According to the National Weather Service in Cleveland, OH (2019), by early afternoon of May 31, 1985, thunderstorms developed in Ontario, Canada just ahead of the cold front. Over a dozen tornadoes occurred in Ontario, with at least four F3s and two F4s reported. However, as the afternoon progressed, the thunderstorm activity developed south into Northern Ohio. The initial thunderstorms in the state occurred between 3:00 pm and 4:00 pm EDT near Cleveland. At 4:10 pm, the NWS Office in Cleveland issued the first severe thunderstorm warning of the day for Ashtabula County. From that point on through the evening, weather conditions worsened. As the first reports of damage trickled in to the NWS offices in the area, it quickly became clear that a tornado outbreak of an unprecedented magnitude was taking place across the region. By the end of the evening, a total of forty-one tornadoes had occurred in the United States and Canada. Twenty-one tornadoes tracked across Northeast Ohio and Northwest Pennsylvania during the evening of May 31st. According to Ferguson, Ostby & Leftwich (1987), there were 94 fatalities in 1985 related to tornadoes and 76 of those fatalities occurred on May 31st. This is the story behind this historic tornado outbreak.
The Forecast
Figure 2 depicts the surface analysis on the morning of May 31st. In Figure 2, we can see a warm front advecting northward across Ontario and a cold front moving eastward (entering Michigan). The cold front would later provide the trigger for explosive supercell thunderstorm development. According to the National Weather Service in Cleveland, OH (2019), the upper air features from the the morning analysis gave classic indications of a significant severe weather event across Eastern Ohio and Western Pennsylvania. At 850 mb (Figure 3), very warm/moist air was surging north into the Ohio Valley and a dryline was observed over the Western Great Lakes and Midwest.
At 500 mb, a negatively tilted trough was positioned over the Midwest (Figure 3) with strong westerly winds in excess of 80 knots directly in front of the trough. The combination of strong westerlies aloft and strong southwesterly jet at 850 mb (Figure 3) allowed for increased vorticity over Eastern Ohio and Western Pennsylvania (NWS, 2019).
The main severe weather feature that was unusual is seen in Figure 5 on the 700 mb chart. The trough is shown with dry air aloft or “cap”. According to the NWS Cleveland, OH (2019), this is a classic signature of severe weather outbreaks for this region. This warm air aloft allowed surface temperatures to climb in the 80’s for the forecast area.
At the surface, an elevated mixed-layer (EML) with nearly adiabatic lapse rates (~13C/km) between 750 mb and 550 mb was noted (Figure 6). According to the NWS Cleveland, OH (2019), research has shown that this signature on a Skew-T is a good indicator of significant severe weather.
The sounding of Figure 6 shows a small capping inversion near the surface and an inversion from roughly 850 mb to 550 mb. Convective available potential energy (CAPE) at 1257 J/kg, helicity at 355 m2/s2 (which is favorable for the development of mid-level rotation) and energy helicity index (EHI) at 3.1. This sounding is quite impressive for a late-May morning and quite favorable for tornadoes.
Figure 7 depicts a modified sounding depicting the CAPE at Pittsburgh, PA at 7:00 pm. This depicts 2800 J/kg of CAPE in the vicinity, therefore indicating a moderate to high value of instability in the atmosphere for severe thunderstorms.
At 18Z (2:00 pm EDT), the cold front was entering Ontario (Figure 8). According to Leduc et al. (1986), an unseasonably strong low pressure center tracked across upper Michigan during the morning hours to just north of Sudbury by evening. The visible satellite loop in Figure 9 shows the development and explosive growth of thunderstorms across Southern Ontario, Ohio, Western Pennsylvania and Western New York on the afternoon of May 31st.
At 21Z (5:00 pm EDT), the cold front was in Western Ontario (Figure 10).
Leduc et al. (1986) notes that the dynamics in place were strong since a sharp cold front (Figure 2, 3, 8 and 10) and an upper trough (Figure 4 and 5) was crossing Michigan, bringing with it strong westerlies in the upper-levels of the atmosphere.
Please note that Figure 11 and the following figures do not depict actual radar observations, but rather hand-drawn depictions of the supercells by NWS meteorologists. According to the NWS Cleveland, OH (2019), before the NWS WSR 88-Doppler Radar, radar operators hand drew the radar echos on overlay maps. Below is a timeline of actual National Weather Service text from Northwest Pennsylvania on May 31st:
5:13 pm EDT – Tornado Warning
BULLETIN ACTIVATE EBS
TORNADO WARNING
NATIONAL WEATHER SERVICE ERIE PA
513 PM EDT FRI MAY 31 1985 EXPIRES 530 PM
COUNTIES AFFECTED PA ERIE
THE
NATIONAL WEATHER SERVICE IN ERIE HAS ISSUED A TORNADO WARNING UNTIL
530 PM FOR THESE COUNTIES IN NORTHWESTERN PENNSYLVANIA…SOUTHERN ERIE
A
TORNADO WAS SIGHTED BY STATE POLICE NEAR PENNSIDE…SOUTH OF ALBION IN
ERIE COUNTY AT 505 PM…MOVING TOWARD THE NORTHEAST AT 30 MILES AN HOUR.
5:45 pm EDT – Tornado Warning
BULLETIN ACTIVATE EBS
TORNADO WARNING
NATIONAL WEATHER SERVICE ERIE PA
545 PM EDT FRI MAY 31 1985 EXPIRES 630 PM MAY 31 1985
COUNTIES AFFECTED PA ERIE AND CRAWFORD
THE
NATIONAL WEATHER SERVICE IN ERIE HAS ISSUED A TORNADO WARNING UNTIL 630
PM FOR THESE COUNTIES IN NORTHWESTERN PENNSYLVANIA ERIE AND CRAWFORD.
ERIE RADAR SHOWS 3 TORNADOS ON THE GROUND ONE NORTHEAST
OF WATERFORD ANOTHER NEAR CAMBRIDGE SPRINGS AND ANOTHER SOUTHWEST OF
MEADVILLE. THEY ARE ALL MOVING TO THE NORTHEAST AT NEAR 35 MPH.
6:20 pm EDT – Tornado Warning
BULLETIN ACTIVATE EBS
TORNADO WARNING
NATIONAL WEATHER SERVICE ERIE PA
620 PM EDT FRI MAY 31 1985 EXPIRES 700 PM MAY 31 1985
COUNTIES AFFECTED PA ERIE AND CRAWFORD
THE
NATIONAL WEATHER SERVICE IN ERIE HAS ISSUED A TORNADO WARNING UNTIL 700
PM FOR THESE COUNTIES IN NORTHWESTERN PENNSYLVANIA SOUTHERN ERIE AND
NORTHERN CRAWFORD.
AT 620 PM ERIE WEATHER RADAR SHOWS NEW TORNADOS ON THE GROUND WEST OF ALBION AND CONNEAUTVILLE PENNA. MOVING
TOWARDS THE EAST AT 35 MPH. ANOTHER TORNADO SOUTH OF SPARTANSBURG MOVING
INTO WARREN COUNTY AND ONE NORTH OF OIL CITY MOVING INTO NORTHERN
FOREST COUNTY.
Aftermath
Below is a collection taken from the NWS Cleveland, OH archive for this event, unless otherwise stated, these pictures are courtesy of Ohio Department of Transportation (ODOT) District 4:
Collection of newspaper clippings from The Herald (2015):
According to the NWS Cleveland, OH, the deadliest tornado of the day touched down near Jamestown, Pennsylvania along the Mercer and Crawford County line around 5:20 pm (contradicting information with NOAA storm event database, possible outdated time). This tornado was rated an F4 and killed 23 people (contradicting information with NOAA storm event database, possible outdated information). The tornado stayed on the ground for over an hour and produced a 56-mile long damage path. Along the way, the town of Atlantic was virtually destroyed. Cochranton, Cherry Tree, Cooperstown and Tionesta were also hard hit. Fatalities occurred in all five towns and also at mobile home park north of Franklin. The tornado finally lifted near Tionesta (Forest County) after destroying 371 homes.
By the end of the evening, a total of forty-one tornadoes had occurred in the United States and Canada. Twenty-one tornadoes tracked across Northeast Ohio and Northwest Pennsylvania during the evening of May 31st. Of these twenty-one, one was rated an F5, and six were rated F4’s. Tragically, these tornadoes killed 66 people in Ohio and Pennsylvania. This day remains the deadliest tornado outbreak ever documented in Pennsylvania. In Ohio, this was the worst event since the April 3-4th, 1974 outbreak that killed 37 in Xenia (NWS, 2019).
According to Sleptzoff & Dunkle (2009), on June 1st, the Governor of Pennsylvania asked for federal relief to help with the damage left by the May 31st tornado outbreak. On June 3rd, the Federal Government declared a state of emergency for the state of Pennsylvania.
Recap
In total, the Atlantic to Cochranton, PA F4 tornado of May 31, 1985 impacted Mercer, Crawford, Venango and Forest counties in Pennsylvania and Trumbull County in Ohio. According to NOAA (2019), the F4 tornado killed 16 people, injured 125 and caused $125 million dollars in damage. The tornado touched down on the OH/PA state line in Mercer County Pennsylvania at 5:17 pm EDT and travelled 56.2 miles to lift southeast of President, Pennsylvania at 6:30 pm EDT. The maximum width of the tornado was 350 yards.
Tornado near Cochranton, PA 
Tornado near Jamestown, PA 
Tornado near Atlantic, PA
“This tornado touched down in the extreme northeast corner of Trumbull County, OH in Kinsman Township. The storm was on the ground in Ohio for only a few hundred yards. The storm damaged some farm buildings and downed trees. The tornado then traveled through Jamestown (Mercer County, PA), moved through Atlantic, Cochranton (both Crawford County, PA), Hannaville, Cooperstown, a trailer park eight miles north of Franklin, and Cherry Tree (all Venango County, PA), to three miles south of Tionesta (Forest County, PA). There were 23 deaths; five in Atlantic, three in Cochranton, five in Cooperstown, one at the trailer park, two at Cherry Tree, and seven at Tionesta. About 371 homes were damaged or destroyed. A mobile home park just west of Atlantic was completely destroyed. The small town of Atlantic was practically totaled. Just east of Atlantic, a communications tower was toppled by the tornado. Within three days, it was quickly replaced with a temporary tower” (NWS State College, PA, 2019).
Sources
E. W. Ferguson, F. P. Ostby & P. W. Leftwich (1987). The Tornado Season of 1985. Retrieved from: https://journals.ametsoc.org/doi/pdf/10.1175/1520-0493%281987%29115%3C1437%3ATTSO%3E2.0.CO%3B2
Pittsburgh Post-Gazette (2005). The day the twisters came. Retrieved from: http://old.post-gazette.com/pg/05149/511826.stm
NWS Weather Prediction Center (2017). North American Surface Analysis: Surface Analysis 12Z Friday May 31, 1985. Retrieved from: https://www.wpc.ncep.noaa.gov/html/sfc2.shtml
National Weather Service Cleveland, Ohio (2019). The Tornado Outbreak of May 31, 1985. Retrieved from: https://www.weather.gov/cle/event_19850531_85outbreak
National Weather Service Cleveland, Ohio (2019). May 31, 1985 Tornado Outbreak: 34th Anniversary. Retrieved from: https://www.weather.gov/ctp/TornadoOutbreak_May311985#Meteorology
M. Leduc, O. Jacobsen and B. Greer (Winter 1986). The “Black Friday” Tornado Outbreak in Ontario [PDF file]. Chinook, 8, 13-18. Retrieved from: cmosarchives.ca/Chinook/ch0801.pdf
N. Sleptzoff & T. Dunkle (2009). 1985 Tornado Outbreak Revisited [PowerPoint presentation]. Retrieved from: https://www.weather.gov/media/cle/Wx_Events/85outbreak/1985%20Tornado%20Final%5B1%5D.pdf
NOAA National Centers for Environmental Information (2019). Storm Events Database. Retrieved from: https://www.ncdc.noaa.gov/stormevents/
NWS State College, Pennsylvania (2019). Atlantic, PA. Retrieved from: https://www.weather.gov/ctp/Atlantic
