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Here is the current forecast discussion on space weather and geophysical activity, issued 2015 Dec 20 1230 UTC.

Solar Activity

24 hr Summary: Solar activity remained at low levels during the period. An unnumbered region behind the northeast limb produced most of the activity during the period, including a C4 flare at 19/2228 UTC, which was the largest event of the period. Region 2470 (N15W18, Eho/beta) the largest spot group on the disk, exhibited spot and penumbral decay, particularly in the regions trailer portion. Region 2469 (N19W28) lost its lone spot and decayed to a plage region. Little change was noted in Region 2468 (S15W60, Axx/alpha).

At 19/1326 UTC, a long duration C1 x-ray event was observed from a source behind the ENE limb. This source region appears to be a day or so behind the limb based on STEREO-A EUVI 195 imagery. Associated with the C1 event was a Type II radio emission with an estimated shock velocity of 1098 km/s. In addition, a coronal mass ejection (CME) was observed in LASCO C2 imagery off the east limb, first visible at 19/1325 UTC. Due to the source region of this CME, an Earth-directed component is not expected.

Forecast: Solar activity is likely to be at low levels with a slight chance for M-class flares (R1-R2/Minor-Moderate radio blackouts) all three days (20-22 Dec).

Energetic Particle

24 hr Summary: The greater than 2 MeV electron flux was at predominately moderate to high levels with a brief period of normal levels from 19/0245-0535 UTC. A peak flux of 2,825 pfu was observed at 19/1655 UTC. The greater than 10 MeV proton flux continued at background levels.

Forecast: The greater than 2 MeV electron flux is likely to drop to normal to moderate levels on day one (20 Dec) due to electron redistribution associated with the arrival of the 16 Dec CMEs. Moderate to high levels are expected on days two and three (21-22 Dec) as CME impacts wane. The greater than 10 MeV proton flux is expected to continue at background levels.

Solar Wind

24 hr Summary: Solar wind parameters, measured at the ACE satellite, reflected shock passage due arrival of a CME. At 19/1528 UTC, a shock was observed causing total field strength (Bt) to become enhanced and ranged between 10-17 nT through most of the period. After 20/1000 UTC field conditions began to stabilize and decreased to near 5-7 nT. The Bz component varied until near 20/0230 UTC when it switched to a sustained southern orientation, reaching a maximum deflection of -17 nT. By periods end, Bz had decreased to near -5 nT. Solar wind speed reached near 520 km/s with shock passage and remained elevated until near 20/0000 UTC when speeds began to gradually decrease to about 395 km/s to end the period. At shock passage, and through periods end, phi was variable between a negative and a positive (away from the Sun) orientation.

Forecast: Solar wind parameters are expected to remain enhanced on day one (20 Dec) due to CME influences. Solar wind parameters are expected to slowly diminish by late on 20 Dec. By days two and three (21-22 Dec), a gradual return to nominal conditions are expected as CME effects wane.

Geospace

24 hr Summary: The geomagnetic field was at quiet levels through 19/1500 UTC when field levels increased to active to major (G2-Moderate) storm levels due to an enhanced interplanetary magnetic field as a result of the arrival of CME activity from 16 Dec.

Forecast: The geomagnetic field is expected to be at active to minor storm (G1-Minor) levels on day one (20 Dec) due to CME effects. Quiet to unsettled conditions are expected on day two (21 Dec) with quiet levels expected on day three (22 Dec) as CME effects diminish.

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