# Presentation: 641404

## A Multi-Scale Examination

- Jeffrey M. Medlin
- Science and Operations Officer
- National Weather Service Forecast
- Mobile, Alabama

**32****nd****  NWA Annual meeting**
**October 2007**

**A Multi-Scale Examination**
**of the 1 March 2007 Millers Ferry, Alabama **
**EF-4 Tornado-Producing Mesocyclone**

## Wilcox Co., Alabama

**Wilcox Co., Alabama**
- Service Assessment
- 31 verified tornadoes (13 > EF1)
- this day!

## RUC40 - MUCAPE - 17Z – 01 Mar 2007

**RUC40 - MUCAPE - 17Z – 01 Mar 2007**

**Wilcox Co. EF4 mesocyclone**

**Warm Fropa**

-  As part of the notable 1 March 2007 US Deep South tornado outbreak,
- a **long-lived EF-4 tornado-producing **mesocyclone developed from two
- merging updrafts over southeastern Mississippi at 1639 UTC and later moved
-  eastward across much of southern Alabama during the ensuing hours.

## What, Where and When?

**What, Where and When?**

**Wilcox-Dallas County, AL (EF4)**

**Coffee County, AL (EF3)**

- Began 1827 UTC

- Began 1908 UTC

## Slide 5

## Tornado Direction (looking NE)

- Missing and de-barked
- mainly pines; some hardwoods

- Single family homes wiped clean to slab

**Tornado Statistics**:
**EF Scale Rating – EF4**
**  ****(FR12-DOD-10) – 185 mph**
**Path Length =15.6 mi**
**Width = 500 yd**
**Other –**
**- 40 homes destroyed**
**- debris two miles**
**  ****downstream**

## Event Considerations

- Maximum time and space interpolation required.  Used NCEP RUC40 and compared evolution of 12 and 18 UTC. This is an issue!
- Confirmed by multiple hand upper air and surface analyses, this event occurred in the surface warm sector (just after surface warm front passage) and **well downstream **of the main mid- and upper air trough (and assoc/dynamics) and the surface cold front.
- Heavily analyzed satellite data to take note of any resolved jet streaks.
- Pre-storm environment re-constructed using a combination of observed and model soundings and representative surface-based conditions from mesonet site. Differential thermal and moisture advection was found to be primary contributors to de-stabilization of the local lapse rate immediately prior to tornado production.
- Local LAPS took a hit when AWIPS Build just a day before changed scale of map background. No way to re-create LAPS data since it was archived as such.
- Operator-Defined Mesocyclone evolution results given last.

## 250 hPa - 12Z – 01 Mar 2007

**250 hPa - 12Z – 01 Mar 2007**

## 500 hPa - 12Z – 01 Mar 2007

**500 hPa - 12Z – 01 Mar 2007**

## 700 hPa - 12Z – 01 Mar 2007

**700 hPa - 12Z – 01 Mar 2007**

## Unstable 700-500 hPa Lapse Rates poised to advect into region from upstream!

**Unstable 700-500 hPa Lapse Rates poised to advect into region from upstream!**

## 850 hPa - 12Z – 01 Mar 2007

**850 hPa - 12Z – 01 Mar 2007**

## *Nam12-RUC40 interpolated with

**Sfc Parcel**
- 	T  = 72F
- 	Td= 69 F
**MUCAPE** = 2177 J kg-1
**LCL** = 868 ft
**EL** = 40.7 kft
***U*****0-6** = 220 deg 45 kt
**SRH** 0-3 km= 365 m2 s-2
***C***obs = 240 deg 36 kt

- *Nam12-RUC40 interpolated with
- input from 15Z KJAN sounding
- And using sfc conditions from
- Grove Hill, AL @36 km SW of
- Millers Ferry, AL)

**Dry air source, RFD-FFD**

- Near Storm Environment

## U0-6 = 220 deg 45 kt

***U*****0-6** = 220 deg 45 kt
**SRH** 0-3 km= 365 m2 s-2
***C***obs = 240 deg 36 kt

**20R80**

- Near Storm Environment

## U0-6 = 220 deg 45 kt

***U*****0-6** = 220 deg 45 kt
**SRH** 0-3 km= 365 m2 s-2
***C***obs = 240 deg 36 kt

**ω****h**

- Near Storm Environment

## 18 UTC Severe Weather Composite

- 300 hPa

- 500 hPa

- 700 hPa

- 850 hPa

- 8 g/kg

- 12 g/kg

- 8 g/kg

## Composite - 18Z – 01 Mar 2007

**Composite - 18Z – 01 Mar 2007**

## 500 hPa Main Jet Axis (85 kt)

**500 hPa Main Jet Axis (85 kt)**

**500 hPa Jetlet (80 kt)**

**500 hPa jetlet (75 kt)**

**850 hPa**
** ****55 kt jet**

## 500 hPa Main Jet Axis

**500 hPa Main Jet Axis**

**500 hPa 80 kt Jetlet**

**500 hPa (75 kt) jetlet**

**850 hPa jet**

**Wilcox Storms**

## 500

**500**

**700**

**850**

**1000**

**400**

**300**

**250**

**3-6 cm s****-1**

## 1000

**1000**

**850**

**700**

**500**

**400**

**300**

**250**

## 18Z – 01 Mar 2007

**18Z – 01 Mar 2007**

**Differential Moist Advection**

**(1000-850hPa)-(500-700 hPa)**

**3.5-4 g kg****-1**** / 12h**

- Destabilization of the lapse rate

## 18Z – 01 Mar 2007

**18Z – 01 Mar 2007**

**Differential Thermal Advection**

**(1000-850hPa)-(500-700 hPa)**

**8-10 C / 12h**

**This term became dominant over Enterprise, AL, 1h later**

- Destabilization of the lapse rate

## Basic Characteristics of Parent Mesocyclone

- At 1636Z, the storm began as a cell merger over Wayne County in southeastern Mississippi.  The southern most updraft became dominant.
- A long-lived mesoscyclone with several significant pulses on the storm SE flank. The first pulse was strong and did not produce a tornado. The second pulse was strong and produced an EF-4 tornado. Each updraft pulse exhibited a BWER with a marked increase in rotation intensity
- Viewed from 63-84 n mi range using both KMOB and KBMX WSR-88D
- Vr Shear was not very helpful because we were not very close to the ground. For long range mesocyclones, ***V***rot is really preferred as a diagnostic tool because of velocity averaging in the sample volume. Of course, one also has to place heavy weight on _***REFLECTIVITY***_ Characteristics.

## Slide 25

## Slide 26

## The Operator-Defined Mesocyclone

**KBMX 0.5 deg Z – 1821 UTC**

**KBMX 0.5 deg SRM – 1821 UTC**

## Determining Rotational Velocity and Assigning Intensity to Operator-Defined Mesocyclones

***V***rot = [abs(***V******i***n) + abs(***V***out)] / 2

**Determining Rotational Velocity and Assigning Intensity to Operator-Defined Mesocyclones**

**Step 1** – determine Vrot

- Where:

- Also:
- measure mesocyclone diameter

## Determining Rotational Velocity and Assigning Intensity to Operator-Defined Mesocyclones

**Determining Rotational Velocity and Assigning Intensity to Operator-Defined Mesocyclones**

**Step 2** – determine range (n mi)

## Step 3) ->

***Use appropriate nomogram***

## Weak

- MOD

-  Strong

## Slide 32

## Other Observations of the Parent Mesocyclone

- Timelines do not reflect the use of KBMX 8-bit velocity information. As it turned out, KBMX Level-II data showed (as viewed from *GR2 Analyst Version*) that the 1813, 1821, 1830, 1834 and 1828 UTC volume scans all exhibited velocity data dropout.
- Upon computing the mesoscyclone observed motion vector from 1817-1843 UTC, I found that each 5 min volume scan was a constant 42 kt except for an observed 34 kt in the 1821-1826 interval (i.e., the time interval when an EF-4 tornado was forming).
- Of course the aspect ratio tells us we can merely only observe the mesocyclone (much larger than the length scale of a tornado). You will note in the 1826Z volume scan that the mesocyclone is well to the NW of Sand Island-Millers Ferry where the tornado first formed (see Velocity animation).

## Summary

- Confirmed by multiple hand upper air and surface analyses, this event occurred in the surface warm sector and **well downstream **of the main mid- and upper air trough (and assoc/dynamics) and the surface cold front.
- Being located within a mid-tropospheric divergent zone and just downstream from the nose of a 27 m/s lower tropospheric jet streak (where 0-2 km Sr Helicity values were maximized) kinematics worked in concert to enhance mesoscale lift in vicinity of the relatively shallow-sloped low-level frontal circulation.
- It is surmised that via the kinematics of the wind field, differential thermal and moisture advections in the 700-500 and 1000-850 hPa layers acted to further destabilize the local lapse rate where the tornado developed (see below).
- When time is afforded, would like to examine with higher resolution mesoscale model.

##  Questions?

- Tornado Direction (looking NE)

- Missing and de-barked
- mainly pines; some hardwoods

- Single family homes wiped clean to slab

**Tornado Statistics**:
**EF Scale Rating – EF4**
**  ****(FR12-DOD-10) – 185 mph**
**Path Length =15.6 mi**
**Width = 500 yd**
**Other –**
**- 40 homes destroyed**
**- debris two miles**
**  ****downstream**

** ****Questions?**