The locally enhanced descent of the rear-inflow jet near the mesovortex is forced primarily by the dynamically induced downward vertical pressure gradient force while the buoyancy force only plays a minor role there. These high winds are mainly caused by the descent of the rear-inflow jet at the bow apex, but the MV-induced vortical flow also has a considerable contribution. Moreover, the model results show that these bow-apex MVs are accompanied with damaging straight-line winds near the surface. MVs located at (or near) the bow apex are found to persist for a notably longer lifetime than the other MVs. Vortex mergers occur between MVs during their forward movement, which causes redevelopment of some MVs in the decaying stage of the bow echo. MVs that develop on the southern bow tend to be weaker and shorter-lived than their northern counterparts. Both the observed and simulated bow-echo MVs predominantly form north of the bow apex. Significant MVs are detected from the radar radial velocity using a linear least squares derivatives (LLSD) method, and from the model simulation based on calculated vorticity. The genesis of near-surface high winds within the system is also investigated. Emphasis is placed on documenting the existence, evolution, and characteristics of low-level mesovortices (MVs) that form along the leading edge of the bowing system. If the radar animation of the last hours shows local thunderstorms or precipitation cells forming and disappearing in an irregular manner, then the forecast is not vey accurate.A derecho-producing bow-echo event over the central United States on is analyzed based on radar observations and a successful real-data WRF simulation at 0.8-km grid spacing. The forecast works very well when weather fronts or large organized precipitation structures are moving regularly, without disappearing or being created. Real weather is more complex than just the displacement of existing precipitation cells. Longer forecasts are not possible, as new precipitation cells are developing or existing ones are disappearing within a short time. This so called precipitation nowcast is the most accurate precipitation forecast possible but the forecast horizon is limited to about an hour.
The rain/snow forecast is computed by estimating the movement of precipitation cells observed by radar and extrapolating this movement into the future. United States: How accurate is the radar based forecast? Moreover, some countries do not operate a weather radar network, and in those countries satellite data is used to estimate rainfall, which is less accurate than a realtime weather radar.
Note that lightning is not shown on the forecast, as it cannot be predicted. Light blue indicates drizzle, blue a medium intensity, and red and yellow indicate very strong precipitation, usually associated with thunderstorms.Ĭurrent lightning strikes are marked with small orange dots on the map (Europe only).
The different colours indicate the intensity of rainfall or snowfall. The radar map is updated every 5 minutes with a new radar observation. The weather radar ( United States) shows where it is currently raining or snowing.