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
19th December 2025
HF
3
Last week, we suffered from the double whammy of a reduced solar flux index and an increased Kp index.
The SFI went down to 119 by Thursday the 18th, with the sunspots looking pretty spartan when compared with just a week or so ago. Unfortunately, a coronal hole contributed to a fast solar wind with a south-pointing interplanetary magnetic field or Bz. The net result was a Kp index of five and a minor (G1) geomagnetic storm.
Nevertheless, the MUF over a 3,000km path mostly remained above 28MHz, at least during daylight hours, and there was DX to be worked.
As it’s Christmas, let’s focus on special calls for the season. YR0XMAS in Romania has been worked on 20m CW and will be active until the end of the month.
A little further afield is the 12 days of Christmas event in the U.S. It runs until Christmas Day with 12 three-letter callsigns in the W2 and K2 series. You only have to work one to get a certificate, so it should be possible for most hams. If you are lucky enough to work all 12, plus a bonus station in Puerto Rico, you can get a special “Clean Sweep Plus” endorsement. W2S has already been spotted in the UK, and more details are available by Googling “12 days of Christmas ham radio”.
Next week, we have another large coronal hole to contend with, which NOAA predicts may push the Kp index to five from December 22 to 26. The good news is that the SFI may increase over the same period, perhaps up to 180 by the 28th.
Make the most of the low bands as we hit the winter solstice, with its long periods of darkness. And certainly check 14-28 MHz during daylight hours.
VHF and up
The tail end of the previous week ended on a dramatically mild, wet and windy note, with heavy rain and gales in places. It might be good for the earth, but little else springs to mind other than some chance rain scatter for the GHz folk.
The main feature of this Christmas propagation report is that we have a major change becoming established after this weekend.
This change takes the form of swapping out the mild, Atlantic pattern for a blocked, cold easterly flow with high pressure parked to the north of the British Isles near the Faeroes.
If this takes place as suggested by some of the models, then a much colder easterly wind will remain with us for much of the Christmas week. The strength of the high means that the flow is only likely to produce shallow cloud, barely enough for an isolated wintry flurry on the east coast of England.
Lighter winds over northern Britain, closer to the high, will possibly allow some Tropo, but it is not convincing in view of the shallow dry layer below the inversion, but it will mean some sharp frosts are possible where skies clear.
Long dark winter nights are potentially good for seeing meteors and it is worth mentioning two showers this time. The first is the Ursids, which peak around December 22-23rd, and just in case you don’t get a chance to hear another bulletin over the holidays, the second shower to be aware of is the Quadrantids peaking January 3-4th. This is a much larger shower than the Ursids, so maybe the one to focus on for radio activity.
Aurora remains on the list, especially in view of the large coronal hole recently and as ever keep an eye on the Kp index for high values, but it is even better to note conditions on the LF bands for signs of ‘watery ‘sounding signals.
The Sporadic-E folklore often speaks of isolated mid-winter events and, in view of the two meteor showers adding fuel and there being some useful jet streams, it is certainly part of this bulletin. Using the jet stream over the Pyrenees for paths to Spain early this week is a good place to start.
For EME operators, Moon declination is rising again and path losses are decreasing. We are past apogee for the month, the point where the Moon is farthest from the Earth. 144 MHz sky noise is also reducing again after reaching a peak around the 20th.
G3YLA JIM
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G0KYA STEVE
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