An approaching storm system will bring warmer air with it tonight into Tuesday, but the cold air which has settled in over our area will be stubborn initially. The situation becomes somewhat complicated tonight, as warm air surges into the area in the middle levels of the atmosphere. At the surface, however, cold air will hold on a bit longer than usual, creating an unbalanced "sounding" of the atmospheric profile. Essentially, the warm air aloft will cause the snow flakes to melt, but the cold air at the surface could cause sleet, or the rain that falls to freeze. In some interior locations, there could be a period of snow as well before the mid levels of the atmosphere warm up. This will create a few hours of wintry conditions, mainly over the interior. And although we may see a few flakes or sleet in the city...it will be short lived and a quick change to rain is expected thereafter. The change to rain will work through the entire area by Tuesday, as the cold air settled in at the surface loses the battle with the push of much warmer air associated with the storm system. By mid-afternoon, in fact, the city could reach the middle to upper 40's. Pictured right: Forecast assessment for the system tonight into early Tuesday. A period of wintry weather is expected over the interior, and although snow/sleet accumulations are forecast to be less than an inch, freezing rain or sleet could cause some slick roads and travel difficulties.

The process which causes the potential for sleet and freezing rain (or as we refer to it, a "wintry mix") is pretty complicated, and sometimes difficult to understand. But to make things more simple, it involves warming of the atmosphere above our heads...and stubborn cold air right near our heads at the surface. Warm air advection (or a push of warm air towards our area) occurs in the mid levels of the atmosphere, while the cold air at the surface remains. The image to the left is a forecast sounding, or a vertical profile of the atmosphere. The forecast is valid at Morristown Airport, New Jersey...at 15 hours from the 1800 UTC run of the NAM model, or valid for the early AM hours on Tuesday. The red line shows the temperature throughout the atmosphere, and the pink line represents 0 degree celsius, or freezing. You can see the warm air push in the mid levels (the red arrow points this out), and the cold air remaining in the very low levels (the blue arrow points this out). The area which we live in is the very lowest point of the sounding. If you could imagine a snowflake forming around the middle of the sounding and falling, the flake would melt where the temperature rises to greater than 0 degrees celsius, and then re-freeze into either sleet or freezing rain at the surface. Some stray snowflakes could make it down as well.

With time, these soundings warm up by Tuesday morning and afternoon...and precipitation will change to all rain throughout the entire forecast area. Still, the period of wintry weather over the interior, however brief it may be, could cause some slick roads and travel difficulties as well as some very light accumulations. The National Weather Service has issued Winter Weather Advisories for much of the interior. Check it out, and stay here for more information throughout the night and into Tuesday.