Case Study of Torrential Rain and Flood in the Merrimack River Valley in May

2006

Case Study of Torrential Rain and Flood in the Merrimack River Valley in May

2006Jian-Hua Qian

University of Massachusetts LowellJian-Hua Qian

University of Massachusetts Lowell

Acknowledgement: Alex Brown, Joel Dupont, Lance Frank, Chris Hampton, Bill Leatham, Kurtis Malone, Todd Miller, Shawn Moynihan, Chris Roller, Zongyao Yang

The Results of Expanding the Domain in a WRF Model Run

April 25, 2013

The 2006 Flood of the Merrimack River in Lowell

Like most river valleys, the Merrimack River valley prone to minor flooding.

However, on May 15, 2006 heavy rainfall caused extreme flooding the Merrimack River raising the river more than 8 feet above flood stage in Lowell, MA.

This extreme event caused severe property damage, forced evacuations and in nearby Haverhill, MA their main sewage pipeline broke causing 35 millions gallons of raw sewage per day to be dumped into the Merrimack

2

Terrain of Northeast US

Observed Rain

UMass Lowell at the north end of the University Ave Bridge over the Merrimack River

View of Merrimack River from the University Ave Bridge in Lowell MA in May 2013

Synoptic Scale

Anomalous negative NAO

Blocking High Pressure in Eastern Canada

Cut-off Low Pressure over Great Lakes

Diffluent flow

Duration of event

North Atlantic Oscillation

Extremely negative NAO

Leads to blocking

2006 5 7 -0.5952006 5 8 -1.4442006 5 9 -1.9222006 5 10 -2.0282006 5 11 -2.0192006 5 12 -1.8182006 5 13 -1.6042006 5 14 -1.2752006 5 15 -1.0452006 5 16 -0.8382006 5 17 -0.8462006 5 18 -0.811

Rex Block

A “Rex Block” formed due to negative NAO

Idealized Case

May 2006 Case

Diffluent Flow

Divergence at the 500 mb level

Gives rise to upward vertical motion

We all like upward vertical motion!! Right?

Jet Level

• A not so typical; but still favorable Jet Position developed.

• Divergence at the 300 mb level; contoured in yellow (especially one the 14th)

May 13th 12z May 14th 12z

Negatively tilted a couple times during period

Water Vapor Satellite Image Valid 12Z 14 May 2006

Note the “Rex-Block” evident over eastern North America, and the attendant deformation zone extending from Hudson’s Bay through

the central US. Also note the “atmospheric river” of subtropical

moisture streaming onshore into New England.

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NOAA

Observed total Precipitation & average 700 hpa mixing ratio and

winds on may 13-15

Low Level Moisture

• Mixing ratio plots highlight stream of moisture

May 13th 12z

May 14th 00z

May 14th 12z

May 15th 00z

Low Level Moisture

Flow around High & Low pressure = consistent SE wind.

Lots of Atlantic Moisture picked up

FNL - Default Settings6 day 12 hr – Valid 5/18/2006 1200 UTC

http://www.ncdc.noaa.gov/sotc/hazards/2006/5

=

127 mm

DELTA (MAX TOTAL)

0 – 127 mm LESS

Simulation by Mesoscale Model WRF

Approx 7 Day Comparison Ending 5/18/2006WRF

Observation

Conclusions

•Extremely negative phase of the NAO leads to blocking

•Due to blocking over North Atlantic a Rex Block develops; giving rise to a cut-off Low Pressure over Great Lakes region

•Upper level divergence at both the 500 hPa & 300 hPa level provide a favorable region for upward vertical motion

•Combined low level flow around both pressure centers draws in copious amount of Atlantic moisture into Southern & Central New England

•Negatively tilted 500 hPa low and trough (in NW-SE direction) favors rain

•Moisture transport from the Atlantic to the Merrimack

•WRF successfully simulated the Mother’s Day flood