Earlier this week, the Dr. Gray and his team at Colorado State University issued their initial outlook for the 2009 hurricane season. The early outlook predicts a continuation of the above-normal tropical activity we’ve seen over the past few years. The outlook is for 14 storms, compared to over nine in a normal year, and seven hurricanes, compared to six in a normal year. There should be three major hurricanes, and there’s a 63% chance of a major hurricane making landfall somewhere in the United States–about 20% greater than in a normal year.

Last year at this time, CSU predicted there would be 13 named storms, seven hurricanes and three major hurricanes. The result ended up being 16 storms, eight hurricanes and five major hurricanes, so they underestimated. However, their new model for predicting hurricanes from this far out is apparently more accurate than the model they used previously.

A few other weather tidbits:

if tonight’s full moon seems brighter than usual, it’s because the moon is closer to the earth than it’s been for the past few years, and the first time in 15 years that the close approach, caused by the Moon’s elliptical orbit, has occurred during a full moon. Coincidentally, the moon is riding higher in the sky than any other full moon this year. The sun and moon follow opposite visual paths–when the sun is low close to the winter solstice, the moon is high in the sky, while in the summer, when the sun is overhead, the moon is low in the sky.

Another astronomical factoid — today is the first day that the sun begins to set later in the evening than it has since back on July 5th. Day will continue to shorten for another ten days, due to the sun rising later. We won’t get an earlier sunrise until January 13th.

The storm that brought welcome rain to much of the southeast is now history, having moved up the east coast and causing major power outages in the northeast. Much of Massachusetts was caught in an ice storm, with considerable damage. Albany, New York had .6 inches of ice, while Schenectady reported .88 inches of accumulated ice.

We are about to see a big pattern change in the weather across the United States. The past month or so has been dominated by an upper level trough in the east and a ridge in the west. This pattern brought warmer than normal conditions to the west, and colder than normal weather to the east, as the jet stream dived south, following the path of the trough.

Now, a trough is developing in the west, which will bring colder than normal weather there, but more seasonable, if not warmer than normal weather to the Southeast. There’s a better than normal chance of above normal temperatures for most of the south through Christmas, and it looks like we’ll get some additional rainfall, too. Lake Lanier’s current level is 1051.88 feet–more than ten inches above where it was on Wednesday before it started to rain. The AJC reports that yesterday was the first day since the record low level last December that the lake level in 2008 was higher than it was on the same day in 2007.

Wednesday night’s threatened winter storm didn’t end up causing too much difficulty for the metro Atlanta area. The onset of snow between 5 and 5:30 PM managed to put about a quarter inch of the white stuff on my yard and caused the temperature to drop below freezing, but by 7:30 PM, temperatures rose above 32 degrees, and stayed constant or warmed up as the overnight hours passed.

Nonetheless, at least some freezing rain was noticed in parts of Gwinnett, even if it was in limited areas. I noticed that ice was still sticking to trees after noon today along Wisteria Drive in Snellville, and the pine trees along Ronald Reagan Parkway were similarly burdened. So much of what happens in a winter storm is temperature dependent, so just a variation of a degree or so can make a big difference.

The continually varying weather we’ve seen this winter has brought relatively normal precipitation to drought-starved North Georgia. December ended up with more than the normal amount of rainfall, and the official rain gauge in Atlanta is close to what we would expect so far in a normal January.

The latest drought outlook, released today and shown at right, calls for improving conditions for much of the northern part of the state including Atlanta, with at least some relief for the rest of the state. We should see another chance of rain and/or snow Friday night and Saturday morning, with more precipitation for the latter part of next week.  Both the 6-10 and 8-14 long range outlooks call a better than average chance of rainfall.

We’re not out of the drought yet.  But, with drier than normal conditions predicted for the winter due to the presence of La Nina, it can’t be a bad thing that precipitation is running close to normal.

It looks like things could get fairly nasty Wednesday Night and into Thursday for much of the Atlanta area north of Interstate 20, and especially for the northeast counties, including Gwinnett.  An incoming low pressure system in the Gulf of Mexico will bring precipitation to Georgia beginning Wednesday morning.  Meanwhile, the high currently over the eastern part of Kentucky will move northeast, running into the Appalachians, and causing a ‘wedge’, or cold air damming to affect northeast Georgia.

What happens is that the colder air gets trapped on the western edge of the mountains, and the approaching lower pressure, warmer air slides above the colder, heavier air. You can tell when we’re in a CAD situation when the wind comes from the east, and it doesn’t warm up much during the day.

The presence of warm air above cooler closer to the ground tends to favor the formation of sleet or freezing rain, since the warm air layer will melt any snow as it passes through, while the cold air close to the ground will either re-freeze the precipitation, or cause freezing when the water hits the surface.

In the last day, forecasters have increased the total amount of expected precipitation from the storm to almost an inch, while dropping the low temperature Wednesday night, especially in the northeast counties most affected by the wedge.

Here’s what to expect tomorrow in the Gwinnett area:

7 AM  – The leading edge of the precipitation moves to the Atlanta area, but nothing may hit the ground because the air is so dry.  Look for dew points to increase in the morning, and the temperature to rise above early morning below freezing lows.

11 AM – Light rain begins, with temperatures above freezing, so no problems.

7 PM – After sunset, temperatures begin to cool, and the rain increases in intensity.  We may see a little sleet in the early evening.

11 PM – Temperatures drop below freezing.  Continued rain and sleet, with some freezing rain.

4 AM – The intensity of the rain begins to slow, but because temperatures have been below freezing, we’re probably seeing freezing rain at this point.

11 AM – Temperatures rise above freezing, as most of the rain  has passed from the area.

Of course, this is just my best guess, and things could  change. The further south and west you are, the better the chances that this is just a rain event. In any case, Thursday morning could be nasty.

While it may not get as bad as the winter storm in North Georgia two years ago, it looks like Thursday morning is going to be pretty nasty.

The Weather Service has issued a winter storm warning for the northern part of the state, including Gwinnett County. They have also issued a winter weather advisory north of a line from LaGrange to Macon to Augusta. The warned area could expect up to half an inch of sleet and a quarter of an inch of ice before Noon Thursday.

Cold temperatures today — the high was only 42 degrees — and dropping temperatures due to the still-clear skies will push the morning low below 30 degrees. Meanwhile the precipitation will arrive starting in the northwest corner of the state, and will most likely arrive in Atlanta after 1 AM, with the worst arriving shortly before sunrise.

The good news is that the precipitation will bring warmer air, with temperatures rising above 32 degrees by noon, and probably staying there through the overnight hours early Friday morning, so the worst should be over Thursday afternoon. Overall, we could get more than an inch of liquid precipitation before things start to dry up late Thursday night.

The longer range outlook keeps things cold in the Atlanta metro area through the middle of February. The Weather Service issued an updated forecast for the month, and while the predictions for the Southeast US didn’t change much, they are calling for colder weather than originally thought in the Northeastern states.

In a near-repeat of weather conditions from two weeks ago, the possibility of freezing rain has raised its ugly head in North Georgia.

As you may remember from this post, we had a situation two weeks ago with a low pressure system approaching from the south, and cold air in place. This brought the threat of freezing rain or sleet. Although there was a bit of freezing rain overnight, the ground was warm enough, and the precipitation amount was small enough that there weren’t any problems.

The situation this week is different. Unlike two weeks ago, when we set a new high temperature record, it’s been much colder, which increases the chances of any freezing sticking around. Also, instead of 1/10th of an inch of precipitation, we are likely to see about an inch between 7 PM Wednesday and 7 PM Thursday.

Right now, forecasters believe that what does fall could be freezing rain north of a line between LaGrange and Milledgeville. Even after sunrise on Thursday, the line between rain and freezing rain will be just south of Gwinnett County.

Everything is subject to timing of the storm, and the exact temperatures on Wednesday night. We’ll have a much better picture of what is to come on Wednesday morning.

There’s a reasonable chance that metro Atlanta might get its first wintry weather Wednesday night and into Thursday, but the forecast is tricky, and a lot of what will happen will depend on exactly how conditions set up.

During the day Wednesday, North Georgia will be under control of a high pressure system located over Virginia. This will make for a chilly day again. Meanwhile, a low pressure system is moving east. It’s the same one that has brought freezing rain to Texas earlier this week. Whether we get a major winter event depends on how these two systems interact.

As the warm, moist air moves into Georgia, it will meet the colder air. Since the colder air is heavier than the warmer air, it will remain below the warm air. This effect is called Cold Air Damming, or popularly, ‘the wedge’. The possible effect is that instead of temperatures rising with the incoming rainfall, it will remain cold enough at the surface to cause sleet or freezing rain.

Below is the Weather Service graphical forecast for 7 AM on Thursday:

You can see that below Macon, there will be heavier precipitation, and it will be all rainfall. There’s an area north of that that may see heavier icing, since it will be in the more active part of the rainy sector, while also under the influence of the wedge. North of a line from Columbus to Athens, including Gwinnett County, freezing rain is also predicted.

So what happens on Thursday morning is a function of how strong a wedge develops, and how fast the precipitation moves. Since the ground is warm because of the springlike weather we saw before today, there isn’t likely to be any accumulation on the ground. However, if we do get freezing rain, it will affect trees and power lines, and things could turn nasty. If it’s too cold, we get sleet, which won’t be a problem. And, if the wedge is weak, we may get all rain as temperatures close to the surface remain above 32 degrees.

Stay tuned…

In what could be the first of three pre-Christmas winter events, Gwinnett County is waking up this morning to an ice storm. Originally predicted to stay north of our area, temperatures dropped enough prior to the onset of rain to create a hazardous situation once the rain began to fall.

The Weather Service gave up shortly after midnight and issued a winter storm warning for Gwinnett County and Northeast Georgia until 6 PM on Thursday. Peering outside, light ice has formed on the trees. Several areas are without power, including parts of Lilburn and Duluth, although the situation so far doesn’t seem too serious.

Here, temperatures dropped as low as 30.9 degrees around 1 AM before starting to rise slightly, although the thermometer hasn’t gone above the present 32.5 degrees. Once day breaks, the question is how fast and far the temperatures will go up. For areas to the south and west, we’re likely to see above freezing temperatures after sunrise. North and east may see temperatures hover in the 32 degree range until afternoon. Both areas will see up to a quarter of an inch of precipitation before things slow down this afternoon.

Forecasters were slightly caught by surprise this morning by the extent of the cold weather’s reach. Atlanta is on the edge of two frontal systems – a high pressure system centered over New England bringing in cold, dry air in from the east, and a low pressure system bringing in the rain from the southwest. This mixture caused a wedge of cold air to get stuck over the north Georgia mountains. Yesterday was expected to make it into the low 40s in northeast Atlanta, with temperatures staying above the freezing mark overnight.

Instead, the wedge was stronger than expected, reaching farther south. the temperature here hit a high of 38 degrees shortly after noon before beginning to fall slightly. By the time the rain arrived in the early evening, the thermometer began to drop even more as dewpoints began to rise.

Even if we manage to dodge the bullet today, there are two more chances of winter weather in the next week – on Sunday, and again on Tuesday or Wednesday. I’ll post more on these possibilities later.

As of noon Saturday, temperatures were hovering around 29 degrees, up from an overnight low of 26°. We had a high of 31° shortly after 7 PM, still below the freezing mark. There is a possibility of additional precipitation this evening, with an upper wave rotating into Georgia. The National Weather Service extended its Winter Storm Warning until 1 AM, citing the lack of improvement in the weather conditions.

It looks like much of the precipitation overnight on Friday night was sleet, with about 1/2 inch on the ground, and less than 1/4 inch of ice on the trees. Later on during the day Saturday, this changed to mixed rain and sleet, which built up the ice on exposed objects to about 3/8 inch, and made driving difficult. The Weather Channel was reporting an inch of sleet as of late afternoon in metro Atlanta. By Saturday night, you could hear the trees crackling as the wind blew, and over 100,000 Georgia customers had lost power due to the storm. The good news is that by 10 AM on Sunday, temperatures will begin to warm up, with a high on Sunday of 44.

To the right is a picture of ice-laden dogwood trees backlit by the neighborhood streetlight on Saturday evening. Click here to view additional pictures of the effects of the weather in our area.

That’s what the forecaster at the National Weather Service called this weekend’s weather in North Georgia. After a brief round of sleet around sunset, the second wave of wet weather arrived in mid evening as far south as Americus, and moved northward, with significant icing across much of North Georgia.

Temperatures continued to drop as the wet weather arrived, caused by evaporational cooling. In metro Atlanta, temps were in the mid 20s at 5 AM, with freezing weather as far south as middle Georgia. At this point, temps are not expected to go above freezing until sometime Sunday morning. Freezing rain, and possibly some snow will continue throughout the period, with the heaviest icing in the metro Atlanta area. After 7 PM, the chance of freezing rain drops overnight.

The winter storm warning remains in effect until 4 PM. Travel isn’t recommended, with I-85 closed in the Hamilton Mill area. Looking out my window, I can see what looks to be about a quarter inch of snow/sleet on the ground, not only in grassy areas, but also on the street. I’ll try to get out once it gets light to get some pictures. Some folks have posted their experiences from earlier last evening in the ‘comments’ area of the post below. Please tell us what you see using the Comments link.

The National Weather Service forecast map for today shows the wide-ranging effects of the storm. While we’re getting freezing rain, heavy snow is possible in an boomerang shaped area from eastern Illinois, to West Virginia, and on south through eastern Tennessee. The freezing rain will move up through North Carolina and Virginia.

It’s beginning to look like the area of freezing rain predicted for this weekend is being extended south and west of where it was estimated to be on Tuesday.
As you can see in the image at the left, light rain moves into Gwinnett county by 10 PM on Friday, and turns into freezing rain by 4 AM on Saturday. The area of freezing rain moves eastward and becomes more widespread by 10 AM, and should be all rain by 4 PM. The freezing rain should stay north Interstate 20.

Temperatures should drop below freezing around midnight Friday, and could reach 28 degrees just before sunrise Saturday, and will probably rise above freezing around noon. Of course, all of this is still two days away, and the forecast could change, but it might be a good idea to get your errands out of the way today and tomorrow.

Although the threat of freezing rain ends as things warm up Saturday afternoon, we’ll still see cloudy, wet weather typical of a wedge situation until Tuesday, when high pressure moves into the area. We’ll probably see a total of about 1/2 inch of precipitation throughout the period.

January is likely to end up being a dry month. We should normally have just over four inches of rain by the end of January; I’ve only recorded 1.14 inches of rain so far, with most of that recorded on January 14th. Hartsfield Airport has had 1.57 inches. Even if we get half an inch over the weekend, we will end the month with two fewer inches of rain than normal.