OHD/HL - Surveys/Flood96: Executive Summary

                      
EXECUTIVE SUMMARY







INTRODUCTION

An unusually intense rainfall and rapid snowmelt on January 18-19, 1996, resulted in

major flooding on rivers from Virginia to New York and Vermont, and in the upper

reaches of the Ohio River drainage.  Above-average snow cover over the region and

high melt rates produced by above freezing temperatures, high relative humidity, and

high wind speeds produced large snowmelt contributions to the flood.  Record flood

crests were set in Pennsylvania, New York, West Virginia, and Maryland.  The

Delaware River crested at its highest stage since Hurricanes Connie/Diane in 1955. 

The Hudson crested as its highest stage since 1977.  The Ohio River at Pittsburgh, the

Susquehanna River at Wilkes-Barre, and the Potomac River at Little Falls, Virginia, all

crested at the highest stages since Hurricane Agnes in 1972.





DESCRIPTION OF FLOODING

A succession of snowstorms brought significant and widespread snow accumulation

across much of the northeastern United States by Wednesday, January 17, 1996.  Snow

depths of 40-50 inches were common from central Pennsylvania into New York State. 

From southern Pennsylvania, across Maryland and West Virginia into Virginia, snow

depths averaged 12 inches or more, with significantly higher amounts in the mountains. 

A strong storm system then moved through the eastern United States January 18-19,

1996, bringing heavy precipitation as well as high temperatures, humidity, and winds

into the Ohio, Susquehanna, and mid-Atlantic drainages.  Mean areal basin average

rainfall varied from 1.2 inches to slightly over 3 inches, with some individual gages

reporting over 4 inches.  At most locations, the intense rain lasted for only about 6

hours.  The heavy rains combined with significant snowmelt, and in some cases ice

jams, to produce major flooding in Pennsylvania, West Virginia, New York, Virginia,

Maryland, Vermont, Ohio, and New Jersey.



The magnitude of the flooding varied between basins, but it was a major event

throughout the area.  More than 100,000 people were evacuated in the Wyoming

Valley region of the Susquehanna River Basin in Pennsylvania.  The entire town of

Marlinton, West Virginia (1,100 people) on the Greenbrier River was evacuated. 

Many evacuations also took place in the Allegheny, Susquehanna, and Finger Lakes

drainages in Pennsylvania and New York.  The Ohio River at Pittsburgh had its highest

crest (crest was affected by ice) since Hurricane Agnes in 1972 (Table 1).  On the

Susquehanna River at Wilkes-Barre, the crest of 34.5 feet on Saturday, January 20,

exceeded all past floods except for Hurricane Agnes in 1972.  Record floods occurred

on Loyalsock Creek at Loyalsock, Pennsylvania; the Greenbrier River at Marlinton,

West Virginia; Wills Creek at Cumberland, Maryland; and Opequon Creek at

Martinsburg, West Virginia.  Record crests were also observed on the Lower

Conemaugh River, Lower Mahoning River, West Branch Clarion River, Aughwick

Creek, Towanda Creek, Tunkhannock Creek, and Frankstown Branch (Little Juniata),

all in Pennsylvania.



Table 1.  Selected Northeast Flood Crests - January 1996







As flood waters began to recede, there were reports of flood-related deaths. A total of

33 deaths was reported with 18 in Pennsylvania, 10 in New York, 1 in West Virginia,

3 in Virginia, and 1 in Vermont.  Based on the widespread nature of the flooding and

comparisons to historical floods, it is estimated that total flood-related damages

exceeded $1.5 billion.





SNOW COVER AND SNOWMELT

The abnormally large snow cover that accumulated over the northeastern United States

in the weeks prior to the flood event was the result of a number of storms and below

normal temperatures that inhibited snow melt in the weeks prior to the flood.  The

"Blizzard of 96," which occurred from January 6-8, 1996, was a major contributor to

the snow cover from Virginia, across Maryland, and through much of Pennsylvania

and New Jersey.  Following the blizzard, two additional storms dumped up to 3 feet of

snow across portions of the Catskills of New York and northeast Pennsylvania adding

to near record November through December snow falls in this region.  During the

period before the flood event, January 14-17, above freezing temperatures occurred

over most of the area.  Significant snowmelt occurred west of the Appalachian

mountains.  The snow cover was also partly depleted in parts of Virginia and eastern

Maryland prior to the flood event.  Over portions of Pennsylvania, New York, and

New Jersey, this warming period caused some ripening (warming and preliminary

melting) of the snow cover, but there was little reduction in the water equivalent.  An

estimate of the water equivalent of the snow cover over the primary flood area on the

morning of Thursday, January 18, using all available data, ranged from zero inches in

the far southeastern portion of the area to over 5 inches in areas from south-central

Pennsylvania to the Catskill Mountains of New York.  



On the morning of Thursday, January 18, unprecedented snowmelt occurred just prior

to the onset of the heavy rains associated with warmer temperatures in the western

portion, and continued through the afternoon of Friday, January 19, in the eastern

portion of the region.  For example, at Binghamton, New York, just over 3 inches of

water equivalent was reported before the event, and the snow was gone at the site by

mid-morning on Friday, January 19.  Changes in water equivalent of 3-5 inches were

typical in open, non-wooded areas.  Generally, any given area experienced between 18-

30 hours of high snowmelt rates.  The rapid snowmelt was caused primarily by the

turbulent transfer of latent and sensible heat due to the high temperatures, dew points,

and wind speeds.  By taking the difference between the estimated water equivalent

before and after the event, the estimated snowmelt contribution to the flooding, on a

watershed basis, was in the range of 2.5- 5 inches.





FORECASTS AND WARNING SERVICES

The Northeast Floods of January 1996 created challenges for all National Weather

Service (NWS) offices involved in issuing timely and accurate watches, advisories,

warnings, statements, and other public products.  Hundreds of river forecasts were

issued under very complicated and unprecedented conditions.



Public forecasts and warning products issued by NWS offices in areas impacted by this

major flood event accurately highlighted the weather as it developed across their areas

of responsibility.  Most products were well written, timely, and contained good call-to-

action statements.  Outlook statements issued earlier in the week provided the public,

media, and public safety officials with information concerning flood potential.  Since

state and local emergency managers from New York, Pennsylvania, New Jersey,

Maryland, West Virginia, and Virginia were still mobilized due to the recent blizzard,

it was fairly easy for most of them to prepare to handle a flood event; however, on-

going disaster mobilization taxes resources.



Flood watches were posted by the NEXRAD Weather Service Forecast Office

(NWSFO) Pittsburgh, Pennsylvania, for selected rivers of eastern Ohio and west

central Pennsylvania on Wednesday, January 17, and extended for all of east central

Ohio, western Pennsylvania, and northern West Virginia on Thursday, January 18. 

Also on January 18, watches were posted by NWSFO Charleston, West Virginia, for a

significant portion of West Virginia and the New River Valley of southwest Virginia. 

Additional watches were issued on Thursday afternoon, by NWSFOs in Buffalo and

Albany for central and eastern New York, and by NWSFO Baltimore,

Maryland/Washington, DC, for portions of Virginia, West Virginia, and Maryland. 

NWSFO Philadelphia, Pennsylvania, issued a flood watch for extreme southeast

Pennsylvania and portions of New Jersey, Maryland, and Delaware on Thursday

afternoon, and for the remainder of eastern Pennsylvania and New Jersey early Friday

morning.





QUANTITATIVE PRECIPITATION FORECASTS (QPF)

Areal average 24-hour Quantitative Precipitation Forecasts (QPF) issued on Thursday,

January 18, by the NWSFOs in Pittsburgh, Pennsylvania, and Charleston, West

Virginia, ranged from 0.25-0.5, and 0.5-1 inch, respectively.  QPFs released early

Friday morning, January 19, by NWSFOs Pittsburgh, Pennsylvania; Philadelphia,

Pennsylvania; Albany, New York; and Baltimore, Maryland/Washington, DC,

contained amounts ranging from 0.25-0.75 inch.



All QPF products were later updated after heavier precipitation amounts were observed

as the storm system moved into and across the region on Friday morning.  Doppler

Weather Surveillance Radar (WSR-88D) precipitation estimates, the National Center

for Environmental Prediction (NCEP) numerical model, and the Hydrologic Prediction

Center (HPC) value-added QPFs underestimated the amount of rainfall as revealed by

the gage observations, although the HPC value-added QPFs represented a significant

improvement over the model QPFs.





DATA

Automated and manual data networks and equipment had performance problems during

this flood event; sporadic equipment problems and many critical outages of automatic

and manual gage networks were noted during this event that impacted data acquisition. 

Many unheated tipping bucket precipitation gages became blocked with snow due to the

heavy snowfall from the previous weekend.  River gages were affected by ice jams,

and there was water in several gage houses which washed out or contaminated the

antifreeze.



All offices are equipped with a state-of-the-art WSR-88D, which provides an areal

assessment of rainfall amounts based on returned power processed through a series of

hydrometeorological algorithms.  The radars at Binghamton, New York; State College,

Pennsylvania; and Philadelphia, Pennsylvania, did a good job of providing reasonably

accurate rainfall amounts.



In general, WSR-88D precipitation products underestimated the rainfall by a factor of 2

or more.  In most areas, forecasters were able to make adequate manual adjustments to

the estimates based on comparison to rain gage reports.  Most forecasters who worked

this event were pleased with the precipitation products generated by the WSR-88D. 

While rainfall estimates were not perfect, they provided a good representation of the

rainfall patterns when compared to rain gage measurements.  Rainfall estimates

provided by these radars, along with critical rainfall reports from cooperative

observers, were crucial to the issuance of early Flood and Flash Flood Warnings.  The

Susquehanna Flood Forecast and Warning System is a nonstructural flood mitigation

measure that was implemented in 1985; it provided significant additional data which

helped the NWS issue timely watches and warnings.





PREPAREDNESS AND COORDINATION

All office Station Duty Manuals (SDM) were up to date and provided the staff with

specific information concerning office operations and actions during both river and

flash flood events.  All SDMs, along with NWS Form E-19, depicted flood-prone and

flood inundation areas.



Specific hydrologic drills had been accomplished by all offices to ensure all office

personnel were trained to handle any type of flooding.  Most drills had been completed

within the past 6 months.  Hydrologic service drills and staff training are usually

conducted by the Service Hydrologist (SH) and/or Warning Coordination Meteorologist

(WCM).



During the past year, numerous outreach activities and hazardous weather training,

focusing on flooding and severe weather, were provided by NWSFOs in Pittsburgh,

Pennsylvania; Baltimore, Maryland/Washington, DC; Philadelphia, Pennsylvania; and

Charleston, West Virginia; and by NWSOs in Binghamton, New York; State College,

Pennsylvania; and Wilmington, Ohio.  Extensive coordination between the RFCs and

their respective HSAs was also accomplished during this period.  All offices have an

excellent line of communication with County Warning Area (CWA) media, and

emergency management and other public safety officials.  During this flood event,

several spotter groups were activated due to the possibility of severe weather Friday

morning, January 19, but they were also used to report flood conditions and

precipitation amounts.





MEDIA AND USER RESPONSE

Overall, media coverage relating to the Northeast Floods of January 1996 -- the worst

flooding in more than 10 years across the mid-Atlantic region -- was positive.  News

stories focused on the cause and extent of the flooding, human interest stories, and

recovery efforts, and they accurately highlighted the weather as it developed across the

region.



The February 4 issue of Newsweek credited the NWS for the advance warnings of the

flooding:



     "Modernized equipment allowed the National Weather Service in January

     to warn the eastern U.S. of flash floods up to 24 hours before major

     rivers crested.  State-of-the-art Doppler radars monitored rainfall, while

     a new computer network let the service swap data in real time with states

     and counties."



On Monday and Tuesday before the event, all NWS offices in the region issued Flood

Potential Statements so the public and media were aware that spring-like ice jam

flooding would occur.  Throughout the flood-ravaged areas, the primary sources of

information for most citizens were radio and television broadcasts.  Most radio and

television stations aired watches and warnings as soon as they received them.  All local

Emergency Broadcast System (EBS) radio and television stations aired watch and

warning information beginning Thursday before the event.



As a result of the significant impact of the major flooding in Pennsylvania, a special

State House committee reviewed the operations of the NWS and other state and Federal

agencies.  The five-member bipartisan committee, which held hearings in Charleroi and

Williamsport, Pennsylvania, concluded that the NWS provided timely watches and

warnings.



SUMMARY

The Northeast Floods of January 1996 provided many challenges for all NWS offices

involved with the flood.  In spite of the rapid onset and complexity of this event, the

warnings and forecasts provided by NWS personnel, in cooperation with emergency

managers and the media, provided excellent service to the public and specialized users. 

The NWS did an outstanding job in recognizing the flood potential, a full 5 days in

advance, and getting the word out to the public, emergency services, and hydrologic

agencies so that they could take the necessary actions to prepare for and fight the flood.

 

In spite of the outstanding efforts of the NWS, the media, and the emergency

management community, there were 33 fatalities.  In an effort to mitigate potential

future losses, one responsibility of the disaster survey team is to review operations,

highlighting positive aspects and identifying any weaknesses.  Toward that end,

detailed findings and recommendations are contained in Chapter 6 of this report.







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