From the ABC 7 Weather team

Archive for category Forecast Discussion January 2015

Tuesday's Snow Forecast and Perception Versus Reality

January 7, 2015 - 08:41 AM
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A school bus struggles to navigate snow-covered roads in Arlington. Photo: Eric Mensh

Public perception of a forecast is all that really matters. I have to admit that the forecast and what happened wasn’t a perfect match, but it was right on for the two most important factors of timing and impact. The snow totals fell short.  The storm started on time as advertised and created gridlock on area roads.

Despite this, there were many comments on social media stating that people weren’t expecting the snow to be a problem around Washington, D.C. on Tuesday morning. In particular, I’m talking about school authorities. As a meteorologist, I was surprised that some schools chose not to at least delay classes yesterday based on the best information available at 5 a.m. This was even before it was clear the heaviest band of snow was setting up right along the I-66 corridor.

As a parent, I was concerned about my daughter taking the bus five miles down winding, snow-covered roads to her school (my son is a walker, so no problem there). In addition, (full disclosure here, my kids go to Fairfax County Public Schools) I was confused as to why my county changed the calendar to build in as many at 15 snow days and yet chose to stay open. Many parents were outraged and expressed their opinions on Twitter. Soon the hashtag #closeFCPS was trending on Twitter worldwide.

So, what happened? I wrote a blog on Monday morning that you can find at this link. The headline is “Snow may snarl the Tuesday morning commute.” The StormWatch 7 Team was predicting snow to begin between “4 a.m. and 6 a.m.” and that “snow showers will continue until about noon.” The snow began at 4:52 a.m. at Reagan National. I also sent out tweets with this information.

In each of my weather forecasts on the air, I emphasized that the morning commute would be ugly. I said that while this isn’t a big storm, it will be a big impact while everyone tries to get to work at the same time as the snow is coming down. Heck, around here, just a little rain can make for a bad commute.

The Totals: This is where the message interpretations were likely different. Our forecast snow bands map was short of what fell in the major metro area due to a narrow band of heavier snow. I had most of D.C. in the same color band as southern Maryland in the Trace to Around 1” category. While Northwest D.C. along with Fairfax, Loudoun, and Montgomery Counties in the 1-2” range. While I mentioned the potential for a few spots with higher totals for banding, it's nearly impossible to predict where that sets up.  Here is that map we used to forecast snow totals before the storm.

Snowfall Forecast

  Obviously this is short of the final tallies you can find on this map.

Final Snowfall Reports via National Weather Service

I’m certainly not above criticism and improvement on my forecast. I take full blame for missing the higher snowfall totals. On this one, I’ve learned to watch the snow/liquid ratio more closely and to do a better job warning people about snow banding that can bring higher totals.
At Reagan National we had 2.4” of snow. If you melt that down, it equals .20” of liquid. That’s a 12/1 ratio. At Dulles, 4.2” of snow melted down to .28” of liquid which is a 15/1 ratio. On average, 10" of snow will equal 1" of liquid. This time around, it was a light, fluffy snow due to drier air and cold temperatures.
My main disappointment comes with finding that some people didn’t think the IMPACT message was clear. Even after admitting officials were wrong to keep school in session yesterday in Fairfax County their wording still blamed the weather or the forecast, not themselves.
“We apologize for the difficulties the weather caused this morning," the county's statement read. "Please know that significant area government entities were coordinating at a very early hour. The decision was made with the best information we had very early this morning. Needless to say, the conditions were far worse than anticipated." 
Maybe there was a bit more snow than expected, but the impact was as advertised. The right decision made with the best information available would have been to close schools for the day.

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Snow may snarl the Tuesday morning commute

January 5, 2015 - 02:09 AM
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It's been a bit of a snow drought so far this season with only a trace reported at Reagan National Airport. As of this blog, we have a snow deficit of 3.3" and a deficit of 3.1" at Dulles. However, we should put a dent in that tomorrow with a good chance of around an inch of snow in the Capitol City.  It's not much, but it would be the first measurable snow this year. When you sync that up with the morning commute, it often means trouble on the roads. An Alberta Clipper will dive through the Midwest today and arrive in the Mid-Atlantic before dawn Tuesday. Here is the latest ABC 7 snow futurecast model to show the timing of the snow.

Snow Starts Before Dawn

A clipper is a fast moving system. Temperatures in all layers of the atmosphere will support nothing but snow. However, since it moves pretty quickly, accumulations will stay light. The snow is expected to develop in D.C. between 4 a.m. and 6 a.m. Snow showers will continue until about noon. Areas north and west of the city could see around 2" with around 1" downtown. Southern Maryland will get just a trace of snow.  Here is our ABC 7 computer model snowfall prediction through Tuesday evening.

ABC 7 Futurecast Snow Totals

And here is what the ABC 7 Stormwatch team of meteorologists is predicting.

Stormwatch7 Team Forecast

Good Morning Washington will go on the air early at 4 a.m. to give you the latest information to help you through this inconvenience. Set your alarm early for that and also to give you extra time to navigate the roads.

The winter weather doesn't stop with the snow on Tuesday. Following the clipper will be bitter cold arctic air. It will be the coldest so far of the season. It will have been almost a year since we've experienced temperatures this cold. Thursday morning will be the worst of it with temperatures in the low teens downtown and many spots north and west will drop into the single digits. Here's a look at the GFS computer model temperatures on Thursday morning.

Model Map WeatherBell

Highs on Thursday afternoon will only reach the mid 20s. Temperatures will slowly warm up this weekend into the 30s. Make sure you have the Stormwatch7 app downloaded for live radar and updated blogs and conditions this week. you can download it here. Also, I will be tweeting through the morning drive and broadcasts. Follow me @JacquiJeras.

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