Imagine this: you're cruising along in instrument meteorological conditions (IMC) in an airplane without weather detection/avoidance equipment. You know from your pre-flight weather briefing and from chatter on the air traffic control frequency that there is some heavy precipitation in the vicinity. ATC is busy approving pilots' requests for weather deviations. The cloud around you starts to turn dark and the cockpit dims. Some light then moderate rain starts to splatter on the windshield, and it starts getting bumpy. The flying begins to get difficult and airspeed and altitude fluctuations are occurring. You suspect you may be flying toward a thunderstorm, but you rest assured that ATC is keeping an eye on your position and will advise you of any weather ahead and suggest a course alteration. You're safe, right? Wrong. ATC does not separate aircraft from weather, it separates aircraft from aircraft.
I've always had a special interest in air traffic control since before I started flying. Throughout my flying career it has been one of my areas of specialty and I've acquired much expertise on this topic through formal training and independent study. I also recently accepted a job offer to become an air traffic controller. As I've worked with flight students and interacted with my peers, I've frequently been astonished by how little most pilots know about the ATC system. Pilots aren't required to have in-depth knowledge of the ATC system because, after all, they're pilots and not controllers. However, knowing as much about what the guy on the other side of the radio is doing can be of great tactical assistance to pilots when flying in the system. For instance, understanding that ATC is not required to separate your aircraft from hazardous weather is not only helpful for a pilot to know, it's imperative. Fatal accidents have occurred in the past because pilots did not know this and flew headlong into dangerous weather because they thought ATC was looking after them.
The primary function and role of ATC is to separate IFR traffic. Period. Just about anything else a controller does is on a workload-permitting basis and is somewhat optional (for instance, providing VFR flight following radar advisories or providing detailed information about severe weather in the area). ATC is not in any way responsible for keeping airplanes away from thunderstorms, areas of severe icing, severe turbulence, or any other weather-related hazard. That job lies with the pilot-in-command and no one else. Some pilots have gotten spoiled by extra helpful controllers who go out of their way to assist aircraft in avoiding hazardous weather. Perhaps these pilots think that because they've heard controllers suggesting headings for aircraft to fly to avoid areas of heavy or extreme precipitation that controllers are required to do this for all aircraft, so they relinquish their pilot-in-command responsibility of avoiding dangerous weather to ATC. That is a dangerous mistake to make, and it causes pilots who are under this impression to relieve themselves of their accountability for keeping the flight safely away from hazardous weather. Once this happens neither the pilot nor ATC is keeping the aircraft away from the hazard, and the pilot is in for a rude awakening when the aircraft roams its way into a thunderstorm.
Air traffic controllers are highly trained professionals. They know their role and what's required of them extremely thoroughly. They are also educated on the boundaries of their role, where their influence over the flight must stop and give way to the pilot's decisions. You can observe this with clarity when adverse weather is around. For instance, when thunderstorms exist in a controller's sector of airspace he is operating with the understanding that the pilots he's communicating with are aware of the thunderstorms' position and intensity, or if they're not that the pilot has evaluated the general weather situation and concluded that the conditions do not pose a threat to the flight. The controller is depending on the pilots to let him know what they need in order to separate themselves from the weather, and he'll do his best to approve their requests while still maintaining separation of air traffic. Controllers know that it is not their responsibility to hold your hand and help you pick your way through convective activity. And while some controllers are more helpful than others during times of bad weather, pilots must not depend on this as a crutch to compensate for their lack of planning or inability to find their way through the weather on their own because they do not have weather detection/avoidance gear aboard. It's also important to note that most controllers are not pilots, and they may not have as great of an understanding of weather and its effects on flight operations as you think they do.
Controllers can be a tremendous help and valuable resource to assist pilots with avoiding dangerous weather, but if the controller is extra busy or grouchy we may be on our own. That's okay, and that's how the system was designed to function. Pilots are expected to be the experts on knowing exactly what their flight needs to stay safe, not controllers. Controllers are there to keep you from bumping into another aircraft. Many pilots rely too heavily on controllers to keep them out of dangerous weather, and it's this lack of personal responsibility and accountability that makes the system fail occasionally (i.e. when an airplane is lost to a thunderstorm because the pilot refused to perform his role of keeping the airplane away from the thunderstorm). There have literally been instances where controllers have silently watched their radar scope as airplanes have traveled directly into extreme precipitation. Controllers are entitled to think, "Well, the pilot must know what he's doing. It's not my airplane. I assume if he needs deviations around that cell that he'll tell me. Until then, he's in charge." In fact, I believe that's in good form. A good controller knows his role and performs it fully and properly while simultaneously respecting the pilot's role and leaving the pilot space to make his own professional decisions. Again, that's the way the system is designed to work, and when a good controller meets a good pilot on frequency, the two work together in perfect harmony.
So, remember, you're the pilot-in-command. Step up into that role. You're the authority, and you're responsible for keeping your aircraft safe. No one else, including ATC, is tasked with that responsibility. If you're too insecure to handle that level of responsibility, you have no business flying airplanes. Too many accidents have occurred (weather related and others) because the pilot-in-command was not actually in command at all, and he was unable to step up and take the reins when things got serious. When it comes to weather avoidance, step up and take the reins because ATC is not going to do that for you, nor should they. When a pilot refuses to keep up his end of the weather avoidance bargain and depends on someone else (ATC) to do it, the system fails and flight safety is compromised.
When there's weather around that poses a threat to flight safety, key up and let ATC know exactly what you need. Be specific, and be confident. They'll do everything they can to accommodate you, and they'll feel comforted that you're taking responsibility for the safety of your flight. Pilot-controller interaction always works best when both parties know their roles and responsibilities and carry them out while respecting and honoring the other's duties.
