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The Flooding of Late June 2006

Summary

By: Dave Ondrejik (WCM), John La Corte (Senior Forecaster),Greg DeVoir (Senior Forecaster), Robert Radzanowski (Forecaster), Aaron Tyburski (Forecaster) Peter Jung (SSH), Ron Holmes (ITO), Les Thario (ESA), and Victor Cruz (HMT)

The combination of a stalled surface front, an upper trough over the Midwest, and an anomalous upper ridge over the western North Atlantic caused heavy rains and serious flooding over portions of Central Pennsylvania beginning on Tuesday 27 June, and continuing into the end of the week.

On Friday 23 June, a weak surface cold front moved through Pennsylvania accompanied by scattered convection. Parts of the central mountains and Laurel Highlands received more than an inch of rain, with most locations seeing a quarter to a half inch. The front then stalled just south of the region providing a focus for heavy convective rains that at first affected only far southeastern parts of the state, then gradually moved northward over the weekend resulting in more widespread heavy rains Sunday through Tuesday. Over a period of several days, beginning during the weekend, most locations in central Pennsylvania received more than 3 inches of rain (see graphics below), with some eastern locations seeing more than a foot of rain from the entire event (Holtwood Dam had 13.01 inches). See Table 1 for an unofficial list of the rain totals for the several day period of heavy rain, and the images below for plots/contours of precipitation reports and estimates.

Ensemble models, as well as NCEP operational runs of the GFS and NAM models, began zeroing in on the heavy rain potential days in advance. As early as the morning of 22 June, MREF forecasts began portraying the development of an anomalous ridge over the western Atlantic, and a trough over the Midwest which was forecast to become quasi-stationary throughout the weekend and continue into at least Tuesday of the following week. This resulted in the development of a strong low level jet on the order of 40 to 50kt out of the south-southeast (3-5 standard deviations above normal) along with a plume of deep tropical moisture as evidenced by precipitable water forecasts near or above 2 inches (2-3 standard deviations above normal) which persisted for several days.

The last of the widespread heavy rain moved up and through the region during the day Tuesday before moving east of the region quicker than expected early Wednesday morning. Rainfall of between about 2 and 6 inches fell from Franklin County east and north up through Sullivan County in the northeast. This final slug of rain resulted in widespread county and flash flooding, as well as river flooding over much of the lower Susquehanna Valley.

See a Loop of the Daily Weather Maps (produced by the NWS Hydrometeorologic Prediction Center) for the last week in June.

See a Loop of the Daily Precipitation (past 24 hrs) (produced by the NWS Hydrometeorologic Prediction Center) for the last week in June.

Table 1. Unofficial Storm Rainfall Totals
ADAMS COUNTY
ORRTANNA11.53
BIGLERVILLE7.49
BEDFORD COUNTY
BUFFALO MILLS4.49
EVERETT 2.83
BLAIR COUNTY
WILLIAMSBURG3.03
TYRONE 1.84
CAMBRIA COUNTY
PRINCE GALLITZIN STATE PARK3.00
CAMERON COUNTY
EMPORIUM4.06
SINNEMAHONING2.14
STEVENSON DAM2.14
CENTRE COUNTY
CLARENCE3.65
PHILIPSBURG2.94
CLEARFIELD COUNTY
GRAMPIAN5.01
CLINTON COUNTY
LOCK HAVEN4.62
RENOVO2.06
COLUMBIA COUNTY
BENTON9.75
CUMBERLAND COUNTY
PINE GROVE FURNACE8.84
DAUPHIN COUNTY
HERSHEY7.29
HARRISBURG7.27
ELK COUNTY
RIDGWAY2.70
FRANKLIN COUNTY
SOUTH MOUNTAIN9.45
HUNTINGDON COUNTY
HUNTINGDON4.04
HESSTON3.72
LANCASTER COUNTY
HOLTWOOD DAM13.01
SAFE HARBOR DAM11.34
MILLERSVILLE6.58
LYCOMING COUNTY
SOUTH WILLIAMSPORT4.90
MCKEAN COUNTY
KANE 2.67
PORT ALLEGANY2.61
MIFFLIN COUNTY
LEWISTOWN5.24
MONTOUR COUNTY
DANVILLE9.14
NORTHUMBERLAND COUNTY
SUNBURY5.66
POTTER COUNTY
OSWAYO2.79
SCHUYLKILL COUNTY
MAHANOY CITY8.40
SNYDER COUNTY
SELINSGROVE7.55
SOMERSET COUNTY
LAUREL SUMMIT4.48
SOMERSET4.17
CONFLUENCE3.56
GLENCOE 3.41
MEYERSDALE2.48
SULLIVAN COUNTY
LAPORTE6.25
TIOGA COUNTY
COVINGTON10.40
COVINGTON4.99
SABINSVILLE4.50
COWANESQUE DAM3.42
WELLSBORO2.54
UNION COUNTY
LEWISBURG4.72
YORK COUNTY
YORK HAVEN DAM6.32
HANOVER5.88

Hydrologic Impacts

Heavy rain associated with a stalled frontal boundary and the remnants from a weak tropical system affected the CTP Hydrologic Service Area (HSA) for about a week. Flooding came in several waves, with one round of Flash Flooding on Sunday June 25th, a second round of Flash Flooding and the onset of river flooding on the 26th, then significant widespread Flash Flooding and River Flooding on the 27th . Flooding from smaller streams and creeks subsided on the 28th , but River flooding persisted until the morning of July 1st .

Because of the nature of the rainfall, Flash Flood warnings were issued several times for many CTP counties. Flood waters would recede, only to once again rise with the next batch of heavy rain. A widespread rainfall during Tuesday and Tuesday night with the remnants of a weak tropical system (that was never a tropical depression or cyclone) ended the event.

River Flood Warnings were issued for several smaller Susquehanna tributaries on June 25th, only to be cancelled later when the first round of heavy rain was less widespread than originally expected.

A majority of the River Flood Warnings were issued on the 27th. Again, these were well in advance of any flooding. During the afternoon of the 27th, significant upward revisions to existing flood warnings were made. This was based on the inclusion of much higher and widespread QPF Forecasts than previously incorporated into the river model. Ultimately, the areal extent of the heavy rainfall was lower than projected, and shifted eastward by 50 to 75 miles. This shift brought considerably less rain (and hence runoff) into the West Branch and Chemung basins, which feed into the Main Stem Susquehanna. This made considerable differences in the hydrologic forecasts (lowered) for the Main Stem Susquehanna River in the CTP HSA, and updated forecasts were issued.

Even with the downward revisions, Moderate, Major and even Record category flooding was observed at 11 of the 12 CTP forecast locations which did flood. (Harrisburg only reached the Minor Flooding category). Hershey on Swatara Creek recorded a new record stage of 16.12 feet on the 29th. The old record was 15.4 feet set in 1975 due to the Remnants of Hurricane Eloise. It should be noted, however, that records at Hershey began after Hurricane Agnes, and anecdotal accounts rate that flooding as higher than the current event.

At this time there appear to have been no deaths in the CTP HAS related to flooding. However, several fatalities were being investigated as possible flood related deaths.

Widespread damage was noted throughout the eastern third of the CTP HSA, and throughout all of Eastern Pennsylvania. This included a number of washed out roads and bridges, as well as numerous water rescues.

    Some preliminary highlights of actions taken in Pennsylvania, and damages incurred:
  • The Governor signed a Declaration of Disaster Emergency on June 28, 2006 due to widespread flooding, and extensive damage to public and private property in the 46 counties of Adams, Armstrong, Bedford, Berks, Blair, Bradford, Bucks, Carbon, Centre, Chester, Clinton, Columbia, Cumberland, Dauphin, Delaware, Franklin, Fulton, Huntingdon, Indiana, Jefferson, Juniata, Lackawanna, Lancaster, Lebanon, Lehigh, Luzerne, Lycoming, Mifflin, Monroe, Montgomery, Montour, Northampton, Northumberland, Perry, Philadelphia, Pike, Potter, Schuylkill, Snyder, Sullivan, Susquehanna, Tioga, Union, Wayne, Wyoming, and York.
  • On June 30, 2006, President Bush declared a major disaster, and authorized Public Disaster Assistance under the Robert T. Stafford Relief and Emergency Assistance Act. The declaration was for eight (8) counties for the period beginning June 23, 2006 and including the Counties of Bradford, Bucks, Columbia, Luzerne, Northampton, Northumberland, Susquehanna and Wyoming for debris removal and emergency protective measures, including direct Federal assistance.
  • On July 4, 2006, President Bush designated Monroe, Schuylkill, Susquehanna, Wayne and Wyoming counties for individual disaster assistance, qualifying residents and businesses in those counties for Individual Assistance. On July 5, 2006 President Bush added Berks, Bradford, Chester, Luzerne and Pike counties to the list of counties approved for individual assistance. This brings to ten the total of Pennsylvania counties approved
  • In all, 204 Municipal disaster declarations, within 28 Pennsylvania Counties, were received by the State Emergency Operations Center (EOC).
  • During the event, 15 counties issued evacuation orders (Adams, Berks, Bradford, Bucks, Carbon, Columbia, Cumberland, Lackawanna, Luzerne, Monroe, Schuylkill, Snyder, Susquehanna, Perry and Wayne).
  • Army National Guard conducted 484 air rescue missions.
  • As of July 4, 2006, 94 roads remained closed in 14 counties. 65 bridges were listed as damaged, or out, in 10 PA counties. Total bridge replacement is required in 23 instances.
  • American Red Cross - Since the start of operations at least forty eight (48) shelters were operational, housing more than 2,500 people. All of the shelters have been closed. To date, Red Cross has assigned at least 173 vehicles, including Emergency Response Vehicles (ERV) and additional trucks from multiple states to assist affected areas. ARC has provided nearly 77,000 meals and snacks through 60 fixed and mobile feeding sites.
    Locally:
  • Lancaster County - 36 water rescues performed
  • Schuylkill County - The Lower Owl Creek Dam in Tamaqua Borough was determined to be eroding. The Department of Conservation and Natural Resources (PA DCNR) began drawing down the dam.
  • Snyder County - A landslide closed State Route 104 in Perry Township. No injuries were reported.
  • A propane release occurred when a cylinder was discovered floating in the Swatara Creek.

Summary of River Flooding

Summary of Flash Flooding

    20 of CTP's 33 counties reported Flash Flooding. With the rainfall occurring in several waves (June 25, June 26 and June27-28), numerous counties had multiple Flash Flood Events.
  • Adams, Clearfield Columbia, Cumberland, Dauphin, Franklin, Juniata, Lancaster, Lebanon, McKean, Montour, Northumberland, Perry, Schuylkill, Snyder, Sullivan, Somerset, Tioga, Union and York

Precipitation Plots

MultiSensor Precipitation Estimate plot for the week.
MultiSensor Precipitation Estimate plot for the week.

CoOperative Observer Precipitation Totals for the week.
CoOperative Observer Precipitation Totals for the week.

Point Plot of Observed Rainfall for the week, automatic and manual gages.
Point Plot of Observed Rainfall for the week, automatic and manual gages.


 
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Page Last Modified: 08 July 2006 21:30:51 UTC
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