Meteorological Images of March 2013   A Matter of Degrees  Image
credit: NOAA  And, last but not least, the most notorious
happening in weather in the U.S. in March 2013.  During the
storm which got the "S" name on The Weather Channel's list -
Saturn - the atmosphere in the nation's capital was teetering on
the edge between being just cold enough for snow or a little too
warm, while just to the west there were big accumulations in
places such as Front Royal. The difference between, say, 72 and
a few degrees higher usually doesn't matter much in weather, but
the difference between 32 and 38 sure can!  This graph is of a
"short range ensemble forecast" (SREF) model prediction of
temperatures for Reagan National Airport for March 6-7.  The
lines show "ensemble members," in which a bunch of forecasts are
made by the model with the goal being to depict a range of
possible outcomes and the degree (pun intended) of uncertainty.
 Well, in this case the actual temperatures - the dots - were
consistently higher through