Winter Doesn’t Give Up That Easily…

If you’ve lived in the Northeast for any length of time (in years), you know full well that spring almost never comes without a price. Temps in the 60s, 70s, and even 80s over the last week are going to give way to the harsh reality that winter can still rule in March and even April.

Latest plot of recent and forecasted NAO from CPC

To the left you’ll notice a plot of the NAO..the North Atlantic Oscillation. You’ve probably heard of it before, but in layman’s terms, it’s a measure of atmospheric blocking (high pressure) in the vicinity of Greenland. Traditionally in winter, a negative phase of the NAO spells more troughing and thus colder conditions in the Eastern US. You’ll notice from the graph that since the beginning of February, the NAO has been almost locked in a neutral or positive phase. As such, you haven’t seen quite the harsh conditions you all experienced earlier in the winter. But the red lines indicate the forecast, and that, my friends, is what we call a tanking NAO.

Latest Plot of Recent and Forecasted PNA from CPC

Off to the right, you’ll see another, similar chart…this for the PNA, or Pacific-North American Oscillation. This measures blocking near the West Coast. When this is positive, there is traditionally a ridge present out west, which usually can translate to a downstream trough. When you have the NAO in a negative phase and the PNA in a positive phase, that’s a usual rock solid combination to generate warmth out West and cold in the East. It appears, we have these factors ready to lock in for a good 10+ days, with the +PNA holding on a little longer perhaps than the -NAO.

What’s this mean? With them both in concert, it spells strong cold conditions for the Eastern US and a developing warm pattern and end to storminess out West. As the NAO starts to fade, but the PNA stays relatively positive, it means the cold in the East will ease some, but there’s absolutely no sign of a return to the 60s and 70s you’ve seen recently. Expect some 30s, 40s and maybe occasional 50s if you live in the Northeast Corridor through at least next weekend.

How about snow?

A few snow chances exist over the next week or so. I won’t go into many details about the one on Sunday and the one next Wednesday, but suffice to say, the conditions do exist for potential snow.

3/22 12Z GFS Snow Forecast from Earl Barker's Model Site: http://wxcaster.com/regional_snowfall.htm

In the immediate term, we’ve got a situation tomorrow. The map to the left is this morning’s projection of accumulated snowfall from the GFS model. If you live in NYC, you can ignore this for the most part (think the model is a little too aggressive with snow there). This is mainly west of I-287 and north of I-80…but you can clearly see the risk. For Northwest NJ and the Scranton area, despite what this model is showing, I’d be shifting those bands south a bit, and a solid 6-10″ thumping seems likely…very elevation sensitive this time of year, so the higher up you are, the better your odds for snow. The highest amounts seem banded in an area east of I-81, north of I-80, west of I-87, and south of US Route 20. There is some model debate as to how far south the snow will get (one model brings heavy snow as far south as Central NJ). I am going against that model for now due to a poor track record this winter. But you will want to keep an eye on this situation. And if you live in Northwest Jersey/Northeast PA, tomorrow and tomorrow night look very unkind.

Wish I had better news, but enjoy this last gasp of winter if that’s your thing.

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Winter Starting Off Strong for Some

CPC Graph of NAO and Forecast

Winter is off and running. It’s not terribly uncommon for La Nina winters to start off bursting out of the gate. But this winter is almost a carbon copy of last. And one of the big reasons we have to thank is the NAO. If you look at the image on the right (top frame), it shows a chart of progression of the NAO index since late summer and the red lines indicate the forecast. The NAO has been negative for months. We’re clearly in some sort of funk or cycle of it. When the NAO goes negative, in a nutshell, you get a large ridge of high pressure centered near or over Greenland (NAO is often synonymous with “Greenland Block.”). When you get large ridges, that usually means there are large troughs on opposite sides of the ridge. And geographically, Europe and the Eastern US are on the opposite sides of Greenland, so…there you have it.

Greenland blocks can often be favorable for lake effect snow, and there has been a LOT of lake snows. We’ve seen this pattern several times in the last few years, but because often times the winds have been either too northerly or too westerly, the snows have hit more remote areas. Now, Syracuse is getting hammered with over 30″ of snow so far this month (and potentially a LOT more coming)! When snow records start being set in the ‘Cuse, that usually means we have a pretty impressive weather pattern or storm ongoing. Here’s a look at the NWS watch/warning map from this afternoon. You can see the lake effect snow warnings in Central and Western New York, as well as the deep blue on the Gulf Coast, indicating hard freeze warnings. This is VERY early for cold of this intensity in places like Florida. So we’re in it pretty hard right now, and it’s only going to continue for the next 10+ days.

Want relief? My forecast highs out here in SoCal are in the mid 80s for early next week…that’s balmy! It’s all related though, as the sharp trough in the East, generally means an amplified sharp ridge in the West.

So what about the storm for the weekend? I’ll probably talk more about this tonight after a nap and some errands. But the operational models track the storm over NY, with both the Euro and GFS ensembles slightly further east with the center of it. To me, this would imply the operational models are a little too far west, and I’d hedge my bets a little further east. This means: Heavy interior snow, with some area of freezing rain somewhere in between, and mainly rain on the coast and for the big cities. I have a feeling that parts of Central or Western NY might get clobbered with this. Especially if we trend more toward a slightly flatter GFS storm.  Expect a sloppy mess in the interior regardless Sunday and Monday. Again, more on this later