National Weather Service forecasts for Chicago point to a mid-70s high on May 19 amid a transitional spring pattern, aligning with the market's strongest consensus around 76-77°F. Recent model runs show a warm southerly flow ahead of an approaching cold front, though timing and cloud cover introduce notable spread across outcomes. Historical May highs average near 72°F, providing context for why traders assign meaningful probability to both cooler and warmer bins. Key variables include precise frontal passage, afternoon mixing, and any last-minute adjustments from updated guidance expected in the next 48 hours. This distribution reflects the inherent uncertainty in short-range temperature predictions during variable late-spring conditions.