January Thaw Moving In

After a cold couple days our January thaw is ready to move in. Melting snow, unseasonably mild temperatures, and a rain storm or two will leave winter lovers with a stream of tears come next weekend.

While the usual winter weather weenies are doubting the coming torch using arguments like, “Well, January’s temperatures have largest standard deviation of any month so +10 really isn’t that unusual,” the signs are strong for an impressive period of above normal temperatures. Many of us in Connecticut will have no snow on the ground in a week’s time.

The big question is how long does the thaw last? Current indications are that while the next 10 days will be mild, potentially quite mild compared to typical January weather, the thaw may be on borrowed time. I expect a return to winter by January 15th at the earliest but more likely by January 20th.

— Meteorological Discussion Below —

Day 1-5 00z Euro Ensemble 850 T Anomalies

Day 1-5 00z Euro Ensemble 850 T Anomalies /  Courtesy Alan Huffman

Day 6-10 00z Euro Ensemble 850mb T Anomalies

Day 6-10 00z Euro Ensemble 850mb T Anomalies / Courtesy: Alan Huffman

The synoptic setup is pretty torch-tastic for the east coast. Above you can see the 850mb temperature anomalies with the greatest departures centered over New England. Below is the 00z Euro Ensemble day 6 to day 10 500mb anomalies.

Day 6-10 00z Euro Ensemble 500mb Height Anomalies

Day 6-10 00z Euro Ensemble 500mb Height Anomalies

A strong -PNA signal with a large trough over the west coast will pump up the ridge in the southeast. A southwesterly flow begins to advect milder air into New England and we’re looking at a pretty classic January thaw. Here are the raw 12z GFS MOS temperatures (lows/highs) for BDL. Keep in mind climo is 18/34 so that’s 7 days above average with 3 days of greater than +10 departures next week!

Screen shot 2013-01-04 at 2.17.15 PM

Beyond day 10, however, it’s unclear how much longer our thaw will last. This weather pattern is far different from last year and the warm-up is likely on borrowed time. The polar vortex over the North Pole is getting a big shake up.

The typically roaring zonal flow above the Arctic Circle thanks to the Polar night jet is slamming on the brakes.

ecmwfzm_u_f24

ecmwfzm_u_f144

In fact the night jet essentially reverses around 80N in the next couple days which will effective disrupt the Polar Vortex. The Euro forecasts of the polar vortex disruption can also be seen in through a potential vorticity perspective. Here’s the 600K PV analysis from today and the 10 day Euro forecast.

ecmwfpv600a12

ecmwfpv600f240

This PV split (notice the high PV lobes over the North Pole near D0 and separate at D10) will introduce some solid Arctic air into North America. The Arctic Oscillation will go strongly negative as the PV slides off the North Pole. The question will be where does the storm track set up and whether or not the true Arctic cold is able to slide far enough east for New England. The Euro Ensembles also couple the -AO with a -NAO thanks to ridging over Greenland. Cross your fingers snow lovers!

Models do show the milder pattern breaking down post-day 10 and it seems reasonable to expect winter will make a pretty sizable come back later this month. Stay tuned!

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January Thaw (Sort of…)

Don’t get too excited. The thaw probably won’t last longer than a day and don’t think you’ll be able to head out and play some frisbee either. A burst of heavy rain will accompany the brief thaw before we cool down again.

Our computer models are honing in on an “inside runner” storm for next Tuesday. Though this will likely start out as snow or ice it looks like it will flip to rain everywhere with a track west of Connecticut. Thankfully we are not talking about enough rain or warmth to cause flooding (like January 1996) but the snowpack will certainly take a beating.

No sustained period of above normal warmth seems likely in the near future.