An outbreak of severe storms seems likely across SE Germany, Czechia, N Austria, N Slovakia and S Poland this afternoon and evening hours as cold front moves through. Extreme instability with good overlap of moderate to strong shear should support both discrete supercells and bowing segments with very large hail and destructive wind threat.

Strong to extreme instability will be present ahead of the front, supportive of the explosive development of storms by mid-afternoon hours. Locally more than 2500 J/kg of MLCAPE will be present and therefore very large hail will be possible with most organized supercell storms. ARW model is quite aggressive will a large area of 3000-4000 J/kg of MLCAPE across SE Germany and Czechia.

Surface winds will generally be from SSW ahead of the frontal boundary, resulting in a relatively straight hodograph with relatively little vertical veering, supportive of splitting storms. However, better wind profiles with backing SSE surface winds and enhanced SREH over Czechia should also contribute to the potential for discrete supercells. These will be able to take advantage of dry mid-levels and strong to locally extreme instability and produce large to very large hail! A potential limiting factor for very large hail potential may be high PWAT values, in the 35 mm range, favouring high-precipitation storm mode.

Additionally, dry mid-levels will support locally severe wet downbursts. High PWAT values and high-precipitation storm mode will combine with relatively moderate storm motion of about 25 kt (during the initial phase with discrete supercells) for enhanced threat for torrential rainfall and local flooding.

Here are simulated radar reflectivity maps by ARW model, indication storms initiating along the N Alpine flank and SSE Germany, spreading and organizing into the Czechia during the late afternoon. The clustering of the storms with bowing segments is likely.

See Severe Weather Outlook for today:

Outlook DAY 1 (valid: 01/07/2019)