:Product: Weekly Highlights and Forecasts
:Issued: 2026 May 18 0431 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC web contact www.swpc.noaa.gov/content/subscription-services
#
# Weekly Highlights and Forecasts
#
Highlights of Solar and Geomagnetic Activity 11 - 17 May 2026
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Solar activity reached moderate levels on 16 May due to four M-class flares. The largest were an M1.9/2N (R1-Minor) at 16/1612UTC from Region 4436 (N18, L=330, class/area=Dao/200 on 11 May) and a second
M1.9 flare (R1-Moderate) at 16/1742UTC from Region 4435 (N22, L=040, class/area=Dao/070 on 15 May). The 1612UTC M1.9 was associated with a Type IV radio sweep, two 10.7 cm radio bursts, and a filament
eruption that was centered at approximately N21W07, which lead to a complex CME signature in coronagraph imagery. The first front was first seen in LASCO C2 imagery at 16/1636UTC, and the second front
became visible at approximately 16/1700 UTC. Analysis and modeling of the event suggests potential for a glancing blow at Earth by mid UTC-day on 18 May, with the bulk of the material passing northward
of Earth's orbit.
The other two M-flares, an M1.4 at 17/0339UTC and an M1.3 at 16/1629, were also from Regions 4435 and 4436, with the M1.3 following on the heels of the 16/1612UTC M1.9. The other 11 numbered
active regions on this visible disk were either quiet or only produced C-class activity during the past week. 3 Type II radio sweeps and an additional 10.7cm radio burst were observed during the
summary period, but they were not associated with any Earth-directed activity
No proton events were observed at geosynchronous orbit.
The greater than 2 MeV electron flux at geosynchronous orbit was at normal to moderate levels for the majority of the summary period, before increasing to high levels at 16/1740UTC. During the summary
period, the maximum value reached was 6,120 pfu at 17/1740UTC.
Geomagnetic field activity reached G1-G2 (Minor-Moderate) geomagnetic storm levels on 15-16 May due to a negative polarity coronal hole high-speed stream becoming geoeffective late on 15 May.
Total magnetic field strength, Bt, increased all throughout 15 May, from approximately 3 nT to a peak of 17 nT at 15/1555UTC. The north-south component, Bz, rotated between +/- 11 nT, with maximum
southward deflections of approximately -13 nT. The interplanetary magnetic field had returned to background levels by the end of 16 May. A smaller positive polarity coronal hole high speed stream
became geoeffective on 13 May with a max Bt of 13 nT and maximum Bz southward deflection of -9 nT; however this only produced unsettled geomagnetic conditions and no NOAA Geomagnetic Storming thresholds
were reached.
Forecast of Solar and Geomagnetic Activity 18 May - 13 June 2026
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Solar activity is expected to be at low to moderate levels throughout the outlook period, with M-class activity (R1-R2, Minor-Moderate) ranging from a chance to likely and X-class activity (R3, Strong) ranging from a slight chance to a chance, due to the flare potential of several active regions currently on the visible disk and those both expected to return and indicated by Solar Orbiter magnetic imagery.
No proton events are expected at geosynchronous orbit.
The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at high levels on 18 May and 21-23 May due to the influence from the current negative polarity coronal hole high-speed stream and an anticipated solar sector boundary cross on 21 May. The remaining days of the outlook period are likely to be at normal to moderate levels.
Geomagnetic field activity is expected to reach G1 (Minor) geomagnetic storm levels over 18-19 May due to potential influences from the CME that left the Sun on 16 May, arriving in the near-Earth environment in the midst of the current high-speed stream. The remainder of the outlook period is anticipated to be at largely quiet to unsettled levels.
:Product: 27-day Space Weather Outlook Table 27DO.txt
:Issued: 2026 May 18 0431 UTC
# Prepared by the US Dept. of Commerce, NOAA, Space Weather Prediction Center
# Product description and SWPC web contact www.swpc.noaa.gov/content/subscription-services
#
# 27-day Space Weather Outlook Table
# Issued 2026-05-18
#
# UTC Radio Flux Planetary Largest
# Date 10.7 cm A Index Kp Index
2026 May 18 105 21 5
2026 May 19 110 21 5
2026 May 20 115 8 3
2026 May 21 115 10 3
2026 May 22 110 8 3
2026 May 23 112 5 2
2026 May 24 112 5 2
2026 May 25 115 5 2
2026 May 26 115 5 2
2026 May 27 115 12 4
2026 May 28 120 10 3
2026 May 29 125 8 3
2026 May 30 130 8 3
2026 May 31 135 8 3
2026 Jun 01 130 5 2
2026 Jun 02 130 5 2
2026 Jun 03 130 5 2
2026 Jun 04 125 12 4
2026 Jun 05 120 5 2
2026 Jun 06 115 5 2
2026 Jun 07 110 5 2
2026 Jun 08 105 5 2
2026 Jun 09 105 10 3
2026 Jun 10 100 5 2
2026 Jun 11 95 30 6
2026 Jun 12 95 25 5
2026 Jun 13 95 12 4
(NOAA)
