Seeing the northern lights from the lower 48 states

SWPC's tips page describes the aurora at four Kp bands. At Kp 0 to 2 it stays far north and dim. At 3 to 5 it moves away from the poles and brightens. At 6 to 7 it becomes bright and active, and SWPC says it might be possible to see it from the northern edge of the United States. At 8 to 9, aurora may be seen directly overhead from the northern states.

The NOAA storm scale gives place names for each level. G1 (Kp 5) is commonly visible at high latitudes, with northern Michigan and Maine as SWPC's examples. G2 (Kp 6) has been seen as low as New York and Idaho, typically 55 degrees geomagnetic. G3 (Kp 7) reaches Illinois and Oregon, typically 50 degrees. G4 reaches Alabama and northern California, and G5 Florida and southern Texas.

Glow features five towns in the lower 48 and two in Alaska. The table converts each to dipole latitude and applies both SWPC rules: the Kp at which the oval's average edge reaches the town, and the first G level whose typical latitude covers it.

Duluth ranks highest of the five at 55.4 degrees, just above the G2 line of 55. Minneapolis at 53.5 and Seattle at 53.0 sit about 2 degrees lower, followed by Portland, Maine at 52.9 and Buffalo at 52.0. All four fall between the G2 and G3 lines, so G3 is the first level whose typical latitude reaches them.

The edge rule asks more. Duluth needs Kp 6 for the oval's average edge to sit overhead, and Buffalo needs Kp 7. You do not need the edge overhead to see aurora, though. SWPC's 1000 km viewing distance is about 9 degrees of latitude, so a Kp 5 edge at 56 degrees can already sit within range of every town in the table.

SWPC publishes average frequencies per 11-year solar cycle. G1 storms come about 1700 times per cycle, on 900 days. G2 comes 600 times on 360 days. G3 comes 200 times on 130 days. G4 comes 100 times on 60 days. G5 comes 4 times on 4 days.

Divided over 11 years, G3 averages about 12 storm days a year and G2 about 33. These are averages over a whole cycle, so any single year can run well above or below them. And a storm day in daylight, under cloud or near a full moon shows little from the ground. The storm levels hub breaks down each level, and G3 strong storms covers the level that reaches most of these towns.

• Drive away from city light and find a low, open northern horizon. SWPC's first tip is to get away from city lights.
• Watch SWPC alerts for Kp 6 and up, then check the live oval map and southern edge once it is dark.
• Read NWS cloud for your spot and a few alternatives.
• Stay out through SWPC's 10 PM to 2 AM window, and past solar midnight.

Region pages collect the local numbers: the lower 48 hub compares the five towns, and the Alaska hub covers Fairbanks and Anchorage, where aurora needs far less activity.