The 2011 Summer Heat Wave and Drought: A Recap and the Winter Outlook Jason Hansford Senior Forecaster National Weather Service Forecast Office Shreveport, LA
Record Extremes Breakdown:(from 7 major Climatological Stations) Daily temperature records consisted of Record Highs and Highest Minimums: • June: 58 daily records • July: 53 daily records • August: 166 daily records (greatest ever) • September: 33 daily records
Record Consecutive Number of 100 Degree Days *Longview also recorded 100 degree day streaks of 18 days (T4th with 1939) and 15 days (T7th with 1951 and 1954) during August as well. ** Shreveport also recorded a 12 day string of 100 degree days (T3rd with 1980 and 1875), ending on 8/10.
Six Month Rainfall Map Observed Rainfall: Departure from Normal:
2011 Year-To-Date Rainfall Ending Oct. 31 * Each of these stations are on course to set the driest year ever on record, or fall within the Top 3.
Drought Impacts • County/Parish wide burn bans remain in effect. • Increased instances of wildfires, which have charred tens of thousands of acres. • Farmers/ranchers are culling their herds. • Lakes continue to recede/ponds remain low or have dried up. • Hay remains scarce as only one or two cuttings have been produced this summer. • Water restrictions are in effect areawide.
Hydrological Drought Impacts Toledo Bend Lake near Hwy. 6 Measured near 160.3 ft on 10/18/11 Record Low: 159.9 ft on 10/31/11 Previous Record Low: 161.25 ft on 10/16/2006 (Photo courtesy of Wiley Butler) Cane River in Natchitoches, LA Measured near 2 ft. on 10/11/11 (Photo courtesy of Wiley Butler)
Fall/Winter Outlook Issued by the Climate Prediction Center
La Niña Returns! • 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. • 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.
SST’s in the Equatorial Pacific Niño 3.4 Region: 5°N - 5°S and 170° - 120°W [ ] [ ]
How Strong will La Niña be This Winter? Niño 3.4 SST’s Model Forecasts
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 La Niña impacts. • 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. • 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 (Nov. – Mar. 1950 - Current) 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.
How Have Back to Back La Niña’s Contributed to Precipitation Deficits in the Past???
Calculated Soil Moisture Soil Moisture is ONLY 200-300 mm (8 - 12 in.) deep. That’s 140-180 mm (5.5 - 7.0 in.) BELOW normal!
Drought Severity Indices • Palmer Drought Severity Index: Is most effective in determining long termdrought by using temperature and precipitation to calculate dryness. It is also standardized to the local climate. • 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. • Uses the same scale as the Palmer Index.
The End Any Questions???