A Normal Winter?

The National Climatic Data Center (NCDC) released its analysis of the past winter today and the assessment for South Carolina? Near normal. The statewide average turned out to be the 66^th coldest and 65^th wettest winter on record.  The ranking was based on 120 years of data.

The statewide rank of temperatures (top) and precipitation (bottom) based on 120 years of records (since 1895).  A rank of 1 for temperature would be the coldest while for precipitation it would be the driest.  Click on the image for a larger view. Image credit: NOAA/NCDC.

Coming in the Back Door

This winter has been a wild one for temperatures in South Carolina.  There have been big swings from hot to cold and back again.  Now that meteorological spring has begun (March 1^st) the pattern continues.

A dramatic change to our weather is about to take place.  Cold arctic air is already in place across much of the central U.S.  Normally a cold front moving in from the west would bring the cold air to our state.  However, occasionally it comes in through the “back door”.

High pressure builds east and the cold air slides down the eastern seaboard faster than it can come in from the west.  It becomes trapped between the ocean to the east and the Appalachians to the west.  The cold front that surges south is known as a “back door” cold front.

Typically a wedge of cold air stays in place until something comes along to move the cold air out, which is a very difficult thing to do.  The result can be days of overcast skies and chilly northeast winds.

This time the back door cold front will be accompanied by a dramatic temperature drop.  When the front passes the temperatures will likely drop 20-25° F in an hour or two.  The front will be preceded by a band of rain which will begin the temperature drop.  Winds will shift from a westerly direction to a northerly direction as the front passes.  The winds will increase and there will be a wind chill to worry about in the late afternoon.

The RPM model forecast for 1:30 p.m. EST on Monday, March 3, 2014.  This is from the 21z run of the model using the 12 km grid.  Click on the image for a larger version.  Image Credit: WLTX-TV\WSI.

For Entertainment Purposes Only

For almost a week there has been a persistent rumor that another snowstorm is on the way.  I traced this back to radio spreading the rumor that Farmers’ Almanac had predicted the past two snowstorms and was predicting a third.  I was frequently asked if there was another snowstorm on the way, for which I answered no.  The response was almost always “Well, Farmers’ Almanac is predicting another snowstorm and it predicted the last two.” What?

So I investigated this claim.  First let me point out that there is a Farmers’ Almanac (dating back to 1818) and an Old Farmer’s Almanac (dating back to 1792).  It was Old Farmer’s Almanac that was predicting snow.  Second the forecasts are so vague as to be of little value.  Neither ever forecasted sleet or freezing rain and thus the ice that was so devastating.

Yet there were a few that were adamant that Old Farmer’s Almanac got it right.  If that is the case, then why ever watch the media.  Let’s explore the claim.

I do not have the forecast breakdown for January, but I did get it for February.  For the period of February 7-14, the forecast is for “periods rain and snow, then sunny, cold”.  It was during this period that the snowstorm occurred (11-13).  But, wait!  The forecast is for the entire region from south Georgia to southeast Virginia.  It also includes the Piedmont as well as coastal areas.

Does this forecast apply equally to all locations?  Are we to apply this with rain in the south and snow in the north?  If so, where is the rain/snow line?  Where is there any mention of ice?  Where does it even say snowstorm?  Merriam-Webster Dictionary defines snowstorm as a disturbance of the atmosphere marked by a heavy amount of precipitation in the form of small white ice crystals.  In their forecast how much snow will fall?

Remembering #WinterMess 2

Little did we know that the winter storm at the end of January would be the prelude to a bigger storm two weeks later (February 11-13).  A complex storm system came through South Carolina in two waves.  The first occurred on Tuesday with snow over the northern Midlands and rain/sleet elsewhere.  This was followed by the main batch of precipitation on Wednesday ending Thursday morning.

Most of the snow occurred over the northern half of the Midlands.  It was mainly sleet with some snow in Columbia, but the precipitation became more snow farther north.  The northern most counties of the Midlands saw a considerable snowfall.

Total snowfall as of 7 a.m. Thursday, February 13, 2014.  This is based on observations from the National Weather Service Forecast Office in Columbia, SC.  Image Credit: WLTX-TV.

South of Columbia it will a sleet/freezing rain mix.  The farther south you went the more freezing rain occurred.  The southern Midlands saw the greatest accumulation of ice as shown on the map below.

Total ice accumulation as of 7 a.m. Thursday, February 13, 2014.  This is based on observations from the National Weather Service Forecast Office in Columbia, SC.  Image Credit: WLTX-TV.

The Midlands ended up on the dividing line between snow and ice.  The northern half saw a snowstorm while for the southern half saw an ice storm.  Travel became difficult if not impossible through some sections.  The worst of the storm occurred over the southern Midlands with the accumulation of ice.  An estimated 350,000 people lost power at the end of the storm.  Some were without power for over a week.  Schools remained closed for Wednesday through Friday with some of the northern counties closing schools on Tuesday.

The #BigMelt

There is finally some relief after a week of snow and ice followed by an earthquake.  It was quite cold this past week following the 12^th coldest January on record for Columbia.  It was the 11^th coldest for South Carolina as a whole in January.  The weather warmed after the first winter storm at the end of January.  Little did we know that it was a warm-up act for the next winter storm.

Most of the snow and ice melted as the sun returned on Friday and a warming trend began.  A cold shot of air on Saturday only slowed the melt, but the warming trend continued on Sunday.  This week will be noticeably warmer this week.  In fact, temperatures will be in the mid to upper 70s by Thursday.

The 7-day forecast for Columbia, SC, for February 18-24, 2014.  Click on the image for a larger view.  Image Credit: WLTX-TV.

#WinterMess the Sequel

And this time she means business!

The big picture described in yesterday’s blog post is still on track, but the details are a little different.  This is based on the latest computer model runs.  Basically, an upper-level system now in the southwestern part of the country will combine with a disturbance moving in from western Canada and will intensify over the Southeast.  This will induce a surface low to form first in the Gulf of Mexico and then off the Southeast coast.  High pressure over New England will push cold air into the Carolinas setting the stage for winter precipitation.  It will be a “big ol’ mess” when all comes together.

A Winter Weather Advisory has been issued for the northern midland counties of Saluda, Newberry, Fairfield, and Kershaw.  This will be for an accumulation of snow and sleet mainly Tuesday morning.  The following is an update from the previous post.

As mentioned yesterday the forecast is a difficult one based on the timing and various forms of winter precipitation that will occur.  The Midlands will see it all; rain, freezing rain, sleet, and snow.  It appears that the onset of precipitation will be late tonight as rain moves into the area.  The rain will likely change to snow during the early morning hours for the northern part of the Midlands (Saluda, Newberry, Fairfield, and Kershaw counties).  There could be enough accumulation to cause travel problems, so travel through the northern Midlands needs to be monitored.  The snow will change to rain and taper off during the afternoon.  This will be the first surge of moisture into the region.

A computer model view (RPM) of precipitation at 6 a.m. Tuesday.  This is from the 21z RPM model run.  The bluish areas are snow and could contain sleet.  The green areas are rain.  The pink is for a wintry mix.  Click on the image for a larger view.  Image Credit: WLTX-TV.

Another #WinterMess?

Just two weeks ago a winter storm moved through the region producing a combination of rain, freezing rain, sleet, and snow.  Many thought this was it for the winter, but Mother Nature had other ideas.  Look here for a rundown of WinterMess #1.

Incredulously another winter storm is headed through the Southeast.  This time it will be a little different from the previous storm (i.e., no two storms are identical).  A complex weather pattern will develop over the Southeast with an upper-level disturbance moving east and helping to develop a low pressure system off the Carolina coast.  A surge of cold air will be pushing into the Carolinas ahead of this which will turn the rain into a wintry mix.

The models are a little better in converging on a solution.  There is still considerable uncertainty due to the tight area that the worst will fall.  A difference of just 20 miles can make a huge difference in the forecast even at this time range (less than 48 hours).

This blog post is designed to give you a heads up on our thinking and the time frame that things will occur.  There is only moderate confidence in the details, but the overall picture has good confidence.  The scenario and forecast that follows was derived from the 09z, 12z, 15z, and 18z runs of the WSI RPM model along with the 12z runs of the WRF, GFS, ECMWF, and GEM models on Sunday, February 9, 2014.  Each model is slightly different, but the details were mainly from the RPM model.  This represents my best guess at this point.

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:

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.

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.