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September Cold Fronts Disc./Obs.


WilkesboroDude

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UPDATED for colder and frost potential...

Main aspect will be the arrival of a strong fallish type cold front

over the weekend including the passage of a deep 500 mb trough from the

Great Lakes across the eastern Seaboard into early next week. This

system will bring the coolest air of the season with at least some

patchy frost potential in the deeper valleys by Tuesday morning as

high pressure settles overhead. Ahead of the front/trof...appears

enough moisture should get injected under the SW flow aloft to

promote a band of pre-frontal rain showers that may affect the mountains Sat

night...and out east on Sunday when the true 850 mb front/colder air

aloft will arrive. Latest guidance shows a little instability ahead

of the boundary in the Piedmont so including an isolated -tsra

mention there Sunday. Otherwise models rather close except for timing

issues with the front so opting to go closer to the slower European model (ecmwf) for

now. Post frontal temperatures the main issue with MOS showing some 30s in

the valleys for both Monday/Tuesday mornings and highs staying in the 60s

mountains into early next week. Temperatures should moderate some by

midweek as the air remains dry and the surface high starts sliding

off to the south by Wednesday.

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09/08/2012 0130 PM

6 miles se of north wilkesb, Wilkes County.

Thunderstorm wind damage, reported by 911 call center.

One tree down on Highway 115 near Spring drive and

Fishing Creek Road

09/08/2012 0345 PM

2 miles WNW of lake townsen, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down along Plainfield Road.

09/08/2012 0347 PM

Browns Summit, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down near intersection of doggett Road and

Highway 150.

09/08/2012 0350 PM

1 miles NNW of Monticello, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down near U.S. 29 and Highway 150.

09/08/2012 0345 PM

2 miles W of Lake Townsend, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down along air Harbor Road.

09/08/2012 0322 PM

Piedmont triad apt, Guilford County.

Thunderstorm wind gust m40 mph, reported by ASOS.

09/08/2012 0330 PM

2 miles SSE of Summerfield, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Trees blown down along battleground Avenue.

09/08/2012 0345 PM

2 miles WNW of lake townsen, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down along Plainfield Road.

09/08/2012 0347 PM

Browns Summit, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down near intersection of doggett Road and

Highway 150.

09/08/2012 0350 PM

1 miles NNW of Monticello, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down near U.S. 29 and Highway 150.

09/08/2012 0345 PM

2 miles W of Lake Townsend, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Tree blown down along air Harbor Road.

09/08/2012 0322 PM

Piedmont triad apt, Guilford County.

Thunderstorm wind gust m40 mph, reported by ASOS.

09/08/2012 0330 PM

2 miles SSE of Summerfield, Guilford County.

Thunderstorm wind damage, reported by 911 call center.

Trees blown down along battleground Avenue.

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09/08/2012 0545 PM

1 miles NNE of Durham, Durham County.

Thunderstorm wind damage, reported by Fire Dept/Rescue.

Power lines down along Duke street.

09/08/2012 0545 PM

3 miles NNE of Durham, Durham County.

Thunderstorm wind damage, reported by Fire Dept/Rescue.

Tree blown down near Avondale and Interstate 85.

Highway at a standstill in both directions.

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NWS Greenville

Overall though...quantitative precipitation forecast has been reduced a bit. Not

only that...but the timing of the main low passage is a bit

later...into Tuesday. What this trend suggests is less of a flooding

threat and more of a severe weather threat to the Carolina Piedmont.

The new GFS has a cold front moving across the forecast area during the

afternoon. East of the front...the GFS develops a plume of cape

around 1500 j/kg with 150-250 srh and sufficient low level shear to

make one take notice of the potential for organized severe storms

and perhaps supercells. This trend is interesting and should be

monitored.

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We have quite an event coming up for the Southeast, and this one is the first major, widespread, Cool season type of system. First, the big Aleutian Low is pumping up the western Canada ridge, much like the models showed it would. And now there is a decent wave in Texas that will be opening up. As the western ridge builds, it forces the longwave in the northern Plains to enlarge and deepen, capturing and phasing with the southern stream. This will be good first look at how far east or west systems tend to trend (get into that later).

A warm front will surge north across Ms, Al, Ga and SC by early Monday with steady rains along it, meanwhile height falls in the nations Midsection are rocketing southeast, so the flow backs strongly. At one point, GFS had a very strong 850 flow with 55knots into the Southern Apps, but it's backed off a little on that. Still, being on the backside of an initially damming high should offer steady, significant rain in the Carolinas and Georgia, while west of the mountains more warm advection rains associated witha developing surface low in Mississippi on Monday. Here's where it gets iffy. The GFS has shifted its axis of heavy duty totals to west of the Mountain Chain, while ECMWF and NAM remain right along it. The pattern all last Winter, last Spring and this Summer probably lends more to a west of the chain for the heaviest totals, but I still expect another max around northeast GA and western NC to western VA mountains thanks to the warm front rains, then the steady southeast windflow rains. But a QLCS line with an embedded meso low might form west of the mountains in the TENN Valley early Tuesday and that could be why the GFS now has its heaviest totals through TN and KY into West VA ...but we'll see. Either way, this is a pretty big event where a lot of folks catch a good rain, and some areas could get near 3" to 4" total, esp. in upslope regions of the southern Apps and anywhere in that qlcs line or meso low (if one forms). This whole mass of rain will get sucked northeast in a wall of rain as height falls and a very deep meriodonal flow slowly works through the East by later Tuesday.

The next thing to come from this is the cold air....very cold for September. The year 1981 stands out with some records. It looks like by early Wednesday morning the surface high will be in western TN and with +3 or even +2 at 850 dropping down to the Ky/TN border, if everything goes right like radiating conditions, light winds, then by Wednesday morning some areas of KY and TN especially will be flirting with records.

On the left is the current Wednesday morning prog, on the right is 1981:

post-38-0-77953900-1347759342_thumb.gif

post-38-0-61404300-1347759466_thumb.jpg

Looking down the road at the remainder of September, I have zero doubt it will finally be a below normal month in terms of temperatures for quite a few sites in the Southeast. We haven't had a below normal month seems like in over a year now, with all the consecutive months of well above normal. Also, if the ECMWF is right in it's next cut-off and deep trough later in the month, the Southeast will have another big rain event, so there's a chance some areas will be above normal on precip...a below temp/above precip combo has been hard to come by since Winter 2010/11. So far it looks overdone though, but the idea of a trough in the nations midsection or the East is probably here to stay the rest of the month.

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kinda a silly/stupid question, but I will still ask... has anyone ever counted how many cold fronts come through the southeast each year?

Then broken it down per month? (ie: September always get two cold fronts; October gets three and November get two in a la nina year, and in an el nino year September get 5; Oct get 2) something along those lines... Or no matter what the pattern each year the Southeast will always have 15 cold fronts.

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NWS Blacksburg

Main aspect will be the arrival of a strong fallish type cold front

over the weekend including the passage of a deep 500 mb trough from the

Great Lakes across the eastern Seaboard into early next week. This

system will bring the coolest air of the season with at least some

patchy frost potential in the deeper valleys by Tuesday morning as

high pressure settles overhead. Ahead of the front/trof...appears

enough moisture should get injected under the SW flow aloft to

promote a band of pre-frontal rain showers that may affect the mountains Sat

night...and out east on Sunday when the true 850 mb front/colder air

aloft will arrive. Latest guidance shows a little instability ahead

of the boundary in the Piedmont so including an isolated -tsra

mention there Sunday. Otherwise models rather close except for timing

issues with the front so opting to go closer to the slower European model (ecmwf) for

now. Post frontal temperatures the main issue with MOS showing some 30s in

the valleys for both Monday/Tuesday mornings and highs staying in the 60s

mountains into early next week. Temperatures should moderate some by

midweek as the air remains dry and the surface high starts sliding

off to the south by Wednesday.

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