Long Range: Warmth on the way, but for how long?

A happy Friday morning to you all! A large-scale pattern change is underway throughout much of the hemisphere — well, to be completely transparent, has been underway throughout much of the hemisphere — for the past few days. The seeds of the pattern change were planted long ago, almost 10 days before today, when a large ridge in the Eastern Pacific Ocean began to retrograde westwards towards the Aleutian Islands.

But even as recently as early this week, a ridge stood along the US West Coast, allowing northern stream energy (emanating from Canada and the arctic/polar regions) to drop southwards into the Northeast States. This ridge will finally collapse this week, dropping eastwards and flattening out. As it does so, arctic air over the Northeast states will be fleeting northeastwards into the Canadian Maritimes.

Ridges along the west coast that collapse eastwards into the Central and Eastern United States are notorious for allowing Pacific, maritime air to flow eastwards. Think of it this way: A large ridge on the West Coast, like a wave, holds Pacific air along its western fringes. When the jet stream collapses east, all of that air can flow eastwards as well, with no impetus to keep it away.

All of this adds up to the simplicity of moderating temperatures and tranquil weather over the next several days. These temperatures will, in fact, be quite warm and quite anomalous in their own right. High temperatures in the Mid Atlantic and parts of the Northeast on Saturday and Sunday will reach well into the 50’s, a solid 10 degrees above average for this time of year.

By Sunday, high temperatures could reach 60 degrees in those very same areas, including parts of New Jersey and even the Northeast urban corridor up towards New York City. The warm, although transitional at times, is expected to continue, by and large, into the middle part of next work week.

That brings us near the February 25th mark. Snow lovers, naturally, are starting to sweat.

But in a winter full of transition and a lack of consistency, they should know better. Alas, a look at the hemispheric pattern progression beyond Day 5 offers the increasing likelihood of some changes. Signs of the very same progression that occurred earlier this winter, allowing a warmer pattern to gradually break down, are starting to appear on forecast model guidance.

Mid level ridges in the atmosphere start a “Wave breaking” process across the Pacific Ocean during the Days 5-8 time frame. This is nearly opposite to the retrograding pattern we had seen 10-15 days ago. Imagine the ridges (pictured below) as waves, breaking from west to east across your screen. Eventually, higher heights start to build towards the Eastern Pacific again, causing a response in the higher latitudes as well.

Many of our “colder” patterns that have developed this year have featured below normal temperatures dumping into the Western USA first — and this pattern through the end of February and into early March looks likely to feature much of the same. Forecast models and ensemble guidance are already indicating the return of temperatures below normal averages for this time of year in those regions by Days 7-10.

But beyond that, after ridging is re-established in the Eastern Pacific, we turn our attention to the higher latitudes. See, having a ridge near the Eastern Pacific is certainly important for the Northeast US. It offers a higher likelihood of below normal temperatures than otherwise. But it doesn’t ensure anything without the cooperation of the higher latitudes to our north.

Forecast models continue with considerable uncertainty in that regard. There are hints, however, that a continually disrupted polar vortex will allow some ridging and blocking to build into the higher latitudes on both the Pacific and Atlantic sides of the Arctic. This could be an impetus for cold to air to make further southward movement into the Northern 1/3 of the U.S.A during the beginning of March. But for the details — we will have to be patient.

The final word

While a warmer pattern is likely to become established over the next 5 to 7 days, hemispheric pattern changes and drivers are already indicating a return to a normal and eventually below normal temperature pattern across the Western and Central Northern 1/3 of the USA by Days 7-10, into the early part of March.

It remains to be seen how well established or intense these below normal temperatures will be. Much of this will depend on the state of the higher latitudes, the details of which we will continue to iron out over the next several days. Enjoy the warm, tranquil weather and stay tuned for details on what we expect to be a cooler and more active period developing in 10 days time.