1/30/11: Forecast - Another Midweek Threat

Another week, another significant storm threat

We are in a very active pattern right now and it continues to produce major storms in the Eastern US.  This week's storm will not be a coastal storm however, as all model guidance take it west of the Appalachians.  This storm track will ultimately mean rain for the area, but there looks to be frozen precipitation for a period, before we change over.

Take a look at the following GFS model graphic for 1am Tuesday morning:

If you look along the east coast, you can see the isobars (black lines) and the isotherms (red and blue lines) bending south.  This is a classic representation of cold air damming.  As the storm moves in, it is bringing a surge of warm air.  This warm air runs over top the cold air that is trapped near the surface.  The high pressure to the north of us keeps the cold air locked in east of the mountains.

This map also shows some light precipitation over the area.  This is a result of the rush of warm air ahead of the system.  At this time (1AM) it should be cold enough for this precip to be all snow, but as we head into the morning afternoon hours on Tuesday, it will change to sleet and then freezing drizzle.  

Here is the map for 7am Tuesday morning:

 This map continues to show the cold air damming and the freezing line down to near the VA/NC border.  Surface temperatures are still below freezing, but the warm air continues to surge northward aloft.


1PM on Tuesday:

Here we see the freezing line moving back north and basically right through the state. As the storm continues its northward trek, the warm air continues to surge and displaces the sub-freezing temperatures at the surface and changing the precip to just plain rain.

The good news is that most of the precipitation that falls from this storm will indeed be plain rain.  The bad news is, most models do a fairly poor job at handling cold air damming situations and tend to erode the cold faster than it actually does.  What this means is, we could see a fairly long period of light sleet and freezing rain into Tuesday evening.

By Tuesday night, the transition should be well underway and temperatures will continue to climb all the way to the mid-40s on Wednesday. The bulk of the precip will fall late Tuesday night and Wednesday so there is no concern of a major ice event for our area.

7AM Wednesday morning:

The freezing line has moved well to our north by 7AM Wednesday morning, while the heavier precip is falling as rain.  Expect Wednesday to be a relatively mild day, with rain lasting into the late afternoon, early evening hours.  When all is said and done the GFS shows us ending up with an inch of liquid precip, but again this will fall mostly as rain:

While it will be mostly rain for us east of the track, those west of it appear to be line for a heavy snowstorm.  Illinois and Indiana appear to be in the jackpot zone, where Winter Storm and Blizzard Watches are already posted for snowfall totals in "feet" not inches.

Looking ahead


Several models are hinting at yet another coastal low possibly affecting the area by the end of the week.  It will take a few days to sort through everything to see how it may affect us, if at all.  For now, it is just something to keep an eye on.