Possible Major Upper Level Pattern Change in Mid-February & Opportunities for Snow in DC

The ground hog is being mocked after predicting 6 more weeks of winter. Winter is being “declared over” by some.  Snow lovers in the big cities of the northeast from DC to Boston are gnashing their teeth. Fans of snowless winters are cheering! Headlines, Hype and Potential Premature Judgements aside, I want to briefly visually walk you through the current upper level pattern and offer a glimmer of hope for those of you who want at least one decent snowfall before winter is over.

The image below shows the continuation of this “broken-record pattern” that has allowed for a relentless winter across the western United States and winter void of snow in the big cities of the Northeast:

  • Negative PNA Oscillation (Unrelenting trough across the western United States) with a fast west to east flow (jet stream) across the continental United States and mild conditions in the eastern United States.

22500bb7-f13f-4c2c-925f-31f120114cf2

Check out the difference between a negative PNA and a positive PNA and how it affects the upper level pattern:

Negative PNA (Pacific North America) Oscillation (image courtesy NOAA/ESRL):

  • Cold and snowy conditions across the western United States, Mild and dry conditions across the eastern United States

pna_negative_1985

Positive PNA & Negative NAO (North Atlantic Oscillation), image courtesy NOAA/ESRL:

  • Mild and warm conditions across the Western United States, Cold and Snowy conditions across the Northeastern United States

pna_positive_1981

This Winter we have not yet had a prolonged period with a Positive PNA and negative NAO. In fact, the NAO has been neutral to positive all winter long while the PNA has mostly been negative.

Negative NAO Oscillation:

nao_schematic_0

This awful upper-level pattern may just be about to change as we sail into the next 7 to 15 days!

Latest Ensemble forecasts for the PNA and NAO:

First up the latest PNA forecast:

GFS (GEFS) and Euro (ECMWF) currently forecast the PNA to move into its Positive Phase after February 9th. Whether or not this actually occurs is of course up in the air but the forecast trends here are headed in the right direction. 

gefs_pna_18

eps_pna_bias

Now for the latest NAO forecast from GFS (GEFS) and Euro (ECMWF):

gefs_nao_18

eps_nao_12

Now visually, take a look at the latest GEFS model (image below) showing how the upper-level (500mb) pattern changes with a positive PNA and negative NAO between February 13th and 16th.

  • A ridge of high pressure builds across the western United States and a trough (dip in the jet stream) sets up in the eastern United States while blocking builds over the north Atlantic Ocean and Greenland.
  • Also notice the “horse-shoe” pattern to the orange colors (high pressure anomalies) from the western United States northward into northern Canada and then stretching down into the north Atlantic ocean.  If this can actually materialize it would present a decent set up for a Nor’easter along the Mid-Atlantic coastline. 

gefs_500mb

The image above looks a lot like the image below:

pna_positive_1981

What can go wrong/Thoughts?

  • Forecast models are not always reliable past ten days.
  • I will not throw the towel in on snowfall until St. Patrick’s Day. I have even seen some local meteorologist “refine” their winter forecasts. I am not one of those that refines my winter forecast and then grades myself an A at the end of Winter (that’s cheating).  You won’t find me touting “Spring is here”, “Winter is over”, “I get an A on my Winter Forecast after changing it on February 1st”.  
  • I have lived in the Washington Area now for over 20 years. I have seen miserable snow-less winters that drag on and on and then out of nowhere a storm finally forms providing plowable snow.  
  • I am not trying to sound stubborn here. Yes, by all means there is a chance that this winter will in fact end with pathetic snowfall totals across the DC Region.  And yes it is also possible that a meteorite could slam into the United States in the next two months. #EYEROLL

Remember the “warm blob of water” over the North-Pacific Ocean (Warm PDO) that a lot of national media outlets latched onto with such ‘certainty’ that it (the warm PDO) would continue be a huge driving factor during this winter? One of the variables that I was not sure of in my winter forecast was if this warm PDO was in fact going to hold.  The Warm PDO favors a ridge over the western United States.

Here was my exact Quote from my Winter Forecast

“Secondly the Warm Phase of the PDO (the abnormally warm water that has been parked off of the Alaskan, Canadian and West coast of the United States) has also been weakening a bit.  Will this trend continue? Will the water temperatures continue to cool breaking down a western ridge/eastern trough setup that we had through much of last winter?” 

So there you have it… there is the potential for a new pattern setting up over the next 7 to 15 days that could provide a decent snowfall. Not to mention, March is one of the most fickle months in the calendar year (and my 2nd least favorite to the disgusting month of August). Those of you true Washingtonians know as well as I do that we can go from 65 degrees one day to heavy wet snow the next in March. 

Have a great weekend everyone!

3 Replies to “Possible Major Upper Level Pattern Change in Mid-February & Opportunities for Snow in DC”

  1. To those snow lovers that believe this winter is hopeless, all you need to do is look back to 1960. After a miserable 4″ winter (1958-1959), the 1959-1960 winter was promising to be even worse. Until February 13, 1960, there had been NO measurable snow. Talk about a snow drought!. But aided by a near record snowy March, the 1959-1960 winter ended up with over 28″ at National Airport.

    The following 1960-1961 winter was one of our best, with 40″ of snowfall at National Airport, all falling before 2/13/61. So from 2/13/60 till 2/13/61, National Airport has a whopping 68″!

    I guess the moral of the story is that DC snowfall can be extremely erratic. You just never know what to expect.

    Like

    1. Andy, Thanks for digging into the historic climate data… extremely interesting. Excellent point, you’re hired!

      Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s