Flood Potential Outlook
Issued by NWS Burlington, VT

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FGUS71 KBTV 021859
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NYC019-031-033-089-VTC001-005-007-009-011-013-015-017-019-021-023-
027-041900-

WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE BURLINGTON VT
259 PM EDT THU APR 2 2015

...SPRING FLOOD POTENTIAL OUTLOOK /8/...

...ABOVE NORMAL POTENTIAL FOR SNOW MELT OR ICE JAM FLOODING
THROUGH MID APRIL...

THIS IS THE EIGHTH FLOOD OUTLOOK FOR THE 2015 WINTER/SPRING
SEASON. FLOOD OUTLOOKS ARE ISSUED BI-WEEKLY THROUGH THE WINTER AND
SPRING BY THE NATIONAL WEATHER SERVICE IN BURLINGTON VERMONT TO
SUMMARIZE THE FLOOD POTENTIAL DUE TO SNOW MELT AND BREAK UP OF
RIVER ICE ACROSS CENTRAL AND NORTHERN VERMONT, AND NORTHERN NEW
YORK.

...OVERVIEW...

ABOVE NORMAL SNOW PACK AND THE PROSPECT FOR WARMING TEMPERATURES
AND RAINFALL IN APRIL HAVE INCREASED THE SPRING FLOOD THREAT TO
ABOVE NORMAL. AN ICE JAM THREAT REMAINS PRIMARILY IN NORTHERN
VERMONT AND NORTHERN NEW YORK, WHILE THE ICE JAM THREAT WAS
REDUCED IN CENTRAL AND SOUTHERN VERMONT WHERE RIVER ICE WAS
MELTING AWAY.

...SNOW DEPTHS AND WATER EQUIVALENT...

OVERALL SNOW DEPTH AND WATER EQUIVALENT HAS TRENDED TO ABOVE NORMAL
FOR THIS TIME OF YEAR AS COLD TEMPERATURES HELD ON THROUGH MARCH.
HOWEVER PERIODS OF WARMING TEMPERATURES AND RAINFALL IN THE COMING
WEEK WILL BEGIN SNOW MELT IN EARNEST.

SNOW DEPTH IN NORTHERN NEW YORK RANGED FROM FOUR INCHES OR LESS IN
THE SAINT LAWRENCE VALLEY TO ONE TO TWO FEET IN THE LOWER
ELEVATIONS OF THE ADIRONDACKS. ABOVE TWO THOUSAND FEET ELEVATION
SNOW WAS 1.5 TO 3 FEET DEEP, AND THE HIGH PEAKS REGION OF THE
ADIRONDACKS HAD 3 TO 4 FEET OF SNOW.

IN VERMONT, SNOW DEPTH RANGED FROM FIVE TO TEN INCHES BELOW 1500
FEET, AND ONE TO THREE FEET OVER HIGHER TERRAIN AND IN THE
NORTHEAST KINGDOM. IN THE HIGHEST PEAKS SNOW DEPTH REMAINED FOUR
FEET OR MORE.

THE CHAMPLAIN VALLEY OF NEW YORK AND VERMONT HAD ONLY PATCHY SNOW.

SNOW WATER EQUIVALENT, OR THE AMOUNT OF LIQUID WATER HELD IN THE
SNOWPACK, WAS LESS THAN TWO INCHES IN THE SAINT LAWRENCE VALLEY.
IN THE ADIRONDACKS AND VERMONT SNOW WATER EQUIVALENT WAS 3 TO 6
INCHES IN THE LOWER ELEVATIONS AND 5 TO 9 INCHES ABOVE 2000 FEET.

...RIVER AND SOIL CONDITIONS...

THE DELAY IN SNOWMELT AND SIGNIFICANT LIQUID RAINFALL HAS KEPT
RIVERS BELOW THEIR NORMAL FLOWS. TYPICALLY BY EARLY MARCH THE
SPRING THAW IS WELL UNDERWAY WITH RISING RIVER LEVELS. THIS WILL
CHANGE IN THE COMING DAYS AS TEMPERATURES RISE ABOVE FREEZING AND
RAIN FALLS ACROSS THE REGION.

RIVER ICE WAS DETERIORATING, WITH SMALLER TRIBUTARIES AND STREAMS
BECOMING NEARLY ICE FREE. LARGER RIVER CHANNELS IN VERMONT SUCH
AS THE LAMOILLE, WINOOSKI, WHITE, AND OTTER CREEK WERE BEGINNING
TO OPEN UP WITH LARGE OPEN LEADS AND EVEN ICE-FREE AREAS. THESE
AREAS ARE UNDER A REDUCED THREAT FOR ICE JAMS. CONSIDERABLE RIVER
ICE REMAINS ON NORTHERN VERMONT RIVERS SUCH AS THE MISSISQUOI AND
PASSUMPSIC, AS WELL AS RIVERS IN THE NORTHERN ADIRONDACKS. AN ICE
JAM THREAT REMAINS FOR THOSE NORTHERN RIVERS THAT RETAIN THEIR
EXTENSIVE AND THICK ICE COVER.

RIVERS WILL LIKELY EXPERIENCE BREAKUP AND MOVEMENT THROUGH THE
WEEKEND AS RIVER LEVELS INCREASE.

SOIL MOISTURE WAS NEAR NORMAL. THE THIN SNOW COVER AND FRIGID
TEMPERATURES HAVE ALLOWED FROST TO PENETRATE DEEP INTO THE SOIL,
WITH FROST DEPTHS DOWN TO 20 INCHES IN AREAS THAT HAD A LITTLE
SNOW COVER THROUGH JANUARY. AREAS THAT HAVE RETAINED SOME
INSULATING SNOW COVER REPORT FROST DEPTHS OF SEVEN TO TEN INCHES.
ANY THAWING THAT HAS OCCURRED HAS BEEN IN THE TOP LAYER OF THE
SOIL, AND ONLY BRIEFLY UNTIL COLD TEMPERATURES RETURNED. GROUND
WILL THAW IN THE COMING WEEKS AS TEMPERATURES RISE ABOVE FREEZING
FOR A LONGER TIME.

...WEATHER OUTLOOK...

THE WEATHER PATTERN IS BECOMING MORE SPRINGLIKE, WITH PERIODIC
WARMTH AND LIGHT PRECIPITATION EPISODES. ONE SUCH SYSTEM WILL
AFFECT THE AREA THROUGH THE WEEKEND WITH LIGHT PRECIPITATION
TONIGHT AND ABOVE FREEZING TEMPERATURES TO BEGIN SNOWMELT. A
RETURN TO BELOW FREEZING TEMPERATURES FROM SATURDAY NIGHT ONWARD
WILL CHECK RUNOFF INTO RIVERS. HEADING INTO NEXT WEEK FORECAST
TEMPERATURES WILL VARY ABOVE AND BELOW FREEZING. THIS SEESAW OF
TEMPERATURES IS FAVORABLE FOR A SLOWER MELT OF SNOW AND RIVER ICE.
HOWEVER IF ANY PRECIPITATION FALLS DURING THE COLDER TEMPERATURES
THEN SNOWFALL COULD ADD TO THE SNOWPACK OVER THE NORTHERN PORTIONS
OF THE AREA.

...SUMMARY...

THE RISK FOR SNOWMELT FLOODING HAS RISEN TO ABOVE NORMAL THROUGH
MID APRIL AS THE LATE SEASON SNOW COVER HOLDS ON. AS WE HEAD
DEEPER INTO APRIL THE PROBABILITY OF HEAVY RAINFALL ON TOP OF
ONGOING SNOWMELT INCREASES. IN THE NEAR TERM, WARMER TEMPERATURES
AND LIGHT RAINFALL WILL CAUSE WITHIN BANK RISES ON RIVERS AND SOME
ICE BREAKUP AND MOVEMENT. NORTHERN VERMONT AND NEW YORK RIVERS
RETAIN THE HIGHEST ICE JAM THREAT.

DESPITE THE LATER SEASON SNOW MELT, THE PROBABILITY FOR LAKE
CHAMPLAIN FLOODING IS LOW BASED ON MELT OF THE EXISTING SNOW
COMBINED WITH NORMAL PRECIPITATION. THE LAKE LEVEL REMAINS BELOW
NORMAL AND HAS THE CAPACITY TO ABSORB THE COMING SNOWMELT.

THE NEXT WINTER/SPRING FLOOD OUTLOOK WILL BE ISSUED ON THURSDAY
APRIL 16.

ACCESS CURRENT WEATHER CONDITIONS AND FORECASTS ON OUR WEB SITE
AT WWW.ERH.NOAA.GOV/BTV.

$$

HANSON


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