"WARM NOSE" EXPLAINER, UPDATE TWEAKS

We now await the arrival of our wintry forecast this afternoon. I don't have anything to add or change from my previous post...a 'warm nose' is what we'll be dealing with, which should be keeping us more in ice and minimal snow.  However, we should start out as snow before the precipitation type kicks over this evening.

  I always like to share/educate with information to maybe better understand what we are dealing within our particular area.  Below is the Sat AM national map showing all of the watches and warnings.  To say this winter storm is expansive is an understatement.  Notice the black circled area, a noticeable bump upward with a break in the ice storm warnings, not a straight line across.  That's the warm nose of air trying to push up from the Gulf of Mexico thanks to a smaller area of low pressure on the LA/MS coast. (Click on any pics to enlarge):

National warning/watch map Saturday AM

As a rule of thumb, the higher you go in altitude the colder the air should get, but often times the air will warm up just a few thousand feet above the surface.  All precipitation begins as snow, even in the summer, and then it melts.  If the air column stays below freezing, it's all snow.  This one missed us as it will fall farther north.  If the air column warms above freezing at some point, we're now back in rain.  The kicker for us is how close that freezing line is above our heads.  If it's high enough, say 10,000 feet, it will turn back into sleet/ice pellets on its way down.  If it's low, like 5,000 feet, it may not have enough time to refreeze and will hit the below-freezing surface as rain, freezing into a glaze of ice (the worst-case scenario).  

I'm afraid the latter is where we fill find ourselves tonight.  As I mentioned earlier, the High Country above 5,500 feet may find itself in the above-freezing temps and mostly rain, ultimately.  Warm air is lighter than cold air, so the warm air can't push out the cold at the surface, but aloft it can 'nose' in, creating our problematic forecast.

The massive engine driving out storm is a huge low back in the Desert Southwest, with an equally massive high pressure near the Great Lakes driving in some bitterly cold air. With the counterclockwise flow around the low, it will pull in a tremendous amount of moisture from the Gulf of Mexico...but at the same time, it's pulling in the warmer air, as well.  The map below is for this evening, and I drew in the white arrow to show the intrusion of warmer air into our set-up:

SATURDAY evening surface map

And that's the end of this missive.  Forecasting just where that freezing line aloft will be for us in Haywood County has been a real bugaboo for this ever-changing winter storm.  I still see us in rain and above freezing Sunday afternoon, and we'll take all of that we can get to dispel what ice/sleet we have, but Sunday night into Monday will be NW flow snow showers and deeply cold temperatures.  What sticks will stay for days.

Icy roads are a no-go.  Our decks and stairs will be the first to ice up, as well as the vegetation, so I'll be watching the ice on the deck railing.  Once ice gets thick and heavy enough, then power lines and trees can start to snap.  With power, often it's the transformers that blow, so don't be surprised to hear a kaboom or two.

As we all say, prepare for the worst and hope for the best.  Over and out.

Bob