Part IV – Forecasts

Part IV – Forecasts


During the field campaign, a forecast secretary will analyse and report the meteorological situation for the operations. The task consists in:

  • Using the BOC to analyze all interesting outputs (forecasts and observations): analyses, forecasts from ARPEGE and AROME, satellite images, radar images, early morning sounding, etc…
  • Calling the French local forecaster from Tarbes Meteorological Center. There will be a call in the evening to discuss the situation for the following days and sometimes, when needed, another call just before the morning briefing.
  • Summarizing the info in a PPT file
  • Discussing with the secretary and coordinator if time allows
  • Presenting the forecast in the morning briefing
  • Making a pdf forecast report to be put on the BOC
  • Updating the forecast for the evening briefing

A synergy station will also be available for the forecast secretary to look at other products than available on the BOC if needed.


The models:

During the field campaign, specific outputs from two French operational Numerical Weather Prediction models will be saved.
The first model is ARPEGE, this is a global model with a stretched horizontal resolution varying from 10 km over France up to 55 km over Australia. It is run every 6 hours for 96h. There is a 4D var data assimilation system.
The second model is AROME, this is a non-hydrostatic model with a regular horizontal resolution of 2.5km. It is also run every 6 hours for 30 hours. There is an assimilation system for the surface (optimal interpolation) and for the atmosphere (3D var assimilation system with mesoscale data assimilation, Doppler radar reflectivities and winds). This model is forced at the lateral boundaries by the forecast of ARPEGE. During the campaign, this model will be rerun on a smaller domain covering the South-West of France with lateral boundaries from the operational AROME model. This will allow the computation of diagnostics. This run will be used for the real-time and time-delay outputs.

The real-time outputs:

During the field campaign, specific outputs from those two operational Numerical Weather Prediction models will be available on the BOC. These will concern model runs from 00h and 12h.They consist of horizontal map of cloud cover (low, medium, high and total), wind, temperature and humidity at 2/10m, 100m, 500m 1000m and 4000m, the boundary-layer height diagnosed as the first level where the turbulent kinetic energy gets lower than 10-2 m²/s² and hourly cumulated rainfall. The principal area covers a zone from 41°N to 46.5°N and from 2.5°W to 4°E. A zoom on a domain of 1°x1° centered over Lannemezan will also be available for the AROME outputs as well as temporal series of vertical profiles of cloud cover and relative humidity at Lannemezan and Toulouse.

The time-delayed model products:

Supplementary products will be available after the field campaign. This includes :

  • vertical profiles of prognostic variables (t, q, ,u, v, tke) and their budgets
  • horizontal cross-section of tke
  • u*, w*
  • surface fluxes, surface variables and soil variables
  • horizontal variability on a box of 10x10km² (5×5 points in AROME)
  • very high-frequent outputs (every timestep): for T,q, u, v to compare with tower observations (-> 65m), tethered ballons, lidar…

Tarbes CDM local forecast

During the field campaign, the forecasters from Tarbes CDM will provide forecast report for up to 5 days that will be posted on the BOC at about 6 UTC. Moreover, they can be called directly (05 62 32 65 01) in the evening to get an overview of the situation for the following days, and discuss it. If needed, when the situation is really delicate, another call could be made just before the morning briefing.