A slow-moving Pacific disturbance responsible for the past few days of heavy low elevation rain and mountain snow in portions of the West will eject east of the Rockies late Monday night. Unseasonably warm air flooding the Eastern half of the U.S. ahead of this system forecast to peak in the 70s across most of the northeastern quadrant of the U.S. (~15° above average) during the 1^st half of this week are more typical of late May than mid April.  However models which were slow to latch onto the pattern reversing nature of the approaching Western disturbance shifted markedly colder in latest runs, and are likely not yet cold enough across the Eastern half of the U.S. in forecasts valid from midweek into the start of week 2 (Apr 18-22). Substantial temperature drops over 30° relative to the warm start to the coming week ensure widespread double-digit below average temperatures which may include overnight freeze or frost conditions (low-mid 30s) deep into the southern Plains  and Southeast Friday through next weekend (Apr 19-21). The 6-10 day period is forecast to feature the coldest temperatures of April across the Eastern half of the U.S. while the West warms sharply including upper 90s across the Desert Southwest (10°-15° above average). While Western warmth is forecast to begin spreading into the central U.S. early next week (Apr 22-23) models generally agree temperature moderation along the Eastern Seaboard will be slowest delaying return of above average temperatures through the end of April. However, longer range forecasts valid early-mid May are trending warmer and drier across the Great Lakes and Northeast setting the stage for an early start to summer-level heat across the regions.