12z Model Sunday NowCast | American Models Trend North & Exceptionally Snowy DC To Baltimore

Today 12z model updates will vary in two posts, (1) This post which will feature the NAM and GFS (2) A later post which will also feature the EURO and CMC.  So far this afternoon we have found both GFS and NAM model further North and not far from producing a large swathing snowstorm from cities like Washington DC, Baltimore, to even Philadelphia (possibly).

GFS Model

The GFS 0z to 6z held their ground in a stable stationary position with the storm and even a bit further North.   At 12z the GFS kept consistent to this and produced now the largest swatch of snow directly for Washington DC to Baltimore much of Virginia and even just North of the Mason-Dixon.

Figure 1: Since the 0z update the GFS has not changed all the much but a bit of a lift Northward.  Blue colors represent the highest impacts while the grey to white can be still significant but a bit lighter or less for snow.  The low is about at the same as the NAM and around Southeast Virginia entailing all snow to impact Northern Virginia, DC, Maryland, Delaware, and now  Southern Pennsylvania.  The low pressure is visioned at a 995MB

NAM Model

The 0z to 6z NAM kept on its track to affect the central heart of the Mid-Atlantic from interior to coastal and also North like the GFS.  There is model consensus at this time with the NAM and GFS.  This model appears to have posed some of the most aggressive amounts throughout the region as known for it’s bias to do so.  Though, the NAM still has the same direct swath of heavy snow over those of the GFS.  Why is this so?

Figure 2: Again those in the blue colors are shown to be in the heaviest snowfall and hardest impacts.  The greys and whites are still significant just a bit lighter and less.  The team used the model’s hi-res component which only derives out of a certain time frame.  We have shown here the date up to Mach 7.  Snow in the broader NAM does show it reaching throughout Maryland, Delaware as a historical snowstorm while also New Jersey and Philadelphia (though still light).   Notice the low pressure is around Virginia Beach or south of Delaware but a winding storm at below 1003MB.

Northern & Southern Stream Interaction
The majority of the energy being played into this storm firstly comes from the Northern extent which combats where most precipitation lies.  As this begins to sink Southeastward spreading snow throughout the Upper Midwest it will eventually meet a vigorous second extending energy from the Southern stream which will cause intensification.  Both the NAM and GFS models agree for this to happen at about the same location and just West of the region given their close output among each other.

Model Snowfall Output

Table 1: Since Saturday overnight a few of the totals for the major cities from the NAM and GFS have gone a bit up.  We provide the model accumulation outputs below.  Note this is not a forecast.

12z GFS 12 NAM
Philadelphia, PA – 1-2” Philadelphia, PA – 0-1”
Baltimore, MD – 6-8” Baltimore, MD – 10-12”+
Washington, DC – 8-10” Washington, DC – 12-14”+
Richmond, VA – 10-12” Richmond, VA – 2-4”
Roanoke, VA – 1-2” Roanoke, VA – .5-1”
Charlottesville, VA – 8-10” Charlottesville, VA – 12-14”+

Remember we still need to observe the secondary run out models of the CMC and EURO to see what fits and what should be thrown out from this afternoon.  The American OP (operational models) continue to show for some a historic snowstorm and trending further North.  We need to keep a close eye out on this.  More model updates can be expected through Sunday and Monday but by Tuesday we will be in crunch time to forecasts where needed “if” the storm is still looked to impact the region.

What You Might Ask?

Whats the likelihood of this happening?  We at GeoEnvironmental Atmosphere look at multiple variables.  But one that grabs our attention is the amplified extent of the trough.  The interaction of both Northern and Southern streams into a trough as we are witnessing gives us no reason why with the right amount of moisture and blocking to the North that a storm of this magnitude could not happen. What we believe certain is of a storm to impact the region next week, what we still are searching for is where and how much, this willing to change until then.  Please keep here for the latest!

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