Dear Tom,
On Jan. 21, the national radar picture showed some snow off of Lakes Erie and Ontario and patchy rain over California, but nothing elsewhere. Has there ever been a time when the whole nation was dry?
— Joseph Morgenstern
Dear Joseph,
Precipitation-free periods can occur across the 48 contiguous states, though only rarely and briefly. Retired meteorologist Robert Johns, a 40-year veteran with the Storm Prediction Center, says, “The most likely period for a few dry hours would be the fall [probably late September or October] after low-level moisture has been swept out of the nation and before the cold blasts needed for Great Lakes snow/rain bands have developed. During this period you would need a west-to-east weather pattern with the jet stream displaced north into Canada, possibly with a weak high pressure system over the north and central Plains.”
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