Sunday, January 27, 2013

January 27, 2013: Maybe A Slight Ice Glaze Tonight

Headlines are being issued by NWS Sterling about the potential for icy precipitation tonight and tomorrow morning.   However, this event seems to have more "have nots" than "haves" in terms of creating a mess.  The "storm" is a actually a warm front that will move north through the Mid Atlantic tomorrow morning.  But as warm air with moisture begins to stream in from the south, it will overrun what's left of the arctic air mass in place over the metro region.   This is the familiar cold air damming or "cold wedge" scenario - and that spells the possibility of sleet and freezing rain.

What this event lacks:  (1) moisture;  most models churn out about a tenth of an inch;  (2)  persistent cold air;  temperatures will be increasing through the day tomorrow.  

What this event could do:  Even the slightest ice accumulation i.e. a few 1/100ths of an inch can mean slick spots, for the morning commute.  Again, as has been the case in the past week, its not so much about the amount of precipitation, but bad timing of light amounts that coincide with rush hour.

At 3 pm today, NWS issued Winter Weather Advisories across a broad region:

The threat of significant icing (the kind that brings down limbs and power lines) is not expected. 

The warm front ushers in a dramatic change in our weather pattern for mid-week - the arrival of mild air and showery weather.  This will be caused by a vigorous low pressure system approaching from the Plains - and one that could very well produce severe thunderstorms in the Wed-Thurs time frame - for our region - perhaps even the threat of a derecho (!)  No's the Storm Prediction Center's forecast for Wednesday of this week, highlighting the potential for widespread severe thunderstorms, carrying a probability of wind damage:

Intense wintertime low pressure systems sometimes produce a type of derecho, called a serial derecho, in their warm sector - as part of a squall line of thunderstorms.  

To say the least, it's going to be a very interesting week.

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