Friday, January 31, 2014

A Look Back at the #WinterMess

The snow that everyone graved finally came to the Midlands.  The same storm system that affected Birmingham and Atlanta also affected Columbia, SC.  Rain and sleet began to fall before noon on Tuesday, but it wasn’t enough to measure and didn’t cause any problems.  The lower atmosphere was quite dry so that it would take hours of light precipitation to moisten the atmosphere enough to allow for any significant precipitation.

Finally a band of rain/freezing rain moved across the southern half of the Midlands just before dark.  This was followed by snow in the northern part of the Midlands.  It eventually reached Columbia in the form of freezing rain.  At WLTX we pick up an ice accumulation of 1/10 of an inch before the precipitation changed over to snow.  The southern third of the Midlands saw ice accumulations of a ¼ to ½ inch.

The air was chilled by the rain/sleet/snow mix and temperatures fell below freezing over all of the Midlands shortly after sunset.  The precipitation changed to snow which fell mainly from 7:30 p.m. to about 2 a.m. across the Midlands.  Snow ended from west to east and the amounts didn’t vary a great deal across the Midlands.

A map of the midlands of South Carolina showing total snow depth as of Wednesday morning January 29, 2014.  This is from preliminary data.  Click on the image for a larger view.  Image Credit: NOAA/NWS/CAE.

Amounts were generally 2 to 3 inches across much of the area.  It was a wet snow which made for great snowmen and snowball fights.  Here is a view of the region from the satellite the next day:

Tuesday, January 28, 2014

A Major #WinterMess

The National Weather Service issued a Winter Storm Warning for all of the Midlands of South Carolina beginning at 11 a.m. Tuesday and ending at 9 a.m. Wednesday.  The warning was issued for significant accumulations of winter precipitation.  While the warning covers all of the Midlands the effects of the winter storm will be quite nuanced.

First, the jet stream in the upper atmosphere is diving far to the south from the Arctic region.  The term polar vortex was used earlier in January to describe to cold weather seen at that time.  Well, it’s baaaaack!  This time a piece of the polar vortex is centered just east of James Bay in Canada.  Cold Arctic air is plunging south to the Gulf coast and covering much of the Southeast.

The 500 mb pattern for 00z Tuesday, January 28, 2014.  Click on the image for a larger view.  Image Credit: WLTX-TV.

All of the computer models have been signaling this for the past few days.  However, their solutions have differed as to how and when the precipitation will develop across the Southeast.  Some of the models have brought the cold air in too fast resulting in primarily a snow forecast.  Others have slowed the advance of the cold air which has produced forecasts of freezing rain, sleet, and snow.

Sunday, January 26, 2014

A #wintermess for Tuesday, January 28, 2014

The National Weather Service issued a Winter Storm Watch for the midlands of South Carolina Sunday afternoon.  It is for the time period from Tuesday morning to Wednesday afternoon.  Immediately everyone was jumping up and down for joy over the prospect for snow.  Not so fast bucko!  Everything is not as it seems.

It took quite a bit of careful analysis to decipher what the scenario would be.  The computer models have been all over the place with this system; from no snow to more than 15” of snow.  Even our own in-house model has seen big run-to-run swings with 2 to 4 inches of snow in one run to no snow the next.  So what to do?

I have decided that the American model (GFS) seems to be preforming the best for now.  The NAM model has been showing wild swings run-to-run and the European model (ECMWF) seems too cold.  None of the models are perfect, but the GFS seems to be closest to actual observations in the forecast.

Thus, here is the forecast for Columbia, South Carolina over the next seven days.  This was posted Sunday, January 26, 2014:

The seven-day forecast posted Sunday, January 26, 2014 for Columbia, SC.  Click on the image for a larger view.  Image Credit: WLTX-TV.

Tuesday, January 21, 2014

A Cold End to January 2014

A weather pattern we have seen many times since late October, 2013, has reappeared in its amplified form.  The ridge of high pressure in the upper atmosphere has been building since late last week along the Pacific Coast, stretching from northwest Mexico to Alaska.  This has pushed the jet stream far to the north into Alaska and the Yukon. 

The 500 mb pattern for North American at 00z January 21, 2014.  Click on the image for a larger view.  Image Credit: WLTX-TV.

The result has been unseasonably warm temperatures for this time of year.  It is still cold, but in Fairbanks the temperature averaged 24° F above normal on Monday.  There have been wild swings in Fairbanks, AK, this month with its coldest temperature of -41° F on January 12th & 13th, and its warmest temperature at 34° F on January 17th.  On that day the temperature averaged 32° F above normal.

Alaskan temperatures at midnight January 21, 2014.  These are warm readings for central Alaska in January.  Click on the image for a larger view.  Image Credit: WLTX-TV.

Tuesday, January 14, 2014

The Polar Vortex & More

The first major North American weather event of 2014 was the cold Arctic outbreak in the first week of January.  The term polar vortex became the buzz word (in the media) for the cold outbreak, though it was much more.  As a previous post notes this was a pattern extending back to late October of 2013.

The term polar vortex has been around since the 1940s.  From the American Meteorological Society Glossary of Meteorology:

Polar vortex - (Also called polar cyclone, polar low, circumpolar whirl.) The planetary-scale cyclonic circulation, centered generally in the polar regions, extending from the middle troposphere to the stratosphere.

The westerly airflow is largely a manifestation of the thermal wind above the polar frontal zone of middle and subpolar latitudes. The vortex is strongest in winter when the pole-to-equator temperature gradient is strongest. In the Northern Hemisphere, the vortex has two centers in the mean, one near Baffin Island and the other over northeast Siberia.

I prefer to use the term Arctic outbreak to describe what happened in early January.  The polar vortex was involved, but the overall pattern was much more than the polar vortex.  The winds in the upper atmosphere plunged from northwestern Canada into the southeastern U.S. due to an amplification of the ridge of high pressure off the West coast and the deep trough over the eastern part of North America.

NASA put together a movie of temperature observations from NASA's Atmospheric Infrared Sounder (AIRS) instrument on NASA's Aqua spacecraft.  The Atmospheric Infrared Sounder, AIRS, in conjunction with the Advanced Microwave Sounding Unit, AMSU, sense emitted infrared and microwave radiation from the Earth to provide a three-dimensional look at Earth's weather and climate. Working in tandem, the two instruments make simultaneous observations all the way down to the Earth's surface, even in the presence of heavy clouds. With more than 2,000 channels sensing different regions of the atmosphere, the system creates a global, three-dimensional map of atmospheric temperature and humidity, cloud amounts and heights, greenhouse gas concentrations, and many other atmospheric phenomena. The AIRS and AMSU fly onboard NASA's Aqua spacecraft and are managed by the Jet Propulsion Laboratory, Pasadena, California, under contract to NASA. JPL is a division of the California Institute of Technology in Pasadena.

The temperatures shown are at a pressure of 850 hectopascals (hPa, also known as 850 mbs) which is at an altitude of 4500 to 5000 feet over much of the U.S. It begins on December 1, 2013 and runs through January 7, 2014.  The most obvious feature of the movie is the tongue of cold air moving out of Canada and southward to cover much of the eastern United States during early January 2014.

This is a picture of the last day of the movie, Tuesday, January 7, 2014.  The dark blue areas start at -12° C and become purple at -24° C.  This was the farthest extent south and the surface temperature dropped to 13° F in Columbia, SC, with a wind chill temperature of 3° F.  Click on the image for a larger view.  Image Credit: NASA.

Tuesday, January 7, 2014

Weather? Climate? Confused?

Have you noticed the attention the weather has been getting in the media?  The cold blast for much of the U.S. & Canada, the trapped ship in the Antarctic, and the storms hitting Europe around Christmas are just a few examples.  Other news reports that you may not have been aware were the floods in southern Brazil and in the Caribbean, the heat wave in Argentina, the usually cold weather in the Middle East.  These are all weather events.

Some media outlets are reporting the cold events indicate that we have little to fear from global warming.  Yet global warming does not cancel the seasons.  In fact what we know about our changing climate is to expect more weather extremes worldwide.   Not just heat waves, but more floods, droughts, and even energized storm systems.  This is how a changing climate translates into daily weather.

Often many in the media confuse the difference between weather and climate.  Don’t worry, because some meteorologists do too.  The weather is basically composed the events that unfold in the present.  Meanwhile climate looks at the long term average of weather.  By definition this is a 30-year period.  We can look at shorter term trends to look at how changes are progressing, but we still have to look at the climate period of 30 years.

Sunday, January 5, 2014

Arctic Cold? I'll take a Double!

The new year is taking up where the old year ended.  The weather pattern discussed in a previous post continues to dominate North America.  Each time the pattern amplifies with a strong ridge-trough-ridge look, cold air invades the U.S.  The pattern relaxes and becomes more zonal causing milder conditions to return.  This is the up and down pattern that has resulted in a roller coaster of temperatures.

This was the 500 mb pattern for North America at 12z December 9, 2013.  Note the ridge-trough-ridge pattern.  Click on the image for a larger view.  Image Credit: WSI.

This was the 500 mb pattern for North America at 00z January 6, 2014 (taken from the ECMWF model 12 hours earlier.  Note the ridge-trough-ridge pattern returns.  Click on the image for a larger view.  Image Credit: WSI.

However, this time there has been a bit of a twist.  A surge of cold, arctic air invaded much of the country at the end of last week.  The temperature in Columbia dropped to 22° F Saturday morning.  The high pressure center moved quickly to the east causing winds to shift bringing clouds back into the area before daybreak.  This locked in the cold air for the weekend and there wasn’t much of a rebound in temperatures.