Canadian air surged into the Upper Midwest and Northeast during the past weekend cooling daytime high temperatures sharply (30° in 24-hours in Chicago). Unlike earlier in April this cold air outbreak is only slightly below average due to strong warming immediately ahead of the surface cold front  which produced the warmest temperatures of the year across the Northeast yesterday (mainly 70s-80s), and little to no cooling penetrated farther south into a more resilient warm airmass entrenched in the Southeast. Warm air residing in the South ensures below average temperatures across the Great Lakes and Northeast will remain brief and quickly warm again by Tuesday, in a milder spring-like pattern maintaining late April temperatures mainly between seasonal and slightly above average levels. The West is also warming quickly in the wake of last weekend’s winter storm which produced widespread 15°-20° below average temperatures and substantial snow deep in the southern Rockies. Additional Pacific storms lined up to move into the West are significantly milder focusing seasonal to slightly below average temperatures mainly along the West Coast through late April. Spring-like volatility clouds the picture in longer range forecasts, but most extended range models are latching onto the next fundamental pattern transition early in the 1^st week of  May shifting periodic weak cooling (seasonal- slightly below average) to the Great Lakes and Northeast, which latest 30-day MWA ensemble forecasts maintain into late May. The Plains and Midwest remain the focus of heaviest spring rainfall which will be important to monitor going into summer, but reversal of expansive drought in the West and Plains is unlikely favoring these west central regions for early onset of summer-level heat before May is out.