Forecasting
The following are rules of thumb for forecasting the weather.
| Question | Answer |
| Will it be cloudy or clear? | On the 700 mB chart, the 70 percent relative humidity line usually encloses areas that are likely to have clouds. |
| Will it rain? | On the 700 mB forecast chart, the 90 percent relative humidity line often encloses areas where precipitation is likely. If upward velocities are present, the chance of measurable precipitation is enhanced. |
| Will it rain or snow? | On the 850 mB forecast chart, snow is likely north of the -5° isotherm, whereas rain is likely south of this line. |
| Will the surface low intensify? | For the storm to intensify, an area of upper-level divergence must be over the cyclonic storm. On a 500 mB forecast chart that shows vorticity, look for a vorticity maximum. To the east of an area of positive vorticity we usually find upper-level divergence, upward air motions, and cyclonic storm development. |
