Tuesday, December 30, 2014

Accumulating Snow Likely by the Weekend, Cold to Follow

An area of low pressure will create travel problems in the Midwest by the weekend.  Widespread accumulating snow is increasingly likely as new model runs come in to our weather center. Coincidentally, it appears we will yet again have two pieces of energy coming together over the Midwest to amplify snow totals across the area.
The southern stream will have more moisture to work with, as Gulf air is deposited into the expanding area of cold air to the northwest. Specific accumulations are still unclear, but an area of 3-6" or more would be a good bet at this point.  Snow totals with the northern stream may be on a similar scale, as the snow will be light and fluffy and have the ability to accumulate quickly. Pockets of air below will become trapped within the snowpack, allowing for more beefy totals. Below are two computer model projections of total snow, both are relatively very similar.

As the are of low pressure departs, very cold air will be ushered in from Canada.  Winds will shift to the northwest and open the flood gates of cold Canadian air directly into the Midwest by Sunday. Look for highs to be well below normal, as winter shows its full face by next week.  Below are the temperature anomalies compared to average forecasted off the GFS model.

Winter Storm to Unleassh Widespread Cold Air this Weekend

The next best shot for accumulating snow in the Midwest will come in late this week into the weekend. A rapidly deepening area of low pressure will track through the Midwest Friday into Saturday and interact with a northern stream Alberta Clipper.  Accumulating snow is possible in parts of the Midwest this weekend.  We will look more into the set up early this evening with a post explained the cold and models differences. Until then.

Friday, December 26, 2014

Several Inches of Snow Friday Night into Saturday

A storm system pushing in from the southwest will bring several inches of snow to parts of the area tonight. Winter weather advisories have been posted for the areas seeing the heaviest snow.  It looks like a swath of around 2-3" will pile up before the storm departs, with up to 4", maybe 5" especially in northern Wisconsin, as the system deepens it mean sea level pressure. Areas further south will see most rain than snow, the cut off from accumulating snow to rain will be sharp. A closer look below:

Tuesday, December 23, 2014

Update: Christmas Eve Winter Storm

Here is the latest: The storm has now began to form over the southern Gulf Coast. It looks to take a track through the Ohio River Valley and lower Michigan, dumping moderate snow on the back side of the system. Unfortunately, models and National Weather Service offices for that matter, are having a tough time forecasting the exact track and impacts. One question is whether or not thunderstorms will take away from available moisture in the cold sector of the system.
Below is our best forecast for the area of snow Christmas Eve.  Winter weather advisories and winter storm watches have been posted in Illinois and Lower Michigan. This is a highly irregular storm system, the origin of development and fact that the Midwest is still waiting for another storm to clear, has created problems in the numerical models. We will make tweaks as needed to the forecast.

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:

Christmas Winter Storm Likely! Models having Difficulties

Models are all over the place with the Christmas Winter Storm.  The trend has been to the west, which is common with such a complex and strong area of low pressure.  The afternoon will be spent sifting through the latest date and model outputs. We are working on a more formal post on this system that will be posted early this evening, be sure to check back. You will not want to miss this one!

Pre-Christmas Blanket of Snow for Parts of the Midwest

The northern stream of a large piece of energy will dump several inches of snow in parts of Minnesota, Iowa and Wisconsin.  As moist gulf air streams north into Wisconsin, just enough cold air will be in place to produce accumulating snow. Northern Wisconsin will see the area of largest deformation and consequent moderate snow, 3-5" with an isolated 6" amount is likely. A wintry mix or all rain can be expected points south. A larger winter storm will impact the Midwest Christmas eve! An update will be posted latest today.

Saturday, December 20, 2014

'Tis the Season, Winter Storms, Blizzards oh My

A complex and possibly travel crippling area of low pressure will affect the Midwest Christmas Eve into Christmas Day.  The pattern next week will feature two storms, both a which will have a travel impact. However, models continue to be all over the place with the track, timing and extent of the cold air. We are still 4-5 days out, which is on the edge of confidence for most winter storms.  The following will lay out the latest thinking, concerns and scenarios for Xmas travel.  Updates will be persistent the next several days.

Concerns and Trends:

  • THE TRACK, always the largest component of who sees what, snow or rain
  • The strength of storm #1, and its influence on the track of storm #2
  • The extent of the cold air, will the strong Canadian air mass crash into the precipitation field fast enough to create the heaviest of snows
  • Will thunderstorms rotate into the cold air quick enough, i.e. before it departs into Canada
  • Will the pressure gradient forecast pan out, if so BLIZZARD conditions are likely
  • EURO vs. GFS  Illinios and Wisconsin 6"+   or    Michigan 4-7"+    or   something else?
Something to note:  This set up is eerily similar to a winter storm from November 24th.  A strong surface cyclone with the influence of a northern stream dumped near 6" of snow in parts of Wisconsin (Post). Models did not show the heavy snow until a few days before the event, as models thought the northern stream would block the cold air from impacting the precipitation field.  This storm, a month later, is even stronger and we are placing a 70% chance of an area of 6"+ somewhere in the Great Lakes by Christmas Day.

The most consistent model (over the past few runs) has certainly been the GFS. It brings a deep low pressure from Mississippi into lower Michigan, dumping heavy snow on the back side in Illinios and Wisconsin.  It has all the makings of a full blown blizzard, with tightly packed isobars in the area of heaviest snow.  The storm will continue to strengthen as it pushes off to the north.

Above are the two latest model runs from the the two major weather computer models.  To wet the appetite, the GFS had a couple runs of 12-15"!  The GFS, or American Model, has been more consistent in a solution similar to this, while the EURO has also been somewhat consistent.  The EURO believes the cold air will not be present in time for heavy snow.  As stated before, recent history would suggest the contrary, but this will certainly be something to watch closely in the coming days, be sure to check back here and our facebook page for continued updates.  To put in proper weather terms...this could be a big one! 

Wednesday, December 17, 2014

A White Christmas? Major and Complex Winter Storm Possible Dec 22nd-25th

A couple systems will effect the eastern half of the country right in time for Christmas.  A broad area of accumulating snow is possible with storms one, with an area of heavier snow possible for storm #2. Confidence on the first system for December 22nd-23rd is fairly high, but specific track and snow amounts are still up in the air.  The major unknown deals with system number two, where it will go and how it might interact with system #1 somewhere in the Great Lakes, such a scenario would amplify the forcing and subsequent snow in the area.

The Set Up:
A large trough will set up over the eastern half of the country during the time period of our storms.  This will provide the relative cold air needed for snow, but more importantly will determine the track of system number two.  An area of low pressure will develop in the left exit region of a jet core, somewhere over the Mississippi River Valley.  It will then propagate to the northeast, along the jet stream.  The exact location and amplitude of the trough/cold air mass will determine the effects of system #2.

On the left is the vorticity at 500mb along with geopotential heights in solid black contours. Notice signs of the trough, or dip, in the middle of the country.  Areas of positive vorticity advection will likely see ascent and precipitation. This atmosphere is setting up in a way where there is ample vorticity or "spin" to work with.  Along with the fact that system #1 is closed off from the jet stream and not going anywhere until system #2 influences its core, complexity may be an understatement.  The exact influence will need to monitored and we will update as this possibly active period draws closer.

Dreaming of a Midwest White Christmas?

A white Christmas is defined in the record books as a snow depth of at least an inch on Christmas morning. The plot to the left shows the historical percent chance of seeing a white Christmas across the Midwest (courtesy of noaa data). For the most part; North Dakota, South Dakota, Minnesota, Wisconsin and Michigan have the best year to year chance of seeing such an event. After a snowy November brought snow to much of the are, the snow pack has since dwindled, as seen below.  A post about a potential Xmas Eve storm will be out soon!