Skip Navigation Links 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center

HOME > Outreach > CPC Seminars > Future Seminars
Large-Scale Regime transition and its impact on Cool-Season Precipitation in the Northeast
Heather Archambault
(with Daniel Keyser, Lance F. Bosart and Anantha Aiyyer)
Dept. of Earth & Atmospheric Sciences,
University at Albany/SUNY, Albany, New York

Date:  Wednesday, 6 September, 2006
Time:  10:00 AM
Place:   Room 707, NOAA Science Center
            5200 Auth Road
            Camp Springs, MD 20746


This presentation investigates relationships between large-scale regime transitions and cool-season (November–April) Northeast precipitation from statistical and synoptic perspectives. In this study, regime transitions are identified as periods when the North Atlantic Oscillation (NAO) index or Pacific–North American (PNA) pattern index undergoes a two-standard deviation change centered on zero over seven or fewer days. To identify regime transition periods, 56-year (1948–2003) time series of daily NAO and PNA indices were generated from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP–NCAR) reanalysis dataset. A daily precipitation anomaly time series for the Northeast derived from NCEP’s Unified Precipitation Dataset for the same 56-year period was used to calculate precipitation anomalies during these periods.

Statistical results indicate that two types of large-scale regime transitions are conducive to above-normal cool-season precipitation in the Northeast: (i) positive-to-negative NAO transition periods and (ii) negative-to-positive PNA transition periods. Statistical results also show that the NAO index tends to decrease and the PNA index tends to increase in conjunction with major cool-season Northeast precipitation events. Composite analyses of positive-to-negative NAO regime transitions bracketing major Northeast precipitation events reveal that extratropical cyclones associated with these precipitation events contribute to the evolution of a negative NAO regime by transporting warm air to high latitudes and creating a high-over-low (Rex-type) block.

The security procedures to all interested non-NOAA attendees  for entry into WWB are: You need to give your name, affiliation, and phone #  to the security at the front desk when you arrive.  You need to have a valid photo ID upon entry.  Moreover,  you need to be accompanied during your stay here. I am sorry for the inconvenience.  It may help to make a printout of this announcement and show to the guards for your purpose of visit when u come. If u are interested in giving a seminar at CPC, or for further information, please call (301-763-8000 ext. 7546) or email me (

Directions from Washington Beltway 495: Take exit 7B (Branch Ave), make a right at  first signal, and the building is immediately on your left.

NOAA/ National Weather Service
NOAA Center for Weather and Climate Prediction
Climate Prediction Center
5830 University Research Court
College Park, Maryland 20740
Page Author: Climate Prediction Center Internet Team
Page last modified: August 28, 2006
Information Quality
Privacy Policy
Freedom of Information Act (FOIA)
About Us
Career Opportunities