Sunday, February 9, 2014

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.

Clouds will be increasing across the Midlands Monday and it should be mostly cloudy into the evening.  There is no concern about the weather through Monday night, so if you have plans, no need to change.

A depiction of the surface weather pattern for 7 pm EST Monday (top) and 7 am EST Tuesday.  Little if any precipitation is expected Monday night, but a wedge of cold air will be developing as high pressure to the north builds down the eastern seaboard.  The cold air wedge will be in place by daybreak Tuesday.  Click on the image for a larger view.  Image Credit: WLTX-TV.

The onset of precipitation is likely to be during the day on Tuesday.  It may begin as rain until evaporational cooling and cold air advection changes it to snow over some parts of the Midlands.  The timing of precipitation is uncertain, but roads will likely be fine into the early afternoon.  However, they could deteriorate rapidly toward sunset.

A depiction of the surface weather pattern for 7 pm EST Tuesday.  The onset of precipitation is likely around midday changing to snow and tapering off toward 7 pm.  Click on the image for a larger view.  Image Credit: WLTX-TV.

It may get quite interesting Tuesday night.  The snow may change to rain and freezing rain which will change to sleet overnight.  Much of the Midlands will see sleet or freezing rain early Wednesday morning.  There could be an prolonged period of sleet into daybreak for the central Midlands.  This will likely change to freezing rain shortly thereafter which could last until early afternoon.  During this time the ice accumulation could be significant leading to power outages.  The precipitation may diminish some in the afternoon, but it will not end until Thursday morning.

A depiction of the surface weather pattern for 7 am EST Wednesday.  There will be a significant amount of winter precipitation overnight.  The intensity of the cold air wedge will be greatest on Wednesday.  Click on the image for a larger view.  Image Credit: WLTX-TV.

A depiction of the surface weather pattern for 4 pm EST Wednesday.  The precipitation may diminish near sunset, but precipitation to the north is likely to move through overnight before ending.  Click on the image for a larger view.  Image Credit: WLTX-TV.

The precipitation could increase and change to sleet and snow Wednesday night before ending.  Any additional amounts during this time are NOT figured into my snow and ice forecast.  Thus, it could get a little worse Wednesday night.  The precipitation should be over by daybreak on Thursday as the storm moves up the eastern seaboard.

One of the biggest complexities in this forecast is the fact that the Midlands will be on the boundary between rain and snow.  In fact the precipitation is likely to change phases many times before ending.  This makes any forecast of snow and ice exceedingly difficult.

The following forecast is a snow forecast ending at 7 a.m. Wednesday morning.  In this forecast is also an accumulation of sleet which I did not break out since both may fall at the same time.

A forecast of snow accumulation (not snow depth) by 7 am EST Wednesday.  Most of the snow will be Tuesday with sleet (included) Tuesday night.  Note the tightness of the snow bands.  Click on the image for a larger view.  Image Credit: WLTX-TV.

The ice forecast is ice accumulation from freezing rain.  Significant ice buildup is not expected until Wednesday.  The greatest accumulation of ice may be Wednesday morning.  Thus, the ice forecast is up to 7 p.m. Wednesday evening.

A forecast of ice accumulation by 7 pm EST Wednesday.  The most significant ice accumulation from freezing rain is likely Wednesday morning.  Note the maximum ice accumulation is through the central Midlands.  Click on the image for a larger view.  Image Credit: WLTX-TV.

It is hard to express the difficultly in this forecast.  Many hours were spent comparing computer models and analyzing their results.  There is moderate confidence in the result.  The biggest uncertainty lies in the narrow range of ice.  This may be adjusted north or south based on later information, but the overall pattern seems good.  This will be a longer event than the last one and could last into Thursday.

The biggest problem for decision makers may be Tuesday.  The onset of precipitation may determine how fast conditions deteriorate.  What is certain is that a winter storm for Wednesday is likely.

Be sure to catch breaking news by following me on Twitter: @JimGandyWLTX along with my colleagues @Daniel_Bonds, @amyaaronson, @ChristineWLTX.  Also you can follow News19 on Twitter at: @WLTX and also on Facebook.  I will have on updated blog post on this late on Monday.