Sleet, Hail, or Graupel: What Falls on SoCal Peaks

Sleet, hail, and graupel are all frozen precipitation, but they take three different paths through a storm cloud and land very differently. Sleet is a snowflake that melted and refroze into a small, hard, clear ice pellet. Hail is a stone built in repeated passes through a thunderstorm updraft, sometimes with an onion-like layered structure. Graupel is a snow crystal that picked up a soft, opaque coating of frozen droplets on the way down. In Southern California's mountains, above Wrightwood and Big Bear Lake, graupel is by far the most common of the three, with hail showing up in isolated thunderstorms and true sleet remaining unusual.

What is the difference between sleet, hail, and graupel?

Sleet, hail, and graupel are three distinct forms of ice that share a category, frozen precipitation, but not a formation process. Sleet consists of small, hard, translucent ice pellets, usually under a quarter inch across, that started as snow, melted partway down through a warm layer of air, and refroze into solid ice before reaching the ground. Hail is a harder, denser stone that forms exclusively inside thunderstorms, built in layers as it cycles through a powerful updraft, and can range from pea size to well over golf ball size in severe storms. Graupel, sometimes called soft hail or snow pellets, is a soft, crumbly, opaque white pellet formed when a snow crystal collects a coating of frozen liquid droplets as it falls through a cloud.

One naming note worth flagging for anyone reading a British or Canadian weather source alongside a U.S. one: American meteorologists, including the National Weather Service Los Angeles/Oxnard office, use "sleet" to mean the frozen ice pellets described above. In the United Kingdom and some other English-speaking countries, "sleet" instead commonly refers to a mix of rain and wet snow falling together, a genuinely different phenomenon. This article uses the American definition throughout, matching NWS terminology, since it is the standard for every Southern California forecast product.

How does each one form?

Each of the three follows its own vertical path through the atmosphere, and that path is the real distinguishing feature, not just the size of the resulting ice. Sleet requires a specific layered temperature profile: snow forms high in a cold cloud, falls into a layer of air that sits above freezing and partially or fully melts it, then drops into a subfreezing layer near the surface that refreezes the resulting droplet into a solid ice pellet before it lands. That refreezing layer has to be deep enough and cold enough to do the job; too shallow, and the result is freezing rain instead, since the droplet never fully refreezes before hitting the ground.

Hail takes an entirely different route. It forms only inside thunderstorms strong enough to generate a sustained updraft, sometimes tens of miles per hour, that carries a small ice embryo up into the supercooled portion of the cloud, where it collects a new layer of ice. Gravity and the storm's internal air currents send it back down and up again, sometimes several times, with each pass adding another layer, which is why a hailstone cut in half often reveals visible rings similar to an onion or a tree trunk. The stone finally falls once it grows heavy enough that the updraft can no longer support it.

Graupel forms through a gentler, single-pass process called riming. A snow crystal falling through a cloud region containing supercooled liquid droplets, water that remains liquid below 32°F because it lacks a surface to freeze onto, collects those droplets on its surface as they freeze instantly on contact. Enough droplets accumulate that the crystal's original branched shape disappears under a rounded, opaque coating, producing the soft white pellet meteorologists call graupel. Unlike hail, graupel does not require a thunderstorm updraft, just a cold cloud with both snow crystals and supercooled droplets present together, a combination common in ordinary post-frontal mountain snow showers.

How can you identify what is falling?

The fastest field test is hardness and sound. Sleet is hard, clear to translucent ice that produces an audible tap or click when it hits a windshield, umbrella, or hard pavement, and it tends to bounce slightly on contact rather than splatting or crushing. Hail shares that hardness but is typically larger and, critically, only falls alongside an active thunderstorm, so the presence of thunder, lightning, or heavy convective rain nearby is a strong confirming clue. Graupel behaves almost the opposite way: it is soft enough to crush between two fingers, looks like tiny white foam balls or mini styrofoam pellets rather than clear ice, and commonly falls from a shower without any thunder at all.

Opacity and layering are the next-best clues, especially for photos or video after the fact. Sleet is clear or lightly frosted and does not show internal banding. Hail, when cut open or broken, frequently shows onion-like internal layers from its repeated updraft cycles, a telltale sign no other frozen precipitation shares. Graupel is opaque all the way through with a rough, granular surface and no internal structure. It is worth being honest that marginal cases exist. A brief burst of small, soft pellets from a weakening shower can be genuinely hard to sort from a photo alone, and even trained observers sometimes rely on context, storm type, elevation, and season, more than the ice itself to make the call.

Which is most likely in Southern California?

Graupel is the frozen precipitation Southern Californians are most likely to encounter, particularly in the San Gabriel and San Bernardino Mountains during cold, showery weather behind a winter cold front. The region's typical cold-season storm pattern, a Pacific frontal passage followed by cold, unstable post-frontal showers, is close to ideal for riming: cold cloud tops with plenty of supercooled water mixed with snow crystals. Towns at elevation, including Big Bear Lake and Wrightwood, see graupel showers several times in a typical winter, sometimes whitening the ground briefly before melting.

Hail is less frequent but far from rare, and it is not confined to winter. Southern California's summer monsoon season can produce isolated, sometimes intense thunderstorm cells over the mountains and deserts, and any of those cells can drop small hail. Stronger winter storms with enough instability can also generate hail-producing cells, and when that happens, it is not limited to the mountains; hail from an isolated cell can reach the Los Angeles Basin itself, including areas near Pasadena and Downtown Los Angeles, though basin hail events are typically brief and localized to a single storm cell's path.

True sleet is the least common of the three in this region. It requires a fairly specific layered temperature setup, warm enough aloft to melt a falling snowflake, cold enough near the surface to refreeze it, that Southern California storms do not reliably produce. When forecasters or residents report something that looks like sleet locally, it is worth checking whether the event was independently confirmed, since graupel and small hail are both far more common and easy to mistake for it from a distance. Local event reports should be weighed against official NWS confirmation rather than assumed from a single video or photo.

How are these different from snow and freezing rain?

Snow never melts on its way down, so it keeps its original branched crystal structure and falls as light, low-density flakes rather than dense pellets. That is the core difference between snow and all three frozen-precipitation types described above: sleet is melted and refrozen snow, graupel is snow with a rimed coating, and hail is built from scratch inside a thunderstorm, but ordinary snow is none of those things. For a full look at where and how often real snow reaches the region, including the elevations where it becomes reliable, see WeatherEscape's does it snow in Los Angeles guide.

Freezing rain sits at the opposite extreme from sleet on the same temperature-profile spectrum. Both start as snow that melts in a warm layer aloft, but freezing rain falls through a surface layer that is cold but too shallow, or not quite cold enough, to refreeze the droplet before impact. The result stays liquid until the moment it touches a cold road, branch, or power line, where it freezes on contact into a thin, often nearly invisible glaze of ice. Sleet, by contrast, is already a solid pellet by the time it reaches the ground, so it accumulates as loose, granular ice rather than a bonded glaze.

Freezing rain is uncommon in Southern California for the same reason true sleet is: the region's storms rarely stack the precise, shallow refreezing layer that either one needs. Readers comparing the season's broader storm pattern, including how El Niño and La Niña winters shift these odds, can see El Niño vs. La Niña: what's the difference for a SoCal winter for more on year-to-year variability.

When do they create a road hazard?

All three can turn a mountain road hazardous within minutes, but they do it in slightly different ways. Graupel and small hail both fall fast enough during an active shower or cell to whiten a road surface in a short burst, and because both are round and loose rather than bonded to the pavement, they reduce tire traction similarly to marbles scattered across the lane.

Sleet behaves the same way once it accumulates, adding a layer of hard, granular ice that is especially dangerous on bridges and overpasses, which cool faster than the surrounding roadway and ice over first. Any of the three can catch a driver off guard because the parent shower or cell is often short-lived, meaning a road that was dry ten minutes earlier can suddenly turn slick.

Because these events change quickly and locally, this page intentionally does not try to forecast current road conditions. Check the point forecast and any active winter weather or severe thunderstorm advisories from the NWS Los Angeles/Oxnard office or the NWS San Diego office depending on your route, and confirm chain controls and closures on routes like Angeles Crest Highway and State Route 18 through Caltrans QuickMap before heading into the mountains. The NWS winter weather safety guidance covers driving technique and precautions for anyone unfamiliar with icy mountain roads.

The short version: reach for "graupel" first if you see small white ice pellets falling in the San Gabriel or San Bernardino Mountains outside of a thunderstorm, reach for "hail" if thunder is involved, and treat a genuine sleet report as the rarest of the three, worth double-checking against an official source before repeating it. None of that changes what you should actually do before a mountain drive: check the current temperature, precipitation type, and any active advisory on WeatherEscape's Los Angeles forecast pages, and confirm road status before you climb toward Big Bear Lake or Wrightwood during a cold storm.