Gateway Arch National Park Weather, Map & Nature Guide

Area: 193 acres
Established: February 22, 2018
Recreation visits: 2,209,028 / yr
State: Missouri
Established as a national park: February 22, 2018
Area: 91 acres (0.37 km²), the smallest national park

Gateway Arch Weather Forecast

Loading the National Weather Service forecast for Gateway Arch…

Seven-day outlook at the park's reference point (38.626, -90.189). Elevation changes everything in the mountains — expect colder, windier and wetter conditions on high ground.

Map of Gateway Arch National Park

The Park

Gateway Arch National Park is the smallest unit to carry the national park title, a 91-acre green space on the St. Louis riverfront. At its center rises Eero Saarinen's stainless-steel arch, 630 ft tall and 630 ft wide, commemorating the westward expansion of the United States and the city's role as a gateway to the West.

The park, redesignated as a national park on February 22, 2018, also includes the Old Courthouse, where the Dred Scott case began. Its natural story is an urban one: an engineered landscape of allées and groves, a riverbank on one of the continent's great flyways, and a monument that must withstand the Mississippi Valley's heat, storms, ice and wind.

Geography

The Arch grounds occupy a strip of downtown St. Louis between the city's business district and the west bank of the Mississippi River, just south of the historic Eads Bridge. Across the river lies Illinois. The Old Courthouse, a few blocks west, is joined to the Arch grounds by a landscaped park over the interstate.

The landscape, designed by Dan Kiley with Saarinen, is built around tree-lined walkways, two reflecting ponds and broad lawns rather than native wild habitat. The park's river location places it beneath the Mississippi Flyway, one of North America's busiest migration routes, so the lights of the Arch are dimmed during peak migration periods.

Landmarks

Gateway ArchArchSaarinen's 630-foot stainless-steel monument, with trams carrying visitors to an observation deck at the top.
Old CourthouseAreaA domed 19th-century courthouse where Dred and Harriet Scott sued for their freedom.

Geology

Beneath St. Louis lie layers of limestone laid down in warm seas during the Mississippian Period. One of those rock units, the St. Louis Limestone, takes its name from the city. The Arch's foundations reach 60 ft down, including 20 ft into bedrock, anchoring the monument to this ancient sea floor.

The Mississippi River shaped the setting. During the Ice Ages, meltwater from continental glaciers far to the north poured down the valley, carrying sediment and building the broad floodplains around St. Louis. Today the river still rises and falls dramatically with the seasons, and the riverfront is designed to flood.

The Arch itself is an engineering landform. Its shape is a weighted catenary, the curve a hanging chain makes, turned upside down so that its weight flows down through its legs. Built from 142 prefabricated sections with a skin of stainless steel, it is designed to sway up to 18 inches in either direction and to withstand winds of up to 150 mph.

Deep time

Mississippian PeriodWarm, shallow seas laid down limestone beneath the St. Louis area.
Pleistocene ice agesGlacial meltwater surged down the Mississippi Valley, shaping the river's floodplains.
February 12, 1963Construction of the Gateway Arch began.
October 28, 1965The final section was placed at the top, completing the Arch.
February 22, 2018Jefferson National Expansion Memorial was redesignated Gateway Arch National Park.

The rocks

St. Louis LimestoneMississippian
A marine limestone named for the city, part of the carbonate bedrock of the region.

Trees, Plants & Ecosystems

Designed urban landscapeArch grounds
Kiley's allées of London planetrees, baldcypress groves, lawns and reflecting ponds, managed largely as monoculture plantings.
Mississippi riverfrontAlong the levee
A dynamic, flood-prone edge on a continental migration corridor used by birds each spring and fall.

Trees

London planetreePlatanus × acerifoliaChosen to replace the park's Rosehill ash trees because it tolerates the grounds' alkaline soils and resists pests; it now lines the walkways.
BaldcypressTaxodium distichumPlanted in circular groves that are part of the historic landscape design.

Wildlife

Mammals

Virginia opossumDidelphis virginianaOne of the adaptable urban mammals NPS notes living on the park grounds.
RaccoonProcyon lotorThrives in the city and forages around the grounds at night.
CoyoteCanis latransAn urban-adapted predator that NPS reports in the park.

Insects & other invertebrates

Emerald ash borerAgrilus planipennisAn invasive beetle that kills nearly all infested ash trees, which led the park to replace its Rosehill ash with London planetrees.

Species totals are the park's certified NPSpecies checklist (occurrence: present).

Climate & When to Visit

St. Louis has a humid continental climate with four distinct seasons. NOAA normals show mean daily temperatures near 29°F in January and about 80°F in July, and summer humidity from the Gulf of Mexico can make the riverfront feel much hotter. Sunshine peaks in summer, when about two-thirds of days are sunny, and dips to under half of days in November.

The Mississippi Valley is a battleground for air masses, so strong thunderstorms, heavy rain and occasional severe weather come in spring and summer, while winter brings cold snaps, sleet and snow. Floods on the river are a recurring feature of the riverfront, most memorably in the Great Flood of 1993.

Spring
Mean temperatures rise from about 45°F in March to 66°F in May, with frequent storms and the season's highest river levels.
Summer
Hot and humid, with a July mean near 80°F and pop-up thunderstorms. Visit the Arch early in the day to avoid peak heat.
Autumn
Pleasant and often sunny in September and October, with cooling mean temperatures from 70°F to 58°F and colorful trees on the grounds.
Winter
Cold and often gray, with a January mean near 29°F and occasional snow and ice.

Weather hazards

Heat and humidity: Summer heat can be oppressive on open lawns and pavement, so bring water and seek shade.
Thunderstorms: Strong storms can develop quickly in spring and summer, so check the forecast before visiting the riverfront.
River flooding: The Mississippi can rise over the riverfront levee area, so heed closures near the water.
Winter ice: Sleet and freezing rain make walkways slick during cold snaps.

Gateway Arch Questions

When is the best time to visit Gateway Arch National Park?

Spring and fall offer the most comfortable weather for exploring the grounds and riverfront. Summer is hot and humid but popular, and the museum and tram ride to the top are open year-round.

How tall is the Gateway Arch?

The Gateway Arch is 630 ft tall and 630 ft wide at its base. It is the tallest human-made monument in the Western Hemisphere.

Does the Gateway Arch sway in the wind?

Yes. The Arch is designed to sway up to 18 inches in either direction and to withstand winds of up to 150 mph, although in normal winds movement is barely perceptible.

What wildlife lives at Gateway Arch National Park?

NPS notes urban-adapted animals such as opossums, raccoons and coyotes on the grounds. The riverfront also lies beneath the Mississippi Flyway, so many migrating birds pass overhead in spring and fall.

Why are the Arch lights turned off during migration?

Bright lights can disorient migrating birds that travel at night along the Mississippi Flyway. Since 2002 the park has turned off the Arch's exterior lights during peak migration periods to help them pass safely.

What trees line the walkways at the Arch?

London planetrees now line the walkways, replacing Rosehill ash trees that were vulnerable to the invasive emerald ash borer. Groves of baldcypress are also part of the historic landscape design.

More parks in the Great Plains & Midwest

← Gates of the Arctic National Park & Preserve Glacier National Park →

Sources: www.nps.gov · www.nps.gov · www.nps.gov · www.nps.gov · en.wikipedia.org · Official NPS site