By Courtesy of the Propagation team
G3YLA JIM
G0KYA STEVE
G4BAO JOHN
Its all about the weather
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Jim Bacon G3YLA
NARC club member
and Nick Henwood
RSGB President.
Propogation News
12th December 2025
HF
3
We had a bit of everything last week – increased Kp indices, a high solar flux, an X-class solar flare and coronal mass ejections. As the Chinese curse goes, may you live in interesting times!
The SFI hit a maximum of 220 on December 4th, bringing good HF conditions from the 4th to the 7th. It has since declined to 169 on December 11th, which is still more than enough to excite the ionosphere.
We had an X-class solar flare at 05:01hrs UTC on December 8th. This originated from large active region 4298, which has now rotated out of view. We also had more than 10 M-class solar flares over the past week, showing that the prediction of disturbed conditions on the downward part of the solar cycle still holds true.
The Kp index hit 6.33 on the 10th, which knocked MUFs for six. The net result was that digisonde traces have been missing at times, with the MUF over 3,000km being in single figures on Thursday, the 11th.
To cap it all, we now have a very large Earth-facing coronal hole that threatens HF propagation this weekend, the 13th and 14th.
There has been DX around, but mostly on the lower bands. CDXC’s Slack group reports KP2B St Croix was worked on 80m FT8 on the morning of the 11th, as was TO9W St Martin on 30m and 40m CW on the 9th. TT1GD Chad also appeared on 20m and 40m CW on December 8th.
Next week, NOAA predicts the solar flux index will be in the range 130-140, but as we said earlier, geomagnetic conditions may be disturbed on the 13th and 14th due to a fast solar wind stream from a coronal hole.
They might calm down from the 15th to the 20th, before the Kp hits five around the 21st to the 26th.
In other words, get your HF DXing in during next week, before auroral conditions take their toll over the Christmas period.
VHF and up
The present period of unsettled weather will remain the driving force for weather conditions for most of the country for the period up to Christmas.
This will mean that there are likely to be some very windy spells with extensive rain and squally showers. It offers scope for rain scatter operators on the GHz bands, but scarcely any hint of good Tropo conditions.
The item of interest is the meteor scatter prospects from the Geminids, which peak on December 14th. It is one of the busiest showers of the calendar with a peak hourly rate of 120, so it should provide plenty of opportunities and is worth exploring during the week before and following the peak.
The solar conditions have again remained interesting enough with a red alert on the evening of 10th Dec, and always the potential for the Kp index to produce signs of auroral radio activity once it goes above Kp=5.
Finally, a reminder that this winter period, from mid-December to mid-January, can produce some surprisingly effective Sporadic-E. It’s possibly easiest to see by making a habit for the next four weeks of checking the www.propquest.co.uk graphs to see if the foEs trace is showing any sharp spikes.
Probably 10m and 6m are the more likely bands to show signs of activity in these winter events, but it’s certainly worth checking if the graphs show any promising signs.
For EME operators, Moon declination goes negative on Friday 12th, meaning shortening Moon Windows and decreasing peak elevation. We are past perigee for the month, so path losses are increasing. 144 MHz sky noise starts low, but increases to high by Friday the 19th when the Sun and Moon are close in the sky.
G3YLA JIM
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G0KYA STEVE
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