Georgia State Climatologist David Stooksbury held a press conference today in Athens to discuss the latest Georgia drought conditions, and to explain what he thinks might occur weather-wise over the winter and spring of 2008. Much of what might happen through the next six months depends on the strength of the developing La Nina, including the chances of being able to refill, at least partially, Lakes Lanier and Allatoona.

There is now general agreement that La Nina conditions are developing in the Pacific. La Nina, and her partner El Nino, are descriptions of the two phases of the warmth of the Pacific Ocean surface temperatures compared to normal. In El Nino conditions, temperatures are warmer, while the reverse is true for La Nina. Most climate observers feel that La Nina conditions strengthened in September.

In a press release accompanying the news conference, Stooksbury said,

“The effects of the La Niña pattern differ with its strength. These differences are critical across north and central Georgia, potentially having major impacts on the current drought and the region’s ability to recover this winter and spring.”

If the La Nina conditions remain weak, then there is actually a greater chance of precipitation across extremely north Georgia, and normal precipitation across the piedmont area. In a moderate to strong La Nina, the chance of more than usual precipitation will be limited to the extreme northwest corner of the state. In either case, it’s likely to be warmer and drier over the southern half of the state. You can see the impacts in the image to the right (click on it for a larger version.)

We had best be hoping for a weak La Nina pattern. In the words of Stooksbury,

“If a moderate La Niña pattern develops, there is a high likelihood that north and west Georgia won’t be able to recover from the drought this winter.

The extreme- to exceptional-drought regions of the state may muddle through the winter and early spring. But without significant recharge of the soil moisture, groundwater, streams and reservoirs, conditions next summer could become catastrophic.”

The Climate Prediction Center has issued it’s outlook for the month of November, and the updated forecasts show the predicted effects of the intensifying La Nina conditions. La Nina conditions occur when sea surface temperatures cool in the Pacific Ocean. The cooler ocean temperatures alter upper air patterns, and tend to cause warmer and dryer conditions in the Southeast, and wetter conditions in the Northwest.

In the discussion of the updated outlook, the Weather Service says that while earlier forecasts were based on computer models predicting La Nina conditions, this month, actual measurements confirm that a weak to moderate La Nina has started, increasing the confidence in the forecast.

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Despite a relatively cool July —the mean July temperature was actually cooler than the mean June Temperature, both here in Lawrenceville and in Atlanta— it looks like August is going to be our hottest month of the year.

The short range, medium range, and long range forecasts are all calling for warmer than normal temperatures, and it looks like we may not get much rain to help out, at least until the middle of the month.

Temperatures will be approaching the 100 degree mark all this week in North Georgia. To make things worse, we’ll likely be seeing high dew points as well. That means that the humidity will be approaching the unbearable range. Take a look at the forecast dew points in Georgia for 2 PM Thursday:

If this forecast validates, we’ll see the heat index above 105 degrees, the danger level, several times this week.

Ultimately, it’s the moisture in the air that determines how we feel when we go outside. Although relative humidity is the measurement most people use to measure moisture content, the dew point temperature can provide a better measure of how uncomfortable conditions are. When the dew point rises to near 70 or above, most people are unlikely to want to be outside for very long.

The heat index also measures the apparent temperature. For more detail, take a look at this table showing the relationship between relative humidity, temperature, heat index, and dew point.

The reversal from the cool and wet July conditions to the hot and dry conditions for August isn’t going to do much to help the drought conditions in Georgia. Over the last month, the drought levels in Georgia haven’t changed very much. While the rain has kept lawns green in the short term, we will see a quick return to brown lawns without more rainfall.

As I’ve said before, tropical weather will probably be the key to breaking the drought. Despite the relatively quiet season so far, the latest forecast by Dr. Gray at Colorado State University is still calling for an above average hurricane season. The researchers are predicting 15 tropical storms for the season, down 2 from their May forecast, and eight hurricanes, down from nine in May. There’s also an above average chance of a major hurricane striking the US coast.

It’s been almost two weeks since I’ve had a chance to post some weather news. This time of year is pretty slow as far as weather goes … it’s a little too early for any real tropical weather activity, and except for the occasional thunderstorm, the forecast is typically hot and humid.

But, the weather does move in patterns, and now it looks like we’re back into the same type of weather we saw in late May, which you may remember was highlighted by a lack of rainfall, with high pressure off the Atlantic keeping any moisture well to our west.

We got somewhat of a break from the dry pattern as the first half of the month ended, although it took an unusual storm from the northeast to do it. And, even then, rainfall was spotty, depending on whether a thunderstorm passed through your neighborhood. Since the first of the week, we’ve seen temperatures in the 90s and low dewpoints, which makes outdoor activity bearable, but keeps the raindrops away.

The Weather Service issued its forecast for July, and the three month outlook for July through September last week, and as indicated by the title of this post, for the Southeast, it’s likely to be hot and dry. July’s outlook proffers warmer than normal temperatures for the east and west coasts, and cooler than normal weather for the nation’s midsection. The Plains states are likely to be the only place in the country with more than average rainfall, although there’s an equal chance of above or below normal precipitation everywhere else except for the mountain west.

The three month outlook amplifies the heat, especially in the southwest. Most of the eastern part of the country has a 40% likelihood of warmer than normal temperatures. Expected tropical weather brings a better chance of rain form much of the east coast during the latter half of the summer.

Tropical storm Barry, along with the recent rains further north have provided some drought relief, particularly for south Georgia and Florida. At right is the drought outlook from mid-May, and the latest outlook, issued last Thursday.

While the portion of the map showing a chances of improvement keeps moving north and west, the drought is spreading north as well, with much of Ohio and Indiana moving into a persistent drought. While I wish no ill will towards our friends in the rust belt, perhaps this movement of the center of the drought northward might mean some relief for the southeast.

Maps Update

You might have noticed the new 12 hour regional forecast on the home page, as well as in the map section of the site. I’ve added the ability to click on the map to view a seven day forecast for the location clicked on, much the same way as clicking on a weather warning map displays active warnings for that location. The forecast map, along with many others, can now be animated, showing the changes in the weather over a several day period.

The medium range weather outlook, which now covers the first part of June, is calling for a change in the weather pattern to wetter, and eventually cooler weather. Below is the expected precipitation map for the period from May 30th through June 3rd, as issued Thursday afternoon:

The temperature outlook for the period from June 1st through June 7th is below normal, and the chance of rain for the period remains above normal. This is quite a change from a few days ago, and if it verifies would mean that we will get a good chance of some drought relief in the early part of June.

Basically, what is happening is that the high pressure system that has been just of the Atlantic coast for what seems like weeks now will be moving towards its more regular summer position near Bermuda, which will allow the storms that presently stop at the nation’s midsection to move further east into Georgia. The GFS forecast model that is one of the tools forecasters use to create these outlooks is the one that is most aggressive in its predictions for this weather pattern, hence the forecasters aren’t 100% sure that it is the right one.

Let’s hope that the GFS is right, and we do get some drought relief. The latest Georgia drought monitor, issued today, has 93% of the state in a severe drought, up from 53% last week. The severe drought area includes all of metro Atlanta. 42% of the state, primarly the northwest and southeast corners are in an extreme drought, up from 25% last week.