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View Diary: ALERT: Major Severe Weather (Potential Derecho) Wednesday From Chicago to Washington DC (145 comments)

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  •  The secret is in the shear. (6+ / 0-)

    Vertical wind shear, which is the speed of the wind as altitude increases, will be substantial over Illinois and Indiana.  According to the NAM, at 2 pm Eastern tomorrow wind speeds at 850 hPa (1.5 km) will run at 15-20 knots.  Wind speeds at 500 hPa (5.85 km) will run at 45-55 knots.  This favors the development of thunderstorms.  

    The horizontal wind shear, which is the change in direction as altitude increases, starts moderate and then becomes slight as you go east.  Over western Illinois, WSW winds veer to the WNW between 1.5 km and 5.85 km -- about 45 degrees' change in direction  Over eastern Indiana, they veer from the WSW to the W -- about 20 degrees change in direction.    

    This would argue for supercells forming near the Mississippi river, followed by a bow of storms developing over western Indiana along the gust of the original storms...if nothing goes "wrong".  

    If the gust front does not quickly develop into a bow echo, then it will simply cool the atmosphere ahead of the original storms and the whole mess will devolve into (perhaps) a good soaking rain for a few hours.  There is no guarantee that the original storms will develop.  Similarly, there is no guarantee against a bunch of "popcorn" storms developing in Indiana and Ohio, which would stablize the atmosphere ahead of the main event.  Or the best formation area tomorrow morning might be covered with the previous night's cloud debris, inhibiting temperature rises.  

    Going back to the news media, part of the hysteria may be due to memories of surprising hurricane-force wind gusts, followed by days of power outages in 90+ degree heat.  Part of it may be the media drumming up the story for ratings.  There is more reason to expect a derecho tomorrow than usual, so perhaps taking the first precautions now would be well-advised.

    "Politics should be the part-time profession of every citizen who would protect the rights and privileges of free people and who would preserve what is good and fruitful in our national heritage." -- Lucille Ball

    by Yamaneko2 on Tue Jun 11, 2013 at 04:07:03 PM PDT

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    •  I have to agree to a certain extent (3+ / 0-)

      That even the weather is hyped any more. Our local station for instance calls the weather report STORM TEAM NINE with flashing lights and a nasty looking dopplar image for a background.

      But, on the other hand, a little warning like this is nice.

      I'm not saying I would have fared much better last June if I'd had more warning, but some warning might have helped. I realize that one developed rapidly, but I didn't even hear about any thunderstorm watch.

      Meddle not in the affairs of dragons... for thou art crunchy and good with ketchup.

      by Pariah Dog on Tue Jun 11, 2013 at 07:51:32 PM PDT

      [ Parent ]

    •  As much as I can (1+ / 0-)
      Recommended by:

      I get the meteorological explanation you've noted above.  

      My bone to pick is with the weathercasters.  There is a notable difference between stating something will happen, and stating that conditions are favorable to certain weather happening.  One indicates no room for doubt, the other indicates a possibility.  Therein lies the problem.  Informing folks that they should take reasonable precautions for tying down loose items, and putting the car in the garage is different from saying you are about to meet your doom.

      Does it make sense to hype when all you end up doing is panic folks?  Using "derecho" in the forecast has all the feeling of using a new buzzword to drum up ratings.  It's not like you can predict one 24 hours out.

    •  What do you think of these U of Utah (0+ / 0-)

      animated predictions.

      I've watched this service for a couple of years.  It is always spot on; however, it does not present itself as a weather prediction view but it is.

      Frame A48 is today.

      F180 is in the future, I think 7 days but it might be a shorter period.

      Just click "Animate" to run the service or scroll your curser down the A48-F180 list of frame numbers to view the progression.

      Would love to know your opinion.

      Here's the link.

      It's difficult to be happy knowing so many suffer. We must unite.

      by War on Error on Wed Jun 12, 2013 at 12:26:45 PM PDT

      [ Parent ]

      •  OK, I recorded it for you to see (1+ / 0-)
        Recommended by:
        Kay Observer2

        Sorry for the annoying noise in the background, the wind was blowing my blinds and I didn't notice while I was quickly recording this for your review.

        Your opinion?

        It's difficult to be happy knowing so many suffer. We must unite.

        by War on Error on Wed Jun 12, 2013 at 12:54:17 PM PDT

        [ Parent ]

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