2546 MONTHLY WEATHER REVIEW VOLUME 138 The Antecedent Large-Scale Conditions of the ‘‘Perfect Storms’’ of Late October and Early November 1991 JASON M. CORDEIRA AND LANCE F. BOSART Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York (Manuscript received 10 November 2009, in final form 26 January 2010) ABSTRACT The ‘‘Perfect Storms’’ (PSs) were a series of three high-impact extratropical cyclones (ECs) that impacted North America and the North Atlantic in late October and early November 1991. The PSs included the Perfect Storm in the northwest Atlantic, a second EC over the North Atlantic that developed from the interaction of the PS with Hurricane Grace, and a third EC over North America commonly known as the ‘‘1991 Halloween Blizzard.’’ The PSs greatly impacted the North Atlantic and North America with large waves, coastal flooding, heavy snow, and accumulating ice, and they also provided an opportunity to investigate the physical processes that contributed to a downstream baroclinic development (DBD) episode across North America that culmi- nated in the ECs. Downstream baroclinic development resulted from an amplification of the large-scale flow over the North Pacific that was influenced by anomalous tropical convection, the recurvature and extratropical transition of western North Pacific Tropical Cyclones Orchid, Pat, and Ruth, and the subsequent evolution of the extra- tropical flow. The progression of DBD occurred following the development of a negative PNA regime and the generation of baroclinic instability over North America associated with equatorward-displaced potential vorticity anomalies and poleward-displaced corridors of high moisture content. An analysis of the eddy ki- netic energy tendency equation demonstrated that the resulting baroclinic conversion of eddy available po- tential energy into eddy kinetic energy during the cyclogenesis process facilitated the progression of DBD across North America and the subsequent development of the ECs. 1. Introduction damage (Table 1). A majority of the meteorological impact from the PS occurred in association with high a. Background and motivation winds, large waves, and coastal flooding (Table 1). EC1, The ‘‘Perfect Storms’’ (PSs) were a series of three however, mainly impacted North Atlantic shipping routes extratropical cyclones (ECs) that occurred between with numerous high wind and wave reports. EC2 was as- 25 October and 4 November 1991 that included the sociated with an early-season cold air outbreak and record Perfect Storm (Cardone et al. 1996; Junger 1997) and snow and ice accumulations over the Midwest. The pur- two additional ECs over the North Atlantic and central pose of this paper is to investigate the antecedent large- United States (EC1 and EC2, respectively). EC1 was an scale flow evolution over the North Pacific (NP) and the intense cyclone that resulted from the interaction be- physical processes that contributed to downstream de- tween the PS and Hurricane Grace (HG; 1991), whereas velopment over North America and culminated in the EC2 is colloquially known as the ‘‘1991 Halloween three ECs. Blizzard’’ in the Midwest. The PS, EC1, and EC2 were Six-hourly locations of the PS, EC1, EC2, and HG, notorious cyclones that resulted in more than 34 deaths along with the mean sea level pressure (MSLP) and and over $300 million (1991 U.S. dollars) in property time-mean 500-hPa geopotential heights from 25 October through 4 November, show the positions of the storms relative to the time-mean amplified flow over North Corresponding author address: Jason M. Cordeira Department America and the North Atlantic (Fig. 1a). The de- of Atmospheric and Environmental Sciences, University at Al- bany, State University of New York, ES-351, 1400 Washington velopment of HG followed a baroclinic pathway before Ave., Albany, NY 12222. the system transformed into a tropical cyclone (TC) via the E-mail: [email protected] tropical transition (TT) process on 25 October (not shown; DOI: 10.1175/2010MWR3280.1 Ó 2010 American Meteorological Society Unauthenticated | Downloaded 10/11/21 03:25 AM UTC JULY 2010 C O R D E I R A A N D B O S A R T 2547 TABLE 1. Summary of the meteorological and societal impacts of the PS, EC1, and EC2. Sources: The Environment Canada data are available online at http://www.meds-sdmm.dfo-mpo.gc.ca/ and the PS damage summary is available online at http://www.ncdc.noaa.gov/ oa/satellite/satelliteseye/cyclones/pfctstorm91/pfctstdam.html. Impact Magnitude Location and time Source PS High winds 25.0 m s21 Environment Canada buoys 44141 Environment Canada; (sustained) and 44137 over NW Atlantic Eid et al. (1992) on 29–30 Oct High winds (gust) 28.0 (35.0) m s21 Milton, MA (Chatham, MA) Maglaras et al. (1995) on 31 Oct Maximum wave 28.5 (30.7) m Environment Canada buoy Environment Canada; heights 44141 (44137) on 29 Oct Eid et al. (1992) Heavy rain .100.0 mm Eastern Massachusetts on 30–31 Oct NCDC Property damage .$200 (.$100) East Coast (Massachusetts) Bigio (1992); NOAA (1992); million PS damage summary Coastal flood N/A New England Maglaras et al. (1995) forecasting EC1 Rapid deepening 50.0 hPa (24 h)21 North Atlantic between 0000 UTC ECMWF ERA-40 30 Oct and 0000 UTC 31 Oct High winds (gust) .30.0 m s21 North Atlantic on 31 Oct DeAngelis (1992) Large ocean swells ;10.0 m North Atlantic on 31 Oct EC2 Heavy snow .50.0 (93.7) cm East-central through northeast MN This day in weather history (Duluth, MN) on 31 Oct–2 Nov for southeast Minnesota, Ice accumulation 5.0 (7.5) cm Southwest through north-central northeast Iowa, and western IA (south-central and southeast Wisconsin (Rieck and IA) on 31 Oct–2 Nov Boyne 2006) Property damage $68.0 ($11.7) million IA (MN) Daily record min 219.08/223.38/211.68C Duluth, MN on 4 Nov/Bismarck, ND on NCDC summary of the day temperatures 31 Oct/Chicago, IL on 4 Nov Davis and Bosart 2004). Hurricane Grace subsequently further described this amplified flow pattern on the dy- interacted with the PS, underwent extratropical transition namic tropopause (DT) as the result of possible down- (ET), and influenced the development of EC1 on stream development, diabatic heating, and the modulation 29 October. The PS later retrograded toward the northeast of the DT by TCs and TCs undergoing ET. Bosart (2003) United States, completed a counterclockwise loop over briefly reemphasized the amplified flow pattern from the Gulf Stream, underwent TT, and became a weak a potential vorticity (PV) perspective (Hoskins et al. 1985) unnamed hurricane on 1 November (Pasch 1991; Pasch and suggested EC2 was a ‘‘twin perfect storm.’’ Limited and Avila 1992). Concurrently, EC1 rapidly crossed the research, however, has focused on the evolution of the North Atlantic with characteristics of a diabatic Rossby antecedent large-scale flow. vortex (e.g., Moore and Montgomery 2004, 2005) and Studies have shown that noteworthy cyclogenesis explosively deepened (SLP decrease of 50 hPa in 24 h; events over North America such as the ‘‘Cleveland Su- Fig. 1b) approximately 2 bergerons (Sanders and Gyakum perbomb’’ of 25–26 January 1978 (e.g., Hakim et al. 1980) between 30 and 31 October. Upstream, EC2 formed 1995, hereafter HBK95), the ‘‘Superstorm’’ of 12– in the western Gulf of Mexico downstream of a deep time- 14 March 1993 (e.g., Bosart et al. 1996, hereafter B96), mean trough over the western United States and pro- and the ‘‘1998 Canadian Ice Storm’’ of 5–9 January 1998 gressed toward Hudson Bay between 31 October and (e.g., Gyakum and Roebber 2001) are often preceded by 4 November 1991. large-scale flow amplifications over the eastern NP and western North America. These studies illustrated how b. Revisiting the ‘‘Perfect Storms’’ upstream amplified flow influenced the juxtaposition of Previous research on the PS has primarily focused on equatorward-displaced regions of high PV air (e.g., upper- the extreme sea state in the North Atlantic (Table 1; level positive PV anomalies) and poleward-displaced Cameron and Parkes 1992; Eid et al. 1992; Maglaras regions of warm, moist air (e.g., lower-level positive PV et al. 1995; Cardone et al. 1996). Cameron and Parkes anomalies represented by positive potential temperature (1992), however, first depicted the development of the anomalies) during the cyclogenesis process. In regions PS during an amplification of the 500-hPa flow (e.g., of strong midlatitude baroclinity, conditions were favor- ‘‘strongly zonal to strongly meridional’’) as suggested by able for a mutual intensification of the upper- and lower- Fig. 1 (cf. their Figs. 1–4). Nielsen-Gammon (2001) level PV anomalies (Hoskins et al. 1985) and ‘‘type B’’ Unauthenticated | Downloaded 10/11/21 03:25 AM UTC 2548 MONTHLY WEATHER REVIEW VOLUME 138 FIG. 1. (a) The 6-hourly locations of HG, PS, EC1, and EC2 and the time-mean 500-hPa geopotential heights from 25 Oct through 4 Nov 1991 (dam, solid line). Tropical symbols de- note categorical intensity and characteristics of HG and the PS. (b) MSLP of HG, PS, EC1, and EC2 is given by a combination of the National Hurricane Center best-track data, ECMWF ERA-40 analyses, and surface data. The 1 and 2 bergeron (at 458N) deepening rates are given as reference. cyclogenesis (Petterssen and Smebye 1971). Cyclogenesis of 41 strong cold-season cyclones between 1975 and 1985 of this nature is consistent with the Eady model for baro- in the eastern NP could be traced to the ascent of warm clinic growth (Eady 1949; Hoskins and Valdes 1990) air within the baroclinic environment of upstream cy- whereby baroclinic instability is favored in the presence clones in the western NP.