Understanding Storm Probabilities

Minor Storm (G1): Probability of geomagnetic activity reaching Kp=5. G1 storms can cause weak power grid fluctuations, minor impact on satellite operations, and aurora visible at high latitudes.

Major-Severe Storm (G2+): Probability of any storm at G2 level or higher occurring (Kp ≥ 6). This includes:

  • G2-G3 (Moderate-Strong): Kp 6-7 – Voltage corrections needed, spacecraft operations affected, aurora visible to lower latitudes
  • G4-G5 (Severe-Extreme): Kp 8-9 – Power grid problems, satellite navigation degraded, HF radio blackouts, widespread aurora

Risk Categories (based on NOAA standards):

  • Low Risk (<15%): NOAA “slight chance” – Quiet to unsettled conditions expected
  • Moderate Risk (15-30%): NOAA “chance/likely” – Reasonable expectation of storm activity
  • High Risk (>30%): NOAA confident forecast – Significant geomagnetic activity expected

Geographic Impact: High latitude regions (closer to magnetic poles) experience stronger effects and higher storm probabilities than middle latitude areas.

Understanding Radiation Storm & Radio Blackouts

S1 or Greater: Probability of solar particle events reaching S1 (Minor) level or higher. During high solar activity, NOAA may also forecast S2+ and S3+ forecasts.

Solar radiation storms can:

  • S1-S2 (Minor-Moderate): Affect polar flights, minor satellite operations impact
  • S3-S4 (Strong-Severe): Radiation hazard to astronauts, satellite operations degraded
  • S5 (Extreme): Unavoidable high radiation hazard, satellite operations impossible

HF Impact: Moderate to severe HF radio degradation on sunlit side, especially polar routes. Higher S-scale events cause more severe and longer-lasting HF disruption.

    Radio Blackout Scale & HF Impact

    Radio blackouts are caused by X-ray emissions from solar flares, affecting the sunlit side of Earth immediately:

    R1-R2 (Minor-Moderate): HF radio degraded on sunlit side, some navigation outages
    R3 (Strong): Wide area HF radio blackout, loss of radio contact for ~1 hour
    R4-R5 (Severe-Extreme): Complete HF blackout on sunlit side for hours

    Amateur Radio Impact: Higher frequencies (20m, 17m, 15m, 12m, 10m) most affected during daylight hours. Lower bands (40m, 80m, 160m) may provide better propagation during blackout events.

    Duration: Radio blackouts typically last from minutes (R1-R2) to several hours (R4-R5), depending on flare intensity.

     

    What it means to you

    When space weather gets active, the Sun sends out bursts of energy that can shake Earth’s magnetic field. We call this a geomagnetic storm. During minor storms, your signals on higher bands like 15 or 10 meters might get weaker or fade in and out. Lower bands like 40 and 80 meters are usually less affected, but conditions can still change quickly.

    If the storm gets stronger, especially at higher levels (like G2 or above), it can really mess with the ionosphere — the layer that reflects your HF signals back to Earth. This means the higher bands often become noisy or even unusable, and even the lower bands can be unpredictable. At these times, sticking to 40 or 80 meters often gives you the best chance to make contacts, especially closer in.

    When space weather forecasters say the risk of a storm is low, most bands will be pretty stable. But if they warn of moderate or high risk, expect more disturbances. Also, if you live in northern areas, you’ll notice the impact sooner — sometimes with auroras that look pretty but make HF communications tricky!