The best explanation of this week's expected (mostly) cool and (mostly) cloudy forecast - particularly for eastern New England - lay in the jet stream. Of course, the jet stream is the fast river of air high in the sky that steers storms and acts as a thermostat for the atmosphere, separating cold air to the north from warm air to the south of the fast-flowing winds. This week, the jet stream is sitting very close to New England, which means two important things: 1) Multiple upper level disturbances move near or over New England, and 2) New England remains right on the cusp of deep spring warmth to the south, and cool Maritime air over the ocean and Atlantic Canada. This combination of a temperature clash and multiple disturbances keeps conditions ripe for cloud development and periodic rain or showers. The most likely period for rain is Tuesday morning through midday, with a return of some showers later Thursday into Friday, with clouds and periodic drizzle in between (though some sun certainly may break through away from the ocean).