IAP 12.310
January 2008
Significant U.S. Weather Events
Bitter Cold (Jan 18-21, 2008)
Real-Time
Data:
Surface
Temperature Analysis
The low sun angle over high latitudes and deep snow
pack allows the formation of very cold continental air masses during
the middle of winter. Cyclones then advect this cold air southward in
an attempt to neutralize the pole to equator temperature gradient. A
strong cyclone can sometimes setup in a quasi-stationary position and
advect large amounts of cold air southward over continental regions.
Such a scenario is currently taking place over North America. The
850mb height field and temperature, shown below, indicates that a
region of arctic air over central Canada is currently being advected
southward by a intense low over Hudson Bay. Particularly, the cold
advection is strongest over south-central Canada and north-central US
where the 850mb height contours, and hence the winds, are
perpendicular to the isotherms. Both the flow and temperature gradient
are strong implying strong cold advection, in this case.
850mb heights (white lines) and
temperature (shaded) on Jan 18, 2008 at 6Z.
Already, wind chill advisories and warnings have been
posted for a large portion of Minnesota, North Dakota, South Dakota,
Iowa, Wisconsin, and the upper peninsula of Michigan. Wind chill
readings may fall to as low as -50F (-46C) tonight!
While wind chills of that magnitude are not expected
in New England, we will also take quite the tumble, especially on
Sunday when the cold advection reaches us in earnest. The Jan 18 12Z
GFS forecast 48 hours out (valid Jan 20 12Z) is displayed below.
Notice that the cold advection is very strong over most of the East
Coast. This will prevent the temperature from increasing much on
Sunday during the afternoon despite ample sunshine. Both football
games at Foxboro and Green Bay will certainly be ones to enjoy inside.
Jan 18 12Z GFS forecast 48 hours out valid Sunday
morning. 850mb heights in dm (black lines), winds in knots (barbs),
and temperatures in C (colored lines) are plotted.
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