Propagation News – 4 May 2025

After the previous week’s geomagnetic disturbances, as described in last week’s GB2RS, the last seven days have been relatively quiet.

The Kp index has mostly been in the ones and twos, however the rise to a Kp value of four on Thursday 1 May could herald a return to unsettled conditions.

The solar flux index peaked at 170 on the 24 April, before declining to 148 at the end of the month. HF conditions have been acceptable rather than outstanding and many stations struggled to work DX at times during International Marconi Day on the 26 April.

Nevertheless, there is DX about including ZS8W Marion Island, TX9A Austral Islands and HD8G Galapagos Islands.

A look at the Proppy propagation prediction tool will help you work out the best times for making a contact with each station and on each band. You can find it via the RSGB website

Looking ahead, a large sunspot has rotated into view. Now designated 4079, this region has returned and was previously sunspot region 4055. It has already emitted an M-class solar flare and we may expect greater activity as it becomes more Earth-centric over the next week.

NOAA predicts that the solar flux index will climb again in the coming week, perhaps rising to between 160 and 165. Geomagnetic disturbances are also due to rise, with the Kp index forecast to reach five on the 5 and 6 May.

If this becomes a reality, expect lowered MUFs and poorer HF paths, especially over the poles as the Kp index rises.

And finally, this week traditionally marks the start of the Sporadic-E season so keep an eye on 10m and 12m for short- and medium-range openings to Europe.

VHF and up 

The current spell of high-pressure Tropo weather weakened a little as last week ended and we’ll see the return of unsettled conditions with showery rain, perhaps even the odd thunderstorm.

This is unlikely to lead to a total removal of high pressure and Tropo will still be worth looking for, especially over the western side of the UK. Some models place a new high just west of Britain during the coming week.

This means that the rain prospects are not great, although probably just enough for a hint of rain scatter in any isolated heavier showers.

The HF bands sounded a bit ‘watery’ at times last week, which is a classic sign of potential aurora to explore on the higher bands. Look out for aurora in the coming week if the Kp index climbs above five.

Meteor scatter is worth thinking about and, after last week’s Lyrids, we now have the Eta Aquariids shower peaking in the early hours of the 6 May.

Remember that Sporadic-E ionisation is largely composed of long-lived meteor ions so be on watch for Es openings. From now onwards through to mid-September, Sporadic-E will dominate the lower VHF bands so check the clusters for signs of activity. Remember that Es starts on 10m and moves HF as an opening develops, even reaching 2m in the peak summer.

Unlike Tropo, Es events are often fleeting, so the best you can do is monitor conditions as the Es intensifies and be ready when it reaches the band you want. Don’t forget to check the daily Es blogs on www.propquest.co.uk which discuss the potential links between location of jet streams and Es formation.

EME path losses are increasing, but apogee is still a week away. Moon declination passed maximum last Thursday so Moon windows are shortening along with reducing peak elevation. 144MHz sky noise is low all week.

Category: GB2RS Propagation News