KATC StormTeam 3 Weather BLOG

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.

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.

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.

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.

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.

Our very dry weather pattern over the last several months has manifested into a severe to extreme drought for western portions of Acadiana and for much of the southwestern and western part of the state.  Fortunately rains earlier this week have eased the drought over portions of Acadia, Lafayette and St Martin Parishes.

Assuming Acadiana experiences normal precipitation patterns through the rest of the year, 2010 will likely fall within the top 10 driest years over a 117 year time span. 

Currently Lafayette has officially received 32.53″ of rain when normally we should be near 49.79″.  If Acadiana receives normal precipitation for the rest of the year (roughly 10″) then 2010 go into the record books in the top 10 driest years.

With La Nina developing the long term pattern this winter should bring continued below normal rains.  So it will be interesting to see how things play out for the balance of the year. 

Normally Acadiana receives approximately 60″ of rain per year with the driest being 35.80″ in 1924 and the most 98.72″ in 1940 (where a slow moving August hurricane produced more than 24″ in 48 hours in Lafayette).

Below are the top 10 driest years on record in Acadiana.

1.  1924-35.80″                             

2.  1902-37.25″

3.  1917-37.70″

4.  1936-41.15″

5.  1954-41.65″

6.  1962-42.33″

7.  1938-42.92″

8.  1960-42.98″

9.  2005-43.38″

10. 1999-44.86″

It promises to be a rather wet week for most of Acadiana as we continue to deal with the remnants of TD5 as it drifts westward toward Acadiana  Tuesday and the northward Wednesday.   A FLOOD WATCH has been posted for portions of Acadiana from Tuesday morning through Wednesday in the anticipation of the heavy rain threat.

 As expected over the weekend this remnant system persisted across the interior portions of the Gulf States and then dropped back to the south with the circulation getting back out over open Gulf water late Sunday night.

Hurricane Hunters flew this system Monday afternoon just south of Mobile, Alabama.  The reconnaissance plane found broad low pressure, like last week, but disorganized thunderstorm activity near the center, like last week.  This time around upper level conditions are a little more favorable for development through Tuesday prior to the circulation making landfall over Eastern Louisiana Tuesday afternoon.  If thunderstorms cluster near the center of circulation later tonight it will likely become an “official” tropical system

Based on upper level conditions and broad lower surface pressures this system is very close to being a depression and may become one at any time through tomorrow.  If the system is upgraded, tropical storm warnings would probably be issued for portions of Louisiana through the Alabama coast.

The bottom line with this system is that it will be a major rain-maker with rainfalls of 3-5″ likely around this system and up to 8-10″ possible near where the center of circulation travels through mid-week.  Rainfall totals will likely be directly correlated to the speed, or lack of, this exhibits over the next few days.  Most computer models earlier today indicated the greatest threat of flooding rains will be in the eastern part of the state Tuesday and then the central part of the state Tuesday night into Wednesday. 

More recent computer model runs this evening are much more robust with rainfall totals in Acadiana with  3-5″  possible through Thursday with isolated spots receiving possibly more than double depending ultimately where the center of circulation goes and how quickly it moves.  Stay with KATC and katc.com for the latest information.

The tropical moisture plume will re-establish across Southern Louisiana this week as two areas of weak low pressure will be players in Acadiana’s weather.  The front burner system is a weak (1010mb) low just south of Atchafalaya Bay which is expected to drift northwestward through Wednesday.  Although this system is not truly tropical in nature nor is it expected to strengthen much, it will be responsible for enhancing Acadiana’s rain chances (daytime and night-time) for Tuesday and Wednesday.

Locally heavy rainfall will be possible as this system will open the door to deep tropical moisture through mid-week. 

A secondary system in the Northwestern Caribbean is associated with a broad area of surface low pressure with deep disorganized tropical showers and storms.  This feature will push in the central Gulf of Mexico by mid-week and should help to provide another day of enhanced showers and storms for Acadiana Thursday. 

The bottom line is that this week will be another wetter and cloudier than normal one…at least this will keep our high temperatures closer to the mid-upper 80s.  Few storms and hotter temperatures should return for the weekend.

Another vigorous storm system will advance toward Acadiana Friday bring clouds and rain.  Look for clouds to increase through the morning hours with rain developing from noon onward.  This system has a very cold upper level core making conditions aloft quite unstable.  Therefore embedded thunder may be possible tomorrow afternoon with even the possibility of some small hail or soft hail (also known as graupel…see the link for a definition) through tomorrow evening.  Our in-house models are showing anywhere from 1/2 to one inch of rain will be likely area-wide with isolated amoounts up to 1.5-2 inches possible if convection (thunder) gets going.  For a meteorologist this is and interesting system…for most of us it’s just plain wet and sloppy.  While this will be just a wet weather system for Acadiana, I wouldn’t be surprised if some snow flurries follow this system as near as southwestern Mississippi into interior portions of Alabama.  Lingering rain showers and drizzle will be likely through much of Friday night but conditions will likely begin to dry toward daybreak Saturday.  Any lingering cloud cover early Saturday will likely burn off by the afternoon or sooner so at least expect a mostly sunny and cool weekend.  Highs will top out Saturday in the low-mid 50s, drop into the mid-30s for Sunday morning, and rise into the upper 50s to near 60 for Sunday afternoon.  Another quick-moving weather system will arrive Monday bringing another shot of chilly rain, and perhaps soaking rains, to Acadiana.  The Monday system will likely turn into another Southeast and Mid-Atlantic snowstorm…no rest of the winter-weary!  At least for Acadiana, milder tempartures will return for later next week.

Updating Dave’s most excellent and honest blog entry…we are still on course for cold, sloppy rains Thursday into Thursday night.  Once again, we are faced with marginal conditions that could generate a rain/snow mix Thursday night with a possible change-over to all snow in the northern most portions of Acadiana before the precipitation ends during the pre-dawn hours of Friday.  For this reason the NWS has issued Winter Weather Advisories for Beuaregard, Allen, Evangeline and St Landry Parishes for Thursday night for the possibility of a light slushy accumulation.  Temperatures however should stay above the freezing mark at the surface through tomorrow night…but aloft conditions should be cold eneough for snow and/or sleet to mix in with the rain.  With that being said cold air to our north and aloft could get entrained into this system, especially if our surface winds stay consistent out of the NE or NNE.  Farther to the north a significant accumulating snow may be possible from Alexandria to Baton Rouge while the best target for a good snow will be in SW Mississippi where 2-4″ of snow will be likely with up to 6″ possible there.  Winter Storm Watches are posted from Northeast Texas eastward through CenLa into Mississippi including the Baton Rouge Parishes.  For most of us the precipitation will start off lightly and sporadic Thursday morning with some sleet quite possible to mix in, then all rain for the balance of the day and then possibly a slow changeover to a wintry mix Thursday night.  I am not expect any roadway hazards in Acadiana with this system with the exception of the northern portions of the northern parishes of Acadiana ground temperatures may be too warm.  But grassy areas, trees and roof tops may whiten by Friday morning.  Most of us along and south of the I-10 corridor should stay almost all rain.  But like the last two December snow events (2008 and 2009) we may wake up Friday morning with some folks to the north making snowballs while others just getting to see it on video!  Stay tuned for the latest computer model runs and radar trends!