2013 Drought and Seasonal Temperature and

Precipitation Outlook for the Ark-La-Tex Region

Jason HansfordSenior Meteorologist

National Weather Service Forecast Office Shreveport, LA

U.S. Drought Monitor (Six Month Comparison)

August 28, 2012 March 19, 2013

Six Month Rainfall MapLate September 2012 - March 26th, 2013

Observed Rainfall:Observed Rainfall: Departure from Normal:Departure from Normal:

Twelve Month Rainfall MapMarch 26th- March 25th, 2012-13

Observed Rainfall:Observed Rainfall: Departure from Normal:Departure from Normal:

11+ Month Rainfall and Departures (Apr. ’12 - Mar. 13th,‘13)

City: Total Precipitation:

Departure from Normal:

% of Normal:

Shreveport, LA 49.71 -1.26 98%Monroe, LA 59.41 +5.96 111%

Natchitoches, LA 55.27 +0.41 101%Texarkana, AR 29.90 -19.33 61%El Dorado, AR 40.85 -11.32 78%

Hope, AR 41.55 -12.39 77%Dequeen, AR 24.32 -24.39 50%

Idabel, OK 33.46 -19.54 63%Mt. Pleasant, TX 38.00 -7.83 83%

Tyler, TX 31.34 -12.22 72%Longview, TX 38.73 -8.09 83%

Lufkin, TX 37.22 -6.46 85%

Southern Plains Yearly Average Temperature and

Departure from Normal

Winter Rains Have Eased Drought Conditions

(December 2012 - February 2013)City: Dec. – Feb.

RainfallDeparture from

Normal% of Normal

Shreveport, LA 13.10 inches -0.62 inches 95%Monroe, LA 19.18 inches +4.25 inches 128%Texarkana, AR 9.91 inches -2.53 inches 80%De Queen, AR 8.01 inches -3.35 inches 71%El Dorado, AR 12.72 inches -1.55 inches 89%Tyler, TX 8.33 inches -2.78 inches 75%Longview, TX 12.49 inches +0.64 inches 105%Lufkin, TX 11.12 inches -1.37 inches 89%

Three Month Precipitation Totalsand Surpluses

60 Day Precipitation Deficits(Late January-Late March 2013)

30 Day Deficits are Mounting(Late February-Late March 2013)

Hydrologic Drought(Lake Pool Stage as of 3/26/13)

Broken Bow: 601.16 ft (+1.66 ft)

Millwood: 259.67 ft (+0.47 ft)

Wright Patman: 223.78 ft (+3.18 ft)

Lake O’ Pines: 225.48 ft (-3.02 ft)

Caddo Lake: 169.10 ft (-0.90 ft)

Lake D-Arbonne: 80.88 ft (-0.12 ft)

Toledo Bend: 169.40 ft (-2.60 ft)

Lake Fork: 398.59 ft (-4.41 ft)

Sam Rayburn: 162.45 ft (-2.05 ft)

Hydrological Drought Impacts

Measured Pool Stage at 7am: 589.55 Feet

Normal Pool Stage: 599.50 Feet

BROKEN BOW LAKENovember 22, 2012

Hydrological Drought Improvement at Broken Bow Lake

What Factors Have Contributed to the Drought???

• We must look at sustained temperature patterns in the Equatorial Pacific, stretching along the equator from 170W to 120W longitude, and 5N to 5S latitude.

• Based on certain temperature patterns over a period of time, El Niño or La Niña episodes may develop, which will alter the path of the jet stream, and ultimately determines temperature and precipitation patterns all over the world.

What is El Niño?• Operational Definition: Operational Definition: defined by a warming of Sea

Surface Temperatures (SST’s) in the Equatorial Pacific. This phenomenon is characterized by a trend of the 3 month running mean of SST’s 0.5C above normal.

• SST’s are measured across various regions in the Pacific, but the Niño 3.4 Region (5°N – 5°S and 170°-120°W) is what is particularly monitored for ENSO conditions.

• To be classified as a distinct El Niño episode, these SST conditions must be met for a period of at least 5 consecutive months.

El Niño Effects on Temperature/Precipitation

What is La Niña?• Operational Definition: Operational Definition: defined by a cooling of Sea

Surface Temperatures (SST’s) in the Equatorial Pacific. This phenomenon is characterized by a trend of the 3 month running mean of SST’s 0.5C below normal.

• Just like El Niño, SST’s are measured across various regions in the Pacific, but the Niño 3.4 Region (5°N – 5°S and 170°-120°W) is what is particularly monitored for ENSO conditions.

• To be classified as a distinct La Niña episode, these SST conditions must be met for a period of at least 5 consecutive months.

La Niña Effects on Temperature/Precipitation

Jet Stream Patterns with El Niño/La Niña Events

Recent ENSO Events

SST’s in the Equatorial Pacific

Niño 3.4 Region:Niño 3.4 Region:5°N - 5°S and 170° - 120°W

[ ][ ]

Long Term SST Anomalies

How Strong will ENSO be this Spring?

Model ForecastsModel Forecasts

Neutral

Strong El Niño

Strong La Niña

What if we maintain neutral conditions for much of the

year???

Arctic Oscillation• Refers to the atmospheric circulation pattern in the northern

middle and high latitudes in the Arctic. These can generate strong shifts in the climate pattern than can overwhelm or amplify the typical El Niño/La Niña impacts.

1) Exhibits a negative phase when higher pressures develop over the Polar region, and low pressures develop in the mid- latitudes (near 45°N). This results in frigid air plunging south into North America east of the Rockies.

2) Exhibits a positive phase when lower pressures develop over the Polar region, and higher pressures develop in the mid- latitudes. This will keep the frigid air locked up in the Arctic region, but also drives ocean storms farther north. Thus, wetter weather is usually associated throughout Alaska, Scotland, and Scandinavia.

Arctic Oscillation (1950 - Current)

Limitations to Forecasting:Limitations to Forecasting:Strong AO episodes typically last only a few weeks, and are difficult to predict more than a week or two in advance.

North Atlantic Oscillation Fluctuations in the difference of

sea-level pressure between the Icelandic Low and the Azores high.

+ NAO prevents cold air from plunging southward over eastern North America.

Shows multi-decadal signal.

Has an effect on Hurricanes in the Atlantic. (During +NAO events, the Bermuda High is weaker, allowing for a more W-E flow across the Atlantic. SST’s in the Atlantic are also unusually cold following +NAO winters.)

Historical NAO Index(1950-Current)

Strong positive anomalies last winter.

Strong negative anomalies this winter.

Monthly Observed Arctic and North Atlantic Oscillation

Indices

AO/NAO Influences on the Average Temperatures across

the CONUS

AO/NAO used in Developing Probabilistic Maps of Temperature

Very Strong –AO Contributing to the CONUS Deep Freeze

Drought Severity Indices• Palmer Drought Severity Index: Is most effective

in determining long term drought by using temperature and precipitation to calculate dryness. It is also standardized to the local climate.

a) Measured on a scale of -4 to 4, with negative values indicating drought, and positive values indicating moisture surplus.

• Crop Moisture Index (CMI): Is a short term drought index, based on precipitation, dryness, and wetness affecting agriculture. It changes more rapidly from week to week than the Palmer Index.

a) Uses the same scale as the Palmer Index.

Calculated Soil Moisture

Soil Moisture is 400 - 550 mm (15.5 – 21.5 in.)

deep.

That’s 50-100 mm (2.0 - 4.0 in.)

BELOW normal!

Palmer/Crop Moisture Drought Index

How Much Rain is Needed to End the Drought?

Spring Outlook

Issued by the Climate Prediction Center

Long Term Drought Outlook

The End

Any Questions???Any Questions???