SatMet Home PageCase Date -- 21 February 1996
Part One: Flight Route Planning (35 min lab ; 10 min discussion)
The objective of this exercise is to determine the best route for flights from :
Assume a departure time of 1200Z on February 21, with about six hours enroute.
Main factors to avoid: (1) strong headwinds, (2) icing, (3) thunderstorms, (4) clear air turbulence.
Data suggested :
1. Display the satellite loops, using model overlays when available.
2. Locate the major jet streams. Look for poleward boundaries of persistent cirrus cloud (IR) or moisture (WV).
3. Using the distance function in GARP, select a few cirrus tracers near the jet axes, then estimate their velocities. Compare with model forecast winds aloft.
4. Identify significant areas of weather and turbulence. Identify areas of embedded convection (if present) or deep, multilayered clouds. Turbulence is likely in well defined, transverse cirrus cloud bands, and with dark (and darkening) regions in WV images.
5. Using the large scale base map or satellite image, trace the best routes from Los Angeles to Honolulu and to Anchorage. Indicate the recommended flight altitudes along each major segment of the routes. Assume enroute cruising altitudes between FL250 to FL400 (200Hpa to 400Hpa).
In this exercise, we will analyze the datasets to identify regions of possible hazardous aviation weather conditions valid at 1500Z, such as: (1) reduced ceilings and visiblities due to precipitation/fog, (2) embedded thunderstorms, (3) turbulence, (4) icing. Area of analysis will be states over and west of continental divide, and adjacent coastal waters. This will be similar to an area forecast (FA) except it will just be an analysis. Also, estimate maximum cloud top heights in northern California, southern California, and for the open cells offshore.
Data suggested :
Using a base map, sketch or outline the following types of hazardous weather features expected at 1500Z :
1. IFR flight conditions due to low ceilings or restricted visibility. Specify the meteorological conditions which are causing these conditions. Although ceilings are not available on surface obs, temperature-dew point spreads will assist you. Identify areas of embedded convection.
2. Areas of suspected cloud icing. Estimate location of 0C isotherm using standard pressure level model forecasts or raobs. Look at the ETA model 700mb RH and omega fields. Does the GOES-9 "FOG product" provide useful information in this case?
3. To estimate areas of high altitude turbulence (CAT), locate zones: (1) of jet stream convergence, (2) of a strong jet associated with a bulding ridge, (3) of lee cirrus with evidence of subsidence along the ridge lines. Do soundings/model wind foreasts show pronounce shear in any of these regions?
4. Outline the areas of low level turbulence using observed or forecast winds at 850hPA. Look for mountain wave signatures in IR/WV imagery.
5. Estimate the height of cloud tops over: southern California, northern California, and coastal Washington/Oregon, by determining average IR cloud top temperature and comparing to model data. You may also wish to use sounding data (the Met Applications ISP menu has soundings available for 21feb96).
The last exercise involves position analysis for offshore frontal systems and surface troughs, and identification of zones of precipitation, and possible gale force (35 kt or more) surface winds at 18Z.
1. Locate surface fronts by identifying convective cloud lines, or multilayerd cloud bands in visible or IR imagery. Use the satellite image loops to follow the movement of the surface fronts within the viewed region. Sketch frontal positions at 18Z, using the DISTANCE function on GARP to extrapolate, if necessary.
2. Track cloud motion using the GARP Distance function on VIS data, to estimate surface wind speed in the east Pacific. Should the gale warnings be continued?
NOTE: Keep in mind that these motion vectors will represent winds at cloud base level winds. Check your vectors against the model forecast data.
3. Use the visual structure you observe in the VIS imagery above, plus IR cloud top temperatures to indicate precipitation areas off the coast. In which precipitating areas are thunderstorms possible ?
