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Late Fall Through Spring Outlook For Arkansas (Late November, 2012 to May, 2013)
 
A major ice storm affected northern Arkansas in late January, 2009. Will it be ice or snow, or a lack of both and inflated temperatures like last winter?
In the picture: A major ice storm affected northern Arkansas in late January, 2009. Tree damage was extensive due to the weight of the ice. This road was blocked by tree debris about 2 miles south-southwest of Evening Shade (Sharp County). Click to enlarge.

 

For answers to this question, forecasters often turn to the Pacific Ocean near the equator and check water temperatures. If the water is warmer than normal for an extended period (several months), these are El Niño conditions. Given El Niño, a cool and wet bias is favored across the southern United States during the cold season . The outlook is flipped (mild/dry) when the water is cool, which is La Niña. This year, neither El Niño nor La Niña are in play; that is, the water is about normal and we are in a "neutral" situation. So where do we go from here (what is the forecast)?

 

 

Precipitation forecast for December, 2012 through February, 2013 (courtesy of the Climate Prediction Center).
In the picture: Precipitation forecast for December, 2012 through February, 2013 (courtesy of the Climate Prediction Center). Above normal (A) rain is favored from the mid-South into the Tennessee Valley. Below (B) normal rain is expected in portions of California and Nevada.
 

There have been many neutral years, and weather in these years can help reveal what Mother Nature may bring in the coming months. After some research through the Climate Prediction Center, it appears that odds favor at/above normal precipitation locally from December, 2012 through February, 2013. As far as temperatures, mercury levels will undoubtedly fluctuate (sometimes wildly), and there will be some very cold periods. When the dust settles, readings should average above normal. However, it will not likely compare to the mild conditions of last winter.

Now for the snow versus ice question. Recent big snowstorms (such as January, 2000...March, 2008 and January/February, 2011) tended to unfold during or just after moderate to strong El Niños or La Niñas. Major ice storms (December, 2000 and January, 2009) occurred when conditions were much closer to neutral in the long-term. Since we are neutral, there may be more concern about accruals of ice than usual. There will undoubtedly be snow, but it may come in small doses instead of all at once.

 

 

Severe storms are often featured in winter and surrounding months. The most tornadoes on record were counted in La Niña years. There were 107 tornadoes in 1999 and 81 tornadoes in 2008. In these years, outbreaks of severe weather happened early (January) and often. The record for the most tornadoes is 107 in 1999.
In the picture: The record for the most tornadoes is 107 in 1999. More than half of these (56) were spawned during one outbreak on January 21-22, 1999.

 

Sixteen tornadoes were spawned on March 1, 1997.

While it was not quite as active when it was close to neutral, there were memorable events that featured some of the larger and more destructive tornadoes. Sixteen tornadoes tore through the region on March 1, 1997. The worst of these were along Interstate 30 from Arkadelphia (Clark County) to LIttle Rock (Pulaski County). In all, twenty five people lost their lives.

In the picture: Sixteen tornadoes were spawned on March 1, 1997.

 

Two dozen tornadoes tracked across 20 counties in northern and western Arkansas on November 27, 2005. The strongest tornadoes slammed Perry and Conway Counties.

Seven tornadoes ripped across the south and west during the evening of April 9, 2009. Six of the tornadoes were rated at least EF2, and one of these tornadoes cut across Mena (Polk County).

 

 

What about the rain? If there is surplus rain (as in the forecast), it could certainly be excessive if the right ingredients come together (like a stalled front, clashing air masses and abundant moisture). A good soaking rain would be welcome given continuing drought conditions. But it would be bad if there is a lot of flooding. That's what happened in a neutral late 2001/early 2002. There was way too much rain and rising water.
The pattern in late 2001/early 2002 that led to excessive rain in Arkansas.
In the picture: The pattern in late 2001/early 2002 that led to excessive rain in Arkansas. Fronts headed into Arkansas from the north before stalling. Storm systems ("L") approached from the southwest, and drew warm and moist air northward from the Gulf Coast. Heavy rain tended to focus along and north of the stalled fronts.

 

 

There is a wildcard to mention as we look ahead. Did you ever wonder why cold air stayed away last winter? The Arctic Oscillation (AO) was partly to blame, and it may have some bearing on what happens this time. 

 

Timing it Out

Based on past events with neutral conditions, any severe weather outbreaks are most likely from now until mid-December, and from late February through May. If an ice storm materializes, the expected time frame is from late December into January. What about a big snowstorm? While ice chances are enhanced versus piles of snow, there will be snow somewhere in the state. Flakes could fly before Christmas, but the more probable period is from mid-January through early March.

 

The AO has to do with opposing pressure patterns over the Arctic Ocean (from 20 degrees N latitude poleward) and the mid-latitudes (where we live). Last winter, the AO was positive, with low pressure toward the North Pole and high pressure farther south.

 

When the Arctic Oscillation (AO) is in a positive phase, cold air is bottled up by strong westerlies well to the north of Arkansas.

This led to stronger westerlies over Canada, which did not allow many cold intrusions into the United States. A negative AO would increase the frequency of cold waves, which is desirable if you are interested in more snow.

In the picture: When the Arctic Oscillation (AO) is in a positive phase, cold air is bottled up by strong westerlies well to the north of Arkansas.

 

Unfortunately, the AO cannot be used as a long term indicator. More specifically, there is no telling what the sign of the AO will be three months from now, and whether it will warm up or cool down.  


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