wpostServer: http://css.washingtonpost.com/wpost2

Most Read: Local

Posted at 01:48 PM ET, 04/18/2012

Grading our 2011-2012 winter forecast

As always, we grade our winter and summer seasonal outlooks in spring and fall respectively. In short, we did poorly this winter with not much of a silver lining. The major consolation being that we can commiserate with the authors of the other winter outlooks we encountered.

Link: Washington D.C. winter weather forecast 2011-2012

To our knowledge, no one predicted the extremely warm and nearly snowless winter that we experienced and a number called for a cold and snowy winter, which we did not. But let’s not start with the excuses.

Please read on for our harsh and honest grading.

Temperatures


CWG’s winter outlook key points
Overall, the 2011-12 winter, our 3rd warmest on record, finished just over 5 degrees above normal. Our call for normal temperatures with a slight lean below was a big miss, only tempered by the fact that we didn’t call for a cold/very cold winter.

Link: February 4th warmest on record, meteorological winter 3rd warmest

For the winter as a whole (December through February), I would give our temperature forecast a grade of D+, with the D and F grades reserved for those outlooks that went cold/very cold for the season as a whole. I think we could make the case for a C-, but given the historic nature of this winter, I think that grade is a bit of a stretch and perhaps too biased. So a D+ it is.

When we look at the months individually, we see a similarly poor performance. All three months finished right around 5 degrees above normal. It was consistently warm winter wire to wire. Our predictions of slightly below normal in December and January receive a grade of D/D+. If we had gone colder than -1 in either month, the D/F range would be in play but staying closer to normal salvages a sightly better but still awful grade.

February was one of our few silver linings. We predicted our warmest month of the winter as well as our biggest departure from normal. Our prediction of 1 to 2 degrees above normal fell well short of the actual 5.3 degrees, but we did sniff out the right idea and for that we get a C+/B- for February. As a result our final grade for our monthly predictions is a C-/D+.

When considering both our overall temperature prediction for the entire winter and our individual monthly calls, the temperature portion of our winter outlook receives a D+, quite a nasty stain on our report card.

Snow

Our snow prediction is also nothing to be proud of though a bit better than our temperature one. This was our 3rd least snowy winter on record, as only 2” fell for the entire winter. Generally, 2-5” fell across the D.C. metro region with higher amounts well to our west, where the October 29 event had a greater impact, and well to our south where two late season events dumped quite a bit of snow in a small portion of central and southern Virginia.


Our forecast for the probability of different seasonal snow totals at Reagan National Airport.

We predicted slightly below normal snow for the entire region (10-14” at DCA versus our normal 14.5”). But with only a few inches falling across the area we missed by quite a bit, with our final totals falling in our 15% probability range for the winter.

Our miss was even worse in the suburbs where averages are higher yet similar totals were experienced as those in the city. Overall, we get a C- for our snowfall predictions with D’s and F’s relegated to an outlook that called for normal/above normal snowfall.

Overall

So, in summary, we get a D+/C- for this winter, leaning toward a D+, given the historic result and one that we failed to capture.

What went wrong this winter? The answer is actually quite simple. The NAO (North Atlantic Oscillation).

A negative NAO, prevalent the prior two winters and one which we favored in our outlook, typically represents high latitude blocking (areas of upper level high pressure), especially near Greenland. This type of blocking usually leads to colder air masses in our region with a greater likelihood of snow events. In the end, the NAO was sharply positive most of the winter, and this led to colder air being bottled up in Canada, and a storm track to our west - typical of a La Nina without blocking.

What can we expect next winter? It is way too early to have much of a clue, but there are some indications that an El Nino might form. El Nino events have led to some of our snowiest winters (and often cold as well), though a snow winter is hardly a lock, especially if other factors such as the NAO work against it. Of course,after this winter, anything will seem cold and snowy by comparison.

Stay tuned for more thoughts as we get closer as well as our annual summer outlook, coming out soon.

RELATED LINKS

Past winter outlooks

2011-2012 winter outlook
2010-2011 winter outlook
2010-2011 winter outlook live chat
2010-2011 winter outlook recap
2009-2010 winter outlook
2009-2010 winter outlook recap
2008-2009 winter outlook
2008-2009 outlook live chat
2008-2009 winter outlook recap
2007-2008 winter outlook
2007-2008 winter outlook recap
2007-2008 winter outlook
2006-2007 winter outlook
2005-2006 winter outlook

By  |  01:48 PM ET, 04/18/2012

Categories:  Latest, Winter Storms, Local Climate, Capital Weather Gang

 
Read what others are saying
     

    © 2011 The Washington Post Company