Robert Hart and Richard Grumm
Updated 5 January 2004 to include events from 1948 through 2003.
[ Description | Top-20 All Time | Top-10 by variable | Top-10 by month | Case References | Recent Ranking Changes | Latest MRF Rarity Forecast ]
This page presents the results of an analysis performed to objectively rank events based upon how far synoptic-scale fields depart from "normal":
field = The observed field
X = the daily mean value for the variable at that location
sigma = the daily mean field variability (standard deviation) for that location
Therefore, N is measured in the number of standard deviations from normal.
This departure is calculated for each of four variables: temperature, height, wind, and moisture.
Then, the maximum N-value for each variable is found (MTEMP, MHEIGHT,MWIND, and MMOIST respectively).
The total departure is then the full-troposphere mean (1000hPa -> 200hPa) of these four departures:
The expected return period for a given MTOTAL value illustrates the rarity of high values of MTOTAL.
The database used covers the years from 1948 through the end of last month and is limited to the eastern United States, extreme southeast Canada and the Gulf of Mexico.
The top 20 MTOTAL values, their dates, case description and references (if available) are shown below. The database is further broken down into the top cases by variable and by month at the end of the page.
Four-panel plots of the conventional synoptic analyses and associated anomaly fields are available by clicking on the date.
Sincere and deep gratitude go to NCEP, NOAA-CIRES, and CDC for providing historical and current reanalysis data online.
For further details of this project, see:
Hart, R. and R. Grumm, 2001: Using normalized climatological anomalies to rank synoptic-scale events objectively. Mon. Wea. Rev, 129, 2426-2442.
Robert Hart, PSU (firstname.lastname@example.org)
Richard Grumm, SOO, NWS CTP (email@example.com)