Mesoscale Discussion

Mesoscale Discussion
Valid: Thu 31 Jul 2014 15:00 to Thu 31 Jul 2014 18:00 UTC
Issued: Thu 31 Jul 2014 13:20
Forecaster: BEYER

A tongue of humid BL air (mixing ratio around 12 g/kg) stretches all the way from central Poland and the Baltic states to Finland. In the northern part of this area the resulting CAPE values of about 1000 J/kg can overlap with 15 to 20 m/s of deep layer shear. This has already resulted in the formation of a squall line which shows a bowing segment over southern Finland. A short wave trough moving to the northeast leads to strong lift mechanism, especially due to an upper level jet whose right entrance region moves right over southern Finland.

Surface observations already show the formation of a mesolow / mesohigh couplet and a wind shift line embedded in the mesolow. Surface winds are from the southeast downstream while they shift to the southwest behind the squalline. In addition an impressive coldpool is visible by surface temperature measurements. Due to diurnal heating temperature downstream of the squall line shows values of around 30 degree, while they fall to 17 degree behind the line. This temperature difference supports the strength of the squall line and shows the potential for severe wind gusts with the cold-pool pushing from behind in form of a low level jet

Current thinking is that the bowing line will further propagate to the northeast for the next hours having the risk for severe wind gusts which is also supported by a mid-level jet (850 hPa). When the cold pool holds its strength and the bowing of the line is preserved even damaging winds are possible. In addition excessive precipitation events are possible given ppws of up to 40 mm. Furthermore, DLS and CAPE values also point to a threat for large hail. Finally, having high values of LLS (>10 m/s) and enhanced values of SRH, a tornado cannot be ruled out.

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