7:45 AM

I wanted to make a post about the ideas I have on the potential storm on Sunday, however I saw some data on the model guidance coming in at 00Z and thought better to do some research first before posting.  So off I went diving into the KU book for some additional guidance and words of wisdom.  I think many in the forecast area are going to like what I found and am thinking now. 

First,  let’s deal with an equally dangerous issue that will be unfolding over the forecast area on Friday and Saturday, that would be the Arctic cold air.  The 850 MB temperaturs will support bruttally cold temperatures at the surface with a range of 14 below to 20 below zero on both days, that’s in celcius at that level.  At the surface, temperatures will struggle to break 20 on Friday even along the coast and will “moderate” slightly on Saturday with upper 20′s along the southern New Jersey coast.  Not exactly a warming comfort.  Combined those temperatures with the stiff northwesterly wind, and you can bet the Philadelphia Eagles and their fans are glad to be in Arizona rather than at home for this weekend! 

As I have been saying for the past few days, if you do not need to be outdoors in this weather, don’t be.  This type of cold air can cause frost bite and can kill.  If you have to go  outside, layer as much as you can and cover up as much as you can.  This is not the type of cold air to try to be a “tough guy” in. 

Now, on to the topic that everyone is likely excited about.  The research I did on this period is based on the placement and intensification of the ridge out West and why this ridge is so important.  In almost all the text book examples of winter storms, whether a postive or negative NAO state or what ever is going on in the Atlantic, a key indicator of a winter storm a few days out was the placement of the ridge over western North America.  The ridge axis leading up to Sunday is right around western Idaho, which basically is a big flashing warning sign for me that a major east coast winter storm is on the way.  Why?  Because the ridge position and intensification strongly points to intensification and digging of the trough over the East coast and a trough axis that would strongly support a storm track from the Southeast coast to around the 40N/70W benchmark. 

This piece of data seen on all model guidance on Saturday is why I upgraded to Alert Stage 2 for Sunday this morning, by the way.

Now, there’s a lot that I need to adress here first as far as model guidance.  The Non-American model guidance continues to strongly advertise the potentail for Sunday.  The ECMWF, beginning to enter a forecasting period of high accuracy level, strongly suggest a major hit for the forecast area with snowfall amounts of over a foot over the forecast area, yes even you Philadelphia.  The UKMET takes a similar position as well.  The Canadian trails behind, but struggles with the vorticity maximum diving into the trough on Sunday morning.  The GFS is catching on, but is showing an error seen in the model for the entire winter with tracking the initial clipper way too far north, thus producing a redeveloping low over the New England coastal waters.  However, the 500 MB level is beginning to resemble the ECMWF, and I expect a trend in that direction over the next few days.  The NAM (I know, at 84 hours) does show a leaning towards the ECMWF with at least a similar position of features at the surface and upper levels.

Now, there is still a lot of uncertainty here.  For one, these storms don’t like to invite everyone to the “party” and someone is going to miss out.  The question that needs to be answered is at what location and time does the new coastal low develop and intensify.  Expect the model guidance, all model guidance, to waver in the placement of the best QPF.  The fact that the ECMWF has shifted to a very snowy solution last night is promising, but temper that excitement for a moment.  If the low intensifies only a few hours later, than Philadelphia and New York City may see next to nothing due to a significant dry slow between the closing 500 and 700 MB lows and the deepening surface low.  Further, the Arctic air mass will be moderating at this point and the position of the high pressure system is not supportive of CAD.  I do think some locations like Long Island and the immediate New Jersey coast may have boundary layer issues.  What may be an interesting interaction is the strong CAA behind the weakening clipper (old primary) and the bombing out of the coastal low.  The timing and interaction of the coastal front along with the fresh introduction of Arctic air may have very interesting (and promising) developments with mesoscale forcing over the entire forecast area, but will have to wait at least until 24 to 48 hours before this event before discussing this in detail.

The point here is that the potential is high for a major winter storm and I think a winter storm is likely.  Who gets what and how much is unknown, but you have to like the model trends leading up to this situation.

As for after this storm, I do expect a relaxation of the cold pattern for a brief period, however the negative EPO will continue to flex it’s muscles, and drive another cold, Arctic air mass into the eastern two thirds of the nation.  There is potential for a very stormy and cold pattern setting up for late January and early February, but let’s deal with one storm at a time for now.