Monday, December 22, 2014

Potential Christmas Eve Winter Storm to Strike Midwest with Heavy Snow

The threat of a high impact winter storm is on the rise.  A narrow swath of heavy snow is looking more and more likely, but the exact location is not certain.  This is one of the more complicated winter storm set ups in recent years.  Some models are only putting down a couple inches, while other more consistent ones are putting down 6"+ across parts of the Midwest.  The differences deal with the effects of the northern stream (This Storm).  How much phasing or how far northwest can this system pull in system #2 and how rapidly can it deepen before exiting into Canada.  The storm #2 is still off shore of the Pacific Ocean and has yet to be sampled by on shore weather stations. Once this happens and storm #1 has moved out, confidence will become very high, until then we speculate on the forecast...

We have been talking about this storm for nearly a week now, at two days out the models are coming together but still have their differences!  It appears to be a battle of the High Resolution models vs the lower resolution models. The resolution of model deals with the grid size of the data being put into the model. For example the GFS has a grid size of 27km x 27km while the hi res is 13km x 13km. The trend in both solutions has been to the west, but the high resolution runs have been consistently bringing the area of low pressure up from the Mississippi River Valley and passing it over Lake Michigan, with heavy snow on the back size (Illinois and Wisconsin). Below is the highest amount of snow forecasted by all the models, the 4km 18z NAM, Showing very heavy snow, this is one possible solution:

The above model run is the hi-res NAM, the operational NAM has the system pushing through Michigan, which would leave Illinios and Wisconsin dry. This has been quite the forecast challange. For further inspection, below is the difference in the GFS runs during the afternoon model runs.

One major thing to note, the swath of heavy snow has been much more consistent in the hi-res models, does this mean its more likely? Maybe. This storm has the potential to surprise a lot of people, including local TV stations! We will certainly continue to watch and let you know what we know.  Before we leave, here are the latest thoughts and tidbits to leave with:

  • The possibility of a winter storm affecting the Midwest is above 70%
  • The Hi-Res models have been very consistent in forecasting heavy snow
  • Illinois and Eastern Wisconsin have the best shot at over a half foot of snow
  • The trend has been to the west
  • We will update throughout the next couple days, here and at our Facebook Page, be sure to give us a 'like'
Additional note: One thing to look for in winter storms is where the thunderstorms and convection parameters set up, the Hi-Res NAM show thunderstorms wrapping into the cold air, and changing over to heavy snow...this will tend to amplify the snow totals in such areas.  Here is a snapshot of the change over to snow: