Case Study of Torrential Rain and Flood in the Merrimack River Valley in May 2006 Jian-Hua Qian...
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Transcript of Case Study of Torrential Rain and Flood in the Merrimack River Valley in May 2006 Jian-Hua Qian...
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.
13
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