Saint Patrick's Day Flood of March 1936 Part 1: Meteorological Setup
Saint Patrick's Day Flood of March 1936 Part 1: Meteorological Setup
Cold & Snowy Winter
The winter was brutal and it started early for parts of the state. Over a foot of snow fell in northeastern Pennsylvania during November 1935. 12.9" fell in Scranton, ranking as the 5th snowiest November on record. December 1935 was cold statewide with heavy snow especially at the end of the month. Portions of northwestern Pennsylvania and Laurel Highlands measured over 30" of snow for the month.
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| Chart detailing the temperature and precipitation for Pennsylvania compared to average for November 1935 to March 1936. |
January was the coldest January in 16 years for the state. January was slightly wetter than average and very snowy with little thaw. The cold continued with February ranking as the 2nd coldest February in 30 years. Precipitation was below average, however snowfall was above average. The first 3 weeks of February were cold with some of the coldest locations in the state recording low temperatures below zero on more than half of the days during the month.
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| Departure from average snowfall for the winter of 1935-1936. Source. |
Pittsburgh measured a total of 20.4" of snow in December and another 20.9" in January ranking as the 5th snowiest December/January on record. Overall the winter of 1935-1936 ranks as the 6th snowiest winter on record for the Steel City. Bradford recorded 32.4" and Erie measured a total of 22.7" in December 1935. Altoona, Harrisburg, Scranton all picked up over two feet in January 1936. While February was not as snowy, most locations still received 10"+.
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| Snowfall totals for the winter season of 1935-1936 through March 9, 1936. |
The winter months of December 1935 through February 1936 ranks as the 5th coldest on record for the state with precipitation near average. The highest snow totals for the season through March 9th surpassed 80" in higher elevations and lake effect snow belts. For the entire winter snow totals were 10 to 30+ inches above average. Areas near Lake Erie saw the larget deficit of more than 10 inches below average. Snow depths of over 3 feet were observed in many locations throughout the winter.
Late Winter Thaw & Ice Jams
A thaw in late February started to break the ice up and melted some of the snow. The weather observer in Williamsport noted ice thickness of 17 inches on March 2nd. Some ice was likely more than 20 inches thick. Much of the snow in the valley locations had melted. It is estimated that about 1" of liquid melted from the snow during this period
Ice jams caused the Juniata River to flood in Newport with a crest of 24.51 feet on March 6th (8th highest crest). Ice jams caused havoc on the 7th near Amity Hall and Clarks Ferry near where the Juniata River reaches the Susquehanna River. Here dynamite was used to create a channel to divert the water around the jam to relax the water levels.
The ice jams continued down the Susquehanna to Harrisburg through the 8th. Cottages in Dauphin and Summerdale were heavily damaged and water covered the highways. Operators at the Safe Harbor Dam and Holtwood Dam had to deal with large chunks of ice but were able to manage the threat without damage. Dynamite was used to break up ice jams that formed on the Stonycreek River in Johnstown.
Snow depths of 24" to 36"+ were common at times throughout the winter. Before the first storm the snowpack held a liquid equivalent of 2" to 4" with higher amounts in northern Pennsylvania. Some estimates suggest that on March 9th some isolated spots the snowpack may have held up to 10" of liquid.
Multiple Rain Events
The first flood event of the month consisted of two storm systems that brought precipitation to the state from March 9th to 13th. The heaviest precipitation totals during this period were near Williamsport with much of eastern Pennsylvania recording over 2 inches. Snow melt added an additional 1"-2" of liquid on top of the rain. Some of the precipitation fell as snow on the 12th and 13th (Friday the 13th) with a general 1"-4" in spots.
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| Map of precipitation totals from March 9, 1936 to March 14, 1936. |
For some locations the flooding on the 11-12 was higher than 17-18. The weather observer in Pine Grove (Schuylkill County) noted that there was flooding on the 11th and 12th but water levels were not above flood stage on the 17th and 18th. The Susquehanna River in Harrisburg crested at 20.52 feet on the 13th which ranks as the 13th highest crest. This was also the highest crest in 42 years. River height observations in Harrisburg have been kept since 1874.
Following the first storm water levels while still high but were below flood stage.
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| Map of precipitation totals from March 16, 1936 to March 19, 1936. |
The second and biggest flood event began on the afternoon of the 16th with a low moving northward out of the Carolinas bringing intermittent precipitation falling through the afternoon of the 19th. The heaviest precipitation fell from around noon on the 17th to noon on the 18th. The axis of heaviest rain was further west compared to the first storm. High temperatures on the 17th ranged from the low 30s in the northwest to the upper 60s in the southeast. Snow fell in the west while many locations in eastern Pennsylvania reported thunderstorms on the 16th & 17th. Hail was reported in Pottsville.
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| Chart of precipitation totals from March 16, 1936 to March 18, 1936. |
The highest amounts- over 6 inches- and highest rainfall rates were observed in areas along the Allegheny Front and in the Pocono Mountains. Much of this fell in a 12 hour period. These locations were also the same locations that had the deepest snowpack. This is also an area that features headwaters of both the Ohio and Susquehanna River Basins.
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Heavy snow fell in northwest Pennsylvania with a zone of freezing rain, too. Trees and power lines were taken down by ice in Kane and Wellsboro. Roads were ice covered in Saint Marys. Around noon on the 17th temperatures in Pittsburgh fell from a high of 37° and rain changed to snow. Temperatures rebounded on the 18th to the low 40s.
The snow caused 6 foot drifts in Erie with abandoned cars stranded in the streets. Cars were also abandoned on streets of Franklin where 12" fell, the heaviest snowfall there since 1900. 18" in Greenville caused businesses to close, bus routes cancelled, and train schedules disrupted. Drifting snow was also reported in Meadville and New Castle. Rural areas were isolated. In Clarion snow & sleet fell and high winds brought down trees and telephone poles.
It is important to note that with the snow falling in the upper basin of the Allegheny watershed, water levels were not as high downstream had the precipitation fallen as rain instead. The record crest at Pittsburgh would have been even higher!
Following the Saint Patrick's Day Flood temperatures dropped with snow falling across western Pennsylvania on the 21st. Totals were generally 3" to 6" with the highest amounts reaching 10". The weather observer in Clairton noted that the rain started around midnight on the 20th-21st which changed to snow with lightning and thunder at 4:30am. The snow was a heavy wet snow which weighed down trees and shrubs.
Flood Summary
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| Map of river crest rankings from the floods of March 1936. |
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| Map showing the year of the record stream/river crest across Pennsylvania. Record crests from March 1936 are highlighted. |
The Ohio River in Pittsburgh was in flood stage February 27-28, March 12-13 , March 17-21, and March 25-29 with crests of 29.20' on February 28th, 25.80' on March 13th, 46.00' on the 18th, and 30.60' on the 26th. All four crests rank in the top 30 crests on record.
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| Chart showing the water levels along the Ohio River from Pittsburgh, PA, to Cairo, IL, during March and April 1936. Source. |
The crest of the Ohio River did not reach Cairo, Illinois, until April 16th. The river there was in flood stage for an entire month. The weather in Pennsylvania turned drier and much warmer by the end of March with temperatures reaching the 70s for much of the commonwealth.
Wrapping Up
The Saint Patrick's Day Flood resulted in the passing of the Flood Control Act in 1938. This prompted many flood control projects across the state that would reduce the impact of future flood events, although many records would later be broken. Agnes in 1972 is the most notable flood since these mitigation measures were put into place. This storm broke many records especially in the Susquehanna River Basin. In Pittsburgh, however, if not for the flood control efforts it is believed that water levels during Agnes would have surpassed the 1936 record by 2 feet. Instead water levels peaked 10 feet below the record.
Stay tuned for Part 2 where I dive into the impacts of the storm which will be posted later this week. Remember to always look up!
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