####018002210#### FXXX10 KWNP 171231 DAYTDF :Product: 3-Day Forecast :Issued: 2026 Apr 17 1230 UTC # Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center # Product description and SWPC contact on the Web # http://www.swpc.noaa.gov/wwire.html # # 3-Day Forecast # A. NOAA Geomagnetic Activity Observation and Forecast The greatest observed 3 hr Kp over the past 24 hours was 1 (below NOAA Scale levels). The greatest expected 3 hr Kp for Apr 17-Apr 19 2026 is 6.00 (NOAA Scale G2). NOAA Kp index breakdown Apr 17-Apr 19 2026 Apr 17 Apr 18 Apr 19 00-03UT 0.67 6.00 (G2) 5.00 (G1) 03-06UT 0.67 6.00 (G2) 4.67 (G1) 06-09UT 2.67 5.00 (G1) 4.00 09-12UT 2.00 4.00 3.33 12-15UT 1.33 3.67 3.67 15-18UT 2.67 3.33 3.00 18-21UT 4.33 3.00 3.00 21-00UT 5.67 (G2) 4.33 3.33 Rationale: G2 (Moderate) geomagnetic storms are likely on 17-18 Apr due to the anticipated CH HSS influences. G1 (Minor) storming levels are likely on 19 Apr as the CH HSS influences wanes. B. NOAA Solar Radiation Activity Observation and Forecast Solar radiation, as observed by NOAA GOES-18 over the past 24 hours, was below S-scale storm level thresholds. Solar Radiation Storm Forecast for Apr 17-Apr 19 2026 Apr 17 Apr 18 Apr 19 S1 or greater 1% 1% 1% Rationale: No S1 (Minor) or greater solar radiation storms are expected. No significant active region activity favorable for radiation storm production is forecast. C. NOAA Radio Blackout Activity and Forecast No radio blackouts were observed over the past 24 hours. Radio Blackout Forecast for Apr 17-Apr 19 2026 Apr 17 Apr 18 Apr 19 R1-R2 25% 25% 25% R3 or greater 5% 5% 5% Rationale: There is a chance for R1-R2 (Minor-Moderate) radio blackouts through the 19 Apr mostly due to the flaring potential of Region 4419. ####018002579#### FXXX12 KWNP 171231 DAYDIS :Product: Forecast Discussion :Issued: 2026 Apr 17 1230 UTC # Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center # Product description and SWPC contact on the Web # http://www.swpc.noaa.gov/wwire.html # # Forecast Discussion # Solar Activity .24 hr Summary... Solar activity was at low levels. The majority of flaring activity was from Region 4419 (N13E29, Eki/beta-gamma). The largest flare was a C4.1 at 17/0442 UTC from Region 4419. Slight growth and consolidation was observed in the region. Slight growth was observed in the intermediate area of Region 4416 (N20W64, Dso/beta). No Earth directed CMEs were observed in coronagraph imagery. .Forecast... Solar activity is expected to be low with a chance for M-class (R1-R2, Minor-Moderate) flare on 17-19 Apr primarily due to the flare potential of Region 4419. Energetic Particle .24 hr Summary... Electrons greater than 2 MeV at geosynchronous orbit reached high levels with a peak of 2,407 pfu observed at 16/1710 UTC. The greater than 10 MeV proton flux was at background levels. .Forecast... The greater than 2 MeV electron flux is expected to reach high levels on 17 and 19 Apr. A brief drop to moderate levels is expected on 18 Apr with the arrival of a negative polarity CH HSS. The greater than 10 MeV proton flux is expected to continue at background levels on 17-19 Apr. Solar Wind .24 hr Summary... Solar wind parameters continued at nominal levels - although anomalous data spikes have existed through the period. Total field ranged from 4-6 nT while the Bz component was between +4/-3 nT. Phi angle was oriented in a positive sector. .Forecast... Solar wind parameters are expected to become enhanced by mid to late on 17 Apr with the arrival of a CIR followed by negative polarity CH HSS activity. Solar wind speed ranging from 600-700 km/s are likely based on recurrent values. Enhanced conditions are expected to persist through 19 Apr. Geospace .24 hr Summary... The geomagnetic field was quiet. .Forecast... The geomagnetic field is expected to be quiet to unsettled through early on 17 Apr. By mid to late on 17 Apr, CH HSS activity is expected to cause unsettled to active periods with G1-G2 (Minor-Moderate) geomagnetic storming likely. Unsettled to G2 (Moderate) levels are expected to continue through 18 Apr followed by unsettled to G1 (Minor) conditions on 19 Apr as HSS effects persist.