That is the interesting thing about chaotic systems with infinite variables, such as our atmosphere. Regardless of computer power, or observational resolution, predictions will always become significantly divergent beyond about two weeks, due to chaos theory. However, computer modeling and new research is a valuable part of atmospheric science. Short range forecasting has and will continue to become more precise, as will long-range predictions at monthly resolutions . But, mathematical chaos itself causes the inherent impossibility of long-range daily predictions , which will always be present.
Correlations made between solar activity and daily, monthly or seasonal weather are unsubstantiated.
No testable physical mechanism exists to explain correlations between sunspots and climate. Despite much research, no connection between solar variations and weather has ever been unequivocally established. Apparent correlations have almost always faltered when put to critical statistical examination or have failed when tested with different data sets. As a result the subject has been one of continual controversy and debate. If you have suspicions about a new forecasting correlation or technique, ask to see publication references.