Accurate hail size reporting drives warnings. The full NWS standard reference list — BB through grapefruit — with warning thresholds (1.00" quarter = severe; 2.75" baseball = destructive). Why "pea" is too vague.
Accurate hail reports drive warnings, climatology, and damage assessment. Spotters mess this up the same way every time — they size hail by produce ("pea", "marble", "grape"). Those words don't mean anything specific. A "pea" can be anywhere from 1/4" (split pea) to 1/2" (snow pea), spanning an entire category in the NWS hail scale. Always report a diameter in inches if you can measure it; otherwise pick from the NWS standard reference list — not a custom one.
These are the only comparison objects the NWS recognizes as consistent. Every Skywarn class teaches them. The key threshold is 1.00" (quarter) — that's the trigger for a Severe Thunderstorm Warning.
NWS warning text reflects the LARGEST reported size. Calling a baseball-sized stone "tennis ball" can be the difference between a destructive-tagged warning (which triggers Wireless Emergency Alerts on every phone in the path) and a routine warning. Calling quarters "marbles" misses the warning threshold entirely.
1. Wait for the storm to leave the area — getting hit by a baseball-sized stone for the sake of a report is bad math. 2. Photograph the largest stone next to a coin, ruler, or known-size reference (CD/DVD trick works well). 3. Report two sizes: "majority quarter, largest golf ball" gives the forecaster both the typical and peak. 4. Note the duration: 30 seconds of marbles vs. 10 minutes of nickels are very different damage profiles. 5. Skip "pea", "grape", "shooter marble", "jawbreaker" — none have standard sizes.
Reference: NWS Spotter Field Guide.
Part of the BloomWX learn library — beginner-friendly explainers covering every surface of the BloomWX weather dashboard. Open BloomWX to see live data for any U.S. county.