Archive for April, 2009

Severe Weather across the Tennessee Valley and Southeast on Sunday, with Significant Snow across the Southern Appalachian Mountains from Midday Monday through Late Tuesday Night

Posted in Severe weather, Winter weather with tags , , , , , , , , , , on April 5, 2009 by stormstream

Severe weather will be possible on Sunday across parts of KY, TN, AL, GA, SC and NC.  I will concentrate only on the severe weather prospects across south and central GA and north FL, as that will be the area I will target to storm chase if I should decide to head out.

A cluster of elevated thunderstorms is rolling eastward through south-central AL into central and south-central GA this morning.  The strongest of these storms are on the eastern edge of this cluster, and are producing some hail.  As the day wears on and moisture and instability increase south of the MCS, I would expect some of the storms to become surface-based, especially those along the south edge of the cluster across south GA, and any discrete cells that should form in the increasingly unstable airmass across south GA and north FL.  Helicity values will certainly be high enough to support some rotating updrafts across south GA and north FL this afternoon and evening, and an EHI maximum above 2 exists across southwest GA at 00z off the 06z NAM. This environment could be supportive of a few isolated, brief tornadoes of EF0 and EF1 intensity.

STORM CHAE TARGET:  Georgetown, GA to Albany, GA to Waycross, GA to Brunswick, GA to Jacksonville, FL to Tallahassee, FL to Georgetown, GA.

Then there is the cold and snow aspect of this system, which will be significant across parts o the Southeast.

This is going to be a fairly long duration upslope snow event for the mountains of eastern TN and western NC. The upslope snow machine will kick in around noon on Monday and continue until late Tuesday night. Snow levels start out above 4,500 feet, with snow levels dropping through the day and into Monday night , with snow increasing. By Tuesday morning, snow levels will have reached the valley locations. I think 5 to 10 inches of snow above 4,500 feet looks quite possible by Wednesday morning , with most locations in the 5 to 8 inch range. Between 2,500 feet and 4,500 feet a good 3 to 6 inch snow is likely. Below 2,500 feet across western NC a trace to as much as 3 inches appears likely. The mountains of north GA and the upstate of SC will also get in on some snow action Monday night and Tuesday morning, with elevations above 3,000 feet picking up 1-2 inches, and between 2,000 and 3,000 feet getting a trace to 1 inch. There will also be a slug of 700mb moisture dropping down as far south as I-20/I-85 in GA between about 4am and 9am on Tuesday. This could create flurries in the air as far south as Atlanta! Finally, a hard freeze looks likely along and north of the i-20/I-85 corridor across northern and central AL, GA and SC by Tuesday morning. As has been the case so often in recent years, the peach crop in this region is in jeopardy.


Weekend and Early Next Week Weather System

Posted in Severe weather, Winter weather on April 3, 2009 by stormstream

A strong low pressure system will move from KS to IL over the weekend, and be a significant late season snow producer for parts of NE, SD, IA, MN and WI.  Near blizzard conditions look possible across central and northeast NE into northwest IA and southern MN Saturday night into Sunday morning.

Farther south, in the warm sector, thunderstorms will develop across central KS Saturday afternoon and spread east Saturday night.  The dynamics with this system are strong, and if dewpoints were about 10 to 15 degrees higher than they will be on Saturday, then a major severe weather and tornado outbreak would be expected.  However, that is not going to be the case.  Dewpoints in KS will range from 47 to 53 on Saturday, and the moist layer will be shallow.  This will result in only scattered strong storms developing, and and severe storms will be isolated in nature.  Given the expected helicity values, the storms could exhibit some nice LP supercell structure, as well as produce some decent lightning and small to moderate sized hail in the strongest storms.   The best chance for storms looks to be across eastern KS, western MO and northeast OK on Saturday evening.

This system will eventually become a very deep low pressure system as it moves into the Northeast U.S.  which will bring a surge of unseasonably cold air deep into the Southeast U.S. on Monday, April 6 and Tuesday, April 7.  Some Appalachian mountains snows will be possible, and potential frost or freezing conditions at lower elevations as far south as TN, north GA and upstate SC.  Strong winds and clouds could be the saving grace in keeping a damaging freeze away, and by the time the clouds clear and winds die down the cold airmass will be departing.  Peach growers are crossing their fingers.

A Busy and Potentially Dangerous Severe Weather Day Across Dixie

Posted in Severe weather with tags , , , , , , , , , , , , , , , , , , on April 2, 2009 by stormstream

A strong storm system will bring areas of severe thunderstorms to the Southeast U.S. today.

Severe storms with the potential of damaging winds and isolated tornadoes will affect the Gulf coastal and inland areas of south AL, south GA and north FL throughout the morning and into the afternoon. 

Other severe storms associated with low pressure and the cold front will sweep from eastern TX across LA, southern and eastern AR, western sections of middle TN and into western MS through the morning and into the afternoon.  These particular storms could produce hail to the size of baseballs, damaging winds and some tornadoes.  These storms will continue to move rapidly northeast at 50 to 60 mph across MS, middle TN and across AL and the FL panhandle late this afternoon and evening, continuing to pose a threat of damaging winds, hail to the size of golfballs and isolated tornadoes.  Storms will impact GA, north FL and into SC and eastern NC through the early morning hours on Friday.  These storms will mainly be strong to marginally severe, but central and south GA and into the Carolinas could experience more concentrated severe storms with damaging winds, hail to the size of marbles and isolated tornadoes.

The extensive convection occuring along the Gulf coastal region of AL and the FL panhandle will disrupt the low level wind field, and could reduce the amount of low level speed shear, a key ingredient to large tornadoes in the Southeast.  This could spare most of AL, GA and middle TN from any storng or violent tornadoes, with most intensity levels between EF0 and EF1.  Further west during the afternoon, the low level inflow should be stronger thus creating more intense low level spin in the atmosphere, the CAPE higher, and the upper dynamics stronger.  If we are to see any long-tracked tornadoes of EF2 intensity and higher today it would most likely be across MS, the western third of AL, and possibly western sections of middle TN if dewpoints can rise above 62F there.  The most likely time for this activity would be between 2pm and 9pm.

I am fairly confident that this event will produce severe weather that may reach the definition of an outbreak.  I’m more confident in an outbreak of severe thunderstorms than I am of a tornado outbreak.  The low level moosture is there, but I am not sure we are going to see the magnitude of 0-1km speed sheer necessary to get a lot of tornadoes going, and especially ones of strong or violent intensity.  There will likely be more storms displaying mid level rotation, than those that actually drop confirmed tornadoes, so we could see a situation where many radar-indicated tornado warnings are issued, but verification of actual tornadoes may be far less.  Still, having said that, the potential is certainly there for significant tornadoes, especially across MS, western AL and western sections of middle TN, with a threat for isolated and weaker tornadoes in many other areas.  So stay up to date on all forecasts, and pay attention to all watches and warnings that are issued today, and take them very seriously.

Major Outbreak of Severe Thunderstorms and Tornadoes Looking More Likely Across Mississippi and Alabama on Thursday and Thursday Night

Posted in Severe weather with tags , , , , , , , , , , , , on April 1, 2009 by stormstream

The atmospheric set-up for Thursday into early Friday morning will be very supportive of numerous severe thunderstorms, and potentially strong to violent tornadoes across parts of the Southeast U.S., centered on Mississippi and Alabama.  This is a very dangerous, potentially life and property-threatening situation, and those within and near the greatest risk area should review their severe weather action plans and be ready to take measures to protect life and property Thursday and Thursday night.

The area of greatest risk will exist across eastern AR, northern LA, western and middle TN, all of MS and AL, and west-central and southwest GA.  The threat will extend across western sections of this region Thursday morning, then moves eastward through the day and extend from middle TN to eastern AL and west-central and southwest GA by Thursday night into early Friday morning.  Anyone living in this region needs to be prepared.  I can’t stress that enough.

Any severe thunderstorm that develops in the above mentioned region on Thursday has the very real potential of producing damaging winds in excess of 60mph and damaging hail.  In fact, storms will have the potential to produce hail to the size of baseballs.  Many storms will become supercells and be capable of producing large, damaging and long-tracked tornadoes and tornado families in cyclic supercells.  The set-up is one that is much more commonly seen in the traditional Tornado Alley of the Plains, and more rarely across the Southeast.  This system has the potential to be one of the largest severe weather and tornado outbreaks of the season, not only for the Southeast, but for the entire U.S.  I would say that most of Mississippi and western, central and south-central Alabama are ground zero for the most intense and life and property-threatening weather, although the entire region outlined above is under a significant threat.

Still, there are factors that could limit the severity, as well as the overall coverage of the event.  Those factors being the potential of Gulf coastal convection limiting the inflow of deep, quality surface moisture and instability into the system.  The tremendous dynamics could lead to more of a squall line event, which would limit tornado potential, however, it would increase the chance of widespread damaging winds.  Timing is still not certain, and if the main dynamics move across the region during the relatively cooler, more stable overnight hours, then that could lessen the intensity of the event as well.  Overall, however, there are far more factors that lead one to believe there will be a major outbreak of severe weather, as opposed to a lesser event.

Please stay up to date on the weather, and please be prepared.