Foot's Forecast | Weather Intelligence

Wasn't a surprise for you, right? 

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THE CLIPPER HAS SPAWNED SURPRISE WINTER STORM WARNINGS IN NORTHERN VIRGINIA AND THE DC METRO REGION. . 
THE SLIGHT INCREASE IN LIQUID EQUIVALENTS HAS RESULTED IN ABOUT 1" MORE SNOW FOR AFFECTED AREAS. 

4:30 PM 1/5/15 - WINTER STORMCAST TEAM STATEMENT Good evening Mid-Atlantic Powderhounds! This is Forecaster Joe Fitzwater from the Northern West Virginia Page, representing our WSC team for our latest update on the clipper.

We’re keeping a close watch on this little storm heading your way tonight. Currently this fast-moving winter storm is over Minnesota and Iowa. However, by the early hours of Tuesday, this storm will quickly be making its way into the region from the northwest.

• Expect the heaviest snow to fall between 5am and 9am. Due to the quick nature of this storm, snowfall accumulations will be limited. Generally, 1-2 inches of snow is likely to accumulate across the region, with more likely across the spine of the Appalachian mountains. 

• Winter Weather Advisories have been posted for much of Maryland, eastern West Virginia, and Delaware for this upcoming storm, so be sure to take it slow if you have to be on the roads before noon on Tuesday.

By the time we get to lunchtime on Tuesday, the snow will already have dwindled, and we will be left with cold temperatures yet again for the afternoon. This cold weather will be no comparison to what is to come for later in the week!

7:30 PM 1/4/15 - UPDATE FROM THE MID-ATLANTIC WINTER STORMCAST TEAM 

We have been monitoring the potential for traditional winter Clipper to swing through the Mid-Atlantic on Tuesday 1/6. Given past expectations that systems like these usually "dry out" before reaching the East, why would this one be any different?

ANSWER: The most influential factor in this storm's outcome may not be science, but one of our favorite terms-- "Weather Politics." We hope that's not the case, but consider the following 3 factors:

1. LOW LIQUID = LESS SNOW? 

Not always. Projected liquid amounts for this system are low, as indicated in the NOAA Precipitation map above. However, the very dry air to be in place by Monday night will amplify ratios. The Sterling NWS is anticipating up to 1.0" along the PA/MD line, with the bulk of that snowfall occurring in the daytime hours on Tue. Although the moisture equivalent is roughly 0.15", a total snowfall of nearly 1.0" indicates the ratio may be 40:1 or greater. 

WHAT'S THE PROBLEM? If the storm retains more moisture than expected, any slight change in the amounts above will translate into noticeably more snow down below.

2. TO TREAT OR NOT TO TREAT : With low temps and minor snow amounts, it is unknown if state and county crews will expend the resources to treat for a seemingly low impact event. "Less than an inch" would not seem to be a big deal right? Besides, the snow will be light and falling over several hours.

WHAT'S THE PROBLEM? Light snow amounts may not be enough to prompt a Winter Weather Advisory, if there is not a reasonable, data-based expectation for more than 1" of snow. If counties, schools and state crews don't see an Advisory from the NWS, they may be reluctant to pre-empt and spend money unnecessarily. Herein lies the biggest problem-- in part 3.

3. POWDER PAIN: On several occasions in the past 10 years, very light snowfalls in the Mid-Atlantic led to widespread and significant traffic issues when the snow fell in extremely cold temperatures. 

• January 5, 2003 was a classic example of an upper level shortwave that crossed over the Baltimore region, and became unexpectedly enhanced by moisture from the Bay among other factors. A forecast for less than 1/2" turned into 5" of very fluffy,powdery snow on a Sunday that actually closed many schools on Monday. 

• January 30, 2010 was the most memorable and infamous recent example of a widespread surprise snow. Although this is a different large scale setup entirely, the temperature conditions (and forecasts) are similar. In that event, a southern storm was not expected to reach Baltimore/Washington, and hence forecasts ranged from "flurries" to "partly cloudy" in the metro areas. Our forecasts for 1/30/2010 were decidedly different. Roads went largely untreated until everyone realized snow had begun falling state wide and heavily. The result was 6" falling and freezing on contact with cold road surfaces, spawning hundreds of accidents throughout the region and even causing the shut down of I-83 in York County.

OUR TAKEAWAY MESSAGE: Yes, it may be "only a Clipper" with a minor amount of snow for most areas.  But if the public and emergency management do not see an Advisory, normal pre-cautions may not be taken. Whatever snow falls will freeze on contact and make roads slippery, despite recent warm temperatures. We hope that you will take these concerns into account, and make your own wisest choices for your scope of authority, based on local conditions -- and not just on what the Weather Service may or may not do.

Thanks for your continued readership and loyalty to our team as we head into what should become the "Peak season" for Powderhounds in the next few weeks. 

(Forecasters Tyler R., Mr. Foot and the Winter Stormcast Team)

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