# Presentation: 462031

## The La Niña Pattern Effects in Central Alabama

- Rainfall and Temperature

## Latest Forecast

- The chance of a La Niña developing in 2007 is thought to be higher than the long-term average (which is about one in five or 20%) because
- They have a tendency to follow an El Niño;
- The 2006/07 El Niño decayed somewhat earlier than normal thereby giving time for a La Niña to begin developing during the critical March to June period;
- All of the better computer models are predicting one to occur;
- A large pool of cold sub-surface water is persisting in the central to eastern tropical Pacific Ocean

## La Niña in General

- Cooling of sea surface temperatures in the Central and Eastern Pacific with an observed SST of -0.5 below climatic average
- Using data since 1950, the observed breakdown of the previous El Niño in 2006-2007 shows the strongest SST cooling on record
- La Niña conditions tend to develop in spring to early summer with greatest impacts later in the year
- La Niña conditions can tend to favor hurricane development due to lack of shear

## La Niña in General

- La Niña tends to develop every 3 to 5 years but may vary from 2 to 7 years
- La Niñas last for a period of 1 to 3 years
- Drier and warmer than normal conditions are noted across much of the southern U.S.

## La Niña Expectations

- Increased storminess & frequency of significant cold-air outbreaks over Central North America
- Southern states are drier
- Considerable month to month variations in temp and rainfall patterns, due to more variability in atmospheric circulation

## The Tropics During La Niña

- 1950 through 2001
- 14 tropical systems that impacted central Alabama
- 3 Summer storms
- 2 were late August into September; 1 in July
- 11 Autumn storms
- More significant impact on MGM than BHM

## CSU Hurricane Forecast

- Entire U.S. coastline - 74% (average for last century is 52%)
- U.S. East Coast Including Peninsula Florida - 50% (average for last century is 31%)
- Gulf Coast from the Florida Panhandle westward to Brownsville - 49% (average for last century is 30%)

## Birmingham Summer Rainfall

**Notes:**
1.24

## Summer Rainfall Results

- BHM summer rainfall
- 13 events
- Average departure from mean was 4.14”
- Total rainfall of all La Nina’s is 27.78” above climatic average
- 9 of 13 were at or above the climatic average of 12.35” (69%)

## Birmingham Autumn Rainfall

**Notes:**
1.19

## Autumn Rainfall Results

- BHM autumn rainfall
- 18 events
- Average departure from mean was 3.93”
- Total rainfall of all La Nina’s is 22.41” below climatic average
- 14 of 18 were at or below the climatic average of 11.19” (78%)

## Birmingham Autumn Rainfall

**Notes:**
1.19

## Hurricane Adjustments

- BHM autumn rain
- 18 events
- Average departure from mean was 4.08”
- Total rainfall goes from a deficit of 22.41” to a deficit of 33.18” from climatic average
- 14 of 18 were at or below the climatic average of 11.19” (78%)

## Montgomery Summer Rainfall

**Notes:**
1.31

## Summer Rainfall Results

- MGM summer rain
- 13 events
- Average departure from mean was 2.95”
- Total rainfall of all La Nina’s is 8.2” above the climatic average
- 8 of 13 were at or above the climatic average of 13.07” (62%)

## Montgomery Autumn Rainfall

## Autumn Rainfall Results

- MGM autumn rain
- 18 events
- Average departure from mean was 4.07”
- Total rainfall of all La Nina’s is 1.46” below the climatic average
- 11 of 18 were at or below the climatic average of 11.33” (61%)

## Montgomery Autumn Rainfall

## Hurricane Adjustments

- MGM autumn rain
- 18 events
- Average departure from mean was 4.02”
- Total rainfall goes from a deficit of 1.46” to a deficit of 33.70” from climatic average
- 14 of 18 were at or below the climatic average of 11.33” (78%)