fog forecasts
The fog and high fog forecast includes, among other things, the spatial distribution and its changes over time. For a specific location, this means: will the fog dissipate and, if so, when? Another important aspect of the high fog forecast is predicting its upper limit.
persistence
Because fog or high fog often occurs in stable high pressure weather, persistence is a useful forecasting method. Persistence simply means that the fog ceiling tomorrow will be the same as today. This good initial estimate can then be further refined by taking into account small differences in the general weather situation, for example changes in the prevailing flow. The advantage of the persistence method is that a forecast is possible even if the numerical weather prediction model does not have a good handle on the current situation.
Current dictates fog ceiling
An important factor is the wind in the fog layer. The bise wind raises the high fog because the Mittelland basin narrows towards the west. Conversely, with a southwesterly flow, the fog ceiling sinks over time. Whether the wind is bise or southwesterly can be described by the pressure difference between Payerne (PAY) and Strasbourg (STR). A positive difference causes a southwesterly flow in the Swiss Mittelland, while a negative difference causes a bise. This connection between the pressure difference PAY – STR and the resulting high fog ceiling was statistically investigated as early as the 1970s and described by HW Courvoisier.
Relationship between the pressure difference PAY – STR and the high fog ceiling, adapted from HW Courvoisier (1976).
Relationship between the pressure difference panama mobile database PAY – STR and the high fog ceiling, adapted from HW Courvoisier (1976).
modeling
The pressure difference between Payerne and Strasbourg can also be read from the model fields and displayed as a time course. This gives an overview of the expected development of the high fog ceiling.
Forecast of the high fog ceiling based on the forecast
pressure difference Payerne – Strasbourg from how much does a domain name cost? the ICON-CH2 ensemble model. Blue shades show the uncertainty of the forecast.
Forecast of the high fog ceiling based on the forecast pressure difference Payerne – Strasbourg from the ICON-CH2 ensemble model. Blue shades show the uncertainty of the forecast.
The forecast of the high fog ceiling using the pressure difference be numbers between Payerne and Strasbourg is actually a detour, but has proven successful in practice.
As described yesterday, the current high fog ceiling can be determined by the height of the temperature inversion. The ICON model chain also provides us with forecast temperature profiles that directly show us the high fog ceiling. The figures below show the forecast temperature profiles for today, Tuesday, tomorrow, Wednesday, and Saturday at 15 UTC.
With very light winds, the inversion was at just under 800 metres today. Over the next few days, the inversion and thus the high fog ceiling will gradually rise as a result of the developing bise, with uncertainty increasing significantly from Friday onwards.