Comparing Obs. Data with NWP
Here's what we've seen so far. The observational data show:
- Stability and moisture at low levels, with calm winds and stratified low-level clouds over Nairobi and the vicinity
- Drier conditions in the middle levels of the troposphere
The NWP charts show:
- Moisture below 700 hPa will continue through the morning hours (00 to 06 UTC) so existing clouds can be expected to persist and the development of fog is possible.
- The vertical wind profile does not change significantly. There are calm winds at low levels, which are conducive to the development of low cloud and fog
- The dry middle troposphere will enhance radiative cooling and support the maintenance of stratus clouds and the development of fog; the air near the airport is relatively moist up to 700 hPa, and very dry above
- High pressure associated with the East African ridge is over the continent and expected to persist until 09 UTC; this creates an environment conducive for the formation of low clouds and fog
Windspeed
Humidity
MSLP
Question 1: How are conditions near Nairobi expected to change between 06 UTC and 09 UTC? Select the correct option.
The correct answer is B.
The humidity forecast show drying occurring between 06 UTC and 09 UTC. High pressure is forecast to build over this time and winds are not expected to change much over that time, so options A, C, and D are incorrect.
Question 2: Based on the forecast, what aviation-related features or conditions might be of concern and need to be monitored over the next few hours? Select all that apply.
The correct answers are A and C.
Ceilings and visibility are the main concerns over the next few hours. Conditions need to be closely monitored, especially for the development of fog. If it forms, it will cause poor visibility, which can delay departures and arrivals. It can also increase operational costs through additional fuel consumption and possibly result in aircraft rerouting to alternate aerodromes. Passenger comfort may also be compromised.