Here’s the latest propagation forecast from Tad Cook (K7RA).
Views expressed in this Amateur Radio news update are those of the reporters and correspondents.
Content provided by Tad Cook (K7RA), W1AW, and HQ ARRL.
Accessed on 24 April 2021, 0308 UTC, Post 1999.
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SB PROP @ ARL $ARLP017
ARLP017 Propagation de K7RA
QST de W1AW
Propagation Forecast Bulletin 17 ARLP017
From Tad Cook, K7RA
Seattle, WA April 23, 2021
To all radio amateurs
SB PROP ARL ARLP017
ARLP017 Propagation de K7RA
Four new sunspots emerged this week, and were visible every day.
And in this week’s bulletin a large amount of useful material from
Spaceweather.com issued a warning on April 22: “A CME is heading for
Earth and it could spark a geomagnetic storm when it arrives on
April 25th. NOAA forecasters say moderately strong G2-class storms
are possible, which means auroras could dip into northern-tier US
states from Maine to Washington.”
Average daily sunspot number surged from 7 to 35.1, while average
daily solar flux increased from 75 to 78.
Due to seemingly constant solar wind, average planetary A index rose
from 5.1 to 16.4, and average daily middle latitude A index went
from 4.1 to 13.
Predicted solar flux is 84 on April 23-24, 82 on April 25-27, 80 on
April 28, 78 on April 29-30, 68 on May 1-2, 78 on May 3, 72 on May
4-9, 75 on May 10-15, 78 on May 16, 75 on May 17-18, 72 on May 19,
70 on May 20-23 and 68 on May 24-29.
Predicted planetary A index is 10, 8, 25 and 12 on April 23-26, 5 on
April 27 through May 3, 15 on May 4, 5 again on May 5-7, 8 on May 8,
5 on May 9-10, then 8, 12, 20, 30, 15, 12 and 8 on May 11-17, 5 on
May 18-19, then 8, 12 and 5 on May 20-22.
Geomagnetic activity forecast for the period April 23 to May 18,
2021 from F.K. Janda, OK1HH.
“Geomagnetic field will be:
quiet on: May 1-3, 5, 18
quiet to unsettled on: April 28-30, May 6-11, 17
quiet to active on: April 26, May 12
unsettled to active: April 27, May 16, 18
active to disturbed: April 23, (24-25,) May (4,) 13-14, (15)
“Solar wind will intensify on: April 23-25, (then irregularly
between April 26-May 1), May 3-5, (6-7, 10-11, 16,) 17-18, (18).
– Parenthesis means lower probability of activity enhancement.
– Contradictory indications significantly reduce the accuracy of the
Frank Donovan, W3LPL wrote:
“The significant increase in Solar Cycle 25 activity we’ve long
anticipated may have begun on April 19th. As a result 30 and 20
meter night time propagation and 17 and 15 meter daytime propagation
is likely to be enhanced through at least April 26th.
“The solar flux index (SFI) is likely to remain at 85 or higher
through at least April 26th due to two active regions containing a
total of 16 sunspots:
“Two additional active solar regions on the far side of the Sun are
expected to rotate into view later this week possibly increasing the
SFI and extending enhanced propagation through at least late April:
“See my article in May QST: ‘What to Expect During the Rising Years
of Solar Cycle 25.”‘
Frank also wrote that new sunspots are fading faster than he hoped,
but the steady trend of increasing sunspots should soon sustain the
solar flux above 80.
Frank then sent this additional useful content:
“Long distance propagation forecast for Thursday and Friday, April
22-23 from Frank Donovan, W3LPL.
“My propagation forecast derived from today’s NOAA/SWPC web pages is
published five days a week (M-F) in the Daily DX.
“Propagation at low and mid-latitudes is likely to be normal through
Friday. Propagation crossing the auroral oval and polar regions is
likely to be mostly normal with below normal intervals through
“Today’s latest planetary Kp Index, updated every three hours:
“N0NBH’s current HF Band Conditions, updated regularly:
“The solar flux index (SFI) is likely to be about 78 through Friday.
“Three active regions containing a total of 17 mostly tiny sunspots
are having minimal effects on HF propagation.
“We are exiting the most disturbed weeks of the March-April
geomagnetic storm season when the Earth is passing through the part
of the interplanetary magnetic field (IMF) with the most frequent,
longest duration southward oriented IMF. Approximately twice as many
brief minor and moderate geomagnetic storms occur during March and
April compared to the quieter IMF during June and July. Brief minor
to moderate geomagnetic storms may be triggered with little warning
when the IMF rotates to a southward orientation and persists for
several hours coincident with the effects of Earth directed coronal
hole high speed streams and coronal mass ejection (CME) enhancements
in the solar wind.
“160 and 80 meter short path propagation from North America to VK/ZL
is likely to be normal through Friday. 80 and 40 meter short path
propagation to south Asia is likely to be mostly normal at about
0030Z Friday. 80 and 40 meter short path propagation from North
America to east Asia after about 0900Z is likely to be mostly normal
with below normal intervals through Friday.
“30 meter propagation through the auroral ovals and across polar
regions is likely to be mostly normal with below normal intervals
through Friday. 30 meter propagation is always significantly
degraded within a few hours of local noon because of E-region
blanketing of long distance F2 propagation. 30 meter night time
propagation is likely to improve slightly through Friday due to
solar flux index of 78.
“20 meter daytime and evening propagation through the auroral ovals
and across polar regions is likely to be mostly normal with below
normal intervals through Friday. 20 meter northern trans-polar
propagation within a few hours of sunrise and sunset will steadily
improve with gradually increasing electron density in the polar F2
region through June. 20 meter night time long distance propagation
in the northern hemisphere is likely to improve slightly through
Friday due to solar flux index of 78.
“17 and 15 meter daytime long distance propagation in the northern
hemisphere is likely to improve slightly through Friday due to solar
flux of 78. 12 and 10 meter daytime long distance propagation is
likely to be mostly unreliable and limited to propagation from North
America to Southern Africa, South Atlantic, South America and South
“Geomagnetic disturbances caused by coronal hole high speed streams
are likely to remain mostly brief, minor and less frequent through
at least late 2021. The north-south (Bz) component of the IMF plays
a crucial role in triggering brief minor to moderate geomagnetic
storms when it persists in a southward orientation (-Bz) with
enhanced field strength for several hours coincident with the
effects of Earth directed coronal hole high speed stream or CME
enhancements in the solar wind.
“IMF field strength, solar wind speed near Earth and geomagnetic
activity are likely to be at close to background levels through
Friday with a possible enhancement late Friday due to coronal hole
high speed stream effects. There is a slight possibility that an
M-Class solar flare may cause a brief sudden ionospheric disturbance
and short-wave fadeout on the Sun facing side of the Earth late
“Geomagnetic storms and Earth directed CMEs strong enough to affect
HF propagation are not likely through Friday.
“Mid latitude northern hemisphere sunset is now 32 minutes later and
daylength is 81 minutes longer than it was on the March 20th.
“Daylength is increasing by two minutes per day which is steadily
lengthening the duration of common daylight between distant
locations in the northern hemisphere. Solar elevation in the
northern polar region is increasing about three degrees per week,
steadily improving 20 meter northern trans-polar propagation through
“Today’s Penticton 10.7 cm solar flux index updated at 1700Z, 2000Z
and 2300Z daily:
“Today’s three-day GFZ Planetary K Index forecast updated every
“Today’s SIDC Daily Bulletin on Solar and Geomagnetic Activity
updated at 1230Z daily:
“Today’s SWPC Solar Activity Forecast Discussion updated at 0030Z
and 1230Z daily:
“Today’s Australian Space Forecast Centre Summary and Forecast
updated at 2330Z daily:
“The April 2021 NASA solar flux index forecast for Solar Cycle 25
has been published, mostly advancing the date for solar maximum to
2024. The SFI represented by the 50% percentile (green line) is
similar to Solar Cycle 24. A double peaked solar cycle — similar to
recent Solar Cycles 23 and 24 — could delay solar maximum by a year
“Slightly updated wording to W3LPL’s May QST article, unconstrained
by QST page limits and reflecting NASA’s predicted solar maximum in
“If the SFI persists below 90 through December 2021, then
propagation should improve gradually until a solar maximum weaker
than Cycle 24’s arrives in 2024.
“If the SFI persists above 110 through December 2021, then
propagation should improve rapidly until a solar maximum similar to
Cycle 24’s arrives in 2024.
“If the SFI persists above 125 through December 2021, then
propagation is likely to improve more rapidly until a solar maximum
stronger than Cycle 24’s arrives in 2024.
“Don’t forget to vote for your favorite May QST article here:
N4SO recommends an article in the March-April QEX, “The onset of
Solar Cycle 25 and the MGII Index,” by VE6TL.
Jon Jones, N0JK reported an April 20 TEP opening to South America on
6 meters, and sent a long list of stations copied from 2022-2023
UTC, and this report:
“CE6CGX copied me. 10 watts, 1/4 wave whip. Jon N0JK EM28 KS.
“Rx at Tue, 20 Apr 2021 20:25:01 GMT
From N0JK by CE6CGX Loc FF31qp
Frequency: 50.314.248 MHz (6m), FT8, -6dB
Distance: 8846 km bearing 162 deg”
On April 19 Jon reported that VP8EME in the Falkland Islands was
heard on 6 meters by KE8FD and K1TOL around 1800 UTC. “Looks like
the Summer sporadic-E season has begun.”
KA3JAW of Easton, PA reported a long 6 meter opening on April 19,
1435 to 1706 UTC. “Best DX range was with N5DG (EM20AB) Hempstead,
Texas at 1,374 miles.”
And from Cuba:
“Hi, CO7WT, Pavel Milanes here from Camaguey Cuba, FL11bj.
“I like to report a huge opening of 6m band in Saturday
“I was calibrating my homebrew 6m transverter to get access to the
magic band (Noise generator, SDR, NanoVNA) and out of the blue a
digital signal came up for a few seconds on my SDR screen.
“Weird, no antenna is connected, just coax from the tests, then
there it is, a mental calculation spotted the 18.313 MHz, aka 50.313
(32.000 MHz XTAL… That’s FT8!) a local ham, I think at first,
connected my antenna (Cushcraft 3 el 6m yagi) and boom!
“Loud signals from North America and some ones from LU and CE on the
side/back of the yagi, Sadly TX side of the transverter is not ready yet.
“I put some pictures on twitter, I will link them here:
“I spotted at least 3 beacons, one from W4 and the other was too
unstable to decode properly as they came and go… see the pictures,
some of the ones calling on FT8 has signals dancing up and down in a
pattern of a few minutes.
“I think on sporadic-E as this is the season.”
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Service at http://arrl.org/propagation-of-rf-signals. For an
explanation of numbers used in this bulletin, see
An archive of past propagation bulletins is at
http://arrl.org/w1aw-bulletins-archive-propagation. More good
information and tutorials on propagation are at http://k9la.us/.
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bulletins are at http://arrl.org/bulletins .
Sunspot numbers for April 15 through 21, 2021 were 22, 44, 28, 15,
36, 54, and 47, with a mean of 35.1. 10.7 cm flux was 72, 76.5,
75.3, 78.1, 85.9, 80, and 78, with a mean of 78. Estimated planetary
A indices were 13, 19, 29, 16, 18, 13, and 7, with a mean of 16.4.
Middle latitude A index was 11, 15, 20, 13, 15, 10, and 7, with a
mean of 13.