7 June, 2007

Target Area: Wisconsin

Presentation by: Bryce Touchstone

Bear this in mind: The dynamic charts aside from the surface chart shown are for 0Z. The vast

majority of the tornadic events occurred between 20-2230Z, with the hail reports occurring within and an hour on either side of the tornadic time

frame. So the 0Z charts will show a target area for a severe weather threat that will be east of the

bulk of the most severe weather associated with this event.

Dynamic Setup – Surface

(7/6/12, 20Z)

-Deep surface low

-Strong Southerly Flow

Dynamic Setup – Surface

(7/6/12, 20Z)

There are what appear to be two separate cold fronts, and a dry line at the surface moving eastward in association with a strong surface low. There is surface convergence along and ahead of the front and dry line, forcing rising air. There is also moisture convergence near the surface low, centered over Wisconsin, associated with the southerly flow ahead of the dry line/cold front. Lastly, there appears to be an easterly bulge in the dry line over Wisconsin. The fact that this chart is hours after the main severe event must also be considered.

Dynamic Setup – 925mb

(8/6/12, 0Z)

The LLJ present on this chart is displaced temporally from the primary severe event by 2-6 hours, which would have placed its right-front quadrant over Minnesota and Wisconsin. This most likely would have caused low level convergence and ascent. There is also WAA occurring, as well as moisture convergence, ahead of the dry line/cold front. The winds ahead of the front are already beginning to veer, now being from the SW.

Dynamic Setup – 850mb

(8/6/12, 0Z)

There is continued veering of the winds, as well as continued speed shear. There is still an abundance of moisture transport from the S/SW. Hours prior to this, the primary area of transport was over Wisconsin and Minnesota.

Dynamic Setup – 700mb

(8/6/12, 0Z)

Here we can make out two shortwave troughs, one with a negative tilt, and one with a positive tilt. The negatively tilted shortwave trough, which is indicative of an ETC in its maturity, now has its axis over Minnesota. Hours prior to this, the downstream region of this axis was over Wisconsin. There is still continued veering and speed shear in the wind field. Note, also, the strong wind speeds associated with the flow at this level.

Dynamic Setup – 500mb

(8/6/12, 0Z)

NegativeTilt

PositiveTilt

There is a strong jet streak with its right-front quadrant over Wisconsin at the time of this analysis product. The presence of this quadrant over Wisconsin likely suppressed further severe convective activity, as this quadrant at this level is associated with convergence and subsidence. There is also strong difluenceand divergence which would have been over the Minnesota/Wisconsin area 2-6 hours prior to this product time.

Dynamic Setup – 250mb

(8/6/12, 0Z)

The following maps and products are all for 20Z, centered on the estimated

time of maximum severe weather occurrence.

This map was created by manually placing maximum and/or minimum values for specific thermodynamic- and shear-related properties, and composite indices.

0-3km MLCAPE 0-3km Lapse Rate100mb mean LCL Height

100mb mean LFC Height

700-500mb Lapse Rate 850mb Moisture Transport

850mb Height,Temp, Td

DCAPEMUCAPE, mean RH

Mixing Ratio

MLCAPE, MLCINNormalized CAPE

Precip. Water(in.)

SBCAPE, SBCIN Surface Theta-e Td, Lapse Rate

Many of the thermodynamic indicators point to the highest potential for severe weather from Minnesota across Wisconsin. Specifically, LCL and LFC heights are sufficiently low for severe weather. The surface lapse rates are relatively low, while the mid-level LR are higher, pointing to a conditionally unstable environment. There is substantial moisture and warm air being brought in at around 850mb, mostly under force from a LLJ present. The precipital water and mixing ratio are maximized over ESE Wisconsin (in the viewing area). There is, however, also a substantial amount of CIN across eastern Wisconsin. This most likely inhibited severe convection across the southeastern part of the state.

0-1km shear vector Sfc-6km shear vectorSfc-8km shear vector

9-11km SR winds Anvil SR winds

Low-level shear vectors are from the SW, as are the sfc-6km and sfc-8km, with increasing shear magnitude with height. This indicates veering winds with speed shear, which is conducive to sustained severe weather formation. Also to note are the 9-11km SR winds and Anvil SR winds, which are both well below 40kts, indicating the likelihood of any supercell formation to be of a high precipitation nature.

0-1km SRH0-3km SRH

1km EHI 3km EHI

BRN ShearDerecho Composite

Parameter

Effective Bulk Shear Sfc-based Lifted IndexSfc-based CIN

Significant Hail Parameter Significant Tornado

Parameter(eff. lyr)

Significant Tornado Parameter(fix lyr)

Supercell Composite Parameter

The composite parameters and indices point towards a very favorable environment for severe weather, including significant hail, severe winds, and tornadic supercell formation. Both 0-1km and 0-3km SRH values are in the high range, as is EHI. The surface-based Lifted Index is very low, which also indicates substantial instability. BRN, Significant Tornado Parameter, and Supercell Composite Parameter values are all significantly high. Effective bulk shear values are over twice that for potential tornadic formation. Also of note is that the Derecho Composite Parameter values are very, significantly high.

-From the sounding itself, there is a shallow layer right near the surface of slightly less relative humidity, likely from daytime heating. From around 900mb up through 700mb the environment is near saturation. At 700mb, there is a very slight inversion, nearly negligible, above which is a relatively dryer layer up until around 350mb, where the environment again reaches saturation.

Skew-T, Hodograph

(8/6/12, 0Z) – Green Bay, WI

-CAPE on this diagram is not overwhelming, though temporally this diagram is not entirely representative of the environment producing the severe weather earlier(4-6h prior). One consideration is amount and depth of the moisture. 20Z 0-3km and 700-500mb lapse rates would indicate an environment near or at saturation, thus increasing instability.

Skew-T, Hodograph

(8/6/12, 0Z) – Green Bay, WI

-Since this observed sounding is later in the afternoon/early evening, the effects of daytime heating, along with widespread convection has decreased surface temperatures. This would mean that it is very likely that the environment in which the severe weather events occurred hours prior to this sounding contained much higher values of CAPE.

Skew-T, Hodograph

(8/6/12, 0Z) – Green Bay, WI

-Regarding the wind plots and hodograph, directionally we can see veering through the lowest 3km, and speed shear through the lowest 6km. Again, temporally this is likely not entirely indicative of the severe weather environment hours prior, with the current passing of the dry line and/or cold front. 20Z shear and composite parameter/index values would indicate much stronger values of shear at the time of severe convective initiation.

Skew-T, Hodograph

(8/6/12, 0Z) – Green Bay, WI

-Looking at parameter values, surface, mean layer, and D-CAPE values are all still measurably high, with the potential for both air mass and severe convection. Shear, helicity, and BRN shear values are all still measurably high as well, supporting further convection. Likely inhibiting this to a large degree, however, would be surface CIN combined with proximity of the LLJ and upper-level jet streak/jet stream at this time.

Skew-T, Hodograph

(8/6/12, 0Z) – Green Bay, WI

-Dry Region along/directly behind front

-Convective line

-Overshooting tops

-Moisture pumping in

Convection inhibited

1702Z 1745Z 1845Z 1945Z

2045Z 2145Z 2215Z 2245Z

RaDAR imagery showing a supercell which produced 3” hail. Strong updraft indicated by tight reflectivity gradient along BWER. Storm circulation indicated by both BV and SRV products. High precipital water content being held aloft, indicated by VIL. Precipitation being both swept downshear and wrapped around the inflow/BWER.

RaDAR imagery showing a supercell which produced 4.5” hail. It appears there is a WER beginning to form, indicating a strong updraft. Storm circulation is weaker in this storm, as indicated by SRV and BV. Very high precipital water content being held aloft and above the inflow region, indicated by VIL. Precipitation primarily being swept downshear and dropped in close proximity to the updraft.

RaDAR imagery showing a supercell which produced an EF3 tornado. There is a BWER formed. There is storm circulation demonstrated by BV and SRV products. The majority of the precipital water is being held aloft, downshear of the updraft, as is seen in the VIL product. There also appears to be a debris ball on the ground at the time of this imagery capture. This tornado stayed on the ground for at least 40 miles, leaving over $15 million in damage.

Due to the proximity of this tornado to the RaDAR site in Green Bay, WI, this is another look at the storm, using BR 0.5-3.5 products. The Lemon Technique can be useful in getting more of a 3-dimensional view of a storm.

While no deaths or injuries were reported with this event, there was $15 million in damage associated with one single tornado. There were also scores

of trees felled. Strong upper-level divergence and difluence, surface

convergence, an approaching mid-level shortwave trough, abundant CAPE, significant amounts of veering speed shear, and a LLJ pumping in warm,

moist air combined to make this a very serious severe convective weather

outbreak.