northgawx

Confidence is increasing significantly that a major winter storm impacts much of MS/AL/GA/TN/NC/SC beginning this Monday and lasting through Wednesday. Two individual events will happen with the first being an overrunning event beginning late Monday and lasting through the overnight and through mid-morning Tuesday. Then event #2 comes in the form of a bona-fide gulf low later during the day on Tuesday with freezing drizzle lasting through much of the day Wednesday. So, let’s take a peek at each event individually. The higher confidence comes with wave #1 Mon/Tue with less confidence in the actual solution for Tue/Wed.

***LATE MONDAY THROUGH TUESDAY MORNING-OVERRUNNING EVENT***

This is probably the best chance for those north of a line from Gainesville->Dawsonville to see significant snowfall that we have seen in a while. That said, there is going to be a very sharp cut-off from north to south and exactly where that sets up will be literally a last-minute thing. Currently the GFS/Canadian have the cutoff from rain to snow somewhere along a line from Gainesville->Dawsonville, with the NAM being a bit north of that (though bouncing a bit). The Euro is closer to the GFS/CMC, if not a bit further south. The good news is, I suspect the models are probably slightly overdoing both surface temps and upper-level temps with the progression of the arctic front, as well as probably underdoing moisture a tad (especially the GFS). Also, the snow line will slowly work south so even if you start off briefly as sleet/rain you will probably transition over at some point (see maps below). The fly in the ointment for those actually seeing snow will be surface temps, but with snow falling and overrunning occuring and a wedge setting up I fully suspect the models are overdoing surface temps by a few degrees like the generally do during overrunning/wedge set-ups.

GFS valid 11AM Tuesday Precip initially begins overnight and the Canadian moves the first precip in late Monday. Exact timing will be nailed down as we get closer.

CMC valid at precip onset 7PM Monday with approximate RN/SN line:

The Euro as far as timing is concerned moves the precip in early Tuesday morning.

So, how much precip/snow should we expect? That is an EXCELLENT question that probably won’t be answered well until things get going (this is GA after all) but below is an approximate, unofficial first-call map for the Monday night->Tuesday overrunning event. I’m probably underdoing potential totals especially in the mountains but this will be a pretty sharp gradient (reminiscent of Feb 2013) from N->S. My official call map will be posted to the Facebook page probably sometime late tomorrow. This is just to give the general gist of what I am expecting as of right now.

As I am typing this the new Euro has come in and it moves the rain/snow line down south of Gainesville towards Commerce. LIke I said, wait and see.

***EVENT TWO: GULF LOW***

This is the event that has me very, very concerned for two reasons. First, the Euro and its ensembles have been EXTREMELY consistent with this. Second, they have been extremely consistent showing a major ice storm for a large portion of the area. The new 0z Euro continues showing this, with major ice falling all the way down towards metro Atlanta extending north and east including everyone south of the ridgeline. You guys north of the ridgeline are in more of a pickle  to forecast as wedges don’t generally affect you as much, however at this juncture I suspect most everyone remains below freezing in one of the more impressive CAD events we have seen in years, plus the snowcover will help keep surface temps sub-32. The CMC is very similar to the Euro in the track of the low but is a touch further south with the main precip shield.  The UKMET is also on board, with the GFS remaining in it’s own little world but slowly trending towards the rest of the modeling world. It has a really, really bad tendency/bias towards stringing the energy out (keeping systems unorganized for far too long) and that appears to be its continuing issue with this set-up.

All this said, confidence is increasing that a MAJOR ICE STORM occurs from the northeast ‘burbs of ATL north and east, with the highest probability of 1/4″ or more of ice coming in the highlighted areas below. Full disclaimer that this is not a forecast and amounts could decrease depending on how things trend the next 48 hours.

The GOOD NEWS to this is our saving grace could be some dry air working in keeping some of us in a good period of sleet before transitioning to freezing rain.

This is, however, a developing situation and still technically 3 days away despite the overall event beginning in less than 48 hours. A LOT can and WILL change, but at this juncture the modeling consistency leads me to the conclusion that we could see some pretty big issues. I’ll be updating on this second wave as we get closer to the event and modeling converges. AT the very least, expect a prolonged period of freezing drizzle on Wednesday as the system winds up to our east and the wedge keeps a flow of moisture rolling in.

 

Edit: One thing I just noticed about the Euro is taht it develops yet ANOTHER band of precip early Thursday that would drop more snowfall on the area (though not a ton) and really slam areas north of Cornelia->Dawsonville->Rome. THis is the first run to really show this and I suspect the Euro is a little too amped (but the UKMET is similar with the low bombing off the coast) but this is certainly something to watch as we get closer to the event.

I will update again after I get off work tomorrow evening.

~TW