“Upper Level Low Causes Weatherman’s Woe”. That means November snow for us…………….

All,

Very interesting late fall weather awaits us.  You may recall I’ve mentioned a few times over the last couple years the “upper level low pressure sytem”, or “cutoff low”. This is a low pressure system that gets cut off from the general upper air flow(jetstream) pattern and slowly migrates over a longer period of time that is typical for a low pressure system that is being driven by the general atmospheric flow. 

We will have the development of one of these upper level cutoff low pressure systems over the next few days, and that will provide a deluge of rain for us(which will prime us for more winter precipitation than normal this winter), followed by a change to sleet and snow, for Monday through Wednesday morning, for many areas of the southern US.  We could actually see accumulating snowfall for parts of Mississippi, Alabama, Georgia, Tennessee, South and North Carolina, by the time this system is captured by the upper level flow and moved to the northeast. At that time, it’ll provide snowfall for the NE US region.

All the major computer models are in agreement now on this system. Upper level low pressure areas can attach to a northern stream of energy and bring colder air down from the northern plains area, but can also bring down cold air from the upper levels of the system, dynamically cooling the lower levels(surface where we live), depending on the strength of the system. This one looks to develop into a strong system, that will slowly develop over Louisiana and Mississippi tonight and tomorrow, and then migrate to the east on Sunday night through Tuesday, and then to the northeast across North Carolina and Eastern Tennesseee Tuesday into Wednesday. 

If we continue to get these upper level lows into December, which I suspect we will, we may see a couple chances for snow and sleet from these type systems for December, as well.  Another thing this system appears to do on the model output, is help to reconfigure the atmospheric pattern.  The PNA(roller coaster) sets up a ridge in the west and trough(low point) in the south, after this system leaves, and the NAO(North Atlantic Oscillation) appears to go negative, which would promote an intrusion of very cold air, very soon.

Bottom line:  I anticipate 2-4 inches of rain for northern Georgia through central and western North Carolina and eastern Tennessee, followed by a transition to sleet and then snow, at some time on Monday, continuing into Tuesday, in a scattered fashion.  Accumulations are possible for northern Georgia, into eastern Tennessee and west and central North Carolina, with significant accumulations for the northern portions of Mississippi and Alabama, as well as eastern Tennessee and western North Carolina.  Even central areas of Mississippi, Alabama, and Georgia may see at least some snow flurry and snow shower activity overnight on Monday, into Tuesday morning.   I am including a couple maps to show you the upper level low.  These maps are credited to www.raleighwx.net. With these systems, surprises abound. As the saying goes, “upper level low causes weatherman’s woe”………………….Keith

Notice the aqua blue colors that are separated from the green and yellow orange colors. Also notice the general flow to the north is west to east. The upper level low separates from this flow, causing it to slowly migrate to the east north east. The blue colors represent the atmospheric thickness, which is directly related to temperature. Any thickness of 546 or below can support snowfall. At this point, northern Alabama and Georgia, most of Tennessee are in the 540-546 thickness area, and could see snowfall. This map is from Tuesday morning, at 1 am. The map below this one shows the freezing line at 850mb(5000′ above the surface), at 7 am on Tuesday, as well as the precipiation that has fallen for the prior 6 hours(in green).  Notice that many areas of Mississippi, Alabama, northern Georgia, Tennessee, western North Carolina and South Carolina, have freezing(0 Celcius) or below 5000′ temps at this point, as well as precipitation. This would be in the form of sleet or snow, by this time.  The surface temps and upper air temps support snow and/or sleet for even central areas of the southern states, by this time. This area moves to the east and northeast on Tuesday into Wednesday, putting central North Carolina into the snow/sleet area.

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Anyone seen Spring lately??????

Here we are knocking on the door to April, and it feels more like February in NE Georgia, with high temps in the low 50’s the last few days, and an abundance of rain/drizzle and clouds.  The trough I had been mentioning, is firmly established, and we should have a bit of a roller coaster ride with the trough and brief high pressure ridging until the middle of April. After that, as we near Easter, I think we finally say so long to the last remnants of Winter and start warming and getting drier, as the normal seasonal changes in the jetstream structure take place, putting us into a typical Spring pattern.  Look for more rain and chilly weather for today into tomorrow, then we have one of those brief incursions of high pressure ridging this weekend, which should provide a beautiful, sunny, and mild weekend, with 60’s and 70’s for high temperatures. Don’t get too comfy though, as we should see another trough of low pressure moving in next Tuesday, bringing possible severe storms and our first real chance of a Tornado outbreak, followed by much cooler weather the remainder of the week.  We should warm and see more sunshine the middle to end of next week, then another possible major rainmaker and severe weather outbreak around the 10th, followed by our last shot of much cooler weather, before we break out of this with much warmer and drier weather.  The NE US is expecting up to 12 inches of snow in Upstate NY for tonight and tomorrow, and may see a couple more of these events before the middle of April. Then, they should warm also.  I’m hoping some rain will make it down to Florida, as they are now in a pretty severe drought, but with the jetstream moving north, looks like they may have to wait until Thunderstorm season late in the Spring and into the Summer.  By the way, we are at 7 plus inches of rain for March, bringing the NE Georgia region to around 15 inches of rain for the year, which is actually a little above normal.

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Late Spring warmth on the way. Pattern change back to cold likely….

After a cool, rainy early Spring day today, it looks like we are headed toward near record warmth by the end of this week. Pollen counts should be soaring, as the dry, warm air follows the cool, soaking rainfall, and as a result,  the plants and trees burst forth with new life. The warm air will surge up into the eastern US with temps in the 60’s all the way into upstate New York! The temps should continue to stay warm into early next week, but we’ll begin a cooling trend at that time, and the trend may continue through the rest of the month, leading to potential freezing temperatures in the mornings in late March and possibly early April.  This will be driven by a pattern change, with the North Atlantic Oscillation index going negative, while the Arctic Oscillation index also goes slightly negative and the Pacific North American index heads positive. This combination means systems will block the Arctic cold air in Canada from moving east, and it will be driven into the eastern US. A deep trough should become established in the eastern US, into the Southeast, which would bring much colder than normal air into the region, with the potential for storms from the Gulf of Mexico up the eastern seaboard, or possibly storms coming across the South or Ohio Valley and reforming off of the mid-Atlantic coast. This could set the stage for a very dynamic severe weather episode around 3/25-3/28 timeframe, and a late season Nor’Easter for the Northeastern US, as we head to the last week of March into the first week of April.  Be careful about getting the gardens going too soon!  After that 3/25-4/8 timeframe, we should head into “true Spring”, which will probably mean those of us in the South go straight into Summertime mid to late April, as the seasonal shift of the jetstreams continues…………Here is a snapshot of the trough and cold air that should set up in the eastern US after 3/25. Notice the large system in Eastern Canada. This is blocking the Arctic flow and, in conjunction with high pressure in the western US, drives the cold into the Eastern US:

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Flooding rains possible this week and next. More snow for some?

After a nice soaking rainfall last week, it appears we will follow that with an even more impressive rainfall this week, and the potential for another heavy rain event next week, for most of the SE US.  The Canadian and NAM computer models are showing anywhere from 3-5 inches of rain for parts of the south for Wednesday-Saturday time period.  The GFS and European models are a bit more conservative, but still show 1-3 inches of rain for a large area of the southeast.  If the Canadian and Japanese models are to be believed, a cut off low pressure area will slowly drift across the south, bringing the potential for snow to Northern Alabama, Georgia, Northwest South Carolina, and possibly the western and central portions of North Carolina on Friday. This situation closely resembles the storm that left March snow in the South on March 1, 2009. In that case, a cut off low tracked directly over Georgia, bringing a swath of anywhere from 1″ to 7″ of snow from Columbus to Macon to Athens.   However, the only models to show such a scenario are the Canadian and Japanese, although the European has shown a similar scenario in recent model runs.  Until there is more consensus, it’s not a forecast, just a possibility.  Regardless, it looks like we are in a pattern of moderate to heavy rain events every 4-5 days, so look for a repeat of moderate to heavy rain by the middle of next week, after this system moves through. Temps should be fairly cool this week, then warm up this weekend, before cooling again mid next week.  No threat of a severe freeze, at this point although some models are showing possible upper 20’s for low temps this Friday and possibly Saturday, for parts of the South.

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Potentially severe storms followed by cooler weather and a possible return to Winter……

Today we are seeing a line of strong to severe storms traversing the SE US, and currently moving through Northern Georgia. There are reports of significant damage and flooding in areas of Tennessee.  We could potentially see hail, high winds, downpours, with localized flooding, over the next several hours, in Georgia, then over to SC and NC tonight.  Following these storms, it appears the atmosphere is about to go into a pattern shift back to more of a Winter type regime. I had anticipated this to occur from 2/20 to 3/6 timeframe, so it is just in time.  The NAO looks to go negative for the next 10-14 days, along with the PNA going positive during that timeframe. The positive PNA brings high pressure ridging to the western US and low pressure troughing to the eastern US, tapping into colder Canadian air, and sliding it into the Eastern United States.  If the SW Atlantic HP Ridge is beaten down enough the negative NAO may block a storm or two, keeping them from moving to our north and west.  This could provide us with a Gulf of Mexico storm and provide the potential for colder weather, and a storm with potential late Winter snowfall, for the period from 3/5-3/15.  I’ll update more this week.  Stay safe and listen for warnings today and tonight.

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Is Winter finished????

We could see temperatures rise into the low to mid 70’s in some areas this Friday and Saturday, and areas of central Georgia may hit the magical 80 degree mark, as the daylight continues to lengthen and thoughts of flowers blooming, the first pitches of baseball, and outdoor activities begin to pop into our heads.  Have we seen the last of Winter?  I would say definitely not.  It’s only February 16th after all, and we still have over a month of calendar Winter remaining.  After the very warm temperatures on Friday and Saturday, we should see a cold front come through, cooling us down early next week.  It’s also possible, as colder air gets entrenched into the Northeastern United States, a “backdoor” cold front may approach from the Northeast, bringing cooler air to the area for most of next week.  Perhaps some light rain early next week, and toward the end of the week, as a continuing series of cold fronts move through. Currently, the overall pattern is set up with the colder air and trough in the western US and a high pressure ridge controlling the weather in the Southeastern US and bringing warmth.  It appears, however, as I thought would happen, we will see one more pattern change, back to the trough in the SE US, before the Winter is over.  This should bring much colder air back into our area around the 26th, through the middle of March, with potentially a late season snow event between 2/26 and 3/10.  This could be either per a Gulf low, overrunning moisture over a cold air wedge coming down from the NE US, or a closed upper level low pressure area.  I’ll keep you updated. In the meanwhile, enjoy the warmth.

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Here comes sunny and warm!!

Anywhere from a dusting to a few inches of snow fell across many portions of the Southern US yesterday and last night.  Not enough to shut things down, but a beautiful scene for many, as they took a look out the window this morning.  That may be the last snow we see until next Winter season, as we head into a much warmer pattern for a week or two.  The atmospheric trough will now set up out in the western US, as the PNA(Pacific North American Pattern) goes negative, and NAO(North Atlantic Oscillation), and AO(Arctic Oscillation) stay positive. Remember that for cold and snow in the South, we usually have more opportunities when these indices are the opposite of this. As a result, the cold trough that has been over us most of the Winter season, will shift to the west, providing us with a ridge of high pressure, which means warm and dry.  Look for temperatures to moderate gradually through the weekend and early next week, and then possibly into the 70’s for high temperatures by the end of next week!!  There are signs though, that this pattern will shift back to a more negative NAO and AO, and PNA starting to trend positive, by the end of next week.  That means, if it occurs, we could see another trough get established in the Eastern/Southern US after next week, along with more opportunities for cold and possibly Wintry weather.  However, we’re getting later, and our average temperatures are rising now, so it will become more and more difficult to get more snow into the South without a major amplification of the pattern, or cold being dramatically driven into the south by a direct discharge from the Arctic.  Those events usually occur around pattern changes, so if it is to take place, the timeframe from 2/20-3/6 would be the most likely. After that time, unless we have what is referred to as a “bowling ball low”, or closed upper level low pressure, we have very small chances for snow.  Enjoy the warmth and sunshine. Time to wash the cars and trucks!!

For those old enough, today commemorates the 38th anniversary of the great February 10, 1973 South/Central Georgia, South Carolina snowstorm that left up to 18″ of snow in Central Georgia. I lived in the south Georgia town of Fitzgerald, during the storm, and this event is one of the driving forces behind my love for snow. Here is some historical data per www.wunderground.com:

FEBRUARY 9-10, 1973: Piedmont of Georgia, South Carolina, and North Carolina

No snowstorm in the old or modern records can match that that struck the Piedmont regions of Georgia and South Carolina in February 1973. Macon, Georgia received 16.5” of snowfall and Augusta and Columbus both reported 14.0” (all-time records). Even Albany received its all-time accumulation of 3.0”. In South Carolina an all-time state record was achieved at Rimini with 24” and Columbia (16”) and Florence (17”) also set their respective all-time records for both a single snowstorm and a 24-hour accumulation.

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