Text Products for ESF Issued by BTV

Flood Potential Outlook
Issued by NWS Burlington, VT
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Winter/Spring Flood Potential Outlook
National Weather Service Burlington VT
1128 AM EST Thu Feb 29 2024

...Winter/Spring Flood Potential Outlook...
This is the fifth flood outlook for the 2024 winter/spring flood
season. Flood outlooks are issued bi-weekly by the National
Weather Service in Burlington, Vermont to summarize the flood
potential due to snowmelt and break up/formation of river ice
across northern and central Vermont and northern New York. This
outlook is valid for the two week period from February 29 to
March 14, 2024.

...Overview...
The potential for open water flooding through mid-March is below
normal for the St. Lawrence Valley of New York, far northeastern
Vermont and portions of southern Vermont west of the Green
Mountains. Elsewhere, across the Adirondacks, central and
northern Vermont, including the Champlain Valley of Vermont and
New York, and portions of southern Vermont east of the Green
Mountains, the open water flooding threat is normal. Only minimal
amounts of river ice are present, and mainly across far northern
watersheds near the international border, leading to a below
normal threat for ice jams in these areas over the next two weeks.
Further south, river ice is minimal to non-existent. As a result,
the threat for ice jam flooding has largely passed for the season
in these areas.

The overall weather pattern during most of February was one of
unseasonable warmth and persistent dryness as the polar jet
stream remained largely off to the north and remained unphased
with the southern stream jet. Outside a brief intrusion of arctic
air during the middle of the month with some nominal snowfall,
warm and dry was the rule. As such, no large-scale rain or snow
events occurred with monthly precipitation showing negative
departures of one to two inches at nearly all long-term climate
sites. In fact, as of the 28th not one of these sites recorded
over an inch of precipitation. Given this, overall snowfall, not
surprisingly was also well below normal. For example, through
February 28, monthly snowfall at Burlington, VT was a mere 8.4
inches, or only 45 percent of the normal 19.3 inches expected by
that date. As touched on above, monthly temperature departures
were also quite remarkable, with positive anomalies of six to nine
degrees fairly common across most of the region. As such, river
ice formation was minimal during the period and by month`s end,
overall snow cover and snow water content was also well below
normal for all areas outside the highest elevations above 3,000
feet. With the overall dryness, the level of Lake Champlain has
trended lower and is now only about one foot above the long-term
climatological mean for the end of February. As a result, we are
now forecasting only a normal flood threat for the lake going
forward into spring.


The following is a summary of the conditions by region as of
Thursday morning, February 29, 2024:

...St Lawrence Valley...
.Flood Risk...Below normal
.Snow Cover...Below normal, no snow cover
.Water Equivalent...Below normal, none
.Streamflows...Normal to above normal, 50th-90th percentile
.Soil state...Above normal wetness
.Groundwater...Normal to above normal, 50th-90th percentile
.River Ice...Some thin ice noted across northern areas, but
generally below normal thickness.

...Northern Adirondacks...
.Flood Risk...Near normal
.Snow Cover...Below normal, ranging from near zero in the valleys,
to 6 to 18 inches in mid terrain and 2-4+ ft in the High Peaks
above 3,000 feet
.Water Equivalent...Below normal, 1.5 to 4.5 inches, mainly in
mid terrain, with 5+ inches in the High Peaks above 3,000 feet.
.Streamflows...Normal to above normal, 50th to 90th percentile
.Soil state...Above normal wetness
.Groundwater...Above normal, 76th to 90th percentile
.River Ice...Minimal ice noted

...Champlain Valley...
.Flood Risk...Near normal
.Snow Cover...Below normal, no snow cover
.Water Equivalent...Below normal, none
.Streamflows...Normal to above normal, 50th to 90th percentile
.Soil state...Above normal wetness
.Groundwater...Above normal, 76th to >90th percentile
.River Ice...Minimal ice noted

...Central/northern Green Mountains and Upper CT River Valley...
.Flood Risk...Near normal, except below normal far northeast
.Snow Cover...Below normal. Values ranging from a just a few
inches along the Connecticut River, to 8 to 20 inches in mid-
terrain, with 2-4+ feet above 3,000 feet
.Water Equivalent...Below normal, ranging from 1 to 3 inches in
lower elevations to 3 to 6 inches in mid terrain, with 5+ inches
above 3,000 feet
.Streamflows...Above to much normal, 76th to >90th percentile
.Soil state...Above normal wetness
.Groundwater...Normal to above normal, 50th to 90th percentile
.River Ice...Patchy ice cover far north, with minimal coverage
further south

...Southern VT and the adjacent Connecticut River Valley...
.Flood Risk...Below normal west of the Greens, near normal east of
the Greens
.Snow Cover...Below normal, with less than 3 inches and large
areas of bare ground in valleys/lower elevations, and 6 to 16
inches in the mid terrain. At higher elevations, values average
from 2-3+ feet
.Water Equivalent...Below normal, less than an inch in the larger
valleys, 1.5 to 4.5 inches in mid-terrain, and 4+ inches above
3,000 feet
.Streamflows...Above to much above normal, 76th to >90th
percentile
.Soil state...Above normal wetness
.Groundwater...Near normal, 25th to 75th percentile
.River Ice...Minimal coverage

..Snow Depths and Water Equivalent...
The unseasonably warm and dry weather pattern which occurred over
the breadth of February led to little snow across the NWS
Burlington service area. As such, negative snow depth departures
noted in January persisted, or even grew during the month. For
example, Burlington, VT recorded a measurable snow depth on only
10 of the 29 days in February, leading to a negative yearly/winter
departure by month`s end of greater than 30 inches.

Snow water equivalents exhibited similar trends, with all areas
showing below normal values. Only the higher elevations and summit
areas observed values somewhat higher, but even here values are
largely below normal. For example, on February 28, Mt. Mansfield
observed a snow depth of 52 inches, which was 12 inches below the
normal of 64 inches for the date.

...River and River Ice Conditions...
Daily and multi-day averaged streamflows remain at or above
normal across the entire region. This is indicative of residual
interflow and runoff from December`s excessive precipitation, and
some surface recharge through snowmelt in the lower elevations.
However, with the recent dryness a slight downward trend in
general has continued over the past two weeks.

Given the recent warmth, only patchy ice, if any, has formed
across the region over the past few weeks with the most coverage
located across far northern watersheds such as along the
Missisquoi and St. Regis Rivers. However, even here, thicknesses
are well below normal at generally six inches or less with many
open leads. Further south, river ice coverage is minimal to non-
existent with mainly some border ice noted and largely open
channels. This was confirmed by NWS Burlington along the
Missisquoi, Mad, Dog and Winooski Rivers during surveys on
February 27. No ice jams are currently reported.

...Soil Moisture and Groundwater Conditions...
Despite the dry month, moist soil moisture conditions have
persisted across the region over the past two weeks, with latest
CPC data supporting mean values in the 50th to 90th percentile
range for most areas. Some of the moist near-surface readings have
occurred due to recent snowmelt recharge, especially in the lower
to mid elevations. This is supported by the latest groundwater
data from the United States Geological Survey showing most values
ranging through the mid to upper quartiles, or 50th to >90th
percentiles in nearly all areas.

...Weather Outlook...
As we move into the first few weeks in March, the latest long-
term model trends suggest the above normal temperature trends will
continue. This appears reasonable given the most recent forecasts
of the North Atlantic Oscillation and the Pacific North America
Index showing a more progressive weather pattern. The official 6
to 10 and 8 to 14 day outlooks from NOAA`s Climate Prediction
Center tend to agree and are indicating high chances of above
normal temperatures. Precipitation is also expected to be slightly
above normal during the period, but time will tell on how this
pans out. Regardless, the most recent data suggests no large-
scale, heavy rain/snow events are expected for the period giving
confidence to the outlook as a whole.

...Summary...
Based on the above meteorological and hydrological information
discussed above, the potential for open water flooding over the
next two weeks is below normal for portions southern Vermont west
of the Green Mountains, far northeastern Vermont and the St.
Lawrence Valley of New York. Elsewhere, across the Adirondacks,
central and northern Vermont including the entire Champlain Valley
and southern Vermont east of the Green Mountains, the open water
flooding threat is normal as there still remains enough snow in
the pack to cause issues should a big rain event materialize. With
little in the way of ice coverage and thickness on area rivers,
the overall threat of ice jam flooding is below normal across far
northern watersheds through mid March. Elsewhere, the threat of
ice jam flooding has largely passed for the season. Finally, while
the level on Lake Champlain remains about one foot above normal,
the general downward trend in readings over the past month has
given confidence for a more normal flood threat for the lake going
forward into spring.

It is important to remember that heavy rainfall can result in
flooding at any time of year, even in areas that have little or
no snow on the ground and overall predictability beyond 10 days is
generally on the lower side of average.

A graphic depicting the flood potential across the NWS Burlington
service area is available online at:

www.weather.gov/nerfc/springfloodpotential

The next Winter/Spring Flood Potential Outlook will be issued by
NWS Burlington on Thursday, March 14, 2024.

For access to current weather conditions and forecasts, please
visit our web site at www.weather.gov/btv.

$$

93
National Weather Service Weather Forecast Office
