FORECAST PROCESS

When forecasting convective systems in West Africa, it is useful to check all available data, including satellite images and derived products; synoptic surface charts (such as station observations); upper-air charts (from radiosonde stations); radar (if available); and model output. Since the ASMET modules focus primarily on satellite data, we will examine satellite data in conjunction with standard surface and upper-air charts and model output. Note that you can access this information at any point in the module via the Forecast Process link on the left.

Our process of forecasting convective systems in West Africa includes the following steps:

Step 1: Review past and current satellite imagery, synoptic charts, and NWP products to assess meteorological conditions.

1. Review satellite imagery for clouds and atmospheric dynamics.
2. Review synoptic observations and numerical weather prediction (NWP) products to check for the presence, position, organization and strength of the key dynamic and thermodynamic features that drive the West African monsoon systems.

• Synoptic observations:
  • Surface observations: Check the position of the intertropical front/disturbance, and the position, organization, and intensity of heat lows
  • Low-level winds (600 m, 900 m, 1500 m, and 2100 m): Analyze the depth, northward extension, and organization of monsoon inflow to check for low-level instability (indicated by vortices and convergence lines)
  • Mid-level winds (700/500 hPa): Check for easterly waves (mid-level instability), the African easterly jet, and dry air intrusion (low- and high-latitude interactions)
  • High-level winds (200 hPa): Check for the tropical easterly jet and extra-tropical troughs (low- and high-latitude interactions)
• NWP products
  • Mean Sea Level Pressure (MSLP): Check the position of the intertropical front/disturbance and the position, organization, and intensity of heat lows
  • Low-level winds (925 and 850 hPa): Analyze the depth, northward extension, and organization of monsoon inflow to check for low-level instability (indicated by vortices and convergence lines)
  • Mid-level winds (700 hPa/500hPa): Check for the presence of easterly waves, the African easterly jet, and dry air intrusions
  • High-level winds (200 hPa): Check for the tropical easterly jet and extra-tropical troughs
  • Relative humidity (850 and 700 hPa): Check humidity availability
  • When available, check the following derived products for atmospheric instability: vertical velocity, divergence, and vorticity at 850, 700, and 200 hPa
• Check for agreement between the model output and synoptic observations to assess the reliability of the the NWP products.

Note that moderate to fast propagating convective systems, such as squall lines, typically develop between the AEJ and the TEJ.

Step 2: Assess the impact of atmospheric conditions on future weather.

Determine if tropospheric dynamics are favorable for the initiation and/or further development of convective systems based on your analysis.

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