Issued by NWS Burlington, VT
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000 FGUS71 KBTV 221650 ESFBTV NYZ026>031-034-035-087-VTZ001>012-016>019-231700- WINTER/SPRING FLOOD POTENTIAL OUTLOOK NATIONAL WEATHER SERVICE BURLINGTON VT 1150 AM EST FRI JAN 22 2010 ...WINTER/SPRING FLOOD POTENTIAL OUTLOOK /2/... THIS IS THE SECOND WINTER/SPRING FLOOD POTENTIAL OUTLOOK FOR THE 2010 SNOW MELT 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 SNOWPACK MELT AND BREAKUP OF RIVER ICE ACROSS CENTRAL AND NORTHERN VERMONT...AS WELL AS NORTHERN NEW YORK. ...OVERVIEW... THE WINTER/SPRING FLOOD POTENTIAL FOR NORTHERN AND CENTRAL VERMONT AND NORTHERN NEW YORK IS SLIGHTLY ABOVE NORMAL...PRIMARILY DUE TO ICE JAMS. THE CURRENT SNOWPACK AND SNOW WATER EQUIVALENT...OR AMOUNT OF LIQUID WATER CONTAINED IN THE SNOW...ARE BOTH NEAR CLIMATOLOGICAL NORMAL ACROSS THE REGION. WITH THE PRONOUNCED THAWING CONDITIONS OBSERVED ACROSS THE AREA OVER THE PAST WEEK...JANUARY TEMPERATURES ARE NOW AVERAGING 3 TO 6 DEGREES ABOVE NORMAL. THESE CONDITIONS HAVE ALLOWED SOME THINNING OF ICE COVER AND SNOWPACK ACROSS THE REGION...HOWEVER THE OVERALL SCALE OF THAWING HAS BEEN TEMPERED SOMEWHAT AS LOW TEMPERATURES HAVE FREQUENTLY DROPPED BELOW FREEZING DURING THE OVERNIGHT HOURS. A STRONG STORM SYSTEM WILL LIKELY BRING A PRONOUNCED 24 HOUR PERIOD OF RAIN AND MILD TEMPERATURES TO THE REGION BETWEEN SUNDAY AND MONDAY AFTERNOON. AS A RESULT OF THE RECENT THAW...THESE CONDITIONS MAY ALLOW MODERATE RISES AND SOME ICE MOVEMENT ON AREA RIVERS...ESPECIALLY IN AREAS WHERE HEAVIER PRECIPITATION FALLS. MUCH OF THIS PRECIPITATION WILL LIKELY FLOW THROUGH...OR BECOME ABSORBED WITHIN THE SNOWPACK THUS REDUCING THE OVERALL THREAT OF MAINSTEM RIVER FLOODING. HOWEVER...WITH SOME ICE MOVEMENT POSSIBLE AN ELEVATED THREAT OF ICE JAMS WILL BE PRESENT LATER SUNDAY AND ESPECIALLY ON MONDAY. IN THE LONGER TERM...CONFIDENCE IS INCREASING THAT A RETURN TO MID-WINTER COLD AND DRY WEATHER WILL OCCUR BY NEXT WEEK. ...SNOW DEPTHS AND WATER EQUIVALENT... IN VERMONT...SNOW DEPTHS ON AVERAGE RANGE FROM 6 TO 12 INCHES ACROSS THE LOWER ELEVATIONS OF CENTRAL AND SOUTHERN VERMONT...AS WELL AS THE CHAMPLAIN VALLEY. HIGHER TOTALS FROM 10 TO 20 INCHES ARE PRESENT ACROSS THE GREEN MOUNTAINS...MAINLY AT ELEVATIONS ABOVE 1000 FEET WHERE SOME TOTALS WELL IN EXCESS OF TWO FEET EXIST AT THE HIGHEST ELEVATIONS. ACROSS NORTH CENTRAL AND NORTHEASTERN VERMONT...SNOW DEPTHS ARE SOMEWHAT HIGHER...RANGING GENERALLY FROM 10 TO 20 INCHES. ALL THESE AMOUNTS ARE NEAR NORMAL FOR EARLY JANUARY. SNOW WATER EQUIVALENTS WERE ALSO NEAR NORMAL FOR MID TO LATE JANUARY ACROSS VERMONT...RANGING FROM 1 TO 3 INCHES IN LOWER ELEVATIONS AND 3 TO 6 INCHES ACROSS THE HIGHER ELEVATIONS OF THE GREEN MOUNTAINS ABOVE 1500 FEET. LOCAL VALUES IN EXCESS OF 8 INCHES WERE ALSO EVIDENT AT THE VERY HIGHEST ELEVATIONS ABOVE 2500 FEET. IN NORTHERN NEW YORK SNOW DEPTHS WERE SIMILAR...AVERAGING 6 TO 12 INCHES ACROSS THE LOWER ELEVATIONS IN THE SAINT LAWRENCE AND CHAMPLAIN VALLEYS...AND 10 TO 20 ACROSS THE NORTHERN ADIRONDACKS WITH HIGHER AMOUNTS ABOVE 2500 FEET. SNOW WATER EQUIVALENTS ACROSS NORTHERN NEW YORK RANGED FROM 1 TO 3 INCHES ACROSS THE LOWER ELEVATIONS...AND 3 TO 6 INCHES IN THE NORTHERN ADIRONDACKS WHERE LOCAL VALUES IN EXCESS OF 8 INCHES WERE PRESENT AT THE HIGHEST ELEVATIONS. AGAIN...THESE VALUES ARE NEAR NORMAL FOR MID TO LATE JANUARY. ...RIVER AND SOIL MOISTURE CONDITIONS... RIVER LEVELS ARE AT NEAR NORMAL BASE FLOWS ACROSS NORTHERN AND CENTRAL VERMONT AND NORTHERN NEW YORK. FLOWS ARE EXPECTED TO INCREASE IN THE COMING WEEK AS THE AFOREMENTIONED MILDER TEMPERATURES AND RAINFALL SPREAD INTO THE REGION. AGAIN...THE PRIMARY THREAT FROM THIS SYSTEM WOULD APPEAR TO BE LOCALIZED ICE JAM FLOODING RESULTING FROM PARTIAL BREAKUP OF RIVER ICE...AND NOT WIDESPREAD RIVER FLOODING. LONG TERM ANTECEDENT SOIL MOISTURE STATES REMAIN AT OR ABOVE NORMAL ACROSS THE AREA. THE LATEST PALMER DROUGHT SEVERITY INDEX SHOWS MUCH OF THE REGION IS MOIST TO VERY MOIST. FROST DEPTHS RANGE FROM 4 TO 8 INCHES ACROSS MOST OF THE FORECAST AREA WITH SLIGHTLY LOWER VALUES IN AREAS THAT RECEIVED SNOW COVER EARLIER THIS WINTER. ...WEATHER OUTLOOK... THE CURRENT OUTLOOK CALLS FOR A RETURN TO MILD CONDITIONS ALONG WITH WET WEATHER BY THIS COMING WEEKEND INTO EARLY NEXT WEEK. THIS WILL ALLOW MODERATE RISES TO OCCUR ON AREA RIVERS WITH SOME ICE MOVEMENT LIKELY. WHILE THE THREAT OF MAINSTEM RIVER FLOODING STILL APPEARS MINIMAL AT THIS TIME...ANY ICE MOVEMENT COULD LEAD TO THE DEVELOPMENT OF ICE JAMS AND LOCALIZED FLOODING CONCERNS ACROSS THE AREA. THEREAFTER...CONFIDENCE IS INCREASING THAT A RETURN TO MID- WINTER COLD AND DRY WEATHER WILL RETURN BY THE MIDDLE TO LATER PORTIONS OF NEXT WEEK AND CONTINUE INTO EARLY FEBRUARY. THESE CONDITIONS WILL LIKELY REDUCE ANY FURTHER THREAT OF ICE JAMS OR FLOODING. ...SUMMARY... THE SPRING FLOOD POTENTIAL IS SLIGHTLY ABOVE NORMAL FOR NORTHERN AND CENTRAL VERMONT AND NORTHERN NEW YORK....PRIMARILY DUE TO THE THREAT FROM ICE JAMS. THE SNOW DEPTH AND SNOW WATER EQUIVALENT ARE RUNNING NEAR NORMAL FOR MUCH OF THE AREA...WITH RIVERS RUNNING AT OR ABOVE NORMAL. MANY OF THE AREA RIVERS ARE AFFECTED BY ICE. THE FORECAST CALLS FOR THE RETURN OF MILD WEATHER BY THIS WEEKEND ALONG WITH A SIGNIFICANT RAINFALL EVENT. THIS WILL BE MONITORED CLOSELY AS SOME RIVER ICE MOVEMENT AND MODERATE RIVER RISES ARE LIKELY. A RETURN TO COLDER AND DRIER WEATHER IS EXPECTED BY THE MIDDLE TO LATER PORTIONS OF NEXT WEEK...WHICH WILL POSSIBLY CONTINUE INTO EARLY FEBRUARY. ACCESS CURRENT WEATHER CONDITIONS AND FORECASTS ON OUR WEB SITE AT WEATHER.GOV/BURLINGTON. THE NEXT WINTER/SPRING FLOOD POTENTIAL OUTLOOK WILL BE ISSUED ON FRIDAY FEBRUARY 5 2010. $$ JMG
