Identification

Title

The merger of a supercell and squall line in the Great Plains. 1: Initiation of the supercell

Abstract

Using a four‐dimensional variational data assimilation system that incorporates radar and surface observations, we investigated the initiation mechanism of a nocturnal supercell in the central Great Plains on 23 May 2020. This pristine convection occurred ahead of an eastward‐propagating squall line, despite the absence of discernible surface convergence, and later evolved into a supercell that eventually merged with the approaching squall line. The atmospheric environment, which featured a low‐level inversion layer with considerable convective inhibition, was generally unfavorable for surface‐based convective initiation (CI). However, our analysis indicated that the spatial heterogeneous nocturnal southerly low‐level jet (LLJ) played a key role in the elevated CI. As the LLJ advected moisture and warm air, neighboring regions experienced substantial low‐level destabilization. Multiple convergence bands associated with the heterogeneous LLJ were identified, and the timing and location of CI were governed by these bands. CI occurred when one of the convergence bands moved northward to a position beneath a divergence band at the entrance of the mid‐tropospheric jet. This overlapping pattern of convergence‐divergence persisted for over an hour, facilitating both the initiation and development of the supercell. Additionally, we observed two other episodes of CI ahead of the squall line, each with different characteristics. The first, occurring earlier than the supercell initiation, was triggered by topographic convergence in a valley but quickly dissipated. Later, as the LLJ rotated clockwise, the most prominent convergence band shifted eastward, favoring the continuous development of forward‐building cells ahead of the squall line, resulting in a T‐shaped system.

Resource type

document

Resource locator

Unique resource identifier

code

https://n2t.net/ark:/85065/d7q244pg

codeSpace

Dataset language

eng

Spatial reference system

code identifying the spatial reference system

Classification of spatial data and services

Topic category

geoscientificInformation

Keywords

Keyword set

keyword value

Text

originating controlled vocabulary

title

Resource Type

reference date

date type

publication

effective date

2016-01-01T00:00:00Z

Geographic location

West bounding longitude

East bounding longitude

North bounding latitude

South bounding latitude

Temporal reference

Temporal extent

Begin position

End position

Dataset reference date

date type

publication

effective date

2025-07-16T00:00:00Z

Frequency of update

Quality and validity

Lineage

Conformity

Data format

name of format

version of format

Constraints related to access and use

Constraint set

Use constraints

Limitations on public access

None

Responsible organisations

Responsible party

contact position

OpenSky Support

organisation name

UCAR/NCAR - Library

full postal address

PO Box 3000

Boulder

80307-3000

email address

opensky@ucar.edu

web address

http://opensky.ucar.edu/

name: homepage

responsible party role

pointOfContact

Metadata on metadata

Metadata point of contact