Monday, December 27, 2010

Pattern shift means warmer and stormier in the Mid-South

It's been a cold December f0r the Mid-South with an average temperature of 39.1 degrees at Memphis International Airport, or nearly 5 degrees below "normal," and 19 days with lows at or below freezing. The good thing about the cold weather is that it was in place as low pressure moved by to our south and a cold front came through, bringing snowflakes on Christmas weekend. In fact, many places east of the Mid-South, including northern AL, southeast TN , and northern GA, saw a few inches of snow on Christmas Day. That storm then turned into a major Nor'Easter that is bringing blizzard conditions to the Northeast, dumping snow measured in feet from New York City to Boston. (Incidentally, it's also the same system that flooded southern California, Nevada, and Utah last week.)

Pattern Shift
A shift is now in the process of occurring that will transition the overall weather pattern over North America (and even parts of Europe, where snow has also crippled travel and commerce for a couple of weeks). The new pattern will resemble more of what meteorologists are used to seeing in La Nina winters, in which the jet stream flows on a more northerly track. That will bring storms across the northern tier of the U.S. and into the Ohio Valley rather than across the southern U.S. and will mean warmer weather (generally) for the southern U.S., but also chances for a more stormy pattern. Rainfall has been well below normal for the month of December in the Mid-South, but that could change over the next couple of weeks. (More on the global pattern shift can be found on Weather Underground blogger Jeff Master's post from earlier today, in which he also recaps the East Coast Blizzard. It's worth a look.)

Repercussions for the Mid-South
As the trough currently over the eastern U.S. moves over the Atlantic, a new trough will form over the west and begin moving towards the area. Ahead of the trough, surface high pressure will move to our east, bringing wind around to the south by tomorrow and starting a fairly significant warm-up. One piece of energy will move through on Wednesday as a warm front lifts north, bringing high chances of rain during the day. Moist southerly flow will continue Thursday as a couple of low pressure systems begin moving north-northeast through the Plains. A chance of showers will exist in the Mid-South, but mainly it will be much warmer (highs of 60+) and breezes will pick up. For New Year's Eve, a frontal system will move across the region, bringing another round of rain. With the right dynamics in place, thunderstorms could also be likely with a few possibly strong to severe. The map below shows the current probability of precipitation for Friday night (6pm Fri until 6am Sat).

Plan ahead
There are many parameters that are still unknown at this point, but those with plans, particularly outdoors, on New Year's Eve (day or evening) should monitor this system carefully and watch for later statements or advisories. That would include those attending the Liberty Bowl game featuring SEC powerhouse Georgia and Conference USA champ Central Florida and also those heading downtown to Beale Street for New Year's Eve celebrations. At the very least, plan to have umbrellas or ponchos handy (not sure if umbrellas are allowed in the stadium or not). Heavy rain is definitely a strong possibility, even if severe weather is not. will keep you abreast of the latest forecasts and conditions, as will this blog, and MWN on Facebook and Twitter. Now would be a good time to sign up for severe weather alerts by e-mail for any of the metro counties or follow @shelbyalerts on Twitter for weather alerts for Shelby County. These services pass the info directly on to you as soon as they are received from the National Weather Service.

Top 10 Weather Events of 2010
Finally, I'll also direct you to one last article that you should check out. Friend and blogger Paul Yeager of and AOLNews contributor recaps the Top 10 (U.S.) Weather Events of 2010. I strongly agree with #1, which happened to directly impact the Memphis metro area... can you guess?

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