# Presentation: 291608

## OBSERVATIONS OF THE INTERACTION BETWEEN A   SUPERCELL AND A MESOSCALE BOUNDARY

- OBSERVATIONS OF THE INTERACTION BETWEEN A   SUPERCELL AND A MESOSCALE BOUNDARY

*Mark Conder, Steve Cobb and Gary Skwira**	**-   WFO LUBBOCK*

- A study that compares 5-minute surface data from the West Texas Mesonet to the evolution of the storm as depicted by the Lubbock WSR-88D

- 0.5

- 1.5

- 2.4

- 3.4

## 500 hPa

-      @ 500 hPa, CAA and PVA greatest across the northern TX Panhandle
-      @ 850 HPa, deep, rich moist tongue across West-central TX
-          Modest SW wind with WAA – θe advection

- 850 hPa

- Objectively analyzed constant pressure maps for 5 October 2003 12 GMT

## 250 hPa

- RUC model isotach and streamline analysis for 5 October 2003 12 GMT.

- 500 hPa

-      @ 250 hPa, ~60 kt jetmax over NE New Mexico – southern Panhandle in          RR quadrant by afternoon
-      @ 500 HPa, fairly constant 20-30 kt core oriented NW-SE across region of         storm initiation

## Surface to 250 hPa sounding from the West Texas Mesonet Reese Center site for 5 October 2003 20 GMT (position shown by the white star on the visible satellite image.  The sounding has been modified with surface observations taken from mesonet sites west (red) and east (blue) of the outflow boundary.  

- Surface to 250 hPa sounding from the West Texas Mesonet Reese Center site for 5 October 2003 20 GMT (position shown by the white star on the visible satellite image.  The sounding has been modified with surface observations taken from mesonet sites west (red) and east (blue) of the outflow boundary.

## West of outflow boundary

- Hodographs of the wind profile for 5 October 2003 20 GMT.  The hodographs have been modified with surface observations taken from mesonet sites west and east of the outflow boundary.  The fifth point roughly corresponds to one kilometer AGL.

- East of outflow boundary

##  Reese Center sounding derived parameters

-  Reese Center sounding derived parameters

| Parameter | West | East |
| --- | --- | --- |
| LCL | 1364 m | 611 m |
| LFC | 1878 m | 1964 m |
| s-rH* 0-1 km | 46 m2 s-2 | 200 m2 s-2 |
| s-rH* 0-2 km | 67 m2 s-2 | 219 m2 s-2 |
| s-rH* 0-3 km | 92 m2 s-2 | 245 m2 s-2 |
| Total CAPE | 1551 J kg-1 | 1319 J kg-1 |
| Vorticity generation potential (VGP) 0-4 km | .273 m s-2 | .365 m s-2 |
| BRN shear | 7.4 m s-1 | 10.2 m s-1 |
| CIN | -25 J kg-1 | -79 J kg-1 |

- * Using a storm motion vector of 320/18 kts (Bunkers method)

- 0-6 km mean wind: 277o @ 20 kts

## 500 hPa storm relative flow

- RUC Forecast
- Mid-level storm-relative winds of 7- 10 ms-1 mark transition from non-tornadic to tornadic (Thompson, 1998)
- Davies used ETA forecast of 8 ms-1 as a threshold.
-  RUC shows about 9-10 ms-1 for a right-moving supercell – may be over done

**500 hPa storm relative flow**

## Timeline of storm reports on 5-6 October 2003

**Timeline of storm reports on 5-6 October 2003**

- Swisher Co. (9SE Tulia to 8E Kress)	2305-2320Z	Tornado (F1)
- Swisher Co. (6SE Tulia)			2310Z		Hail (2.75 inch)
- Swisher Co. (10ESE Kress)		2334-2335Z	Tornado (F0)
- Floyd Co. (3NW Lockney)			0005Z		Hail (0.88)
- Swisher Co. (5E Tulia)			0020Z		Hail (1.75)
- Large hail reports associated with this storm continued through 0120Z, with no additional tornado reports.
- Additionally, large hail (0.88 to 1.75 inch) was reported with other thunderstorm activity located southwest of storm of interest, as well as with new development immediately west-northwest.

## Visible satellite imagery for 5 October 2003 2001 GMT

- Cold front located across the Permian Basin into central TX – nearly stationary
- Blue line represents an outflow boundary slowly moving west. Low clouds and stable air behind boundary
- Brown and yellow lines are weak dryline and Pacific front
- The location of the Reese Center West Texas Mesonet site is highlighted by a white star.

## Graph of the rotational velocity associated with the mesocyclone for the 3 lowest elevation angles of the Lubbock WSR-88D.	 

## SUMMARY AND DISCUSSION

**SUMMARY AND DISCUSSION**

-   How to explain tornado development in high CIN (79 J/Kg) / marginally high LFC      (~2000 m) environment?
-   Although there was large 0-1 km SRH, stretching of low-level vorticity becomes      disconnected from region of ascent thus reducing chances of tornado       development (Davies, 2004)
-   1. Virtual temperature calculation (Doswell and Rasmussen, 1994)      The general effect raises CAPE, lowers CIN and LFC height on profiles that       have a deep moist layer (Davies, 2004)
-   2. Davies suggests that strong vertical shear may overcome large CIN by      inducing strong vertical pressure gradients that enhance upward accelerations
-   Another mechanism might be an *ADVANCING* warm front, with strong low-level      WAA into region near/below the cap - Questionable in this case
-   Best guess: Combination of all three factors mentioned above proved sufficient to      produce the F1 tornado in this case. Negative factors most likely contributed to       the short life span of the tornado

## SUMMARY AND DISCUSSION CONTINUED

**SUMMARY AND DISCUSSION CONTINUED**

-    West Texas Mesonet observations provided great utility in diagnosing      boundary motion and surface thermodynamic and kinematic fields in      vicinity of the boundary
-   The outflow boundary caused changes in the storm environment that      altered the storm type. The WTXM obs may allow the forecaster to      anticipate these changes
-   The WTXM Sounding provided similar utility in helping the forecaster      assess the vertical profile of the storm environment
-   Subjective analysis of 5-min observations the duty of mesoscale      analyst?