However, they usually are weak by the time they reach Washington, D.C., partly due to the city's inland location. Flooding of the Potomac River, however, caused by a combination of high tide, storm surge, and runoff, has been known to cause extensive property damage in the Georgetown neighborhood of the city. Precipitation occurs throughout the year. The highest recorded temperature was on August 6, 1918, and on July 20, 1930. The lowest recorded temperature was on February 11, 1899, right before the Great Blizzard of 1899. During a typical year, the city averages about 37 days at or above and 64 nights at or below the freezing mark (). On average, the first day with a minimum at or below freezing is November 18 and the last day is March 27. Cityscape Washington, D.C. was a planned city, and many of the District's street grids were developed in that initial plan. In 1791, President George Washington commissioned Pierre (Peter) Charles L'Enfant, a French-born architect and city planner, to design the new capital, and enlisted Scottish surveyor Alexander Ralston to help lay out the city plan. The L'Enfant Plan featured broad streets and avenues radiating out from rectangles, providing room for open space and landscaping. L'Enfant based his design on plans of other major world cities, including Paris, Amsterdam, Karlsruhe, and Milan that Thomas Jefferson had sent to him. L'Enfant's design also envisioned a garden-lined grand avenue approximately in length and wide in area that is now the National Mall. In March 1792, however, President Washington dismissed L'Enfant due to conflicts with the three commissioners appointed to supervise the capital's construction. Andrew Ellicott, who worked with L'Enfant in surveying the city, was then tasked with completing its design. Though Ellicott revised the original L'Enfant plans, including changing some street patterns, L'Enfant is still credited with the city's overall design. By the early 20th century, however, L'Enfant's vision of a grand national capital was marred by slums and randomly placed buildings in the city, including a railroad station on the National Mall. Congress formed a special committee charged with beautifying Washington's ceremonial core. What became known as the McMillan Plan was finalized in 1901 and included relandscaping the Capitol grounds and the National Mall, clearing slums, and establishing a new citywide park system. The plan is thought to have largely preserved L'Enfant's intended design for the city. By law, the skyline of