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Posted at 11:59 AM ET, 02/03/2012

Super Bowl Sunday snow: it’s possible, but probably not consequential

We’ve been watching for several days now the potential for wintry precipitation this weekend. The responsible storm system is on its way to breaking a single storm snowfall record for February in Denver (9” already, 12-24” forecast) but will weaken by the time it reaches the mid-Atlantic. Not to mention, there will be much less cold air to work with here.

A period of precipitation is becoming more likely with each new model run. How much of it might be snow, and whether any snow would stick, remain difficult questions to answer.

Next chance of accumulating snow: February 5
Percent chance of accumulating snow (1” or more):
30%
Snow timing:
late Saturday night into Sunday (best chance Sunday morning)
Forecast confidence: Low

The most likely time for precipitation is between the late afternoon hours on Saturday and Sunday (but not precipitating continuously). Temperatures would almost certainly be warm enough for any precipitation to begin as rain, with Saturday highs likely to be well into the 40s and possibly near 50. But as the air cools aloft, rain could change to snow later Saturday night or early Sunday.

It’s uncertain, however, whether ground temperatures will be cold enough for snow to stick to anything besides maybe grass and sidewalks...

Model breakdown

* The GFS indicates light rain developing late Saturday afternoon or evening, mixing with snow Saturday night and then probably changing to snow towards Sunday morning before gradually tapering off in the afternoon. The precipitation is never terribly heavy, and surface temperatures (mostly above freezing) would probably prevent much accumulation. The exception to this is the colder north and west suburbs which might see a light accumulation if the GFS is right.

* The NAM suggests two waves of precipitation. The first would be primarily light rain from late Saturday afternoon into Saturday night. The second wave, however, would produce steadier precipitation - most likely in the form of the snow starting Sunday morning and continuing in to the evening. If something close to this model verifies, we’d see at least 1-2” of snow in Washington, D.C. with several inches likely in the west and northwest suburbs.

Other models: The SREF model supports the NAM idea that the best chance of snow is during the day Sunday but with lesser amounts, giving at least a 30% chance of 0.5-1” around D.C. (higher odds and amounts west and northwest). The European model from last night is more like the GFS. The UKMet model pushes most precipitation south of the region.

Most likely outcomes


Probability of at least 1” of snow over two 24-hour periods covering the weekend. (Note - latest models actually would suggest higher odds in Washington during 2nd period) (National Weather Service)

It’s still more likely than not that this is a minor event with little (or perhaps no) accumulating snow. However, the odds of some accumulation have increased since yesterday. If we had to make a call right now, we’d say a slushy accumulation possible Sunday (best chance morning) mainly on grassy areas, with perhaps 1-2” in the far western and northwest suburbs (e.g. Loudoun county). But uncertainty for this storm system is high and changes to this forecast are close to inevitable.

Here's how we’d divide up the possible outcomes:

No precipitation: 20% chance
Mostly rain: 20% chance
Rain/snow mix, less than 1” snow, mostly on grass: 30% chance
1-2” snow: 20% chance
2”+ snow: 10% chance

The Snow Lover’s Crystal Ball is posted when there is at least a 30% chance of 1” of snow 24-48 hours or more into the future

By and  |  11:59 AM ET, 02/03/2012

Categories:  Latest, Snow Lover's Crystal Ball, Winter Storms

 
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