- Chris Suchan on Major GFS Upgrade 1/14/15
- Chris on Major Winter Storm To Impact Southeast Then East Coast.
- chris on Major Winter Storm To Impact Southeast Then East Coast.
- Mike Dross on Updated: Ice Storm Increasingly Possible for Western/Central NC/VA Friday/Saturday
- Michael mefford on Updated: Ice Storm Increasingly Possible for Western/Central NC/VA Friday/Saturday
A potent mix of thermodynamic and kinetic forces will become colocated across the lower Ohio and Tennessee Valleys on Saturday to create conditions favorable for destructive, powerful supercells and potentially violent tornadoes.
A very powerful jet stream will work across this very unstable airmass with winds at the 200mb level in excess of 150 mph, as depicted by the NWP guidance. It is very rare to have winds of this strength/a jet stream/ directly across the convective layer and will add significantly deep layer shear aiding in ageostrophic imbalances helping to promote mesoscale ascent. Typically, the mid latitude jet is well removed of the warm/buoyant air mass and rarely directly overlaps. This could be one of the more unique events and we need to watch this very closely given the kinetic forcing in the upper levels of the troposphere in this upcoming event.
Guidance at this time suggests an early round of showers and non-severe thunderstorms will move through the Mid-South during the early morning hours, followed by partial mid-day clearing allowing for solar insolation and destabilization in the Ohio, Tennessee-Valleys. How these lead convective elements ultimately play out will likely define mesoscale outflow boundaries that will determine where supercells and tornadoes develop later in the day.
This midday-afternoon destabilization combined with a rapidly strengthening wind field at all levels will increase the severe weather risk as a strong upper level (300-200 mb) jet streak punches into the region during the afternoon with a jet wind maximum of nearly 150+ mph closely collocated with the storms
Convection with supercells and the risk for strong to violent tornadoes will develop in association with this powerful jet/shortwave from the Ohio-Valley southward into Mississippi/Alabama and spread eastward.
The area at highest risk of tornadoes appears to me from Southern Illinois, Southern Indiana, across Kentucky, Tennessee southward into Central Mississippi and Alabama. The strongest tornadoes would likely occur in Southern Illinois, Southern Indiana, Kentucky and Tennessee closest to the best 0-1km shear maximum, 0-1km SRH and lowest LCL’s. The tornado risk may spread into western Georgia.
Forecasters and those living in these regions should closely monitor developments and SPC outlooks over the next few days.
On to the maps….
Freezing rain mixed with sleet, locally heavy at times, with embedded elevated convection will continue through the overnight into the morning hours across Arkansas and will produce around 1.00-1.25″ of liquid equivalent precipitation. Much of this will fall in the form of freezing rain across Central Arkansas into Western Tennessee. Ice accretion of 3/8″ to as much 5/8″ of an inch are likely before the precipitation finally ends around noon local time. [18Z].
Ice accretion amounts of 1/2″-5/8″ will bring down large branches and some trees. These can fall on power-lines and disrupt electrical service. They can also fall on pedestrians and cars. Ice accretion of this amount can cause widespread disruption of power in urban areas and create life threatening hazards with extended loss of power and falling large limbs/trees.
The area in and around Little Rock, AR is at risk of widespread power outages if the forecast trends continue and ice accretion amounts exceeds 1/2″ later today.
Below.. the total precipitation that will fall as freezing rain as depicted by the HRRR through 22Z. Actual ice accretion will be less due to drip loss.
Click for the latest Little Rock, AR Regional Winter Radar. Updated Every 5 Mins.
The upgraded GFS model went live today. Over the next several days we will be tuning our systems to optimize how we process the new GFS output. The are a number of new variables and higher resolution fields available. We want to make the best use of our resources. You may notice some slight changes in the model graphics or timing of the products for a few days as we make changes in how we process this data.
We are currently working hard to bring on much higher resolution GFS products on our new Linux servers that we just setup. We hope to have the new GFS products available soon for our customers.
Thank you for your patience as we continue increasing our computing capacity and product offering here at Wright-Weather.com
The GFS model will be upgraded tomorrow, 1/14/15. It is under going a major upgrade. The below PowerPoint link will explain in detail the model physics and initialization changes that have been made, as well as, the effect on model performance.
This is a major change to the model and there will likely be new biases and features that we didn’t see in the old GFS due to the higher model resolution. The model is now running at about 13km (near the equator).
We now have several HP DL380 server’s clustered to handle the higher resolution GFS, as well as, HRRR data.
We will have the GFS data in 2 different resolutions. The standard 0.5 degree which have been displaying for years now and soon we will have surface and other 2D fields 0.25 degree.
Look for the higher resolution data in the coming days. The new GFS based model data at 0.5 degrees will begin tomorrow (01/14/15) however, unless NCEP decides to delay the implementation.
NCEP’s servers which we receive some of our model data have been degraded the past 24 hours. Some products will be delayed or possibly incomplete.
Model products which receive via satellite will be on time, which are not affected by the NCEP data servers/network issue.
The GFS NOAAPORT link is:
The NAM NOAAPORT link is:
The latest message sounds encouraging from NCEP. So hopefully any delays will be short-lived:
THE NCEP SUPPORT FOLKS HAVE BROUGHT THE PRIMARY FTP SERVER BACK
UP..FINAL CHECKOUTS HAVE BEEN PERFORMED ON THE PRIMARY FTP SERVER
AND IT HAS BEEN PLACED BACK IN SERVICE AT 0400Z..A PRELIMINARY
CHECK OF FTPPRD AND NOMADS INDICATED THAT DATA IS UP TO
DATE..QUEUES ARE BLEEDIND DOWN..SOME DATA MAYBE STUCK IN QUEUE
BUT FOR THE MOST PART DATA APPEARS TO BE UP TO DATE.. THANKS FOR
YOUR ON-GOING PATIENCE WITH THIS ISSUE TODAY.
A strong upper level low pressure system will move out of the Rockies into the Southern Plains tonight. This will intensify a surface low pressure system over Western Oklahoma that will move eastward through Oklahoma during the morning on Monday.
Returning Gulf of Mexico moisture across Central and Eastern Texas with dewpoints in the middle 60s to middle 70s will continue to advect northward overnight. Showers and thunderstorms are expected to develop across Central & Eastern Texas later this evening, ahead of a cold front that will sweep into North Central Texas around midnight. A triple point region will develop and move near the Red River with other smaller mesoscale boundaries south of the warm front where convection will develop. A strong line of convection is expected to develop along the cold front as it moves east of the dry line region around 4-5Z. Storms will likely become severe as they intensify under a strong 60-70kt cyclonic mid-level jet.
Parameters suggest all modes of severe convection are possible. Linear convection is likely to be the most predominant mode, with embedded line echo wave patterns (LEWP’S) with severe wind gusts, but embedded & discrete supercells are also quite likely given the high shear values, very high 0-3km helicities. Bulk Richardson Numbers also favor some discrete supercells along and south of I-20.
With the low lifted condensation levels, very high 0-1km helicities, shear values and moderate instability. Some tornadoes are quite possible with the stronger mesocylones.
The region at most risk of supercells is south of the Red River in Texas with an enhanced risk of tornadoes along and south of I-20 where the combination of helicities, shear, CAPE and upper forcing will be maximized. South of Waco, convective inhibition values will likely be too high to allow for much activity, but if a cell develops may be severe/tornadic.
The severe threat works eastward across Northeast Texas into Arkansas ans Louisiana during the day on Monday.
A spring like cold front will move through the Mid-West and combine favorable wind shear with strong instability Saturday into Sunday afternoon and will likely produce widespread severe thunderstorms with large hail, damaging winds with the possibility of a few tornadoes.
An unseasonably strong upper level short wave will drop southward into the Ohio-Valley on Sunday and will increase the mid and upper level flow across the region. Favorable instability, bulk shear & moderate helicity will support organized severe thunderstorms beginning on Saturday across IA/MO/IL/IN. The threat shifts eastward on Sunday into IN/OH/KY/TN/WV. A tornado threat exist along the quasi-stationary front across northern IN/OH and a conditional threat also exist within the low level theta-e advection zone across eastern Ohio/Kentucky & West Virgina where 0-1KM EHI’s & 0-1Km bulk shear are highest.
Should be an active 48 hour period. Additional severe storms are likely into Monday across the Northeast and Mid-Atlantic.
Added the ECMWF 500mb winds to the ECMWF regular resolution graphics. These can be useful in projecting the mid-level winds that can aid in organized severe thunderstorm development. These can be found in the drop down menu, as well as, the individual time frames. These are available for the Northern Hemisphere at the moment, but will include all sectors soon.
NCEP has recently upgraded the WRF-ARW/NMM Hires windows for the Eastern U.S. to a CONUS ARW and NMMB ~4km WRF runs. They are run at 00Z and 12z and produce hourly output out to 48 hours at roughly 5km.
We are in the process of making the necessary changes within our software and systems to accommodate the increase in files sizes and processing requirements to handle the larger domains. We should have these new data sets available and finalized later this week. Look for them where the old WRF-ARW/WRF-NMM EAST model pages were located.
Here is the NCEP technical bulletin describing all the changes to the model & physics in the upgrade.
Severe Weather Outbreak Likely Friday Afternoon/Night Midwest – Southern Plains
As an upper level low begins to move eastward, the strong core of the mid and upper level winds will rotate around the upper low. An increasingly favorable kinematic environment for supercells and potentially strong tornadoes will develop from Central Illinois/Central Indiana through Southern Missouri into Eastern/Central Oklahoma and Northern/Western Arkansas.
The area at greatest risk for strong tornadoes is from Central/Eastern Oklahoma through Southern Missouri into Central Illinois. Although there will likely be AM storms, some severe, the storms that will develop Friday afternoon and move into Ohio-Valley during the overnight hours are the ones that pose the greatest risk for that area. Boundaries from earlier convection in the day will likely focus localized helicities values over 400 m^2^s which will enhance the tornado potential with storms that develop in non-linear modes. Bulk Richardson Shear values favor supercell storm modes across these areas, at least initially.
Other storms will likely form further south across Oklahoma where the instability will become extreme with surface capes over 5000 and shear values in excess of 40kts. CIN will drop below 25 j/kg by afternoon and supercells should form with the aid of an approaching shortwave. With LCL’s AOB 1000 meters, tornadoes are quite likely, especially across Northeastern OK.
The Maximum Updraft Helicity product from the 4km WRF/ARW has been consistently generating strong supercells across OK, MO, IL Friday Afternoon & Evening.
1 Hour Max Updraft Helicity. Indicate Rotating storms develop late.
Max 1 Hour Updraft Helicity from WRF-ARW
WRF-4KM Simulated Radar 23Z Friday
High Surface Dewpoints work northward into IL/IN feeding storms.
Surface CAPE is quite high.
Surface Low over MN and Secondary Low over SW OK will help back Low Level Winds.
Supercell Composite Parameter indicates likelihood of rotating storms from OK northeastward into IL.
Significant Tornado Parameter indicates risk of strong tornadoes.
0-1km Helicity 03Z
250mb RRQ of Jet will enhance Vertical Motion
Upper Level Low will move Eastward with cold pool and wind max
St. Louis, MO Forecast Sounding for Friday Evening. Small Cap, but supportive of Supercells and possible tornadoes
GFS Forecast Sounding for Springfield, IL for 00Z. Again kinematics and thermodynamics supportive of supercells and tornadoes.
Extreme Instability at Oklahoma City per the GFS Forecast Sounding
The May 31st EF5 El Reno Tornado that killed several storm researchers was sampled by ground based mobile X-band doppler radar (RaxPol) with very high resolution and found extreme wind speeds of almost 300 mph and rare satellite tornadoes. Other conventional fixed based NWS and FAA radars also captured remarkably high velocities and signatures.
Below is the Terminal Doppler Weather Radar from Oklahoma City (TDWR). A C-Band Radar with a high resolution receiver (250 meter resolution data displayed) and it appears to capture an apparent reflectivity minimum in the center of the tornado at the *exact* same time that the RaxPol indicated the same feature in the tornado. This is quite remarkable considering the distance from the radar is 26 miles. This reflectivity minimum is likely caused by descending air within the tornado and centrifuging of debris and precipitation in this case.
The National Weather Service WSR-88D in Norman, OK recorded some of the fastest winds I am ever aware of. I am quite sure these winds are legitimate. Below is a screen shot of the tornado at 23:24Z
El Reno Tornado before it became extremely large and wrapped totally in rain. Courtesy of Justin Drake @JustonStrmRider
With mobile Doppler radar units that have become available in the past 20 years that have extremely high resolution, we have been able to discover tornadic wind speeds in a few of the sampled tornadoes that have approached or in one case exceeded 300 mph. The recent El Reno tornado on May 31st, 2013 was another example of one of these.
Since the force of the wind does not grow linearly, rather it is squared (wind speed^2), these extreme wind speeds over 200 mph can cause unbelievable destruction. Since the kinetic energy is in the same arena as a small nuclear bomb, should one of these ”Super Twisters” hit a densely populated urban environment the destruction would be exponential compared to a lower category tornado. I created a graph to try to visually demonstrate the energy release or damage potential of the 2013 El Reno tornado as compared to just a few other recent tornadoes that have had good NWS storm surveys and tornadoes that had mobile Doppler radar measurements. There is a cluster of Super Tornadoes in the upper right hand portion of the graph that illustrates how much more destruction they can create than an EF3 or EF4 tornado if they encounter buildings, cars or people.
I think it also illustrates that there is a huge range in the EF5 scale. Maybe now that we have entered the era of reliable remote sensing and we know there are tornadoes with wind speeds near or even above 300mph and the energy release is so much greater than a 201 mph EF5 tornado, the idea should be at least entertained about adding an additional(s) EF categorie(s) to account for these rare, but extremely violent tornadoes given the their potential destruction and design limits required to survive them.
Click graph for larger image
An anomalously strong late spring upper level trough will develop along the Eastern U.S. Coast by Friday. Two shortwaves, one ejecting out of the southern stream over California, will at least partially phase with a second shortwave that drops southward into the Great Lakes on Thursday. These will combine to strengthen a surface low that will traverse from Iowa eastward to the New Jersey Coast.
A two-day event is expected as severe convection will likely generate near the surface low Wednesday afternoon across Illinois and Indiana where the best forcing will exist, however further east across Ohio and West Virginia additional severe storms may develop with the aid of warm air advection and a mid level wind max in the northwest flow, during the afternoon. If discrete convection develops across Ohio/Western West Virginia on Wednesday afternoon there could be supercells and possibly strong tornadoes, given the favorable shear and other parameters. This is well ahead of the main forcing of the the surface low back to the west.
Intense convection is expected to develop across Illinois and Indiana and track eastward during the overnight hours. As the surface low deepens, warm air advection will continue to help destabilize the atmosphere near the warm front which is likely to be near Northern Ohio into Western Pennsylvania . A greater risk of significant tornadoes exist along this boundary. Just north of the warm front elevated convection may produce large hail and damaging winds.
Additional storms may develop further southward into Southern Missouri, Kentucky and Tennessee.
As the upper level shortwaves begin to phase, per the NAM. The surface low is expected to slow somewhat and should allow for some destabilzation across the eastern portion of Virginia, Maryland, Pennsylvania, New Jersey during the afternoon.
Wind fields will support supercells and possible tornadoes from Central Pennsylvania to New Jersey southward into the Carolinas . The best parameters for significant tornadoes on Thursday will exist near the warm front across Pennsylvania, Maryland, Delaware & into New Jersey.
*All of this is highly dependent on surface heating and interaction with prior convective outflow boundaries, none of which the models can properly resolve at this time range.
Below are some of the products used to create the outlook.
NAM Forecast Sounding for Columbus, OH Wednseday Evening.
Forecast Sounding for Baltimore, MD for Thursday Afternoon at 2PM EDT
NAM Sounding would support severe storms and possible tornadoes.
Complicated forecast for the Ohio-Valley into West Virginia and Western Pennsylvania, Wednesday into Thursday Morning. As indicated in last nights discussion, synoptic forcing is very strong and will create favorable conditions for a large area of severe weather as an intense low pressure for this time of year, moves across the Ohio Valley. The primary forecast problems are the convective mode that the storms take once they develop and whether the downstream ambient environment is contaminated by earlier convection that will disrupt the inflow and stabilize the boundary layer. This is exactly what happens with the WRF-NMM and WRF-ARW 4KM models, each a little bit differently. The WRF-4KM NAM CONUS Nest does not, and creates very little convective contamination prior to the main system arriving and develops a very dangerous environment across IL/IN/OH/ Western PA that would support a widespread severe weather event with supercells. While not explicitly, it would likely yield some tornadoes given the intense parameters it is generating.
Below are some animated GIF’s from the WRF-NMM to illustrate the forecast issue of convective contamination of the environment prior to the main forcing/convection related to the surface low. If this AM convection does not develop across WV/VA as indicated, the stable outflow may not be near as strong and may not provide the cool theta-e values and therefore not weaken the main convective system as much or at all when it arrives late Wednesday night.
WRF-NMM Radar Simulation. Note Convection that develops across WV/VA AM Hours Wed Morning.
WRF-NMM Note the Theta-e minimum associated with the AM convection across WV/VA mountains that works westward and helps weakens the approaching convective system late Wednesday night as it arrives in OH.
Even as it is, with some possible convective contamination. The mesocale models are generating some strong indications of a wide spread severe weather event.
Across the Ohio-Valley Wednesday into Wednesday night, the 0-1km helicity and the 0-6km shear will increase as the surface low deepens and the upper level shortwave approaches. Kinematic forcing will favor the formation of supercells and possibly tornadoes over a fairly large area, but the most favorable location will be just south of the stationary front/warm front which will maximize the 0-1km helicity.
Here is just one of the Updraft Helicity products from the various mesoscale models. This is from the WRF-NMM. It’s developing a long lived Supercell from just west of Chicago and tracking it southeastward. Other supercells develop across Indiana and Ohio. This is one of the longest and most intense updraft helicity values I have seen since observing these parameters.
Forecast Sounding 40 Miles South of Chicago, IL 01Z Wednesday Evening. WRF-4KM NAM Nest
Forecast Sounding near Wooster, OH this evening at 00Z. Very Unstable atmosphere in place ahead of main forcing. Supercells and tornadoes are possible if convection can develop ahead of main convective system.
While the threat from widespread damaging wind is certainly high and linear mode convection may very well be the primary mode of convection for the duration of this event. I feel that there very well may be a period of time where there are either discrete supercells or embedded supercells with in a line. Given all the parameters, I believe the tornado risk is quite high along and just south of the stationary front from Central IL through IN into OH. This is a highly conditional forecast, since convective contamination from earlier storms may affect the environment or if the system becomes a large bow-echo or derecho very early in the evolution, then the tornado risk is greatly reduced.
Here is a map outlining the risk area of tornadoes based on all the available guidance through 05Z.
Did the 88D at FFC capture a Tornado ? Dual Pole data may have picked up some debris. Survey may tell later today. Here is a screen shot I took last night while the event was unfolding. The velocity data was not very compelling, but in the previous 3 volume scans there were much better indications of a circulation.
Click images for much larger view
Update: I pulled the archive data from last night. Here are previous volume scans. You can see the progression of the development of the CC min & other radar data.
An apparent brief touch down of a tornado in Central North Carolina yesterday evening was detected by the Raleigh, NC WSR-88D Radar. The RDA was fairly close to the storm with the 0.5 degree beam altitude only around 1390 feet.
While the NWS survey has not yet been completed, it appears this will very likely be an EF0 or EF1 tornado, based on the damage reported, photos and radar data.
Update 2:10 PM EDT: NWS just confirmed EF0 with 85mph winds. Path length 1.25 miles / 150 yards wide
The 22:31:59Z volume scan had a small, but defined TVS with gate to gate shear of ~81kts (+57/-24) and a well defined hook echo. It also developed a significant correlation coefficient minimum which was co-located with a reflectivity maximum in the hook where the TVS was also centered.
All of this convinced me, that there was indeed a tornado on the ground and in progress. I quickly put together a “tweet” and sent it out at 22:36Z indicating that we now had a tornado on the ground.
I also submitted something to the effect, on RAH NWSChat, about a possible debris ball developing on radar.
Shortly there after we started receiving verification of damage and sightings of the tornado.
This is another example of how useful the Dual Polarization data can be when looking for Tornado Debris Signatures. Even for locating relatively “weak” tornadoes. Looking at the dual polarization data, it appears the “debris” was lofted to an altitude of around 2600 feet. My thinking is that much of this “debris” is likely tree leaves & foliage from the wooded areas where the tornado crossed, as well as, some other materials.
Click images to enlarge
Photos of the wall cloud ( Credit: WRAL)
Damage to a home in Youngsville, NC
The numerical models historically have had a very difficult time trying to predict cut-off lows across the Southwestern U.S. that eject and try to phase with northern stream energy.
This is the case now, in regards to next weeks, all important holiday week forecast. The GFS Operational has consistently forecast a strong Nor-Easter with inland snow and a mixture/rain near the coastal areas & major metros in the Northeast.
The GFS Ensembles have trended in favor of the GFS operational, recently. The ECMWF operational is moving a much weaker system more off-shore with less of an impact. The differences between the two can be seen by examining the upper air charts (500mb) and see how the models handle the northern and southern streams (height/vorticity).
The ensembles will be the most useful guidance over the next day or so as we try to get a handle on the likelihood that the streams will phase and to what extent. Until then, I would be very leery of anyone telling you they know which solution is correct or what exactly is going to happen. These patterns are very complex and historically very challenging for the models to accurately simulate at these time ranges (4-5 days out).
GFS Ensemble 500mb Height & Vorticity 12z Wed
GFS Ensemble SFC Pressure & Precip 00Z Thu.
ECMWF 850 00Z THU GFS 850 00Z THU
Notice the large differences. The GFS develops a huge cyclone over the Northeast while the ECMWF does not, because the ECMWF does not completely phase the two streams.
Quite a bit of uncertainty, but the latest data suggest the potential for severe thunderstorms and possible tornadoes across Eastern Texas and the Deep South Saturday as a strong, negatively tilted, shortwave ejects across Texas. Stay tuned over the next couple of days if you live in this area.
Update: 12/20/13 12:40AM EST
After reviewing the 00Z model guidance, it appears that the instability will be somewhat limited on Saturday, due to clouds and marginal lapse rates. Severe thunderstorms with damaging winds are likely to develop across East Texas during the morning and spread quickly eastward during the day. 0-6Km shear vectors are large and 0-1km helicity values will be locally high, so some low-top supercells are likely, including the risk of a few tornadoes. But given the expected limited instability, SFC CAPE <1000, a widespread outbreak of tornadic supercells seems unlikely. The threat of damaging winds is high however, as the low level jet increase to over 70kts during morning and early afternoon.
850 Wind Late Saturday morning near 80 Knots
The GFS Model will be upgraded from ~27KM to ~13KM this summer. The High Resolution Rapid Refresh Model (HRRR) will become operational later this year. Power Point Link (NCEP)
In preparation for these and other expected increases in weather processing volume, we have been adding additional computing hardware to handle this data increase. Using redundant Enterprise HP Proliant hardware in a 24/7 staffed SAS-70 Tier 1 Data Center, ensures we will be ready to handle the next generation of weather data. Below is an image of a few of the servers & equipment that deliver Wright-Weather.com products to you.
2/5/14 1:45 Z
Freezing rain will moving into the populated region of New Jersey and New York City around midnight (2/5/14) and will persist until around noon Wednesday. Temperatures in the New York city metro area are expected to remain near or slightly below freezing the duration of the event. Just northwest and west of the downtown area, slightly colder surface temperatures are likely.
Total precipitation amounts of 1.00-1.25″ is expected. A significant amount of drip loss will occur due to the heavy precipitation rate and the small air temperature delta to freezing point. Where temperatures are likely closer to 29 or 30 degrees just west and northwest of the city, ice accretion amounts of 1/4″ to as much as 1/2″ are possible and could lead to a significant amount of power outages, if ice accretion amounts surpass 1/3″.
New Short Range Ensemble Forecast (SREF) Mean Accumulated Winter Precipitation have been added. They are:
Snow change from previous run (dProg/dt)
Ice Pellets (Sleet)
They can be found in the drop down menu on the SREF model page under “Forecast Parameter (Mean)”
A strong winter storm will bring a variety of winter weather to the Southeastern U.S. as an upper level low develops across the mid-south, in combination with a cold air damming event. A strong coastal low will strengthen and move up along and just off the Eastern seaboard and bring heavy precipitation to the Mid-Atlantic and into the Northeast
A zone of of prolonged freezing rain will extended the I-20 corridor from Atlanta to Augusta to Columbia, SC. Model freezing rain liquid equivalent totals in this area exceed 2 inches. While drip loss will be relatively high with accretion efficiencies likely only being in the 30-40% range due to the high precipitation rates and the temperatures likely remaining close to the freezing point, this still yields radial ice accretion amounts of .50-75″ which would cause widespread electrical distribution disruptions and tree damage.
Here are the latest Freezing Rain Graphics.
An upper level shortwave will move through the Mid-Atlantic region Friday evening. Ahead of this shortwave, conditions will for a short period of time, become favorable for severe weather across Central and Eastern portions of the Carolinas and Virginia.
Thunderstorms will likely develop by mid day across the central portions of the region and move eastward and intensify under a strong mid-level flow. Moderate helicity and bulk-shear values along with surface CAPE in excess of 1500 will support the potential for supercell development. Low LCL levels will also increase the risk of tornadoes in the strongest supercells. Trends in mid-level wind strength and instability should be monitored for an increase in the severe weather risk assessment.
4/24/14 3:00 PM EDT
A slow moving cold front across the lower Great Lakes will provide the low level convergence, combined with favorable instability & shear to ignite numerous severe thunderstorms Wednesday afternoon across the Ohio-Valley. Supercells will be a likely storm mode as bulk shear values will be in excess of 45 knots. In addition, 0-3km helicity values will be over 200, so there is a chance for an isolated tornado in the strongest supercells, although conditions are not ideal for tornado development. Large hail and damaging winds are the primary hazards. Supercells may evolve into a linear or bow echo configuration by late afternoon or evening.
Storms will likely diminish and weaken as they move east-southeastward into Central Kentucky Wednesday night where the low-level theta-e values will be significantly less, resulting in much less instability.