06/25/09 Beginners NOW: KS

[Eric Baker]

There is an interesting severe warned cell just north of Lyons, Kansas. GR2AE is showing 1.5" hail and some signs of rotation on velocity products and NROT. The upper air seems to be very interesting over the region. SPC mesoanalysis shows quite a bit of directional sheer although the flow is weak. The rotation also seems to be on the northwest side of the storm. Can anyone weigh in on this with me.

 

[Mike Smith]

The main reason it is warned is due to the relatively high potential of wet microburst winds. SLN has nearly perfect microburst conditions with a temperature of 101° and a Td of 63°.

The nearly perfect conditions are reflected on the latest WINDEX data: www.star.nesdis.noaa.gov/smcd/opdb/aviation/mburst/ge/WDXNC.GIF at 1915Z (which is the most recent available, updates hourly) with 77 kt. over the McPherson Co. grid point and 79 kt. over the SLN grid point.


(4:18pm) And, sure enough...
691
NWUS53 KICT 252109
LSRICT

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE WICHITA KS
409 PM CDT THU JUN 25 2009

.TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON

.DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.

..REMARKS..

0401 PM HAIL 4 WSW GENESEO 38.48N 98.22W
06/25/2009 E0.88 INCH RICE KS TRAINED SPOTTER

0401 PM TSTM WND GST 4 WSW GENESEO 38.48N 98.22W
06/25/2009 E65 MPH RICE KS TRAINED SPOTTER

TREE LIMBS KNOCKED DOWN AND A BARBEQUE GRILL BLOWN OVER.


Mike

 

[Eric Baker]

Thanks Mike, do you know if a single storm can produce more than one microburst?

 

[Mike Smith]

Yes, they can.

But, the more common situation is where a first microburst occurs and its gust front induces a second storm to grow firing a second microburst, etc.

4:34pm Tilts 1 and 2 from ICT radar show a cell growing on the gust front from the first cell. It is an excellent candidate to produce a strong microburst.

Here is a photo of a downburst in progress with the arrow pointing at its roll vortex.
http://wattsupwiththat.files.wordpress.com/2009/05/downburst_mrsmith_1978.png

There were multiple downbursts that afternoon from several small cells southeast of Wichita.

 

[Eric Baker]

Okay because at 3:52 the storm had 55 thousand foot tops, and by 4:00 they shrunk to 47 thousand foot tops. Also the reflectivity dropped from 68dbz to 62dbz. Maybe that is representative of a microburst. You can also see what resembles a gust front coming out of the northwest side of the cell.

 

[Mike Smith]

Okay because at 3:52 the storm had 55 thousand foot tops, and by 4:00 they shrunk to 47 thousand foot tops. Also the reflectivity dropped from 68dbz to 62dbz. Maybe that is representative of a microburst. You can also see what resembles a gust front coming out of the northwest side of the cell.

Yes, your observations are correct. The trick is to get the warning out before the microburst is in progress.

There is a peer-reviewed paper that discusses that one or two CG's often occur as the downburst/microburst makes its descent and I have observed that, too. So, a collapsing cell, especially if CGs are present, is a prime candidate to produce a downburst.

Just went out to our Ops center and there are considerable CG's with the cell, so I believe it is producing multiple microbursts.

 

[Eric Baker]

I think it just did it again...

 

[Eric Baker]

Okay just before the microburst around 4, it was developing what seemed to be a weak couplet. If you look at the northernmost section of the storm, it seems to be doing that currently.

 

[Eric Baker]

Also a look a spectrum width showed more intensity on the northernmost side of the cell, it is doing that again now.