by Gerald Mulvey, CCM #571 (Trenton) Northrop Grumman Corporation and Elliot Abrams, CCM #340

1. A Forensic Meteorological Perspective on the American Revolutionary War Battles of Trenton and Princeton byGerald Mulvey, CCM #571 (Trenton)Northrop Grumman CorporationandElliot Abrams, CCM #340 (Princeton)AccuWeather January 21, 2008, Updated Sep 17, 2009 Princeton Trenton

2. Introduction Historical Significance Trenton Princeton • Battle of Trenton Overview • Supporting Data • Synoptic Situation • General Snowfall & Temperature Trends • Weather in the Battle Theater • Battlefield Temperature • Meteorological Impacts • The Official Report • Battle of Princeton Overview • Battlefield Location • Clark House • Battlefield Paintings • Princeton Battlefield • Supporting Data • Battlefield Reports • Thomas Jefferson’s Weather Records • Battlefield Temperature • Battle field Reports What if …… References & Acknowledgements

3. Trenton Princeton Historical Significance • Series of defeats of the revolutionary army • Enlistment ends January 1, 1776 • Position of the British forces • Washington’s goals • Strategic importance of Trenton and Princeton

4. Trenton Battle of Trenton Overview Date & Time 12/25/1776 ~4:00 PM to 12/16/1776 ~9:30 AM Force Summary American: Gen. Washington: 2,400 troops, 18 pieces of artillery – McConkey’s Ferry Brig. Gen. Ewing: 700 troops – Trenton Ferry Col. Cadwalader: 1,800 troops, 2 pieces of artillery – Dunk’s Ferry British (Hessian): Col. Rall: 1,400 troops, 6 pieces of artillery Location Courtesy of the University of Texas Libraries, The University of Texas at Austin http://www.lib.utexas.edu/maps/histus.html#military.html Trenton

5. Trenton Supporting Data(Trenton, NJ) • Sunset 12/25/1776: 4:39 PM Sunrise 12/26/1776: 7:21 AM • Moonrise 12/25/1776: 5:31 PM Moonset 12/26/1776: 8:36 AM Moon phase 12/25/1776 waning gibbous 12/26/1776 waning gibbous 99% of visible disk illuminated 97% of visible disk illuminated • Tide Predictions at Trenton Falls, Trenton, New Jersey December, 1776 • Ground condition - Frozen • Delaware River river ice conditions near Trenton

6. Trenton Princeton Synoptic Situation 12/25/1776 Strong high pressure cell over western New York weakens during the day. Low pressure off the Carolinas rapidly intensifies during the late night hours. 12/26/1776 Rapidly moving intensifying Low tracks NE off shore through the day. Low positioned off the Massachusetts coast moves ENE by the end of the day. 12/27/1776 High pressure re-established over NE U.S. H H L H L L L Avg. winter Gulf Stream location 12:00 LT 12/25/1776 24:00 LT 12/25/1776 12:00 LT 12/26/1776 24:00 LT 12/26/1776

7. Trenton General Snowfall & Temperature Trends Battle of Trenton Snowfall Observations 12/25 – 27/1776 oF Trenton 24" December January Temperature: Philadelphia 2W, 1776 -1777 12" 1 – Trappe, PA: 12 " 2 – Pennroyal, VA: 24 " 3 – Monticello, VA: 22-24" 4 – Salem, NC: 3-4" 5 – Friedberg, NC: 12+" 8 AM 3 PM

8. , ** ** ** , , , * * * . . * * * * * * * Trenton Weather in the Battle Theater March to Trenton starts Battle begins Hessians surrender Withdrawal starts Troops across to Pennsylvania March to the Delaware begins Crossing begins Washington crosses Crossing complete Weather estimates were interpolated in time and estimated to current descriptions. 16:00 18:00 20:00 22:00 24:00 02:00 04:00 06:00 08:00 10:00 12:00 14:00 16:00 , x x x ** * * 12/25/1776 12/26/1776 Storm Intensity: Initial onset 21:00 to 22:00 12/25 First renewal 4:00 12/26 Final surge 7:30 to 8:00 12/26

9. Trenton Battle Temperature • March to the Delaware starts • Crossing the Delaware begins • Crossing completed for main battle group • March to Trenton begins • Forces arrive at Trenton & the battle is opened • Hessians surrender • Withdrawal starts • Delaware re-crossing starts 12/25 12/26

10. Meteorological Impacts • Troop mobility: river crossing and land • Artillery movement: river crossing and land • Observables: visibility & noise • Defensive operations: pickets, patrols & sentries • Offensive operations: munitions, artillery targeting • Anticipated behavior: Hessians & Americans

11. Trenton The Official Report

12. Battle of Princeton Overview Princeton Date 1/3/1777 Force Summary American: Gen. Washington: 4,600 troops, 18 pieces of artillery – British Gen Cornwallis: 1,200 Troops 6 pieces of Artillery Location

13. Princeton

14. Princeton The Clark House. Wounded officers from both sides were treated here. General Hugh Mercer, mortally wounded by seven bayonet stabs, died here nine days after the Battle of Princeton. Mercer County New Jersey is named for him.

15. Battlefield Paintings: on display at the Edge of the Princeton Battlefield Princeton

16. Princeton Barren trees stand silent sentinel at the edge of the Princeton Battlefield as dusk closes in on a wintry evening 18 days short of 231 years after the event.

17. Princeton

18. Princeton A B Exhibit A: This is an example of how news was relayed. The reports may have been reliable, but they were typically at least second hand and hearsay by the time they reached historians Exhibit B: Indicates low (< 20 degrees) lunar declination around this time. Not shown: a lunar eclipse had occurred two weeks earlier

19. Princeton George Washington’s letter to the Continental Congress. Reference to moving baggage to Burlington “soon after dark” (Jan 2, 1777) suggests the formerly muddy roads were already starting to freeze. Was the march timed to take advantage of some moonlight? Moonrise was at 1:20 AM (though only 33% of the lunar face was lit).

20. Princeton When did the march actually begin? Here, one of the participants, Captain Thomas Rodney of Delaware, mentions a time that was two hours later than the one written by George Washington.

21. Princeton Comparison: Jan1 1996- Dec 31, 2008…56.1 degrees F

22. Thomas Jefferson’s Weather Records Trenton Princeton Monticello, VA December 1776 January 1777 On Jan. 1, temperature remained in the low 40s here but soared to 51 degrees F in Philadelphia. This suggests the low pressure area that caused rain at Princeton the night of January 1 had a warm front that moved along and near the coastal plain but whose warm sector did not reach inland to Mt. Vernon because of cold air damming. Adding support to damming: soldiers encountered snow still on the ground from earlier storms when they reached northwest New Jersey on Jan 6, 1777.

23. Princeton Wind Dir. NW Based on records by Phineas Pemberton, 2 miles west of Philadelphia

24. Princeton Sgt R____ as reported in Pennsylvania Magazine of History, XX (1896): “The horses attached to our cannon were without shoes, and when passing over the ice, they would slide in every direction and could advance only by the assistance of our soldiers. Our men, too, were without shoes or other comfortable clothing; and as traces of our march toward Princeton, the ground was literally marked with the blood of the soldiers’ feet.” From Rebels and Redcoats: a scene from the Princeton battlefield. “At one moment, thirty yards from the enemy, he (George Washington) sat astride his white horse at the head of his troops, such a vulnerable target that young John Fitzgerald, his aide, covered his face, because he could not bear to see the general fall. But, enveloped by smoke, the General escaped harm.” The dawn had been frosty, and near the center of a high pressure area, the wind was weak. A near surface inversion likely prevented the vertical dispersion of smoke, and the light winds allowed it to remain concentrated on the battlefield. At the same scene on the day before post-frontal northwest winds would have cleared the smoke more rapidly, making such behavior much more risky.

25. Princeton General Washington originally wanted to march to (New) Brunswick ahead of Cornwallis. Much equipment and approximately $2 million dollars was being stored there, and a victory might have caused the English government to abandon their war effort. This is speculation.

26. Princeton General Washington explains his move to Morristown, NJ after the Battle of Princeton

27. Princeton General Washington explains efforts to keep ahead of the British, who were trying to race northeastward from Trenton after having been fooled the night before.

28. Trenton Princeton In a period of 10 days, the Revolution had gone from repulsed to revitalized. In two stunning victories, General Washington brought new respect to the American effort. Washington came to realize that it was not necessary to fight his better equipped foe head on. Instead, he needed to keep his forces in play long enough to frustrate the British fighters and erode support for this expensive war back in England. If the Christmas night storm had not occurred, the Hessians might have been more alert to the possibility of attack. If the Delaware had been choked with ice at Washington’s Crossing, the forces could not have crossed the river. If the snow and sleet had not been propelled by north winds behind a soon to depart East Coast storm, the Hessians would have been able to clearly see their attackers. If it had not rained the night of January 1, Cornwallis’ forces would have made more progress toward Trenton and might have been able to rout the rebels before dark. If George Washington had not been weather savvy from his Virginia farming experience, he would not have recognized the opportunity presented by the rapid cooling on the afternoon and evening of January 2.

29. Princeton Trenton In England, a similar northwesterly flow would not have prompted such confidence in a nighttime freeze. The English soldiers were less likely to have recognized this factor and taken action to avoid its consequences. If a near surface inversion and light winds had not been present to make the smoke remain over the battlefield at Princeton, General Washington might have been an easy target for the nearby British soldiers. If Washington had not recognized the likelihood of a thaw on the afternoon of January 3, 1777, he would not have moved so quickly to put distance between his northbound army and Cornwallis’ angry pursuit following the Battle of Princeton.

30. References Ambrose, K., D. Henry and A. Weiss, (2002): Washington Weather: The Weather Sourcebook for the D.C. Area, Historical Enterprise, VA  Chadwick, B, (2005): George Washington’s War, Sourcebooks, Inc., Naperville, IL Dwyer, W. (1983): The Day is Ours! November 1776 - January 1777: An Inside View of the Battles of Trenton and Princeton, Rutgers University Press, New Brunswick, NJ  Freeman, D., (1968): Washington, Simon & Schuster, NY Fisher, D., (2004): Washington’s Crossing, Oxford University Press, NY Gyory, J., A. Mariano, and E. Ryan: The Gulf Stream: Ocean Surface Currents http://oceancurrents.rsmas.miami.edu/atlantic/gulf-stream.html Ketchum, R.,(1973): The Winter Soldiers, Henry Holt & Company, NY Kocin, P. and L. Uccellini (2004): Northeast Snowstorms, vol. 1, American Meteorological Society, Boston, MA  Ludlum, D., (1966): Early American Winters 1604 – 1820, American Meteorological Society, Boston, MA  Ludlum, D., (1998): The Weather of Independence, Weatherwise, Nov/Dec, Heldref Publications McCullough, D (2005): 1776, Simon and Schuster, NY Savas, T and J. Dameron, (2006): A Guide to the Battles of the American Revolution, Savas Beatie, New York, NY  Scheer, G, and Rankin, H.J. (1957): Rebels and Redcoats, Da Capo Press, Chapel Hill, NC Solomon, S., J. Daniel, and D. Druckenbrod, (2007): Revolutionary Minds, American Scientist, vol. 96, no. 5, pp. 430- 437   Stryker, W., (1898): The Battles of Trenton and Princeton, The Riverside Press, NJ (reprinted 2001, The Old Barracks Association, NJ)  Symond, C., (1986): A Battlefield Atlas of the American Revolution, The Nautical & Aviation Publishing Company of America, Mount Pleasant, SC  Winters, H. G. Galloway, W. Reynolds and D. Rhyne, (1998): Battling the Elements: Weather and Terrain in the Conduct of War, Johns Hopkins University Press, Baltimore, MD Wood, W., (1990): Battles of the Revolutionary War 1775-1781, Da Capo Press, Chapel Hill, NC  Acknowledgements: The authors would like thank Todd Ehret at NOAA, National Ocean Service Center for Operational Oceanographic Products and Services, Tide and Tidal Current Predictions, for calculating the tidal timing and heights for the battle of Trenton. They would like also to thank Eric Johnson at the Jefferson Library, Monticello, for research on the observations of Thomas Jefferson. Notes: Astronomical data was provided by the U.S. Naval Observatory, Washington D.C Title page flag images are from the FOTW Flags Of The World website at http://flagspot.net/flags Princeton Trenton