PDA

View Full Version : La Nina is back.


A.T. Hagan
02-23-2009, 01:28 PM
Here comes our long hot summer. Us folks in the Southeast had better prepare for further drought. In other words, same old, same old.

.....Alan.

http://agroclimate.org/forecasts/current_climate_outlook.php

SECC Winter Climate Outlook

Current Conditions

La Niņa returns suddenly to the Pacific Ocean, winter forecast is now for warm and dry conditions. Last month, the Pacific Ocean was still in the neutral phase and the Southeast Climate Consortium predicted rainfall and temperature patterns that are close to normal, but with greater variability within the season. Now, the Pacific Ocean has switched rather abruptly to La Niņa (colder than normal ocean temperatures along the equator in the eastern and central Pacific) and that forecast has been amended to warm and dry for the remainder of the winter and early spring. With much colder than normal ocean waters now in place in the tropical Pacific Ocean, it is nearly certain that La Niņa will persist and possibly strengthen during the remainder of the winter and well into the spring season. La Niņa conditions usually bring warmer weather to the entire region, with temperatures generally averaging 2 to 4 degrees F higher than normal from November through March.

La Niņa also brings drier weather to much of the three states. During the winter season, the dry pattern actually pushes southward and intensifies over the peninsula of Florida and the immediate coasts of Alabama, Georgia, and the Carolinas where average La Niņa rainfall is 30% to 60% less than normal. Inland North Carolina, Central Alabama, central Georgia, and northern Georgia usually see near normal rainfall during this time, while northwest Alabama actually tends to be wetter than normal.

http://agroclimate.org/forecasts/images/012009_jan-lanina.png

The reason for the rainfall patterns seen in January can be attributed to the predominant jet stream configuration that sets up during a La Niņa winter. While the position of the jet stream will fluctuate with the passing of individual low pressure systems, fronts, and air masses, the preferred or average setup of the jet steam is that of high pressure or "ridging" over the Pacific near the U.S. west coast and low pressure or "troughing" over the mid-section of the country. This configuration tends to steer winter storms up the Mississippi Valley and Midwest. Unfortunately, this storm track often leaves the Southeast dry and the cold fronts with a little less punch.

How certain is the forecast? Thus far, the maps above and the discussion have centered around "average" shifts in temperature and precipitation due to La Niņa. However, no two La Niņa episodes are alike, nor are the climate impacts seen from these events. It is important to consider the range of possibilities that accompanies La Niņa episodes rather than counting on climate patterns close to the "average" for La Niņa. The figures below represent the range of possible precipitation amounts in January for four selected counties in the region plotted as exceedance curves. Simply put, each bar in the graphs gives the probability of rainfall equaling or exceeding the given amount for both La Niņa and Neutral (ocean temperature close to normal) climate phases. The graphs demonstrate how the range of possibilities are nearly the same for the two climate phases in central Alabama and Georgia, but shift dramatically towards drier in south Georgia and Florida.

http://agroclimate.org/forecasts/images/012009_totrainprob.png

Will a strong La Niņa make a difference in the forecast? With this La Niņa beginning so late in the winter, we are unsure if it will grow to be a moderate to strong event. Analyses have shown that strong La Niņa's tend to bring even more intense dryness to the affected areas, and that the dry conditions actually extend farther north into central and northern Georgia and Alabama during the winter. The transition zone between dry and wet moves from central Georgia and Alabama into the mountainous regions. With this in mind, drier than normal winter conditions are more likely in the drought-plagued areas of north Georgia and the Carolinas if the Pacific Ocean continues cooling.

So what are the implications for the Southeast? The warmer temperatures will impact winter crops and fruit production, resulting in less chill accumulation over the course of the winter season. Warmer temperatures will also mean greater evaporation rates. Due to the jet stream configuration described above, severe or damaging freezes are less likely during La Niņa than in neutral years. However, the risk of early or late season freezes (like in April of 2007) does not seem to be affected by the Pacific Ocean.

The shift towards drier than normal conditions becomes much more pronounced in Florida and coastal Georgia, Alabama, and the Carolinas as fall progresses into winter, resulting in much higher confidence in a forecast of dry conditions in these areas. La Niņa does not impact central and northern Georgia and Alabama nearly as much, nor inland North Carolina, so there is much more uncertainty in the precipitation forecast for these areas and near normal is more likely. Even with near normal rainfall, drought conditions are likely to persist in the mountainous regions of Georgia and North Carolina, but some lessening of the severity is possible with the winter rainfall. Keep in mind that winter rainfall is vital to the recharge of surface and groundwater in Georgia, Alabama, and the Carolinas where summer evapotranspiration rates are greater than normal rainfall, usually resulting in falling water levels. In Florida and southeast Georgia where drought concerns were eased with recent rainfall, there is a strong possibility for drought to reintensify this winter and spring. Wildfires will also be a concern, where studies show that La Niņa normally leads to an active wildfire season in Florida and South Georgia.

For more detailed information on El Niņo climate shifts in your particular county, please refer to the Climate Risk Tool at AgroClimate:

Sysiphus
02-23-2009, 01:53 PM
Is this current? I read an article last week that La Nina (which did indeed upsurge in late fall 2008) would fizzle out by April.

A.T. Hagan
02-23-2009, 02:20 PM
http://agroclimate.org/forecasts/Agricultural_Outlook.php

February 8th.

.....Alan.

Sysiphus
02-23-2009, 08:26 PM
See slide 28. ENSO Weekly Discussion (http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf)

dyrt
02-23-2009, 08:54 PM
Any continuation in La Nina conditions are exceptionally bad news for large parts of Texas. We have been experiencing extremely dry conditions. The coming warm weather will bring devastating conditions for native plants and animals. A summer in these conditions will bring much hardship on a lot of people living in new houses with water wells. We are already experiencing increased wild fires.

I really really hope that La Nina suddenly changes her mind again.

Sysiphus
02-23-2009, 11:27 PM
dyrt - it fired up in late October, and hopefully now will gradually wane over the next three or four months. The Agroclimate release sounds pretty alarmist, but in fact it did not just fire up again in February.

A.T. Hagan
02-24-2009, 08:35 AM
I expect there will be another release about this in the next couple of weeks. April and May are ordinarily our dryest months here in Florida with the rainy season usually starting in June. When it doesn't is when our fire season runs wild.

.....Alan.

dyrt
02-24-2009, 09:23 AM
dyrt - it fired up in late October, and hopefully now will gradually wane over the next three or four months. The Agroclimate release sounds pretty alarmist, but in fact it did not just fire up again in February.I know when the Pacific cooled because that is when the rain stopped. We watch closely. There was some hope a couple of months ago as some weakening of the winds was measured. We need El Nino now.

Sysiphus
02-24-2009, 12:31 PM
We need El Nino now. I hope so, but that is not the prediction. I also hope Florida doesn't go up again - fires got pretty close to my dad last time.

A.T. Hagan
02-24-2009, 12:42 PM
We've had drier winters before so the fire danger shouldn't be too awful bad here in Florida - yet. We get some every year regardless, but we're not so dry as to approach anything like 1998.

But if we get to late June without seeing significant rainfall then central and north Florida are going to be a bad place.

.....Alan.

Renegade
02-26-2009, 10:06 AM
Fire Weather Outlook: January - March, 2009
Updated January 8, 2009

CURRENT CONDITIONS
The state began 2008 under La Niņa conditions. Despite the La Niņa, the Panhandle experienced above normal rainfall activity through the early spring months due to other atmospheric conditions. Central and southern parts of the state continued to experience below normal rainfall and above normal fire activity. Rainfall activity returned to more normal levels in June and alleviated the fire conditions. Sixteen named storms formed, 8 of which were hurricanes and 5 of which were major (Category 3 or higher). Although there was major damage in the United States due to hurricane landfalls this season, Florida was spared the worst conditions. Tropical Storm Fay made landfall in Florida 4 times and dropped up to 20 inches of rain across the state, erasing the short term drought conditions but also bringing severe flooding problems to many areas.

Dry conditions through the fall and early winter have returned the state to its previously arid conditions. The state-mean KBDI on December 30 was 501. According to the U.S. Drought Monitor, only the western Peninsula area is experiencing long term drought conditions despite the high values of KBDI across the entire Peninsula.

LONG-RANGE OUTLOOK
The outlook for the next three months is for the current neutral pattern to continue. Drought conditions are expected to worsen as a La Niņa-like pattern continues to dominate the weather and will tend to bring below average rainfall to the state and above average temperatures. Periodic freeze events will act to increase fuel loading in already dry areas and increase the fire danger through the spring months.

Rainfall amounts are forecast to be near average by June and above average toward the end of the summer when we approach peak hurricane season. It appears unlikely that El Niņo conditions will develop through 2009.

SUMMARY
Drought conditions are expected to worsen over the spring months as the neutral conditions in the eastern Pacific Ocean persist. The potential will be high for another active wildfire season this spring. Longer term outlooks suggest summer rainfall could be influenced by another active hurricane season.

The next seasonal outlook will be the first week in April, 2009.

http://www.fl-dof.com/fire_weather/forecast/seasonal_forecast.html

BirdGuano
02-26-2009, 03:04 PM
We are already gearing up for an early wildfire season in California.

Central/Norcal may start fire season as early as April this year. (usually starts in June).

The rains of late have done nothing for the fuel moisture content in the heavy fuels, and will only allow the range grass to grow, adding to the fuel ladder as soon as it dries.