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Excessive Heat in the Interior West; Monsoon Conditions in the Southwest

Dangerous heat is expected to be in place across portions of California, especially the Central Valley, and across the Interior Northwest into Friday. Heat Advisories will also be in place across the southern Plains into the Lower Mississippi River Valley. Monsoonal showers and thunderstorms may result in flash flooding and debris flows from the Four Corners region and Southwest through Friday. Read More >

MARCH 12, 2010 TO MARCH 15, 2010 EVENT


A severe nor\'easter impacted the region from Friday March 12th through Monday March 15th. A slow moving upper level low drifted into the eastern United States and spawned a surface low pressure system off the South Carolina coast on the morning of Friday March 12th. Light to moderate rain spread north across the entire region through the day on Friday as the low pressure drifted north and slowly strengthened. With a strong fetch off the Atlantic Ocean, rainfall rates became heavy overnight Friday and through the evening of Saturday March 13th, resulting in small stream and eventually major river flooding. Meanwhile a high pressure system anchored in the Canadian Maritimes also strengthened and a very strong pressure gradient developed between these pressure systems overnight Friday. This resulted in strong, damaging easterly winds across much of the area through the day Saturday, especially along the New Jersey coast where minor to moderate coastal flooding also occurred. The strong winds and widespread heavy rains slackened off overnight Saturday as the surface low was stationary across the Delmarva region. Showers and even a few thunderstorms continued to rotate in off of the Atlantic through the day on Sunday March 14th and continued into Monday March 15th as the low slowly moved eastward and finally out to sea by Tuesday morning March 16th.


Model guidance for days in advance was consistently showing a heavy rainfall threat for the mid-Atlantic region during the event period and the potential for flooding was the overall major concern leading into the storm. A Flood Watch was first issued at 344pm EST on Thursday March 11th and included the entire Mount Holly county warning area. It remained in place until 349am EDT Sunday March 15th when it was lifted, but not before numerous Flood Warnings had been issued for areas along small streams and rivers. Several counties in eastern Pennsylvania, northern Delaware and New Jersey were first issued Flood Warnings starting Saturday afternoon on March 13th as small streams and tributaries initially filled and went above flood stage in response to the copious amounts of rainfall. Eventually many downstream major tributaries would rise far above flood stage as well, particularly in New Jersey where the worst of the flooding was observed. A Flood Warning was first issued for the Passaic River basin affecting Morris and Somerset counties in New Jersey at 316pm EST on Saturday. Major flooding on the main branch Passaic continued through the following week and the warnings were not canceled until the waters fell below flood stage in the worst spots late Sunday March 21st. A Flood Warning was first issued within the Raritan River basin affecting Somerset and Middlesex counties in New Jersey beginning 331pm EST on Saturday March 13th. The Flood Warnings were cancelled when the Raritan River and upstream Millstone River waters subsided below flood stage on the afternoon of Monday March 15th. In Burlington county in New Jersey, a Flood Warning was first issued for the North Branch Rancocas Creek in Pemberton at 326pm EST on Saturday March 13th. The Flood Warning did not expire until the morning of Friday March 19th. Flood Warnings were issued for the majority of the county warning area at some point during the event due to smaller creeks and rivers overflowing their banks.

Damaging high winds also occurred in the county warning area on Saturday March 13th. A Wind Advisory was first issued at 1120am EST on Friday March 12th for the following counties: Kent and Sussex in Delaware; Cape May, Atlantic, southeastern Burlington, Ocean, Monmouth and Middlesex in New Jersey. At 1225pm EST on Saturday March 13th the Wind Advisory was cancelled for Kent and Sussex counties in Delaware as the core of strong winds had already moved through these most southern areas. Further north, the Wind Advisories continued for the other coastal counties previously mentioned, and were also expanded inland to include the entire rest of the county warning area, excluding Kent, Queen Anne\'s, Caroline and Talbot counties in eastern Maryland. However, by 201pm EST on Saturday stronger wind gusts were occurring particularly near the coast where the following areas were upgraded to a High Wind Warning: coastal Cape May, Atlantic, coastal Ocean and eastern Monmouth counties in New Jersey. At 431pm EST on Saturday the core of strongest winds continued to move to the north and were proving to be not only stronger, but also more widespread than initially anticipated. The High Wind Warnings were expanded inland to include all of Burlington, Ocean, Monmouth, Mercer and Middlesex counties in New Jersey. Further south as winds died down, High Wind Warnings were downgraded to a Wind Advisory in coastal Cape May and Atlantic counties in New Jersey while the Wind Advisories were cancelled for the following areas: New Castle county in Delaware, Cecil County in eastern Maryland, Cumberland, Salem and Cape May counties in New Jersey. By Saturday evening winds were continuing to let up from southwest to northeast. At 749pm EST the High Wind Warning was downgraded to a Wind Advisory for Ocean, Burlington, and Mercer counties; however they continued for Monmouth and Middlesex counties. Also at this time the Wind Advisories were cancelled for Atlantic, Gloucester and Camden Counties in New Jersey; Berks, Chester, Montgomery, Delaware and Philadelphia Counties in Pennsylvania. The Wind Advisory continued elsewhere to the north. At 931 EST the last of these High Wind Warnings were cancelled and Wind Advisories continued only for Monmouth, Middlesex, Somerset and Morris Counties in New Jersey as they were cancelled elsewhere. Finally, by 100am EST on Sunday March 14th the last Wind Advisory was allowed to expire.


Light to moderate rainfall overspread the area from south to north starting early Friday morning March 12th and continued through the day. Rain became heavy throughout most of the area from overnight Friday through the evening of Saturday March 13th before significantly letting up. Periods of showers and areas of steadier rain would continue to rotate in off of the Atlantic Ocean through the day on Monday March 15th, adding to the already impressive rainfall totals. The heaviest rainfall amounts averaging 4-6 inches with isolated amounts to 7 inches were reported in the northeastern sections of the Mount Holly county warning area, including the northern New Jersey coastline, east-central New Jersey and northeastern New Jersey. Rainfall totals averaged 3-5 inches with isolated higher amounts in southern New Jersey, west central New Jersey and extreme southeastern Pennsylvania. In a band stretching from northwest New Jersey to just northwest of Philadelphia and down into Delaware and eastern Maryland, lighter amounts averaging 2-4 inches were observed. The lightest amounts were observed over the western sections of the Mount Holly area in the Pennsylvania counties of Berks, Lehigh, Carbon and Monroe where only 1-3 inches fell. 

In response to the widespread heavy rainfall, many small creeks and eventually some larger rivers across Delaware, southeastern Pennsylvania, eastern Maryland and New Jersey would rise above their banks resulting in widespread minor to major flooding. The Passaic and Raritan River basins in particular experienced the most severe flooding. In the Passaic River basin affecting Morris and Somerset counties in New Jersey, a historic flood crest was achieved along the Pompton River at Pompton Plains on Sunday afternoon March 14th. At the same time major flooding was also cresting along the Ramapo and Rockaway River branches. Along the main stream Passaic River, high end moderate flooding was achieved at both Chatham and Millington by Monday morning March 15th. Further downstream along the Passaic River at Little Falls and Pine Brook, a top 3 historic flood crest and top 4 historic flood crest respectively occurred. Major flood stage was met at both these sites early Monday morning March 15th and occurred into Friday March 19th, when moderate and then minor flooding continued through the weekend of March 20th-21st. In the Raritan River basin affecting Somerset and Middlesex counties in New Jersey, the Millstone River at Blackwells Mills went above flood stage by 7pm Saturday evening and peaked above major flood stage overnight, reaching a top 5 historical crest. The waters receded below flood stage by Tuesday morning March 16th. Along the North Branch Raritan River in Raritan, high end moderate flooding crested early Sunday Morning and receded below flood stage later that afternoon. Later along the main branch Raritan River, major flooding occurred during the day on Sunday at both Bound Brook and Manville where a 4th highest historical crest and 5th highest historical crest respectively was observed. The Raritan River waters subsided below flood stage by the afternoon on Monday March 15th. Finally, in Burlington county significant river flooding occurred along the North Branch Rancocas Creek at Pemberton. the Rancocas crested at moderate flood stage during the evening of Monday March 15th, and persistently remained above flood stage through the morning of Friday March 19th. Flooding occurred for the majority of the county warning area at some point during the event due to smaller creeks and rivers overflowing their banks. In certain vulnerable areas, flooding was further exacerbated when excessive runoff combined with coastal tidal surges.

High winds out of the easterly direction occurred on Saturday March 13th and were generated by the pressure gradient between the strengthening low pressure system to the south and a strengthening high pressure system to the northeast. The most impressive winds within the county warning area occurred during Saturday morning and early afternoon near the coast in Delaware and Southern New Jersey, and later during the afternoon and evening further north along the northern New Jersey coastline near the Raritan Bay and extending well inland over central and northeastern New Jersey. Some of the highest wind gusts recorded include 73 mph at the Marina in Atlantic City, NJ; 70 mph at Keansburg, NJ; 67 mph at Atlantic City International Airport; 67 mph at Sandy Hook, NJ; 67 mph at Lakehurst, NJ; 67 mph at Seaside Heights, NJ; 65 mph at Brant Beach, NJ; 65 mph at Chatsworth, NJ; 65mph at Monmouth Beach, NJ; 63mph at Trenton, NJ; 63 mph at McGuire AFB in Wrightstown, NJ; and 58 mph at Dover AFB in Dover, DE. Along with these frequent damaging wind gusts, sustained winds in the hardest hit areas were between 30-50 mph for several hours at the height of the storm. Elsewhere across the area winds were weaker, but still gusted between 40-55 mph. The strong fetch of wind off of the cool Atlantic Ocean also kept temperatures throughout the area ranging from the low 40s to low 50s for the duration of the storm.

Significant Impacts/Aspects

The strong winds and heavy rainfall produced widespread damage and impacts across the Mount Holly county warning area. Even before rivers rose above flood stage, widespread flooding because of the heavy rainfall rates was forcing the closure of many major and secondary area roadways. New Jersey was particularly hard hit with flooding and wind damage and a state of emergency was declared as a result. The strong winds which frequently gusted 50-60 mph in most areas and up to 70 mph in spots wreaked the most havoc statewide, toppling numerous trees onto roads, cars, houses, and power lines causing widespread power outages. In Middlesex County, a large tree fell on a vehicle injuring two people. Wind and rain forced the closure of parts of the New Jersey Turnpike, a near complete shutdown of the NJ-Transit system, and toppled a high rise crane in Atlantic City, NJ causing dangerous debris to drop to the ground. PSE&G reported about 459,000 customers lost power during the height of the storm on Saturday March 13th, making it the worst storm in the utility\'s history. According to Karen A. Johnson, a PSE&G spokeswoman, the previous worst storm was Tropical Storm David in September, 1979 when 432,000 lost power. On Friday morning March 19th, nearly a week after the storm, 2,200 people in the state were still without power and many folks along the Passaic river in northeastern New Jersey still were still dealing with major flooding. Thousands of businesses and residents in flood prone areas across the state received damage where major flooding occurred. Officials say more than 1,300 buildings in Morris County alone were damaged because of flooding along the Passaic, Ramapo and Pompton rivers. Preliminary estimates from flooding and wind damage in New Jersey alone are in the millions of dollars. Elsewhere in the area, flooding and wind damage was not as severe, but impacts from minor river flooding and downed trees and power lines were still felt in many areas. In southeastern Pennsylvania, PECO said that 135,000 customers lost power in the Philadelphia region, with Bucks county bearing the brunt. All of these customers had their power restored by Tuesday March 16th.

Widespread minor tidal flooding occurred along the coasts of New Jersey and Delaware on the 13th. During the evening high tide on the 13th, moderate tidal flooding occurred in Monmouth County, New Jersey. The tide gauge at Sandy Hook reached 8.34 feet MLLW.


Information contained in this summary is preliminary. More complete and/or detailed information may be contained in subsequent monthly NOAA storm data publications.