One of the first rules that FF Dispatchers learn is to select departure airports that are within what we call dynamic weather range (DWR) of the destination airport. The DWR is typically a distance that equates to an estimated time enroute (ETE) of about one hour. The idea behind a dynamic weather range is to dispatch a flight that will terminate with an approach into the selected weather conditions. For example, if you select a VFR flight then you'd like conditions to be VFR as you enter the terminal area.
The rule of thumb used to calculate estimated time enroute is to multiply the straight-line distance (in nautical miles) times 0.15 and add 30 minutes. For example, a flight from Orlando (KMCO) to Miami (KMIA) is 167 NM. The ETE is 167 * 0.15 + 30 minutes which is about 55 minutes. The nice thing about this formula is that it accounts for ground operations. This works out pretty well for commercial jets and probably turboprops on shorter flights (but probably not as well for piston aircraft like a Cessna 152).
Flight assignments will almost always originate with weather conditions as good or better than at the destination. What this means is that a VFR flight will almost always start VFR, but an IFR flight could start out with VFR, MVFR, or IFR weather conditions, but never LIFR, at the time of dispatch. Additionally, IFR and LIFR flights with arrival conditions that include rain, snow, and/or thunderstorms have higher priority - this makes for a more challenging flight, don't you think?
At this hour there are 28 stations reporting IFR in the universe of Part 139 airports in the continental United States, but only 8 are reporting rain. The one that was selected was Newport News with winds from 040 at 5 knots, and visibility 1.5 miles in light rain and mist. If you're looking for rain you came to the right place!
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