Vigorous Shortwave Energy to Bring Snow Squalls to Region Overnight

If you're a weather enthusiast you are going to enjoy the timeframe from say about 3:00 AM to 9:00 AM Sunday morning.  If you aren't a weather enthusiast well hopefully after reading this post you'll have a whole new appreciation for weather and just how crazy it can be at times.

For a good while our long-range computer forecast models have been extremely consistent at hinting at a major, major cooldown just after the first of the month.  In fact, some of the cold project has been near or at record cold type stuff.  Too put this into perspective, the high temperatures for Monday and Tuesday (at least) will be as much as 15-20F below average!!!  That is pretty remarkable.

Let us take a look at the big picture and then break everything down on what we can expect overnight tonight into Sunday morning.  Looking at this morning's run of the GFS forecast model we can see a vigorous piece of shortwave energy associated with an amplifying trough digging out of southern Canada into the Great Lakes.  The image on the left hand side is the forecast position of the shortwave about 8:00 PM EDT this evening and the image on the right is the forecast position of the shortwave about 5:00 AM EDT Sunday morning.  In addition to focusing on the track of the shortwave, note the back contours and the numbers associated with them.  These numbers are the height of the atmosphere in meters where the 500mb level is located.  These numbers are VERY low for this time of year and indicate that the 500mb level is very low in the atmosphere (we will actually discuss this a bit more further down):

What does a shortwave (and in this case a vigorous one) have to do with our weather and what we can expect?  Well several atmospheric variables (ingredients) will be in place for the generation of numerous snow squalls across the region from say about 3:00 AM EDT to 9:00 AM EDT.  Some of these snow squalls are going to be extremely heavy, be associated with high snowfall rates, and be accompanied by strong winds and perhaps even thunder and lightning!  We will explore these variables below.

The first variable we will look at are the forecasted mid-level lapse rates (change of temperature with height).  The steeper the lapse rates (indicating a stronger decrease of temperature with height) the more unstable the airmass (great for enhancing upward vertical motion and also increasing thunder potential).  Computer forecast models are forecasting mid-level lapse rates to be anywhere from 7.5 C/KM  to as high as 8.5 C/KM (meaning a 7.5C to 8.5C decrease in temperature per kilometer of the atmosphere).  Those values are very impressive, especially for our region:

The next variable we will look at is the degree of lift.  Now, it's one thing to have lift and strong lift but if there is no moisture to lift nothing will happen.  While we will not look at it, there will be plenty of moisture available with this system.  Computer forecast models are forecasting a period of VERY intense upward vertical motion moving across portions of southern New England during the overnight period.  This intense lift will be responsible for the development of snow squalls and also be responsible for any of the heavier snow squalls with very heavy snow fall rates.  We will also explore this more further down:

We will now look at a few bufkit forecast soundings for a few select locations across the region.  We will do this to further explore the degree of lift and also look at something very cool regarding the tropopause and the stratosphere.

I've selected three locations (Windsor Locks, CT, Worcester, MA, and Falmouth, MA to illustrate further the intense lifting being advertised by computer forecast models.  The images are from bufkit and overlayed is the area of best snow growth zone (the purple and yellow contours) and omega values (with the red contours indicating upward vertical motion and blue contours indicating sinking or downward vertical motion).  Since the red contours indicate upward vertical motion, the more red contours you have and the more negative the value the stronger the upward vertical motion.  Given how we are looking at values as high as 40-45 -ub/s that is indicative of some exceptional vertical motion!  Given how these values also intersect with the area of best snowgrowth this is a very good indication that we will not only see great snowgrowth but very large and fluffy flakes...the kind that accumulates very quickly:

One very cool aspect of this system will be how low the stratosphere will be or how close it will be to us here at ground level.  Typically around these parts we see the stratosphere up around 30,000-35,000ft or so.  Well given the extreme low heights associated with the shortwave, the stratosphere is actually going to descend to right around or perhaps just below the 500mb level and in this case that may be as low as 15,000ft to 18,000ft AGL!!!  Given how this will in fact occur well below the upper jet stream this is known as a tropopause fold and is something that doesn't happen very often.  Sometimes when these occur you can get a period of exceptionally strong wind gusts (>75-80mph).  Below is an example of how low the tropopause will be (note: the stratosphere begins just above the tropopause):

All in all what can we expect?  As the shortwave approaches and lift increases we can expect numerous snow showers and snow squalls to develop across the region between 3:00 AM EDT and 9:00 AM EDT.  Given the degree of lift and instability that will be present, some of these snow showers and snow squalls will produce periods of very heavy snows with snowfall rates perhaps exceeding 2-3'' per hour, especially if there is any thunder or lightning involved!  Now the one thing to remember is we are not talking about a widespread precipitation shield but snow squalls (think of it as those heavy passing downpours we would see in the summer).  This mean not everyone may see snow and not everyone will see accumulations.  For those who do see accumulations, as much as 1-3'' will be possible, however, there is even opportunity for a few locations to perhaps see as much as 5''...6''...even 7'' of snow!!!  If that occurs it will be extremely isolated but someone may very well receive this.  Don't worry though, despite the cold tomorrow this will melt very quickly with a much higher sun angle and length of day now in place.

Once the shortwave passes we are looking at very strong winds with damaging wind gusts across the region.  We are looking as sustained winds of 25-35 mph with wind gusts as high as 55-65 mph possible.  Winds of this magnitude will be enough to cause isolated to scattered tree damage and power outages.  Sunday is definitely going to feel more like late January/early February than early April!

After tonight's event our attention turns to overnight tomorrow into Monday where in fact more snow will be possible but we'll touch upon this later!  At this time it appears a track will favor more in the way of rain but we will watch.