[Ips-hf-warning] ASWFC HF SHORTWAVE FADEOUT WARNING issued 0803 UT on 18 May 2025 [SEC=OFFICIAL]

[Australian Space Weather Forecasting Centre]

SUBJ: ASWFC HF RADIO COMMUNICATIONS WARNING 25/49
ISSUED AT 0803UT/18 MAY 2025
BY THE AUSTRALIAN SPACE WEATHER FORECASTING CENTRE.

AR4087 has a history of flare activity and still poses a threat 
of M-class flaring.

DEGRADED HF PROPAGATION CONDITIONS EXPECTED
FROM 18-20 MAY 2025
IF COMMS DIFFICULTIES EXPERIENCED TRY A HIGHER FREQUENCY BAND
_____________________________________________________________

SOLAR ACTIVITY FORECAST       HF COMMS FADEOUTS
18 May:  R0-R1, chance R2     Possible
19 May:  R0-R1, chance R2     Possible
20 May:  R0-R1, chance R2     Possible

Note:
An ASWFC MUF depression HF Warning and ASWFC shortwave fadeout 
HF Warning are both current. Shortwave fadeouts degrade 
lower shortwave radio frequencies first (through increased 
ionospheric absorption) and the usual strategy during shortwave 
fadeouts is to try a higher frequency. In contrast, during 
periods of ionospheric MUF depression, the upper frequencies 
are degraded first and the usual strategy is to use a 
lower frequency. 

In general use a lower frequency if you are having trouble
with your normal workable frequency.

If a shortwave fadeout occurs during a period when ionospheric 
MUFs are depressed the available HF bandwidth will be "squeezed", 
with increased absorption raising the lowest usable frequency 
and the ionospheric depression lowering the highest usable 
frequency. Under such conditions it is suggested that the 
HF communicator operates on the highest usable frequency, 
even though this may well be in fact lower than what is normally 
supported for that particular circuit.

Australian Space Weather Forecasting Centre
Bureau of Meteorology
ASWFC at bom.gov.au
www.bom.gov.au | www.sws.bom.gov.au