Friday, February 28, 2014

Mother Nature ignores the calendar as the never-ending winter continues

Meteorological spring begins tomorrow and astronomical spring is only 3 weeks away, but it appears our furry friend Phil may have been on to something a month ago!

Another in a seemingly never-ending chain of Arctic outbreaks will push through the Mid-South late this weekend with yet another round of winter weather possible. So far the majority of the metro has been spared the worst of the snow and ice this winter, though our friends in Tipton County would gladly invite us up to help in debris cleanup from significant ice a couple of weeks ago!  I've also said that the first weekend in March sometimes brings us winter surprises.  It appears this year the month will start off like a lion!

While most of the weekend should be decent with low rain chances and well above freezing temperatures, the period of concern is late Sunday into early Monday. During the day Sunday, an Arctic front will drop through the area, causing temps to plummet from around 60 or a little higher early Sunday afternoon to the lower 30s by Sunday evening. Most precipitation with this system will be along and behind the front, as temperatures are falling.  As always in these scenarios, how quickly the precipitation exits versus when sufficient cold air arrives to change precip type over to a wintry mix will be the key.

As of 2:20pm, the National Weather Service has issued a Winter Storm Watch for northeast AR, the Missouri Bootheel, and west TN generally north of I-40, including Tipton and Crittenden Counties in the metro (blue counties in the map below).

So how do we expect it will play out? Showers will be likely during the day Sunday, the front will move through by mid-day, and temps will fall during the afternoon.  Given fairly consistent model data (though all could and will still adjust some between now and Sunday night), it appears that we'll be in the mid 30s by 6pm Sunday along the I-40 corridor, then continue to fall below freezing a couple of hours after that.

Forecast temperatures at noon Sunday, according to the NAM model. Notice the sharp divide between 60s in the metro and 30s in northeast AR along the front.

Forecast temperatures at 6pm Sunday, according to the NAM model.  The front is south of the metro by this time.
The amount of precipitation falling in cold air is the biggest question mark, but model data currently points to anywhere from about 1/3" to nearly an inch in the metro.  The Winter Storm Watch calls for up to 1/4" of freezing rain and 1/2" of sleet, plus minor snow accumulations, but that is for the entire watch area with higher amounts expected in northern areas and lesser amounts across the metro, including Memphis and Shelby County.  These estimates are highly subject to change.  Most of that will fall before midnight, tapering off after midnight with little additional precip.

As mentioned, precipitation type at this time appears to be mostly ice, perhaps ending as light snow.  As regular readers of the blog know, freezing rain is much more hazardous than sleet as it glazes exposed surfaces, creating an ice skating rink.  Sleet is the type that bounces and, though slippery, does have a little traction to it and does not adhere to power lines like freezing rain.  If we are going to get ice, we want sleet.

Forecast precipitation amounts (liquid) from the NAM model between 6pm-midnight Sunday night show more than 0.25" across the metro.  The NAM is faily conservative on the amount during this time period as compared to other models.
We'll continue to closely monitor the event as it gets closer and provide updates as we have new information or confidence increases one way or another. For now, prepare for the possibility of icy conditions by early Sunday evening that could last into Monday if enough falls.  Temperatures on Monday will be frigid - starting in the 20s and only rising to the mid 30s with a gusty wind that will keep wind chills in the teens to low 20s.

Fortunately, the extended outlook shows a fairly quick warm-up after a couple of cold days to start the week.  Follow our social feeds (listed below) and blog for the latest info and don't get sucked into "hype-casts" based on a single model or an untrusted (or unknown) source.

Erik Proseus, MWN Meteorologist

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