The thing about March is that it lures you in with springlike temperatures, chirping birds, bumbling bees, and just when you start to let down your guard—WHAM!—you get smacked with a winter storm. It happens almost every year, but I am so sorry to say that it's probably going to snow this weekend.

This first two-thirds of this post goes into the pattern that will allow for snow to fall, but if you're a spoil sport and don't care about the awesome jet stream that's leading to a river of tropical moisture producing drought-busting rains in the southern United States, you can just scroll down. (Rude.)

The Pattern

It's been one of those weeks in the southern United States where the walls drip. It's just that nasty, dreary, humid kind of weather pattern that provides endless rain and endless fog. It's better than bitter cold with freezing rain, at least, and much of the region desperately needs the rainfall.

The cause for the constant flow of moisture is an upper-level low that's cut off from the rest of the jet stream, sitting and spinning over northern Mexico (pictured above). The flow around the upper-level low is serving as a conveyor belt that's sucking tropical moisture into the eastern half of the United States. Here's a look at this afternoon's water vapor satellite imagery, which shows moisture in the mid-levels of the atmosphere.

Dark green colors are indicative of areas rich with moisture; the imagery shows deep bursts of convection over the Gulf and Deep South this afternoon. This moist flow goes all the way up to the Mid-Atlantic, and the result is a wide swath of heavy rainfall over the past couple of days, with more to come through Saturday.

The Rain, the Drought, and Other Things

Parts of Texas, Louisiana, and Mississippi have gotten some of the best rainfall over the past seven days (above), with the Houston metro area picking up more than five inches of rain in recent storms. Even though it leaves people complaining on social media and in office small talk, everyone should love this pattern, seeing that most of the south has slipped into some form of drought over the past couple of months.

The downside of this much rain falling so quickly is that numerous areas are dealing with flooding, especially farther north towards the Ohio River Valley, where waterways are having a hard time dealing with the combined effects of the rain, snowmelt, and any ice that's left on the water's surface. As of 3:30 PM EDT today, 111 river gauges across the Southeast and Ohio Valley showed minor (103) or moderate (8) flooding.

The rain is having a small but noticeable effect on the drought.

Even as early as Tuesday, the drought improved across the northern Gulf Coast, eastern Texas, and completely disappeared along the Ohio River in Kentucky. It did get slightly worse in parts of Kansas and Missouri, however, with abnormally dry and moderate drought claiming a few more counties in the states.

And now, the snow...

Now, what does this have to do with snow in New England this weekend?

The above map is a tad messy: it's a model forecast from the GFS showing surface pressure (blue contours) and simulated radar (shading) for 5PM EDT on Friday. The stalled area of low pressure over the southern United States will start to move northeast over the next 24 hours, heading on a collision course towards another low pressure system that's straddling the U.S./Canadian border.

The low over Arkansas will get absorbed by a cold front extending off the low over the Great Lakes (rest in peace), but its moisture will live on and continue flowing towards the Northeast, just in time to crash into the survivor low when it drags sub-freezing air over the region. The result? Snow!

Rain should slowly change over to snow through the day and night on Saturday, resulting in an extended period of white doom across northern New England. It's still just a little too far out for the National Weather Service to include snowfall totals on their forecast maps, but areas from the Adirondacks eastward through Maine (and into Nova Scotia) will likely see a swath of 6-10+ inches of snow by the time the storm is done.

The question everyone is focusing on is whether or not Boston will see the final two inches of snow it needs in order to make this the snowiest winter ever recorded in the city. They've seen 105.7 inches of snow so far this season, and they need to crack 107.6 inches in order to beat the winter of 1995-1996 for the top spot. Will they do it? It will be a very close call that comes down to seeing where the rain/snow line decides to set up. A couple of miles will make a world of difference for Boston. If it sets up far enough south that Logan Airport sees accumulating snow, breaking the record is a real possibility. It would be heartbreaking from a weather geek standpoint to get this close to the record, only to fall short.

Spring has sprung for most, and the rest of you will get there in due time. The light at the end of the tunnel is just behind that snowplow.

[Precip/Drought Maps: author | Observed Rainfall: NWS | Models/Water Vapor: GREarth]

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