24 hour forecast of the surface UV for the antipsoriatic heliotherapy in Poland

•Measurements of the antipsoriatic irradiation possible by standard broad-band meters.•Duration of the next-day antipsoriatic sunbathing could be modeled.•24 h forecast maps for the exposure duration help patients to plan outdoor activities.

Analyses of the spectral and broad-band UV data collected at Belsk (20.79°E, 51.84°N), Poland, show that standard broad-band instrument, Solar Light (SL) 501A, could be used for measurements of both erythemal and antipsoriatic irradiance. A prognostic model is proposed for the next-day duration of outdoor exposure required to receive a dose, the so-called minimum antipsoriatic dose (MAD), equivalent to that received by standard antipsoriatic daily treatment in the phototherapy cabinet containing TL-01 fluorescent tubes. The model uses the 24 h forecast of the column amount of ozone (to predict next day clear sky UV irradiance), and low- and mid-level cloudiness (to estimate a reduction of the clear-sky UV irradiation due to clouds). The predicted duration of sunbathing required to receive a dose of 1 MAD matches the observed value, i.e. the correlation coefficients is 0.68. If the model predicts the antipsoriatic exposure over 1 MAD threshold the observed dose will be also above this threshold in 91% of cases. Thus, the model could be used for planning the next-day outdoor exposure to clear psoriasis. Hourly resolved maps, starting from 6 am up to 1 pm (GMT), showing the duration of antipsoriatic exposure over Poland are made public. The model provides a tool for a psoriatic patient to find the sunbathing starting time and its duration, which has the same healing potential as a single indoor phototherapy session.