Mid-day Saturday look at Monday's winter weather scenario

As advertised, an Arctic blast arrived overnight, bringing us what will likely be the coldest day of the winter so far with temperatures topping out in the mid 30s.  Combining a north wind gusting up to 25+ mph with those temperatures and wind chills are staying in the teens to lower 20s all day!  Many Mid-Southerners even saw periodic snowflakes this morning as the last remnants of moisture were squeezed out of the lower atmosphere by very cold air moving overhead. Tonight, as wind relaxes and high pressure moves nearly overhead, temperatures will plummet into the teens area-wide, resulting in the coldest overnight low of the winter as well.

All of this cold and dry air sets us up for a likely winter weather scenario on Monday as the next upper air disturbance moves by to our south. Not a lot has changed since yesterday's first look at the setup with respect to the computer model data. Monday morning will start off cold (lows in the 20s) with clouds streaming overhead and very dry air in place below those clouds. These two things (clouds and dry air) are important factors in the forecast. The clouds will keep temperatures from climbing as much as if there were sun Monday morning. The dry air will have to be "moistened" by falling precipitation before that precip can reach the ground.  This will likely create virga (precip that evaporates as it falls from the clouds) for a few hours before the precipitation reaches the ground, further hindering the warming process of the air as well.  While I believe the models are biased warm during the morning hours (they are forecasting temps in the 40s Monday morning), I think their timing of the precipitation is probably not far off, commencing early Monday afternoon.

Bottom line: My current thinking is we'll see temperatures reach the upper 30s by noon, then as precipitation begins to reach the ground, temps should fall back to near freezing.  With a little warm air aloft, precipitation type will most likely be a mixture of snow and sleet beginning between 1-3pm. The heaviest precip looks to fall from mid-afternoon through early evening, including the Monday rush hour, mainly as snow/sleet.  Warmer air actually moves in Monday evening (especially aloft), which should change precipitation over to a a mix of rain/snow, then ultimately light rain, as temperatures hover just above freezing.  Snow/sleet totals are currently looking like they could be in the 2"+ range north of the metro, to less than an inch in north MS, leaving most of the metro with around an inch of snow or perhaps a little more.  Forecasting amounts is the hardest part of winter systems that introduce varying precipitation types, as mixing with sleet or rain could drastically affect the amount of accumulation (more on precipitation types).  This is an educated best guess based on recent model data and 17 winters of Mid-South forecasting experience!  Lingering light rain/drizzle Monday night could freeze as temperatures drop to the lower 30s and possibly create a freezing drizzle/black ice scenario Tuesday morning.

I'll have another blog update Sunday afternoon and will continue to monitor the situation very closely and bring you updates via the MWN Forecast and on our social media feeds, including  Facebook and Twitter. In addition, our mobile apps for Android and iPhone include StormView Radar with precipitation type (which shows you rain/snow/ice), the forecast, current conditions, and our Twitter feed (without having to sign up for Twitter). Finally, within the apps, you can upgrade toStormWatch+ which will push you notifications of any Winter Storm Watches, Warnings, or Advisories as soon as they are issued by the NWS.
Erik Proseus
Meteorologist, MemphisWeather.net

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