Using normalized climatological anomalies to rank synoptic-scale events objectively.

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":

N = ( field - X ) / sigma

where:

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:

MTOTAL = (MTEMP + MHEIGHT + MWIND + MMOIST) / 4

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.

Dataset used:

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.


[ Description | Top-20 All Time | Top-10 by variable | Top-10 by month | Case References | Recent Ranking Changes | Latest MRF Rarity Forecast ]

Top-20 Total Normalized Departures from Climatology since 1948

Rank
Date
MTOTAL
Description
References
1
00Z09JAN1956
4.950
"The Great Atlantic Low"
Ludlum 1956
2
12Z15JAN1995
4.722
Deep Gulf of Mexico Storm
3
00Z14MAR1993
4.576
Superstorm of 1993
Kocin et al 1995; Dickinson et al 1997
4
12Z11JAN1975
4.566
Severe Minnesota Blizzard
5
12Z08JAN1998
4.536
NE US/SE Canada Ice Storm
Gyakum and Sisson 1999; DeGaetano 2000
6
12Z28DEC1980
4.469
Deep Carolina Coastal Low
7
12Z17MAR1983
4.464
Low-latitude intense cyclone
Dickinson et al 1997
8
00Z26NOV1953
4.396
9
00Z16OCT1954
4.391
Extratropical Hazel
Knox 1955; Palmen 1958
10
12Z08JAN1958
4.356
11
12Z19JAN1977
4.340
Historic Florida Freeze
Schwartz 1977
12
12Z19JAN1996
4.307
NE US Flooding/Snowmelt
Leathers et al 1998
13
00Z10JAN1978
4.260
Deep NE U.S. Storm
14
12Z31OCT1993
4.232
E. U.S. Elevation Blizzard
Grumm and Nicosia 1997
15
00Z04FEB1970
4.201
16
12Z22DEC1972
4.199
Deep Gulf of Mexico Storm
17
12Z11DEC1950
4.192
18
12Z17NOV2002
4.185
Southern/Central New England Ice Storm
19
12Z26JAN1978
4.179
The Cleveland Superbomb
Gaza and Bosart 1990; Hakim et al 1995,1996
20
00Z20OCT1989
4.179
SE U.S. Record Cold & Snow
21
12Z22JAN1959
4.176
Severe E. U.S. Snow/Ice Storm
Treidl 1959

[ Description | Top-20 All Time | Top-10 by variable | Top-10 by month | Case References | Recent Ranking Changes | Latest MRF Rarity Forecast ]


Last updated: 5 January 2004

Robert Hart, PSU (hart@ems.psu.edu)
Richard Grumm, SOO, NWS CTP (rgrumm@supercel.met.psu.edu)