Earlier this week, rumors were flying around about a potential major winter storm in the East this coming weekend. Though some computer model guidance showed this possibility earlier, it appears the overall threat of a significant snowstorm is low at this time.
Below we have a look at what you can expect this weekend, followed by an explanation about why long-range snowfall forecasts can be highly unreliable and misleading.
What We Know Now: Weekend Snow
This snow event kicks off Thursday and Friday in the West, with significant snow possible Thursday into Friday in parts of the Cascades, Sierra, Mogollon Rim and Rockies.
Beginning late Friday, continuing into Saturday a strip of snow, sleet and freezing rain may develop farther east into parts of the Mississippi Valley, Ohio Valley and East.
For now, Saturday's snow appears to be a light to moderate event for parts of the East Coast, from the Middle Atlantic into the Ohio Valley, Mississippi Valley and Great Lakes.
Sunday, as the main upper-level southward dip in the jet stream, or trough, swings eastward, more light snow may pivot through the Northeast and persist in some areas through Monday.
For now, this storm does not appear to be a high-impact, crippling snowstorm, but we are keeping a close eye on the situation as we receive additional data in the coming days. Check back for updates.
Fact: Specific snow/ice forecast amounts beyond 48 hours may not be reliable
GFS (Global Forecast System) model forecast from early Tuesday morning, February 3, for the following Sunday night/early Monday morning. (WSI)
ECMWF (European) model forecast from Monday night, February 2, for the following Sunday night/early Monday morning. (WSI)
As a general rule of thumb, be wary of any specific forecast graphic or article with explicit snow/ice totals beyond two or three days from any website – including social media sites like Facebook, Google+ or Twitter – or TV broadcast.
Graphics like these are increasingly available on the internet, but they can be a source of misinformation, such as we've seen late last week regarding a potential storm late this week. Let's explain why this is often the case.
There can be complexities and uncertainties – the interaction of upper-level disturbances aloft, the magnitude and depth of subfreezing air near the surface, and, most importantly, the track of the surface low pressure system – that numerical forecast models frequently disagree on beyond a couple of days from the event.
For example, a pair of operational forecast model images meteorologists typically examine are shown at left, for this coming Sunday night into early Monday morning from model forecast output generated during the overnight hours of Monday into early Tuesday.
Without going into all the complexities of the images themselves, you may notice the locations of the precipitation (green, yellow, red shadings) are different in the eastern U.S. These are common differences to be expected in model guidance over five days out.
In the example, the GFS (top image) model shows a major storm affecting the Northeast. The other, the ECMWF or European model (bottom image), indicates the storm would pass far enough out to sea and minimize impacts along the I-95 Northeast urban corridor.
Details like these that can make all the difference between just a rain event, a marginal snow event, and a heavy snow event for tens of millions of residents.
Subsequent forecast model runs can, and often do, shift the track of the surface low, and the depth of the cold air, which means the forecast snow and ice totals would also shift.
It could be the case that one model's snowfall forecast at one particular time beyond a couple days out can be spectacularly wrong in its location and/or timing and/or amounts.
Sometimes, as seen with Winter Storm Janus and the final chapter of Winter Storm Maximus in the Northeast, a significant snow event may not become apparent in forecast model guidance until three days out, or even two days out.
Here at The Weather Channel and weather.com, we may occasionally show a model snowfall forecast graphic. However, that is always presented by either winter weather expert Tom Niziol or storm analysts Dr. Greg Postel or Carl Parker with a full explanation of the results of that model and what it means for the forecast.
In other words, if we show a model snowfall forecast, we are careful to provide proper context about the uncertainty in the forecast, which a static model forecast image by itself going viral in social media may not provide.
The fact that anyone can spread 5-10 day snowfall, ice, or rainfall model accumulation graphics on the internet without any interpretation, can fuel hysteria that can go viral on the internet in a matter of minutes or hours, similar to false rumors spreading during a major news event.
Each day, meteorologists at The Weather Channel, weather.com, Weather Underground, the National Weather Service, local television stations, and other entities in the private and public sectors take in not only computer model forecast guidance, but also first assimilate the current state of the atmosphere as reflected by current satellite, radar, surface and upper-air data.
Using this current picture of the atmosphere, along with years of forecast expertise and knowledge of how certain computer forecast models behave, these trained meteorologists then put together the best forecast possible at the time, knowing full well forecasts beyond 2-3 days are likely to shift a bit, as the forecast guidance begins to clue in on a particular storm and the details surrounding it.
The bottom line is this: one computer model forecast graphic does not constitute the forecast for any given area.
As with anything on the internet or in social media, know the source of that information. In essence, know what you're sharing on Facebook, Twitter, or Google+.
Is the original source a degreed, trained meteorologist you trust? If they are and are posting a 5 or 10-day snowfall forecast, there will be a disclaimer saying, "This is not a forecast," along with a full explanation of what that graphic means for the forecast.
Incidentally, that model forecast snowfall graphic you find on the internet may also not tell you there are multiple storms affecting a certain area.
A 10-day snowfall total of, say, 12 inches over a northern location may sound serious, but, perhaps, it may encompass three separate weather systems over 10 days, each with four inches of snow, rather than one potentially crippling 12-inch snowstorm.
This week, for example, we saw Winter Storm Maximus on Monday in the East, now Winter Storm Nika, then this potential weekend storm. The sum of all of these storms may lead to the snowfall totals you may see in a 10-day model snowfall forecast map in social media.
Check back with us at The Weather Channel and weather.com for the latest on this storm.
MORE: Winter Storm Nika Photos
A commuter walks against blowing snow Wednesday, Feb. 5, 2014, in Chicago. Heavy, blowing snow is moving across much of Illinois as the state gets pelted by the latest round of winter weather. (AP Photo/Kiichiro Sato)