A Cool Start To May 2013

Just as we were getting used to hotter springs, Mother Nature pulls a fast one.  It has been unusual to say the least for South Carolina weather since April 26^th.  Cloudy, cool conditions have been the rule with plenty of rain.  The griping has begun as many are tied of conditions we normally attribute to Seattle.

My favorite tweet during the past week has been “Breaking news: This just in – Cleveland wants its weather back.”  I’m sure those in Cleveland might think this an improvement over what they normally get in early May.

So what has been happening?  Why has it been so cloudy and cool for so long?  When will this go away so that we can get on with summer?

The first half of spring was influenced by a weather pattern associated with a negative phase of the Arctic Oscillation.  This was described in the previous post.  However, that has not driving the weather pattern recently.  Instead the jet stream has retreated to the north leaving upper-level low pressure systems isolated from the main flow.  This has resulted in a blocking pattern where weather systems slow to a crawl and can persist for days.

The weather pattern at 500 mb (~18,000 ft) on Saturday, May 4, 2013 at 12z UT.  The jet stream had retreated farther to the north leaving isolated pockets of low pressure over the mid-latitudes.  Click on the image for a larger version.  Image Credit: WLTX-TV.

When Weather Becomes Climate

Note: It has been a busy three weeks which included a week of much needed vacation.  Much has happened in the interim.  I am working on a number of posts which will be rolled out in May.

Meanwhile, many people often confuse weather with climate.  You have heard the refrains like it is so cold, how could the earth be warming?  Or how can we be in a drought when we’re having a flood?  Just when does weather become climate?  Good question!  Meteorologists at the European Space Agency have produced an answer to that question.

The following video is about 12 minutes long, but it is well produced and worth the time to view it.  They have a wealth of information with which to determine climate change and it is interesting comparing weather in the early 1800’s to weather today.  I hope you enjoy this production.

Click here: When Weather Becomes Climate

Six Days Of Sandy

Much has been or will be written about Hurricane/Superstorm Sandy.  The impacts are still being assessed and it may be weeks before we have the full picture.  It was an historic and unprecedented storm.  NASA has put together a wonderful video of Sandy from its development as a tropical depression to its transformation to a superstorm and finally a weaker system.  The time period covered here is from October 23 to 31.

However, an even better video covering the period October 25 to 31 was produced by NOAA NESDIS.  These rapid scan images were produced into a time-lapse movie as an experiment using the GOES-14 image.  The images are using visible light with a one kilometer resolution.

Movie credit: NOAA/CIMSS at the University of Wisconsin-Madison.

Sandy is too large a storm to be viewed entirely at this resolution.  The view is centered on the central core and extends out a few hundred miles.  It begins in the central Bahamas as a hurricane and transforms north of the Bahamas as a hybrid storm.  Finally, Sandy makes a transition to extratropical just before making landfall on October 29^th.

This is a fascinating view of the storm.  I hope you will appreciate the power being generated by Sandy.  You can see the tops of thunderstorms bubbling up through the cirrus overcast.  Sandy generated a tropical storm force wind field that was up to 1000 miles across at times.  The central pressure was so low that if it had been a pure hurricane it would have been a category 4 storm.  However, the transition to a hybrid spread the winds over a much larger area preventing Sandy from concentrating the winds near the center.

Enjoy!