KATC StormTeam 3 Weather BLOG

So far the winter of 2011/2012 has been warmer than normal by 3-4 degrees in Acadiana with temperatures in December 2011 about 1 degree above normal, while January 2012 was 6 degrees above normal. 

Lafayette’s average high was 68 degrees this January, while last year it was 60.  This makes a big difference in our heating bills, but unfortunately it will likely translate to a mosquito/bug boon this spring and summer.

That is unless we see colder conditions in February; as of this writing, the first two weeks of February should be at or slightly below normal temperature-wise per the Climate Prediction Center while our above normal precipitation pattern may continue for a couple more weeks.

The long-range models offer a chance of a few light freezes mid-February, but not much more.  The second half of February is offering a back to above normal temperature pattern.

There are two major factors that dictate our winter weather pattern: La Nina (or El Nino) and the Arctic Oscillation…La Nina years, which has dominated over the last three winters, usually allows for milder than normal conditions over the lower 48 and Acadiana.

But last winter and the winter before the Arctic Oscillation was positive delivering much colder weather to the US…this year the Arctic Oscillation has been negative over North America but positive over Europe (and that’s where the winter has been more severe so far).

Although it has been a mild winter this year, it’s not a record breaker, but it certainly highlights that each year can be quite variable.  Last year we experienced roughly 25 freezes through this time…this year about 8-10.

The Climate Prediction Center is also forecasting above normal temperatures for the Gulf South through the spring/summer…however, it will likely not be as hot as the record-breaker last summer…we hope!

As 2011 comes to an end, the drought across Acadiana continues to worsen as rainfall totals for the year are roughly 55% of normal area-wide.  The news is worse if after examining 2010′s rainfall for Lafayette of 42.52″, which was the 8th driest on record…and this year is on pace to be the driest…period.

Rainfall records have been kept in Lafayette since 1893 and the driest year in this 118 year period was 35.80″ in 1924.  Unless more than 1.40″ of rain falls between now and New Year’s Eve, 2011 will beat that record with 34.40″ to date through mid-December.  Normal yearly rainfall in Lafayette is near 62 inches.

In fact, the rain totals of 2010 and 2011 combined of roughly 77-78 inches will go down in the record books as the driest back to back years on record.  Similar dry spells/multi-year droughts have occurred in the area in 1901-1902, 1924-1925 and 1962-1963 where 82-85″ of rain fell in these two-year periods.

Even during the Dust Bowl Era of the 1930s Lafayette averaged better than 48″ of rain per year between 1935 and 1939.  This period was preceded by more than 70″ of rain in 1934 and came to a wet and flooded halt during the infamous year of the hurricane flood in 1940, when 98.72″ fell in Lafayette.

So based on records that span more than 100 years, and given we are in the midst of the driest back to back years within this period, it can be definitely determined that Lafayette and many of the surrounding areas are in the midst of a 100 year drought situation.

Due to the nature of how most of our rainfall is delivered in Acadiana, through scattered and generally random shower and thunderstorm activity, there are likely many spots in Acadiana that are doing worse drought-wise, while other areas conversely are likely doing marginally better.

Interestingly enough, if it weren’t for Tropical Storm Lee this year which delivered a 5-10″ rain area-wide in early September, much of Acadiana would be where Texas is this year…in the midst of a 300 to 500 year drought.

Winter Temperature Forecast (December through February)

While I’m not a big fan of making long-term seasonal outlooks (reasons to be explained below), based on the data from the Climate Prediction Center (CPC) and the National Oceanic and Atmospheric Administration (NOAA) it does appear that Acadiana will see a drier than normal winter with temperatures expected to be at or above normal.

While there is high confidence in the precipitation forecast, there is below normal confidence by this author on the temperature forecast.

Cooler than normal equatorial Pacific water temperatures have been developing over the last several months indicating that a “La Nina” pattern has re-developed. 

This pattern is similar to the last two winters for Louisiana/Acadiana which was characterized by below normal rains and well below normal temperatures.

The winter of 2009/2010 (December through February) averaged more than 4 degrees below normal with 17 days of freezing temperatures in Lafayette while the winter of 2010/2011 averaged 2.5 degrees below normal with 27 days of freezing of temperatures.

Last winter would have been considered just as cold as the winter before if it were not for a dramatic swing in the second half of February where temperatures soared consistently into the 70s and 80s.

Interestingly enough there is enormous variability in the number of freezes Acadiana will see in any given winter with some years experiencing just a handful of freezes and other winters more than two dozen.  Last year may have been close to a record for the number of freezes, but these statistics are not readily available. 

Winter Precipitation Forecast (December through February)

In addition, when forecasting winter temperatures we must understand that even in an above normal winter, Acadiana can experience an arctic outbreak that could bring temperatures into the teens or lower.  So perception versus reality also becomes an issue with these type of forecasts.

The real wildcard for winter forecasting, especially for temperatures, is the Arctic Oscillation, which per the last two winters trumped our La Nina influenced weather pattern ushering strong cold fronts to the area.

Per NOAA, “The Arctic Oscillation is always present and fluctuates between positive and negative phases.  The negative phase of the Arctic Oscillation pushes cold air into the U.S. from Canada. The Arctic Oscillation went strongly negative at times the last two winters, causing outbreaks of cold and snowy conditions in the U.S. such as the “Snowmaggedon” storm of 2009.  Strong Arctic Oscillation episodes typically last a few weeks and are difficult to predict more than one to two weeks in advance.”

With all of the above being said, it is with much consternation that we make the long-term outlooks. 

Based on the current information supplied by NOAA and the CPC and given La Nina has kicked back in across the Pacific, Acadiana will likely see drought conditions perpetuating and/or worsening through the spring.

We will buy into above normal temperatures for now, but I would expected several very strong cold fronts nonetheless thanks to a more unpredictable Arctic Oscillation.  

Another key to nailing the temperature forecast is where will the upper level trough axis be most prevalent this winter. 

If the upper “troughing” is similar to the last two years, we will adjust our temperature forecast downward, but just a subtle shift of average trough a few hundred miles to the east will translate to much above normal temperatures.

So there here it is: a low confidence forecast for above normal temperatures and a high confidence forecast of below normal precipitation this winter for Acadiana. 

Based on our late October pattern it would also be a fair prediction that November through early January could actually be below normal in Acadiana with the latter part of January into February possibly more dramatically warmer than normal skewing the numbers for the entire winter. 

And based on the last two winters I would also expect a dozen or more freezes and the possibility of one or two events that may bring temperatures down into the mid-20s or slightly lower.

As for predicting any snow or ice events, your guess will be as good as mine.  If the aforementioned forecast pans out, I wouldn’t be too excited for a winter storm…but if the pattern plays out closer to the last two winters we may indeed get one or two shots at the frozen stuff.

And per usual chances for a White Christmas in Acadiana will remain an abysmal 1 in 1000 year chance…here’s to “wish-casting”!

Rob Perillo

One of the more important tools I have found in recent years on forecasting tropical activity beyond the normal 1-10 day computer model forecasts is the use of the Madden-Julian Oscillation (MJO) analysis.

Without getting too technical, the MJO describes large-scale waves of weather, or atmospheric perturbations that travel across the entire planet from west to east across the tropical latitudes.  These very large waves of weather, that move roughly at 10-15mph, are characterized by large regions of either enhanced or suppressed tropical rainfall patterns.

The frequency of the large scale planetary waves, can influence an area from anywhere between 30-60 days, but also help us to determine shorter scale weather phenomenon, including areas of enhance tropical storm/hurricane activity, monsoonal rainfall patterns and short-term droughts.

The MJO can also dictate on whether an El Nino or La Nina will develop and will influence each pattern’s severity.

But the true benefit to understanding the MJO and its affect on us in Louisiana is during tropical season. 

The Climate Prediction Center provides weekly analysis of the MJO and while very technical, and challenging my meteorological background, the forecast products including the Global Tropical Hazards Assessment Discussion (GTHAD) yield very important information to us as forecasters.

The GTHAD is is a two week global forecast that depicts areas of concern including above or below normal rainfall and areas of tropical development.  I found this forecast product over the last few years to give me extra ammunition when forecasting longer range tropical predictions.

Now mind you we cannot tell you specifically how strong tropical storms or hurricanes will be, nor where will they strike this far out, but we can say with this product we can forecast where activity is expected to develop with greater certainty over a two week time frame.

Today’s note: If you examine the the most recent GTHAD, the Atlantic Basin looks quite busy, as it usually gets this time of year.

April 2011 was the second warmest on record going back to 1893 in Lafayette missing being the warmest all time by 1/10 of a degree.

Mean temperatures (which are the averages of daily highs and lows) near 73.9 degrees this April was nearly 7 degrees above normal.  

This year was also 3-4 degrees warmer than last year so our utility bills will likely be higher for all of us this month.

Although some benefical rains did fall in the last week of the month and recent early May rains have also helped to stall the drought, rainfall deficits area-wide are still near 60% of normal for the year.  Most of the area will likely stay in, or close to severe drought status.

The outlook for May calls for a continuation of above normal temperatures for Acadiana with below normal rainfall.

After a substantially colder than normal December and January, and a very cold first week of February, Acadiana experienced above normal temperatures over the last several weeks of the month.  This pushed February 2011 to  slightly above normal conditions.  Daytime highs for the entire month averaged 1.5 degrees above normal (near 66 degrees) while overnight lows were right on mark (at 44.9 degrees).

Continuing from the 2010 theme, precipitation for February was 43% of normal in Lafayette, with significant drought conditions possibly developing over the next few months.

The long range outlook from the Climate Prediction Center into March calls for above normal temperatures to continue while precipitation should be below normal. 

I would certainly expect more of the same for April and May as this would be consistent with continuing La Nina or Nuetral conditions with the Southern Oscillilation.

The question I’m getting most right now, is if we can start planting our gardens?  In Acadiana, on average, we see our last substantial freeze usually in the last week of February through the first week of March.  However, freezes have been recorded as late as the first couple of weeks in April.

Climatologically speaking, there is a 50% chance of a freeze after March 1st.  Factor in current trends it appears we are looking freeze free through the first 10-11 days of March but there will be arctic air lurking in the high U.S. Plains around the second week of the month, but currently I do not see a storm system that will bring that air to Acadiana.

But if you can wait a few more weeks for planting, you’ll all but guarantee not having to repeat the process later in March or April.  I would however recommend to fertilize our lawns as they’re coming out of winter stasis.

After running some of the actual temperatures for Acadiana of December of 2010 through the present our averages have been running significantly below normal.  Average “mean” temperatures for December 2010 (high/low divided by 2) were about 4 degrees below normal.  The mean for January through the third week of the month has been 2.5 degrees below normal.

The forecasts from the Climate Prediction Center this winter was for above normal temperatures…as I blogged about last month, just a subtle shift of the average trajectories of cold Canadian air can make a big difference…and it has across Louisiana. 

Part of the colder than normal temperatures experienced across the Gulf South can also be attributed to an extra stormy pattern along the East Coast with healthy snow storms ushering snow-chilled arctic air farther to the south.

Although the 30 day pattern from the Climate Prediction Center is still insisting on above normal temperatures for the area, I would take that with less than a grain fo salt.  The shorter term “long-range” models through the next two weeks is decidedly colder than normal for Acadiana with a possible major Eastern U.S. arctic outbreak centered around February 1st…we’ll see!

Bottom line for now, expect higher tha normal heating bills this winter.  Rob

Although 2010 finished on the wet side, rainfall deficits for the entire year made 2010 the 7th driest on records.  Were it not for a very wet weather system that produced more than 3 inches of rain on December 29th and 30th, 2010 would have finished in the top five driest on record.  Accurate rainfall records have been kept in Lafayette since 1893, 117 years.

Acadiana-wide rainfall totals ranged anywhere from 15-25 inches below normal.  Average yearly rainfall in Lafayette is near 62 inches while the numbers shade a few inches higher southeastward toward Morgan City and a few inches lower to the northwest.

Drought conditions continue for a good part of Acadiana while the status of the drought worsens farther west toward the Texas border.  Per the last blog entry, not much help is expected over the next few months while a La Nina pattern continues into at least early summer.

I’m not a big fan of saying whether it will be a “mild” or “cold” winter…we have had plenty of milder than normal winters in the past where temperatures have averaged well above normal but we have had one shot of 15 degree weather.  Most folks will remember that as a cold winter. 

Other previously mild winters we have seen accumulating snow…perception cold winter.   I can recall playing golf on a past Christmas Eve in shorts in a colder than normal winter…what did I remember from that winter…playing golf!  Far too many times as we say in the weather and TV business, “perception is reality”.

The bottom line is that each winter we have on average 20-30 days of 70 degree plus temperatures (December through February) and this year will be no different.  Some years we barely get below freezing but for a handful of days or less…other years we’ll see more than 5 or 6 mornings where we plunge into the mid-20s…like last year. 

Incidentally last December through February was a “colder” than normal winter with temperatures in Acadiana ranging more than 5 degrees below normal…and it started with the earliest snow on record on December 4th!  That winter was followed by the warmest summer on record in Acadiana!

Everybody is asking me this year is whether we will see snow?  If your forecast is based just on long-term trend forecasts many think the odds below or above normal can be determined…but as we all know, Mother Nature’s randomness decides whether we’ll see a snow or a hurricane for that matter. 

Long-term trend forecasts are not that good.  So I say with above normal forecast confidence, that anything can happen!  A ringing endorsement by the non-committal!

The Climate Prediction Center did forecast slightly cooler than normal and wetter than normal conditions last winter but they are going with the opposite for the balance of this winter through March. 

The predictions are calling for in general, above normal temperatures accompanied by below normal precipitation patterns.

This year the temperature forecast calls for a fairly good signal for above normal temperatures as the developing La Nina should induce more ridging across the south. 

The pattern of the last few weeks of November through the first two weeks of December may favor this pattern with regular cold fronts but with milder than normal return periods. 

Forecast confidence is below normal for the temperature pattern however, as just a slight shift of the mean winter longitudinal cold front axis could translate to much warmer or much colder than normal.  We’ll see.

Precipitation forecasts are calling for below normal rains which does not bode well for Acadiana and the state for that matter, as most of the region is in a moderate to severe drought with many spots across the west central and northern part of the state mired in an extreme drought.

Finishing off 2010, rainfall in Lafayette is more than 20 inches below normal.  If drier than normal conditions continue through the winter, they may likely perpetuate through the spring.  This could set the stage for a serious drought situation for much of the state until tropical season arrives.   It is never good when you are wishing for a tropical storm or hurricane to end a drought. 

Based on current trends, forecast “confidence” is above normal for the precipitation pattern.

Droughts have had a history of becoming multi-year events in Acadiana and this may be the start of one such period…again, we’ll see.

Widespread rain and thunderstorms in the first couple of days in November brought impressive rain totals to Acadiana mainly across the I-10 Parishes southward.  Coastal parishes experienced the heaviest rains with totals generally in the 4-6 inch range. 

Hot spots in Vermilion Parish exceeded 8 inches across from Abbeville southwestward where flooding occured including water in some homes. 

Rain totals in Lafayette were in the 2.5-3.5 inch range while most areas north of I-10 indicated 1-2 inches of the wet stuff.

These rains have certainly eased the severity of the on-going drought, but the area will likely stay in “moderate to severe” drought status as many areas remain more than 10-15 inches below year to date normals.

In addition, due to the recent rains, the burn ban has been lifted.  Dry conditions will stay in Acadiana through the second week of November with the next significant chances of rain arriving about mid-month.