Monday, December 12, 2016

Serious cold...then weekend storm?
Overview of short- and long-term winter hazards  

  • JANUARY-LIKE CONDITIONS THROUGH SUNDAY 12/18. With the exception of Monday 12/12, PM highs barely crossing 40 F into midweek. HIGHS dropping to the 20s end of the week, AM lows in single digit to teens by Thursday AM. 
  • CURRENT COLD PERIOD RESEMBLES WEEK PRIOR TO DEC 19, 2009. This was the first major snow event of 2009-10 season in the Mid-Atlantic. Click link for a look-back at what our team said before the storm.
  • STORM TARGET PERIOD 12/15 TO 12/19 is next time frame we project conditions will become favorable for significant snow accumulation from the I-81 corridor to the I-95 corridor.

Does this mean a major storm is brewing?

Not immediately, but surface conditions are becoming favorable in the short term:
  • One essential ingredient needed to permit accumulating snowfall in the I-95 corridor and adjacent areas is falling into place: A solid week of serious cold in advance of any approaching storms, whether coastals or clippers. 
  • If snow cover develops throughout Pennsylvania, Ohio and areas on north, and snow cover is added in the metro areas this week, the chances for a significant event begin to rise.

The difference between winter 2016-17 and last winter, or 2009-10:
  • This season, the influence of El Nino and it's associated moisture influx from the Pacific is absent from the indicators. 
  • Instead, U.S. weather is now being strongly influenced by a La Nina- driven pattern where the Pacific sea surface temperatures have cooled dramatically from last year at this time. 
  • The rapid cooling of surface waters induces ridge of High pressure over the western U.S., and in turn drives a Low pressure trough in the Eastern U.S. 
  • Learn more about La Nina's effect on U.S. weather patterns at this NOAA site.

Results of this La Nina so far? You are seeing it now:  

  • An Arctic front blasting through the Midwest heading east, dropping quick amounts of snow -- not crippling but happening fast enough to cause serious disruption.
  • For the metros & coast: Long periods of cold, dry, windy weather. Not much rain. But when it does rain, there are deluges-- but only for 1 day.
  • For areas bordering the Great Lakes:  Higher than normal rainfall and snowfall due to the warm waters being tapped by passing fronts.
  • For everyone east of the Rockies: Reduced snow cover until only just this week due to less moisture available to produce snow. 
Tell me there is some hope, please.

Yes Virginia, there is always hope. Once snow cover establishes in the northern and central U.S., and a period of cold controls the East, the stage will be set for any coastal or clipper storms to "over-perform" and be provided the conditions necessary to generate potentially significant snow in the next 2 weeks. 

We shall be watching as we are certain many teachers & powderhounds will be also...

Latest snow cover from the NOAA National Ice Center

Eastern Powderhounds are yearning to see just a little bit. 
How much longer must they wait?