Flood Potential Outlook
Issued by NWS

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WINTER/SPRING FLOOD POTENTIAL OUTLOOK
NATIONAL WEATHER SERVICE PITTSBURGH PA
1013 AM EST THU JAN 8 2015

...WINTER/SPRING FLOOD POTENTIAL OUTLOOK...

...THE FLOOD POTENTIAL FOR FLOODING IS NEAR NORMAL FOR THE UPPER
OHIO VALLEY...

A NORMAL FLOOD POTENTIAL MEANS SCATTERED FLOODING COULD OCCUR WITH
WATER LEVELS REACHING MINOR IMPACTS.

FOR THE LONG-RANGE RIVER OUTLOOKS AND THE PROBABILITY OF EXCEEDING
FLOOD STAGE OR THE CHANCES OF FLOODING RELATIVE TO NORMAL AT
SPECIFIC FORECAST POINTS DURING THE NEXT 90 DAYS...REFER TO
WWW.WEATHER.GOV/OHRFC AND CLICK ON THE 90-DAY RIVER OUTLOOK ON THE
LEFT HAND SIDE OF THE PAGE. CLICK ON FLOOD CHC VS NORMAL TO VIEW THE
RISK OF FLOODING WITH RESPECT TO NORMAL.

FLOOD OUTLOOKS ARE ISSUED BI-WEEKLY BY THE NATIONAL WEATHER SERVICE
DURING WINTER AND EARLY SPRING TO SUMMARIZE BASIN
HYDROMETEOROLOGICAL CONDITIONS AND TO ASSESS THE POTENTIAL FOR
WINTER/SPRING FLOODING. THE OUTLOOKS ARE BASED ON CURRENT AND
EXPECTED CONDITIONS DURING THE OUTLOOK PERIOD.

IN ADDITION 90-DAY WATER RESOURCES OUTLOOKS ARE ISSUED MONTHLY.

FACTORS CONSIDERED IN ASSESSING FLOOD POTENTIAL ARE...

ANTECEDENT CONDITIONS
FACTORS CONSIDERED IN ASSESSING FLOOD POTENTIAL ARE (1) ANTECEDENT
CONDITIONS (2) PAST PRECIPITATION (3) RECENT STREAMFLOWS AND
RESERVOIR LEVELS (4) SOIL MOISTURE (5) WATER CONTENT OF THE SNOW
PACK (6) ICE CONDITIONS ON THE RIVERS AND (7) FUTURE PRECIPITATION.

ICE CONDITIONS...
ICE HAS RECENTLY FORMED ON PORTIONS OF THE ALLEGHENY RIVER AND ITS
TRIBUTARIES. ICE COVERAGE IS 10 TO 30 PERCENT WITH AN AVERAGE
THICKNESS OF 1 INCH.

METEOROLOGICALLY...
THE PREVAILING STORM TRACK HAS TAKEN ON AN EL NINO SIGNATURE ACROSS
THE U.S.THAT HAS BEEN PREDICTED SINCE THE SUMMER OF 2014. THE RESULT
HAS BEEN FREQUENT STORM SYSTEMS HITTING THE WEST COAST...THEN MOVING
ACROSS THE DEEP SOUTH. THE LACK OF PHASING OF THE POLAR AND
SUBTROPICAL JET STREAMS HAS RESULTED IN RELATIVELY LIGHT
PRECIPITATION EVENTS IN THE OHIO VALLEY DURING LATE AUTUMN/EARLY
WINTER. WITH THE EL NINO PATTERN IN PLACE...THE FAST FLOW ACROSS THE
U.S. HAS PREVENTED THE POLAR VORTEX FROM ESTABLISHING ITSELF
SEMI-PERMANENTLY OVER HUDSON BAY...THUS BLOCKING THE INTRUSION OF
ARCTIC AIR MASSES INTO CONTINENTAL U.S. AS A RESULT...TEMPERATURES
WERE ABOVE NORMAL BY SEVERAL DEGREES IN LATE AUTUMN/EARLY
WINTER...AND THE WINTER SNOW PACK HAS REMAINED NORTH OF THE U.S.
BORDER IN CANADA.

SOIL CONDITIONS...
SOILS ARE NORMALLY MOIST IN THE OHIO VALLEY.

RIVER FLOWS...
28-DAY AVERAGE STREAMFLOWS ARE NEAR NORMAL IN THE OHIO RIVER BASIN
WITH ISOLATED BELOW NORMAL STREAM FLOWS IN A FEW WATERSHEDS.

SNOW COVER AND SNOW WATER EQUIVALENT...
MINOR ACCUMULATIONS (1-3 INCHES OF VERY LOW WATER EQUIVALENT SNOW)
FELL EARLIER THIS WEEK NORTH OF THE MAINSTEM.

HYDROLOGIC OUTLOOK...
ATMOSPHERIC CIRCULATION WILL REMAIN LOCKED IN AN EL NINO PATTERN
DURING EARLY WINTER. FOR THE OHIO VALLEY...THE STORM TRACK WILL BE
PREDOMINANTLY ACROSS THE DEEP SOUTH...THEN CURVE UP THE EASTERN
SEABOARD OR OUT INTO THE WESTERN NORTH ATLANTIC BASIN. WITHOUT
PHASING OF THE POLAR AND SUBTROPICAL JET STREAMS...SIGNIFICANT STORM
EVENTS WILL NOT DEVELOP OR AFFECT THE OHIO VALLEY.

HYDROLOGICALLY...THE RESULTING STREAMFLOWS WILL AVERAGE NEAR NORMAL
WITH ISOLATED OCCASIONAL MINOR FLOODING POSSIBLE IN THE OHIO RIVER
BASIN.

SUMMARY...
RAINFALL IS THE PRIMARY FACTOR LEADING TO FLOODING. HEAVY OR
EXCESSIVE RAINFALL CAN CAUSE FLOODING ANY TIME OF THE YEAR...EVEN
WHERE THE FLOOD POTENTIAL IS BELOW NORMAL.

THE NEXT WINTER/SPRING FLOOD POTENTIAL OUTLOOK WILL BE ISSUED BY
JANUARY 23 2015.


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