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COLORADO SEVERE WEATHER NETWORK

SKYWARN® Trained Amateur Radio Support Team
Providing Ground Truth Under The Radar

Wind & Hail in the Central Rockies & High Plains

Why Wind & Hail Matter Here

The central Rockies and adjacent High Plains are among the most active wind and hail regions in the United States, with frequent strong downslope winds and some of the nation’s highest hail frequencies.[web:19][web:23][web:24] These hazards impact highways, aviation, energy infrastructure, agriculture, and communities from the Front Range foothills eastward across the plains.[web:19][web:23]

A severe thunderstorm is officially defined as one that produces hail one inch in diameter or larger, winds of at least 58 mph (50 kt), and/or a tornado.[web:17][web:19] In this region, many warm‑season severe storms exceed those thresholds, and cool‑season downslope windstorms can produce gusts comparable to or stronger than severe convective winds.[web:23][web:24]

Regional Environment: Central Rockies & High Plains

The high terrain of the Rockies, including the Colorado Front Range, strongly shapes local wind and hail patterns by modifying airflow, moisture transport, and storm initiation.[web:23][web:24] Elevation gradients from mountain ridges above 10,000 feet to plains near 4,000–5,000 feet create sharp changes in temperature, pressure, and stability that can focus both severe thunderstorms and downslope windstorms.[web:24][web:21]

Moisture from the Gulf of Mexico and plains low‑level jets often overruns drier air west of the dryline, while mountain‑valley circulations and upslope events help lift air to its level of free convection.[web:7][web:19] Farther east, the open High Plains favor long storm tracks and organized lines or supercells capable of producing widespread wind damage and large hail.[web:7][web:19]

Hail Formation & Structure

Hail is frozen precipitation composed of solid balls or irregular lumps of ice that form within thunderstorm updrafts in regions of supercooled water.[web:25][web:22] A thunderstorm becomes severe when it produces hail one inch in diameter or larger, roughly the size of a quarter.[web:17][web:25]

Strong updrafts repeatedly loft growing hailstones through layers of supercooled droplets, adding shells of ice and increasing their size until gravity and drag overcome the updraft.[web:25][web:22] In powerful supercells, updraft speeds can exceed 100 mph, allowing hailstones to remain aloft for tens of minutes and reach sizes of 2 to 4 inches or more in diameter.[web:25][web:22]

Why the High Plains Are So Hail‑Prone

Northeastern Colorado and adjacent High Plains counties rank among the most hail‑prone areas in the United States, with averages of six or more hail days per year in some counties.[web:19] The combination of high‑based storms over elevated terrain, strong instability, and deep layer shear favors robust updrafts and repeated hail growth cycles.[web:7][web:25]

Cooler air aloft over the Rockies, underlying high‑elevation warm season boundary layers, and frequent dryline or frontal boundaries all help promote large temperature contrasts that support hail formation.[web:7][web:19] Long fetch across open rangeland and agricultural fields also allows storms to mature without losing access to warm, moist inflow, further increasing hail potential.[web:19][web:25]

Hail Sizes, Speeds & Impacts

Hailstones as small as 0.2 inches are technically hail, but one‑inch stones mark the operational severe threshold due to their ability to damage vehicles, roofs, and crops.[web:25][web:22] Small hail under one inch typically falls at 9–25 mph, while severe hail between one and about 1.75 inches may fall at 25–40 mph.[web:25][web:22]

Large hail between 2 and 4 inches in strong supercells can reach fall speeds of roughly 44–72 mph, and very large stones exceeding 4 inches may exceed 100 mph, especially when driven by strong winds.[web:25][web:22] On the central High Plains, such hail can strip vegetation, shred crops, break windows, and cause significant roof and siding damage across entire communities.[web:19][web:25]

  • Use common objects (pea, marble, quarter, golf ball, baseball) or a ruler to estimate hail diameter when safe.[web:25]
  • Report the largest hail size observed, along with duration and any damage to vehicles, roofs, or crops.[web:17][web:19]

Damaging Winds from Thunderstorms

Severe thunderstorm winds are defined as surface gusts of at least 58 mph (50 kt), though many High Plains storms produce much stronger bursts of straight‑line wind.[web:17][web:19] These winds often originate from strong downdrafts and outflow that spread outward as gust fronts, sometimes forming focused downbursts or long‑track bow echoes.[web:7][web:20]

In organized lines and squall segments, pressure jumps, evaporative cooling in dry mid‑levels, and rear‑inflow jets combine to accelerate air toward the surface and along the line.[web:7][web:20] The open terrain of the High Plains allows these winds to maintain strength over long distances, increasing the risk of widespread tree, line, and structural damage.[web:19][web:23]

Downbursts, Microbursts & Bow Echoes

Downbursts occur when cooled, negatively buoyant air surges downward from a thunderstorm and then spreads out upon reaching the ground, sometimes exceeding 70–80 mph.[web:7][web:20] Microbursts are smaller, intense downbursts that can be especially hazardous to low‑flying aircraft and localized areas of infrastructure.[web:7]

Bow echoes are radar signatures where a convective line bows outward, typically indicating a strong rear‑inflow jet and enhanced straight‑line wind potential near the apex of the bow.[web:7][web:20] Some bowing segments can produce “considerable” or “destructive” wind damage, with updated severe thunderstorm warnings highlighting 70–80 mph or greater wind threats.[web:20]

Non‑Thunderstorm Wind: Downslope & High‑Wind Events

Downslope windstorms along the Colorado Front Range and nearby ranges are common from autumn through spring and can produce gusts from 60 to near 100 mph or higher.[web:23][web:24] These episodes are often associated with strong westerly flow aloft, mountain wave amplification, and stable layers that help transfer high‑momentum air down to the foothills and adjacent plains.[web:24][web:21]

Two primary types of strong downslope winds in this region include warm, dry chinooks and colder events associated with mid‑ and upper‑level trough passages sometimes called boras.[web:24] Locations such as Boulder, the north‑south Front Range foothills, and nearby canyons are especially prone to damaging downslope wind episodes.[web:23][web:24]

Impacts of High‑Wind Events

High‑wind episodes can damage roofs, topple shallow‑rooted trees, overturn high‑profile vehicles, and down power lines across urban corridors and mountain passes.[web:23][web:24] Blowing dust and debris can sharply reduce visibility and create additional hazards on exposed roads and ridgetops.[web:23]

These events often prompt High Wind Watches and Warnings from the National Weather Service, sometimes even in the absence of thunderstorms.[web:23][web:24] Spotters and the public should treat such events with the same seriousness as severe thunderstorm wind threats, avoiding exposed high terrain, ridgelines, and areas prone to falling trees or power lines.[web:23]

Spotter Focus: Wind & Hail in Mountain & Plains Terrain

SKYWARN® spotters in the central Rockies and High Plains play a key role in documenting wind and hail impacts where radar beams are higher above the ground and terrain complicates detection.[web:19][web:23] Clear, accurate reports help forecasters verify severe storms, refine warning polygons, and assess ongoing damage during both convective and downslope wind events.[web:17][web:20]

What to Report for Hail

  • Largest hail size using coins or standard objects, or direct measurement with a ruler or calipers if safe.[web:25]
  • Duration of hail, approximate coverage area, and whether hail is mixed with heavy rain or mainly dry.[web:25][web:19]
  • Damage to vehicles, roofs, windows, crops, or livestock associated with the hail fall.[web:19]

What to Report for Wind

  • Estimated wind speeds (using known thresholds such as large branches breaking or trees uprooted) or instrument readings if properly sited.[web:19]
  • Specific damage: downed trees or power lines, structural damage, overturned semi‑trailers, or blown‑off roofs.[web:19][web:23]
  • Presence of blowing dust, reduced visibility, or lofted debris, especially near canyons and open plains.[web:23]

Terrain‑Aware Safety for Spotters

  • Avoid ridgelines, passes, and exposed east‑facing slopes during downslope wind events where gusts can rapidly exceed 70 mph.[web:23][web:24]
  • Stay out of hail cores whenever possible; large, wind‑driven hail can shatter glass and cause serious injuries.[web:25]
  • Maintain escape routes that avoid low‑water crossings, steep unpaved roads, and heavily forested areas during high winds.[web:19][web:23]

Public Safety & Preparedness

For the general public, the key to wind and hail safety is recognizing warnings, having sturdy shelter available, and avoiding travel in the path of the strongest storms or wind corridors.[web:17][web:23] Vehicles, temporary structures, and exposed outdoor locations are particularly vulnerable to large hail and high winds.[web:19][web:25]

  • Move vehicles into garages or under sturdy shelters when severe hail is forecast or a warning is issued.[web:17][web:25]
  • During severe thunderstorm or high‑wind warnings, stay away from windows and move to interior rooms on the lowest floor.[web:17][web:23]
  • Delay travel on exposed highways and passes when high‑wind warnings mention gusts over 60–70 mph.[web:23]

Additional Learning & Regional Resources

Numerous resources provide deeper background on hail climatology, downslope windstorms, and severe thunderstorm safety in the central Rockies and High Plains.[web:19][web:24] These can supplement local SKYWARN® training and emergency planning efforts in your community.[web:17]