The light at the end of the tunnel is getting brighter in terms of signals for a temperature moderaton. However, old man winter doesn’t want to go down without a fight, and a fight he’ll give next week. The coldest airmass of the winter season thus far is likely to invade much of the Central/Eastern US regardless of any storms. Preceding this arctic blast, a northern stream short wave will be propagating NW-SE, then progged to amplify near the East Coast late next week. Will this happen? What track(s) are more likely? Let’s try to decode the pattern…

If we examine global signalling, notice how the Arctic Oscillation is forecast to tank from about +4 standard deviations (sd) above normal to near -1 sd. This is an enormous drop, and coupled with the NAO decline from approximately +1 to slightly negative, we have an Armchambault signal for cyclogensis/hvy precipitation event on the Eastern Seaboard.

So we have a decent idea that a large system producing hvy precip (snow on the north side, rain to the south, possibly strong T-storms in the Southeast US) is likely, but where will it track?

The set-up prior to the potential time frame is key.

We have a short wave amplifying in the Northeast and tilting negative early next week, not doing much damage in terms of snowfall as it develops to late, but it will aid in pumping heights in the north atlantic, thereby mechanically inducing at least a temporary negative NAO feature.

Porgression of waves. I’ve denoted #1 and #2. Number 2 is the short wave potential big storm later in the week.

Potential problem with this threat is the ridge axis out West.

With the ridge that far west, we could be talking an early tilt of the short wave trough, causing more rain than snow on the East Coast.

What will happen? Will need to monitor the situation closely, but right now, the potential is high for a major precipitation event based upon global signals. However, whether snow or rain is the dominant mode of precipitation is still uncertain. The interior from the immediate coast could be at higher risk for significant to major snows, but considering how this winter season has gone, I would put I-95 at mod-high risk as well for significant snow.

Beyond this storm, arctic air will pour in, but soon thereafter, the pattern will breakdown, giving way to the first real thaw of the meteorlogical winter. With the NAO and AO likely to stay near neutral/slightly positive, but more importantly the PNA going negative — the large scale trough axis will shift into the Mid-west/Rockies. This should give the PAC NW a better taste of winter than they’ve seen over the past couple months.

Bottom lines:

1) First bombing low to pump heights, getting the NAO slightly negative

2) Storm threat high for late next week. Rain/snow concerns due to western ridge axis.

3) Arctic unloads immediately after the storm, but pattern breakdown with temperature moderation for the middle to latter part of February

4) Will the cold/snowy pattern return? My thinking is yes, but possibly not until the end of February or March.