Flood Potential Outlook
Issued by NWS Boston, MA

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Winter/Spring Flood Potential Outlook
National Weather Service Boston/Norton MA
422 PM EDT Thu Mar 21 2019

...SPRING FLOOD POTENTIAL IS ABOVE NORMAL ALONG THE LOWER
MAINSTEM CONNECTICUT AND MERRIMACK RIVERS...
...SPRING FLOOD POTENTIAL NEAR NORMAL ACROSS THE REMAINDER OF
SOUTHERN NEW ENGLAND...

The Spring flood potential is above normal along the lower
mainstem Connecticut and Merrimack Rivers. Elsewhere within
southern New England, the freshwater flood threat is near normal.
Across southern New England, most of the river ice has gone and
the ice jam season is coming to a close. The ice jam flood threat
along the east slopes of the Berkshires is below normal.

The following web site has a map depicting the freshwater flood
potential outlook...
http://www.weather.gov/nerfc/springfloodpotential.

This is the sixth winter/spring flood potential outlook of the 2019
season. This outlook is based on current and forecast
hydrometeorological conditions. This includes snow cover and snow
water equivalent, stream and river levels and the amount of ice
coverage, recent precipitation and temperatures, and expected
temperatures and precipitation over the next two weeks.

...Recent Precipitation and Temperatures...

Temperatures for March month-to-date have averaged 2 to 4 degrees
below normal. However, a recent thaw during the 14th to the 16th of
the month pushed daytime highs into the 40s and 50s, and even the
60s during the 15th. This prompted a melt-off of nearly the
entire snowpack within southern New England. Precipitation amounts
during this timeframe were light, and as a result flooding did
not occur with the snowmelt.

Month-to-date precipitation across the majority of southern New
England has been below normal.

The precipitation was closest to normal was along Cape Cod and
the Islands, with totals ranging from 2.5 to 3.5 inches. This was
within a half inch of normal.

Across the remainder of eastern MA, all of RI, and northern CT,
month-to-date liquid equivalent precipitation ranged from 1.5 to 3
inches. This was a half inch to 1.5 inches below normal.

Month-to-date liquid equivalent precipitation was the lowest across
central and western MA. In this area, totals ranged from a half inch
to 1.5 inches, which was 1 to 2 inches below normal.

...Observed snow depths and water equivalents...

Due to the mid-March thaw, minimal snowpack remained across southern
New England. The only snowpack that remained as of March 21st was
up to a few inches in the northern Worcester Hills and along the
east slopes of the Berkshires. Water content of this snow was up
to 1.5 inches.

The deepest remaining snowpack was in the higher terrain of northwest
MA, where some locales still had 8 to 13 inches of snow depth.
Water content ranged from 1.5 to 3.5 inches.

The snow pack was near to below normal in coverage and extent for
mid-March.

However looking further north into the northern headwaters of the
Connecticut and Merrimack Rivers in Vermont and New Hampshire,
the snowpack and water content of that pack was above normal in
coverage and extent. This above normal snowpack has resulted in
an above normal flood threat along the mainstem lower Merrimack
River in MA, and the mainstem lower Connecticut River in MA and
CT.

...River and Ice Conditions...

Rivers and streams were running at mainly normal levels for this
time of year.

River ice in southern New England had lessened considerably in
coverage and extent over the past couple of weeks. This was due
to temperatures averaging above freezing for much of the period,
and the increasing sun angle. There is a very low chance of an
isolated ice jam within the east slopes of the Berkshires. However
for the remainder of southern New England, the ice jam flood
threat has ended for the season.

...Soil Moisture Conditions...

Soils continued to be quite moist for this time of year. The
ground was also partially frozen. The Cooperative Weather
Observer in Norton MA reported a frost depth to 11 inches, with
the top few inches thawed.

...Temperature and Precipitation Outlook...

A coastal storm will impact the region tonight and Friday, with
periods of rain and gusty winds. Rainfall totals are expected to
range mainly between a half inch and an inch. The rain transitions
to snow showers during Friday and Friday evening, before tapering
off. Windy but mainly dry conditions are expected during
Saturday. Milder and dry conditions prevail during Sunday. There
is a renewed chance for rain early next week, then conditions may
dry out again for midweek.

At this time river and stream flooding is not expected over the next
several days.

The week 2 outlook from the Climate Prediction Center, from March 29
to April 4, calls for above normal temperatures and near normal
precipitation.

...Summary...

The Winter/Spring flood potential is near normal for much of
southern New England. With the exception of the highest terrain in
the area, the ground was bare. Rivers and streams were running near
normal. Soils were still quite moist and the ground was partially
frozen, however thawing is expected as we progress thru late March.

River and stream flooding is not expected over the next several
days. It should be noted that typically in the early spring,
southern New England experiences pockets of minor flooding, so in
the long term, flooding can not be ruled out.

With respect to the lower mainstem Connecticut and Merrimack Rivers,
the above normal flood threat is mainly in the longer term. The
above normal flood threat is directly related to the above normal
snow pack across the northern headwaters in NH and VT. Any
rainfall event that is concurrent with snowmelt in the headwaters
would increase the flood threat on these 2 waterways.

The potential for flooding due to ice jams is below normal across
the east slopes of the Berkshires. Across the remainder of southern
New England, the ice jam flood threat has ended for the season.

Keep in mind that heavy rain can cause flooding any time of the
year. Those with interests along rivers and streams should check the
Hazardous Weather Outlook, which highlights any potential flood
events over the next 7 days. Go to https://weather.gov/boston and
click on the option Current Hazards, then click on Local Outlook.

The next Winter/Spring Flood Outlook will be issued on Thursday,
April 4.

$$

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