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Saturday Severe Weather Threat

The severe threat for Saturday is still very substantial as very powerful storm system to our west moves in late tonight and into tomorrow. Please stay alert for possible watches which means conditions are favorable for severe weather to develop. Then warnings might be issued meaning severe weather has been spotted by trained spotters or on Doppler radar.

The Storm Prediction Center has already put us under a slight risk for severe storms Saturday.

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There will be plenty of wind shear and enough CAPE that we will likely see some kind of watch issued for the region. Then there will likely be some warnings Saturday morning, including possible tornado warnings due to the amount of shear that will be present.

                              Shear                                                                   CAPE

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Here’s the model time line of when the line of storms moves in.

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Severe Weather Outlook

 

Here’s a quick look at why we might be looking at a mutli-day severe weather outbreak from the plains into the Southeast. Even though today and Friday this mess will be to our west it’s likely we could see this spread into the Carolinas on Saturday. Stay tuned for further updates, especially if you have outdoor activities Saturday.

Severe Weather Outlooks

                       Today                                                   Friday

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                                                                 Saturday

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Mountain Wave Clouds

This morning as the upper low and storm system exited the region. Strong northwest flow moved in and we got 2 distinct types of mountain wave clouds. Which can be seen from the visible satellite.

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There are some pretty neat things going on here when you take a look at the surface winds at 10m(image left below) and then take a look at the vertical velocities(image right below). You can see in the wake of the mountains we have some lift in the green areas which is indicative of lee mountain rotors.

Surface Winds                                     700mb Vertical Velocities

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If you look closely you see 2 types of cloud formations. One is a mountain wave pattern over Virginia and West Virginia and also visible in the northern mountains of North Carolina near Boone. If you look further south you can see cirrus clouds coming off the mountains of Southern North Carolina the upstate of South Carolina into NE Georgia.

Wave Clouds                                                Cirrus Clouds

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What is going on here is some chaotic vertical motions caused by the departing low pressure system interacting with the mountains. Moisture at high levels & mid-levels along with cold dry surface air make for some cool cloud formations. Here’s a diagram of the process. You can see how the lee side turbulence and rotors cause the wave clouds but also how those rotors can create higher level cirrus clouds downwind of the mountains.

System Mountain Wave - Rotor

Weekend Hail Storm

What a weekend of damaging hail. The pictures and video tell the story.

Here’s a slide show of photos from wcnc.com.

Photo from Dan Poche

Hail like this is very rare in the Carolinas especially over such a large area. The thunderstorms that produced this hail were between 45-50,000’ tall and had freezing heights were around 9-10′,000’. The key to getting such large hail were the rotating updrafts, which classified them as supercells. These same rotating updrafts called mesocyclones can lead to tornadoes, but only one touched down. These rotating updrafts I estimated to be around 70-80 mph. The hail stones themselves had terminal velocities of between 60-80mph for the golf ball size hail and between 80-100mph for the baseball size hail. These are just estimated based on a perfect sphere, as you can see most were odd shapes due to collisions with other hail stones and raindrops.


Measurement                       Updraft Speed
in. cm.               mph             m/s
bb < 1/4 < 0.64 < 24 < 11
pea 1/4 0.64 24 11
marble 1/2 1.3 35 16
dime 7/10 1.8 38 17
penny 3/4 1.9 40 18
nickel 7/8 2.2 46 21
quarter 1 2.5 49 22
half dollar 1 1/4 3.2 54 24
walnut 1 1/2 3.8 60 27
golf ball 1 3/4 4.4 64 29
hen egg 2 5.1 69 31
tennis ball 2 1/2 6.4 77 34
baseball 2 3/4 7.0 81 36
tea cup 3 7.6 84 38
grapefruit 4 10.1 98 44
softball 4 1/2 11.4 103 46

How hail forms (Courtesy Jetstream NOAA)

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You can see how many times the hail circulated based on the rings inside the hail stone. These are from Fort Mill.

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If you had damage here’s a complete list of all the official reports if you need them for insurances purposes. Here’s a link to the PDF.

Small Severe Weather Risk Friday & Saturday

The stalled front to our north is going to try and slide a bit south tomorrow and Saturday bringing the risk for some strong to severe storms. These will be very widely scattered storms and I wouldn’t be changing my outdoors plans. The chances of thunderstorms will be mainly in the mountains/foothills Friday and area wide Saturday. Those chances will remain in the 30-40% chance. Here’s a look at the severe thunderstorm risk the next 2 days.

                            Friday                                                                 Saturday

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Here’s what 2 of the short term models depict tomorrow evening, not very impressive. I tend to be more optimistic in my forecast right now. I just don’t see a lot of rain unless I see some significant movement of the front south.

                     8pm HRW Model                                            8pm NAM Model

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Now there will be plenty of heat and humidity building south of the frontal boundary Friday and Saturday. So instability won’t be a huge issue it’s the trigger that maybe missing which is the front. So if indeed the front sags as far south as the Virginia border then we could see some strong storms both days, time will tell and I’ll be watching that front the next 2 days for you. Here’s where it is now.

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Severe Weather Threat Overnight

The severe weather threat overnight is looking pretty high. I would caution everyone to make sure you have a charged cell phone and text alerts set-up from WCNC. Or a weather alert radio with battery back-up. We will see severe weather warnings overnight when you will likely be sleeping and even timely warnings can be deemed useless, unless you get them. Here’s the severe threats based on probabilities.

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Here’s a look at the model timeline of when things get cranking overnight based on the HRW model.

                          Futurecast 11pm                                              Futurecast 2am

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                                                               Futurecast 5am2011-04-04_0946

Shear and CAPE tonight

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To get warnings 24 hours a day follow me on Twitter @wxbrad, or on Facebook NewsChannel 36 or sign up for severe weather texts from wcnc.com.

My Ride Along on the TIV (Tornado Intercept Vehicle)

It was an awesome thrill to meet both Sean Casey and Marcus Gutierrez from the Discovery Channel show “Storm Chasers”. I regularly watch the show and after chasing storms back in college and at times in my free time it’s always great to meet fellow weather junkies. The one unique thing about the TIV is unlike when I chased and many other chase we try to stay out of the storm. The TIV drives right into the tornado for what must just be an amazing experience. Sean Casey and Marcus Gutierrez could not be nicer guys. Especially considering all the time and travel they have been doing promoting the movie, Tornado Alley at the IMAX at Discovery Place.

 

Pictures

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