Bees store food to last the winter. A healthy hive won't starve in Nov. or Dec. When they start raising brood and they have 20,000 more mouths to feed, is when the danger looms. The last few weeks before the flow begins is the crucial time. Be sure they don't run out of stores just before bloom time. If warm enough, look at the stores weekly or as needed. If cold, heft the front an inch, then the back, and estimate the weight. If very light, open it and add food. Opening a hive and chancing killing it is preferable to letting it starve and guarantee killing it.