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| More than the usual "red exclamation mark" weather advisories - View of my phone screen earlier this evening, 2/20/2015 |
Speaking of Pandora, I am still trying to wrap my head around the decision (it’s on you, Weather Channel) to bestow the name “Pandora” on any storm, never mind one that’s landing in one of the most challenging New England winters we’ve seen in a long time. Let’s just hope it does not live up to its mythological roots. This weekend’s storm is tricky to forecast, primarily because the storm’s snow/ice/rain line is hardly a sure thing – and I have lived here long enough to know that this is the type of forecast situation that can swing one way or another here in the Valley without a lot of warning. At this point it looks somewhat less fearsome than it seemed earlier in the week, but be prepared for anything. Just a slight shift in temperature, rain amounts, or icing can change the landscape dramatically.
So with that “be prepared for anything” caveat in mind, here’s the outlook for Amherst. First, it will be quite cold tonight as winds diminish and conditions remain clear. Valleys around Southern New England may actually see morning lows of -20 F. A Winter Weather Advisory is currently in effect from 1 pm Saturday through 1 pm Sunday for mixed precipitation that has the potential of bringing some significant icing. This is where the trickiness kicks in – we have incredibly cold ground temperatures, which means that even if temps warm above freezing, any rainfall will most likely freeze on surfaces. And since many of the surfaces around here are actually snow covered… well, it is likely to get extremely icy.
The snow will start to fall around mid-afternoon on Saturday. Depending on how long the precipitation stays snow, we could be looking at a 3-5 inch snow accumulation before warmer air aloft brings a changeover to freezing rain or rain (though I would be surprised if it warmed up enough around here to convert to just rain). In fact, if the snow/ice/rain line ends up where it’s forecast now (south of I-90), we may even get mostly snow, which would be vastly preferable to any other substance falling from the sky.
The National Weather Service acknowledges this is a tough call – in fact, central portions of Southern New England could get as much as 6 hours of freezing rain, with one-tenth of an inch of ice accumulation or more. Or the rain/freezing rain could taper off. Or we could end up with all snow (at least around here). While we’ve certainly seen this kind of set up before (which would normally favor a short period of freezing rain transitioning to all rain), we’ve also never experienced this scenario with such a deep snowpack on the ground. As the NWS forecast discussion put it this afternoon, one “just cannot ignore the fact that it is a frozen tundra outside."
One of the concerns with this storm is the danger of water-loading of snow on roof-tops, particularly because snow absorbs water like a sponge, and we’ve got deep snow across the region and on many roofs. More weight on roofs that are not cleared off is not what we need now.
On Sunday, as high dewpoint air surges in with the warm-moist flow, expect dense ground fog across the deep-cold snowpack, creating very low visibilities and a soupy mess. And as if this all weren’t bad enough, the warmer air will exit by Sunday night, as bitterly cold air surges back. Standing water/slush will freeze solid on Sunday night (think block ice) and the temperatures will not rise above freezing at least until March 1 (which is as far as the 10 day forecast goes). Despite the increasing late February sun angle, wind chills will be back to between -15 and -30 F late Monday into early Tuesday. The high temperature on Tuesday afternoon should recover into the upper teens and lower 20s – which is still 20 degrees below normal!
So that’s the somewhat bleak weekend outlook. If we’re very lucky, we’ll see all snow. May Pandora be kind.
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