interior Maine. Still...despite the
addition of 1-2 inches of water...only portions of the White and
western Maine mountains report water equivalents near normal for the
end of March.

...NEW YORK STATE...

Outside of the Tug Hill Plateau and southern Adirondack Mountains in
northern New York State...only patchy snow cover remains across the
Empire State. Across the Tug Hill Plateau and northern Adirondack
Mountains...snow depths in the valleys have decreased to a few
inches at best. Above 2500 feet in the northern Adirondacks...a foot
or more of snow still remains in the wooded areas. In the southern
Adirondacks and upper Hudson Valley...lower elevations still report
up to 4 or 5 inches of snow due to last weeks snowstorm. These
values increase to between 6 and 12 inches near 2000 feet. Snow
depths in New York State average near normal across localized areas
in the southern Adirondacks but are below normal elsewhere across
northern New York State.

The only areas with organized water equivalents above an inch are
now confined to areas above 1500 feet in the Tug Hill Plateau as
well as across the Adirondack Mountain regions where 1 to 2 inches
of water equivalent are still common. Only above 2500 feet in the
High Peaks region of northeast New York State do water equivalents
increase to between 4 and 8 inches but the areal extent of these
water equivalents is becoming quite small. Much like snow
depths...water equivalents are at most near normal in some areas of
the southern Adirondacks but below normal across the remainder of
northern New York State for the end of March.

...SOUTHERN NEW ENGLAND...

The only area with consistent snowcover in southern New England is
found across northwest Massachusetts where 4 to 8 inches of snow
still blanket the ground above about 1500 feet. Other than
that...there is just some patchy snowcover across north central
Massachusetts and the lower elevations of western Massachusetts.
Snow depths are below normal across north central and western
Massachusetts for late March but normal near the coast where it is
typical for the snow to be gone by now.

Just an inch or two of water is held in the dwindling snowpack
across the higher elevations of northwest Massachusetts which is
below normal. Other than that...there is no appreciable water
available for melt runoff anywhere across the remainder of southern
New England.

...VERMONT...

West of the Green Mountain spine in Vermont...snow depths are near
or below 6 inches with the higher values over west central Vermont.
Bare ground is showing up rapidly in northwest Vermont including
around Burlington. Across the remainder of southern and central
Vermont...snow depths of 6 to 12 inches are common but do increase
to around 2 feet above 1500 feet. Across north central and northeast
Vermont...snow depths in the valleys are generally running under 10
inches but do increase to between 1 and 2 feet above 1500 feet. The
Mount Mansfield snow stake reported 81 inches of snow depth at 3900
feet on 26 March 2024 which was slightly above normal but that is an
aberration. Snow depths are locally near normal across southern and
central Vermont for late March but decrease to notably below normal
across northern portions of the Green Mountain State.

West of the Green Mountain spine in Vermont...snow water equivalents
range from nothing to around 2 inches with the highest values west
and southwest of Rutland. Across the remainder of Vermont...snow
water equivalents are fairly uniform between a Trace and 3 inches in
the valleys but do increase to between 3 and 6 inches above 1500
feet with higher amounts isolated to areas above 3000 feet. Snow
water equivalents are near to slightly below normal across southern
and central Vermont but drop off to notably below normal in northern
Vermont for early Spring.


...NEW HAMPSHIRE...

Far southeastern sections of New Hampshire are reporting bare ground
now. Across the remainder of southern New Hampshire...snow depths
are mostly under 6 inches now with up to a foot above about 1000
feet. Across central and northern New Hampshire...snow depths average
6 to 12 inches in the valleys but do increase to between 1 and 3
feet above 2000 feet with isolated higher depths near treeline in
the White Mountains. For example...43 inches of snow was observed on
the ground on 27 March at Carter Notch at an elevation of 3317 feet.
Snow depths are near normal across portions of southern and central
New Hampshire for the end of March but are generally below normal
across northern Coos County near the Canadian border.

Across southern New Hampshire...between a Trace and 2 inches of
water is available for melt runoff with higher amounts limited to
areas above 1000 feet. Across the remainder of central and northern
New Hampshire...1 to 4 inches of water is held in the lower
elevation snowpack but those amounts do increase to between 4 and 8
inches above 1500 feet with even higher amounts in the highest
elevations of the White Mountains. As of 26 March 2024...Moose
Falls...near the border with Quebec Province Canada...reported 8.6
inches of water in the 30 inch snowpack. And at 4373 feet in the
White Mountains...Gray Knob reported more than a foot of water in
the 49 inch snowpack. Snow water equivalents have recovered to near
normal across a lot of central and northern New Hampshire but remain
a bit below normal across southern portions of the Granite State.


...MAINE...

Along the coastline in Maine...snow depths are near or less than 6
inches. From the foothills of the western and central Maine
highlands into interior downeast Maine...snow depths of 6 to 12
inches are quite common. 6 to 12 inches of snow is also being
reported over most of northeast Maine. From the western and central
Maine highlands into the northwest logging woods of Maine...1 to 2
feet of snow still blanket the ground with localized higher amounts
above 1500 feet. For example...Chimney Pond on Mount Katahdin
reported 53 inches of snow on the ground as of 26 March 2024. Snow
depths in Maine have recovered to near normal over portions of the
western and central Maine highlands but remain somewhat below normal
across the remainder of the state...especially across far northern
Maine.

Across coastal areas of Maine...snow water equivalents are around or
less than an inch now. From the foothills of the western and central
highlands east into interior downeast Maine...1 to 3 inches of water
is still being stored in the snowpack. Across the remainder of Maine
to include the western and central highlands...northwest logging
woods and northeast potato country...snow water equivalents average
between 2 and 5 inches with higher amounts above 1500 feet. Some of
the higher peaks in western Maine have over half a foot of water in
the high elevation snowpack. Snow water equivalents in Maine have
recovered to near normal across the western and central Maine
highlands but are below normal across the remainder of the
state...notably below normal across far northern Maine.

...SOIL MOISTURE AND GROUNDWATER CONDITIONS...

After what was an abnormally dry February 2024...the return to
excessive wetness for most in March combined with snowmelt has
dramatically increased moisture states across New England and
central/eastern New York State. In fact...the latest Palmer Drought
Severity Index issued on 23 March 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 were shown with near normal antecedent
moisture states. The Palmer Index looks at longer term moisture
states...on the order of weeks to months.

Near surface soil moisture anomaly maps from 26 March 2024 continue
to show anomalously wet conditions across all of New England and
eastern New York State with the wettest conditions continuing to be
depicted across east central and southeast New York State extending
into southwest New England. Conversely...western New York State
continues to see anomalously dry conditions in place from the
Genesee Valley west towards the shoreline of Lake Erie due to low
precipitation and lack of snow this Winter. In fact...a stubborn
area of moderate drought continues to be shown 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 an
overall net increase in groundwater levels across New England and
New York State. 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 March include:

Tillson New York - 49 years of record
East Greenbush New York - 33 years of record
Griffen New York - 44 years of record
Orleans County Vermont - 55 years of record
Calais Maine - 41 years of record
Hadley Lakes Maine - 37 years of record
West Brookfield Massachusetts - 60 years of record
Sunderland Massachusetts - 38 years of record
Acton Massachusetts - 58 years of record
Wenham Massachusetts - 55 years of record
Richmond Rhode Island - 46 years of record
Exeter Rhode Island - 43 years of record

Conversely...groundwater levels across portions of western New York
State remain historically low for March. The USGS groundwater
monitoring well at Batavia was setting record low March levels with
a 26 year period of record. The nearby well at Gainesville increased
slightly to just above its historical March minimum. These wells are
located within the area of abnormally dry and moderate drought
conditions indicated in the latest United States Drought Monitor map
from 21 March 2024.

We note that the large...deep aquifer across Long Island east of New
York City...which was at a below normal February level...has
increased closer to normal for March. Moderate drought remains
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 much above normal. Across New York State...water
supply reservoirs range from near to above normal but are generally
not as high as in New England.

Across northern New York State...Indian Lake is running about 2 feet
higher than normal for late March. Great Sacandaga Lake just to the
south was more than 15 feet higher than its normal late March pool
height. Hinckley Reservoir was about 6.5 feet above normal as we
head into April. Just north of Hinckley...Stillwater Reservoir was
about 1.5 feet above its normal late March level. Owasco Lake in
central New York State is now running very close to its target
elevation heading out of March. And in northeast New York
State...Lake Champlain is about 1 foot above its historical normal
heading into April at 97.8 feet on 27 March 2024.

Across southeastern New York State...the New York City Water Supply
System...comprised of 7 large reservoirs...was at 99.9 percent
capacity as of 25 March 2024 which was 5.2 percent above normal. 5
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
80 percent full as of 25 March 2024 which was 123.2 percent above
normal. The nearby Androscoggin River storage was 70.7 percent full
which was 128.8 percent above normal. Penobscot River storage was
66.5 percent full which was 16.6 percent above the long term
average. Union River storage was 82.4 percent full which was 77.7
percent above the long term average. Lake Winnipesaukee...New
Hampshire`s largest lake...was more than 0.5 feet above normal as of
26 March 2024 despite almost continuous releases during February. In
far northern Vermont...Lake Memphremagog in Newport was running very
close to its target elevation heading into April.

Across southern New England...Quabbin Reservoir...the main water
supply reservoir for the Boston Metropolitan area...reached capacity
and was spilling as of 24 March 2024. The smaller Wachusett
Reservoir was also in the normal range for March...at 89.0 percent
of capacity. Scituate Reservoir...the main water supply reservoir
for northern Rhode Island including the city of Providence...was at
285.58 feet as of 26 March 2024. This was 105.9 percent of capacity.
At this level...over 700 cubic feet of water per second were 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...low groundwater levels and long term
precipitation deficits have some concern for water supply on
Nantucket Island in southeast Massachusetts if we don`t experience
above normal rainfall into Spring. Recent readings...however...do
confirm some improvement to groundwater levels on Nantucket.

...RIVER AND ICE CONDITIONS...

River and stream flows are near to above normal across most of New
England and New York State with the exception of central and western
New York State where they are near to below normal. The highest
flows are currently found across downeast Maine...coastal southern
New England and southeast New York State. In these areas...many
gauged rivers and streams are passing flows in the highest 10
percent of the historical record for 27 March. In fact...the Taunton
River at Bridgewater Massachusetts was just dropping out of flood as
of the afternoon of 27 March 2024.

Recent rain and snowmelt have helped low flows across the Genesee
River...Oatka Creek...Tonowanda Creek and Black Creek drainages in
western New York State improve from critically low levels but steady
and significant rainfall going forward will be needed to keep them
from slipping right back to critically low levels.

River ice is on the move across far northern Maine. As of this
morning...an active ice jam was occurring on the Saint John River
near the confluence of the Allagash and Saint John Rivers. This ice
jam is not currently causing any flooding and was confirmed via
webcam imagery. With some rain and above freezing temperatures over
the next 48 hours...this ice should continue to move. Ice is limited
to the Saint John...Big Black...Allagash and Fish Rivers in far
northern Maine. Recent observations show the Aroostook River in far
northeast Maine is largely ice free now as jams have released east
into New Brunswick Province Canada.

Further south and west...there is little to no ice across the
remainder of the NERFC service area where the ice jam season is
deemed over.

...IN CONCLUSION...

Based on the information available at this time...the Winter/Spring
Flood Potential is above normal across most of southern/eastern
Maine and roughly the southern 2/3rds of New Hampshire. In these
areas...river flows...antecedent moisture states and groundwater
levels are all above climatological norms. In addition...reservoirs
in many instances are as high as they have been at this time of year
over the last 20 years. Most of these areas also have significant
amounts of water available for melt runoff even if it is not
necessarily above normal. All these factors point to very little
ability to absorb runoff. In the near term...a large system is
forecast to bring 1 to 3+ inches of rainfall to much of this region
with an additional 0.5 to 2 inches of runoff from snowmelt. All this
points to an above normal chance for flooding not only in the near
term but until the snowpack melts off and evapotranspiration begins.
Although this entire region is at an above normal risk for
flooding...the greatest threat seems to currently be in downeast
Maine...especially along and east of a Houlton to Bangor line.

The Winter/Spring Flood Potential is also above normal from southern
New England west into far southeast areas of New York State. In
these areas...although there is little or no snow on the
ground...river flows...groundwater and reservoir levels and soil
moisture states are all above normal. A heavy rainfall event will
target at least eastern sections of southern New England over the
next 48 hours...likely causing renewed flooding along rivers and
streams that have just receded below flood stage. In addition...as
we head into early April...the weather pattern favors a continuation
of above normal precipitation which could be all or mostly rain. The
combination of rainfall and extremely wet antecedent conditions
overwhelms the lack of snow and justifies an above normal threat for
flooding going forward.

The Winter/Spring Flood Potential is near normal from northwestern
Maine southwest into northern New Hampshire...Vermont and most of
the Adirondack Mountain region in northern New York State. In these
areas...although river flows...groundwater levels and soil moisture
states are above normal and there is some snow left to melt...there
is a bit more available reservoir storage than in areas further
south and east. The near term storm system is expected to spare
these areas from the heaviest rainfall and heading into early
April...there are signs that snow or mixed precipitation could occur
which would also temper runoff compared to areas further east. With
all this in mind...a near normal threat for flooding is expected as
we head into April in these areas.

The Winter/Spring Flood potential is also near normal for much of
east central and interior southeast New York State. In these
areas...very little snow remains on the ground. However...river
flows and groundwater levels remain near to above normal and there
is very little to no storage in reservoirs to capture runoff.
Normally this would edge us into an above normal threat for flooding
going forward. However...it appears the significant rainfall from
the upcoming system will remain mostly south and east of these
areas. And...even with the potential for above normal rainfall in
early April...with no snow water available for melt runoff...we
currently do not think the threat for flooding rises above what
is normal for early Spring.

The Winter/Spring Flood Potential is below normal from the Saint
Lawrence River Valley of northern New York State southwest into all
of central and western New York State. In these areas...river
flows...reservoir levels and groundwater levels are all not too far
from normal. In addition...there is very little to no snow water
available for melt runoff. All this suggests there would need to be
a major rainfall event or perhaps even back to back heavy rain
events to produce flooding in these areas. Currently...there is no
guidance that shows significant rainfall across these areas over the
next 10 days. In fact...western New York State needs rainfall at
this point with abnormally dry to moderate drought continuing to
persist in the Genesee Valley and eastern Buffalo Creek regions. All
these factors point to a below normal risk for flooding going
forward into April even with the potential for rainfall to be
somewhat above normal.

The potential for flooding due to ice jams is near to slightly above
normal in far northern Maine. Along the Saint John...Big
Black...Allagash and Fish Rivers...ice is actively moving and is
likely to continue moving over the next week. We are likely in the
final ice flush for this season. There is a confirmed ice jam near
the confluence of the Saint John and Allagash Rivers that is causing
somewhat elevated stages but no current flooding. Web cam images
show that the ice is weakening but it does appear thick enough to
jam and cause significant backwater should it encounter an
obstruction like a bridge or channel restriction and get hung up.
The threat does not seem extreme as runoff is forecast to only be
moderate over the next week or so. For that reason...it seems a
normal to just slightly above normal threat for ice jam flooding
exists across far northern Maine until the ice completely flushes
out over the next week to 10 days.

Across the remainder of New England and all of New York State...the
ice jam season is deemed over for this Winter. In these
areas...there is very little if any ice remaining in area rivers and
streams and the sun angle is now too high for any significant ice to
form even with any cold weather outbreak.

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 will be issued by the
NERFC on Thursday 11 April 2024.

End/Horwood
$$


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