Somewhat of a better picture coming together for weekend weather

A current look at the overall hemispheric pattern and the low in question for the weekend is still well in the north Pacific.  A trough will help kick a low pressure system near Alaska in our direction by Saturday.  As we get closer to the weekend we're starting to get a little better idea of what may occur.  Will this forecast change?  Yes - expect a few more changes to the forecast until the low moves into the Pacific Northwest by Saturday.

As was discussed in earlier posts, there are basically two scenarios that could play out heading into Sunday and Monday.  I don't think this system will completely bypass us so that one is not an option.  As of this morning, it looks like the general consensus for a likely storm track will be low pressure developing in Oklahoma early Sunday morning and tracking northeast into central Illinois by Sunday night and eventually east of Detroit by Monday morning.  After looking over several morning model runs it appears as if the system may be trying to slow down a bit and there may be enough warm air in the first thousand feet or so above the surface to allow all rain to fall, or a mix of rain & snow, initially by Sunday morning.  Now the further north and northwest of northern Illinois you live the higher the chance of a little more snow than rain.  The reason for the initial thought of rain is because winds ahead of the low will be coming in from the south.  This will allow the surface temperature to warm above the freezing point.  However, roughly around three thousand feet above the surface the temperature will already be below freezing.  So, any deviation from the current thinking storm track could mean a big difference in 4"-8" of snow or 2"-3".  Right now, the only model that is showing that as a possible scenario is the NAM.  It would keep the majority of the event as snow through Monday morning. We'll keep an eye on that one!  As the afternoon continues and the cold front with the associated low begins to move through the cold air advection (cold air moving in) will win and a likely change over to all snow will occur by Sunday night.  This will carry over into Monday before the low moves into eastern Canada.  Now I want to stress this is a POSSIBLE scenario for Sunday.  Any snowfall totals or official snow/rain forecast won't be issued until at least 24, maybe 36, hours prior to the event.  Another factor into how much snow will fall will be the snow to liquid ratios.  The typical snow to liquid ratio is 10:1 - 10 inches of snow is the equivalent of one inch of water.  The higher the snow to liquid ratio, example 15:1, the more fluffy the snow is.  This is what we call a 'dry' snow.  It fluffs up more causing the snowfall total to increase.  The smaller the snow to liquid ratio, example 8:1, the more moisture the snow has and this is what we call 'heart attack' snow because it's usually heavy and hard to shovel.  Going into this event it doesn't appear as if the ratio will be significantly high.  Updates will continue straight through the weekend so be sure to keep checking back!