Sierra Nevada future radar for Truckee, Donner Pass and Lake Tahoe. Five hours of NEXRAD, our own storm-motion projection, the HRRR and GFS models to 48 hours, National Weather Service storm cells with arrival times, and a score on every load.
One live tracker. Drag the timeline from five hours ago to 48 hours out, or press play. The map follows the location set on the weather platform and opens on Truckee.
Convective Available Potential Energy measures the atmosphere's stored energy for thunderstorm development. Higher CAPE values mean stronger updrafts and more explosive storm potential.
Probability of thunderstorm activity near Truckee/Donner Pass based on current atmospheric conditions.
Calculating thunderstorm probability...
Current wind data for the Truckee/Donner Pass corridor.
Extended forecast covering precipitation probability, expected amounts, snow levels, and wind speeds across the Sierra crest.
Most radar pages show you the last hour and stop. This one starts with the raw National Weather Service NEXRAD composite, reads it the way a meteorologist does, and tells you where the rain and snow are going next. It was built in Truckee for the excavation crews who have to make a call at dawn, and it is free for anyone who works or plays outside in the Sierra.
The tracker pulls the national radar composite for the last five hours, converts every pixel back to reflectivity, and animates it. You see the actual returns, not a smoothed picture.
It measures how every storm moved over the last 20 minutes, checks that against the steering wind about 10,000 feet up, and carries the storms forward. Every load grades that projection against the radar that actually arrived; at 30 and 60 minutes it runs about 9 to 12 percent better than assuming storms stay put.
As the projection ages, the high-resolution HRRR and the American GFS take over, out to 48 hours. The point where the hand-off happens is learned from the tracker's own verified runs, not guessed.
National Weather Service storm cell tracks are drawn with each cell's closest approach and estimated arrival at your location, so a crew knows whether a cell is coming to them or passing by.
Every load projects from an older scan and scores that projection against the radar that actually arrived 30 and 60 minutes later. The scores are published on the Accuracy tab, and the tracker only claims skill out to the lead that has verified.
The tracker is additional guidance. National Weather Service warnings and Sierra Avalanche Center forecasts always take priority, and the tracker never tells you a place is safe.
The Storm Tracker is the platform's public safety tool, and it keeps getting stronger. In the works: a feed health monitor that shows when any radar or model feed is running late, an alert service that passes through official warnings and adds ground lightning within 10 miles and inbound storm cells, arrival windows with probabilities instead of a single time, local stations folded into the projection so it can tell whether a cell is strengthening or falling apart, a winter mode that reads precipitation type and rate straight from the multi-radar mosaic, flash flood guidance from the National Weather Service hydrology products, and Storm Loading for the Tahoe ranges shown alongside the Sierra Avalanche Center forecast. Every piece ships only after it verifies.
The Sierra Nevada is one of the most meteorologically dynamic mountain ranges on the planet. Stretching over 400 miles along California's eastern spine, the range intercepts moisture-laden Pacific storm systems and forces them skyward in a process called orographic lift. As moist air rises along the western slopes, it cools, condenses, and releases enormous volumes of precipitation. This single mechanism is responsible for the Sierra's reputation as one of the snowiest mountain ranges in the world, regularly burying passes and summit stations under 30 to 50 feet of cumulative snowfall each winter.
Modern storm forecasting in the Sierra relies on ensemble modeling, where multiple weather models run simultaneously to produce a probability-weighted forecast. Our weather platform blends 8 global models (ECMWF IFS, ECMWF AIFS, GFS, ICON, JMA, GEM, UKMO and CMA), with the HRRR layered over the first 18 hours. Several of those models stop around day 7 to 11, so the later days lean on ECMWF, ECMWF AIFS and GFS. By comparing model agreement and divergence, we identify high-confidence storm windows days before they arrive. When 6 or more models converge on a precipitation event, confidence is high. When they diverge, we flag uncertainty so you can plan accordingly.
Donner Pass sits at 7,056 feet along the Sierra crest and serves as the primary weather checkpoint for storms crossing into the Tahoe Basin and points east. Interstate 80 crosses the summit here, making it the most heavily traveled trans-Sierra corridor and the most weather-sensitive. Storms that stall over Donner Pass can dump 3 to 5 feet of snow in 24 hours, closing the highway and stranding travelers. The pass also marks a critical elevation threshold: storms with snow levels above 7,000 feet will deliver rain at the summit, while those below 6,000 feet produce the heaviest accumulations. Monitoring Donner Pass conditions is essential for anyone working, traveling, or recreating in the northern Sierra.
The most powerful storms to hit the Sierra are atmospheric rivers, narrow corridors of concentrated moisture that can stretch from the tropics to Northern California. When an atmospheric river makes landfall aimed at the Sierra, the results are staggering. Integrated water vapor transport values above 500 kg/m/s deliver multi-day precipitation events capable of producing 10 or more inches of liquid equivalent. The "Pineapple Express" variant, originating near Hawaii, brings exceptionally warm, moisture-rich air that can push snow levels to 8,000 feet or higher before cold air wraps in behind the front. These events produce the Sierra's most extreme flooding and avalanche conditions.
The Sierra Nevada averages 300 to 500 inches of snow annually at elevations above 7,000 feet. Donner Summit, Blue Canyon, and the Lake Tahoe rim consistently rank among the snowiest locations in North America. The winter of 2022-2023 delivered over 700 inches at some Sierra stations, burying structures and breaking modern records. Individual storms have dumped 5 to 10 feet in a single 48-hour window. The orographic enhancement factor means the Sierra receives 3 to 5 times the precipitation of the Sacramento Valley floor just 60 miles to the west.
The Sierra experiences two distinct storm regimes. Winter storms (November through April) are synoptic-scale Pacific systems driven by the jet stream. They bring sustained precipitation, high winds, and heavy snow accumulation over days. These are the storms that close passes and build the snowpack that California depends on for water supply. Summer thunderstorms (June through September) are an entirely different animal. Driven by monsoonal moisture from the Gulf of California and daytime convective heating, these storms build rapidly over the Sierra crest in the afternoon. CAPE values spike, cumulus towers explode to 40,000 feet, and isolated cells produce intense lightning, hail, and localized downpours. Summer storms are the primary wildfire ignition source in the Sierra, with dry lightning strikes starting hundreds of fires each season. Our crew weather dashboard tracks both regimes to keep field crews informed and safe.
Once Pacific moisture crosses the Sierra crest, it descends rapidly into the rain shadow of the eastern slope. Annual precipitation drops from 60+ inches on the western side to under 10 inches in the Owens Valley and Great Basin. This dramatic gradient means storms that deliver heavy snow to Donner Pass may produce nothing at all 30 miles to the east. Understanding this asymmetry is critical for anyone operating on both sides of the range, and it's why granular, location-specific forecasting matters more in the Sierra than almost anywhere else in the country.
Complete 8-model ensemble forecast, hourly breakdowns, and multi-day outlook for Truckee and the northern Sierra.
View Platform →Construction-focused weather dashboard built for field crews. Heat index, wind chill, lightning alerts, and shift-by-shift forecasts.
View Crew Weather →Current conditions, the verified forecast, wildfire cameras and NWS alerts for Truckee, CA at 5,817 feet.
View Truckee Weather →The platform grades every forecast against the Truckee airport station and publishes the errors, model by model, lead by lead.
See the scores →Rain gear, cold weather equipment, and storm preparation essentials. Tested and selected for Sierra conditions.
Browse Gear →The Kerr Storm Tracker is errolkerr.com's own future radar for the Sierra Nevada. It reads the raw NEXRAD radar composite for the last five hours, measures how every storm has been moving, and carries that motion forward. As the projection ages it hands off to the HRRR and GFS forecast models, out to 48 hours, and the ECMWF model carries the picture to 10 days. National Weather Service storm cells are drawn with their closest approach and arrival time for your location.
The timeline runs from five hours in the past to 48 hours ahead. The tracker's own motion projection leads first; each load sets the handoff by grading it against the radar that arrived (at 30 and 60 minutes it runs about 9 to 12 percent better than assuming storms stay put), then the HRRR and GFS models take over. A separate 10 day view uses the ECMWF model through Windy. Only the leads that have verified are presented as skilled.
Every load grades itself. The tracker projects from an older radar scan, compares the projection with the radar that actually arrived 30 and 60 minutes later, and scores the hit rate at 20 and 35 dBZ against simply assuming the storm stayed put. Those scores, and the learned hand-off between the tracker and the models, are published on the Accuracy tab. Official NWS warnings always take priority over anything the tracker shows.
Yes. The map opens on Truckee, California and covers Donner Pass, Lake Tahoe, Reno and the northern Sierra. The weather platform follows the location you set, and the tracker follows the platform, so a crew can point it at any job site in the United States that the NEXRAD network covers.
The Sierra Nevada has two storm seasons. Winter storm season runs November through April, delivering Pacific frontal systems and atmospheric rivers that produce the bulk of annual snowfall. Summer thunderstorm season runs June through September, when monsoon moisture and afternoon heating build storms over the crest.
The Sierra Nevada averages 300 to 500 inches of snow annually at higher elevations. Donner Summit, at 7,056 feet, averages around 400 inches per year. During exceptional atmospheric river events, individual storms can deliver 5 to 10 feet of snow in a few days.