A personal HF propagation tool centered on a single Maidenhead grid, with separate scoring models for long-distance (DX) and short-range high-angle (NVIS) work.
DX mode applies a continuous D-layer absorption term derived from solar elevation, SFI, and current X-ray flare class, weighted per band (80 m hit hardest, 10 m essentially immune). A gray-line bonus boosts 80 m during civil twilight. Geomagnetic Kp adds a uniform penalty above Kp 4–5.
NVIS mode compares operating frequency to the measured foF2 (estimated when no station data is available). Quality is determined by how far foF2 exceeds the band’s operating frequency, with the same flare-blackout penalty applied because the signal still traverses the D-layer twice.
Quality buckets are poor, fair, good, excellent. The +3h and +6h columns reuse the same model with projected Kp and recomputed solar geometry; SFI is held constant (it changes too slowly to matter at that horizon) and flares are not projected forward (they decay in minutes).
For POTA / SOTA activators: the activator’s problem is “will the people who hunt me actually be able to copy my signal from this park, right now or in two hours when I get there?” A generic report gives you global SFI and a vague colored grid, but doesn’t know whether you need DX or NVIS. This tool tells you both, side-by-side, for your specific location and for the future window when you’ll actually be operating.
For regional nets: regional nets live or die by foF2 — if the F2 critical frequency drops below the net frequency, the net fails regardless of what the global SFI says. This tool pulls real measured foF2 from the nearest ionosonde, so when an NVIS net on 75 m starts losing check-ins it’s usually visible here before it’s visible on the air.
For DX: the +3 h and +6 h columns let you plan around band openings. Querying a remote grid (e.g. ?grid=PM85) recomputes solar geometry at the far end, so you can see when the target region transitions through gray-line or when a flare blackout on the path is likely to have cleared.
poor/fair/good/excellent) are subjective and tuned to typical SSB/CW DX or NVIS regional work. WSPR and FT8 routinely succeed on bands labeled poor; that’s expected, not a model failure.This report would not exist without the data and services freely provided by:
This is a non-commercial personal project. Comments, corrections, and suggestions to KD6O.
What worked, what didn’t, what surprised you, what’s missing. Your callsign if you want a reply. Hit Send and your local email client will open with the message ready to send to KD6O.
| Band | now 11:32 · Kp 4.7 |
+3h 14:32 · Kp 5.0 |
+6h 17:32 · Kp 4.0* |
WSPR NVIS <500 km, last 15m |
WSPR DX >1500 km, last 15m |
|---|---|---|---|---|---|
| 80m | poor | poor | poor | 44 · 6 RX · -13 dB | — |
| 40m | poor | poor | poor | 39 · 8 RX · -16 dB | 1 · 1 RX · -23 dB |
| 20m | good | fair | good | 62 · 18 RX · -17 dB | 39 · 11 RX · -20 dB |
| 15m | poor | poor | poor | 24 · 7 RX · -15 dB | — |
| 10m | poor | poor | poor | 16 · 5 RX · -12 dB | — |
:Product: 3-Day Forecast
:Issued: 2026 May 16 1230 UTC
# Prepared by the U.S. Dept. of Commerce, NOAA, Space Weather Prediction Center
#
A. NOAA Geomagnetic Activity Observation and Forecast
The greatest observed 3 hr Kp over the past 24 hours was 6 (NOAA Scale
G2).
The greatest expected 3 hr Kp for May 16-May 18 2026 is 5.67 (NOAA Scale
G2).
NOAA Kp index breakdown May 16-May 18 2026
May 16 May 17 May 18
00-03UT 5.67 (G2) 3.00 3.33
03-06UT 5.33 (G1) 4.67 (G1) 3.33
06-09UT 4.67 (G1) 3.33 2.00
09-12UT 3.67 3.00 2.00
12-15UT 4.00 3.00 3.00
15-18UT 4.00 3.67 3.33
18-21UT 4.67 (G1) 3.33 3.33
21-00UT 4.33 2.67 3.00
Rationale: G1-G2 (Minor-Moderate) geomagnetic storms are likely on 16
May due to the CIR associated with a positive polarity CH HSS. G1
(Minor) storming levels are likely on 17 May due to the CH HSS
persistence.
B. NOAA Solar Radiation Activity Observation and Forecast
Solar radiation, as observed by NOAA GOES-19 over the past 24 hours, was
below S-scale storm level thresholds.
Solar Radiation Storm Forecast for May 16-May 18 2026
May 16 May 17 May 18
S1 or greater 5% 5% 5%
Rationale: No S1 (Minor) or greater solar radiation storms are expected.
No significant active region activity favorable for radiation storm
production is forecast.
C. NOAA Radio Blackout Activity and Forecast
No radio blackouts were observed over the past 24 hours.
Radio Blackout Forecast for May 16-May 18 2026
May 16 May 17 May 18
R1-R2 30% 30% 25%
R3 or greater 1% 1% 1%
Rationale: There is a decreasing chance for R1-R2 (Minor-Moderate) radio
blackouts through 18 May due to the flare potential of the regions on
the Suns visible disk.