Winter Storm Recap : One For The Record Books 3/2/18

A very rare, and very damaging storm took aim on the Hudson Valley on Friday.  The impacts were wide ranging, and depending on what part of the Hudson Valley you live in, your experience was dramatically different.  Some of us saw a heavy rain for the majority of the storm, only picking up a slushy coating on the grass late in the afternoon on Friday.  Some of us were on the line between rain and wet snow, and spent the entire day switching back and forth from heavy rain to heavy wet snow… accumulating several inches in the process.  And then there were those of us who saw a heavy wet snow fall from sunrise to sunset on Friday… picking up anywhere from 1 to 3 feet of wet snow, and likely losing power due to trees and power lines snapping under the weight of the wet snow.

We’re going to focus on the meteorological aspects of this storm in this post.  We’re not going to get too far into the damage and power outages.  We have covered those already extensively on Facebook, and you can find a link to one of the discussions right here: Top 5 Most Damaging Storm for Central Hudson.  The damage was incredible, and worthy of it’s own discussion.  If you have time, check out this photo documentary from our good friends at Central Hudson, as they worked to restore power on Saturday.  Some of the pictures are breathtaking.
Central Hudson Storm Restoration Work.

Lastly, a point of clarification… we’re about to talk about this storm from a meteorological standpoint.  We may use descriptions of awe and wonder.  As snow lovers, we may make the storm sound ‘awesome’.  We want to be clear, that in no way are we minimalizing the hardship many people are facing as a result of lost power and damaged property.

So let’s get down to business.  We’ll begin the recap with 3 images:
– Our final snowfall forecast with our mid storm modification
– The snowfall history map
– Snowfall reports via the National Weather Service

Take a good look at that snowfall history map, you likely won’t ever see another one like it.  A literal bulls eye of rain, within a sea of heavy wet snow.  As snow lovers, Alex and I feel punched in the gut by looking at his map.  I live in the SW edge of the ‘snow hole’, and he lives in the NE edge of the ‘snow hole’.  Widespread 6 to 12 inches of wet snow… and nearly nothing at all for many in central Ulster and Northern Orange counties.

Interesting Spotter Reports
The reports out of Ulster are telling… because typically, if you underachieve in an event, or don’t get any snow… a trained spotter simply won’t call the report in.  But 2 people, one in Kerhonkson and one in Saugerties, were so irritated by this storm, that they reported the 0.1″ to the National Weather Service.  If more trained spotters had done that, the ‘snow history map’ would have been more accurate than it was.  To be honest, we believe the map shows too much snow in the ‘snow hole’.  In Pine Bush, I got 0.1″ as well, just a slushy coating on grass.  But it suggests I got 1 to 2 inches.  But aside from splitting hairs, this map paints an incredible picture.

So What Happened??
How on earth does something like this happen?  Is it magic?  Climate Change?  Do the Snow Gods just hate Bill & Alex?  While we believe the answer is actually the 3rd choice… that the snow Gods hate us… there actually is a scientific explanation.  The explanation is quite complex, but let’s walk through it step by step.

Dynamic Cooling: So remember, we were in the 50s on Thursday, and we needed to cool temperatures dramatically just to get to a place where it could snow on Friday.  The mechanism that did this, was called “Dynamic Cooling”.

This was the “vertical velocity” map we posted on Thursday.  It shows the upper level low pressure marked with the “L”.  The bright colors represent intense upward motion, or “lift” in the atmosphere.  The upper level low pressure generated very strong upward motion over the Hudson Valley.  This caused the air to rise very rapidly, which in turn caused the air to cool dramatically.  As the air cooled, it condensed, and rain began to fall heavily.  As the heavy rain fell, it pulled that cooled air back down to the surface.  As this process repeated over time, eventually the column of air was cooled enough so that SNOW was falling instead of rain.  This process is known as ‘dynamic cooling’.  Ultimately, this storm created its own cold air… which is pretty intense meteorological stuff by itself.  But then things got even more complex.

While forecasting, Alex and I began to see the models suggesting it would rain in parts of the Hudson Valley.  With the tremendous dynamic cooling we were expecting, and the heavy precipitation, this didn’t make sense.  Once cold enough to snow, we thought it should continue to snow heavily, at least until the snow eased up later in the day.  This complex riddle resulted in an hour and a half phone call between me and Alex, because we needed to talk about what the heck was going on.  To Alex’s credit… he called it.  He told me over the phone that he thought the model was detecting downsloping winds off the Berkshire Mountains.

What are downsloping winds, and why would it cause rain in the central Hudson Valley?

The winds around a nor’easter originate out of the northeast for the Hudson Valley.  So as the winds rotate around the storm, they blow through Massachusetts, and over the Berkshire Mountains.  As they do that, the air rises and cools over the Berkshires.  This part of the process is called upsloping, and results in higher snowfall amounts and colder temperatures in the Berkshires.

But as the air continues out of the Berkshires, and moves down into the Hudson Valley, the air sinks and drops in elevation.  When air sinks, the opposite happens… the air warms considerably, and dries out.  The result is quite amazing.  Temperatures were falling due to the dynamic cooling process.  At our HVW Station in Hurley, NY… check out these temperatures, and see if you can notice when the downslope effects started to be felt:
12am: 38.3°… 1am: 36.3°… 2am: 34.8°…(skip a few hours)…  6am: 34.7°… 7am: 37.8°… 8am: 38.4°… 9am: 38.1°

So the dynamic cooling had begun to take effect, and it was resulting in a change over to sleet and wet snow… but once the downsloping effect kicked in, it negated the effect of the dynamic cooling, and made it too warm to snow over a portion of the viewing area.

The map above is a bit of a crude demonstration of the location of the Berkshire Mountains, factoring in the northeast wind, and the net impact area.  Now, you might wonder why the ‘rip off’ zone or ‘snow hole’ is many miles away from the Berkshires.  The reason, is because the elevation remains rather high with the Taconics, and elevation doesn’t decrease with the Hudson Valley until you get much closer to the river.  So the downsloping effect doesn’t really kick in until you get closer to the river.

From a forecasting perspective it’s frustrating… because like I mentioned, Alex called it in our conversation.  And we then discussed it repeatedly, in both posts and live streams, as a possible wildcard.  But we hesitated to nail down a specific area, because it was not something we had seen before… at least not to this magnitude.  But now, having experienced it, we know that it can happen.  Pretty wild stuff.

Blockbuster Wet Snow

So now that we’ve highlighted the meteorological phenomenon that caused a large area in the middle of the region to get do little snow, let’s show the snow map once more, and soak in those incredible snowfall totals…

AMAZING snow totals.  Ignoring the previously discussed snow hole, and we had widespread 6 to 12 inch amounts across the  Hudson Valley.  As you went up in elevation across Dutchess and Columbia counties, you even broke 12 inches.  Unfortunately, we also saw wind gusts reports in the 30 and 40mph ranges.  When we forecasted 6 to 12 inches of wet snow, along with those wind gusts… we were concerned that power outages would become a widespread problem.  We hope that power gets restored ASAP, as it’s really tough this time of year to not have power.

Then there’s the Catskills… woo doggy… the Catskills.  Just take look at Greene county.  28 inches for Hunter, 26 inches for Windham, and similar high numbers of 1 to 3 feet across the Catskills.

This storm was truly dynamic, and when you stack it up against other historical storms… you see just how unique and significant it was.