Mesoscale Discussion
Valid: Thu 13 Jun 2019 13:00 to Thu 13 Jun 2019 22:00 UTC
Issued: Thu 13 Jun 2019 13:10
Forecaster: TASZAREK

This long-term mesoscale discussion is issued to highlight enhanced risk for supercell thunderstorms capable of producing very large hail and in lesser extent tornadoes. A rapid storm clustering into mesoscale convective system in the late afternoon and evening hours will also create a threat for damaging wind gusts and heavy convective rainfall.

DISCUSSION

Multicell storms in the norther Poland move away into Baltic states and enable clearing sky in the corridor from Czech/Slovakia/Poland border up to north-eastern Poland. A 13UTC surface observations indicate temperature of 32°C and dew points in the range of 16-19°C. This provide a rather high LCLs over 1200-1400m AGL. As expected in the convective outlook, ahead of the cold front, diurnal heating and rich boundary layer's moisture (0-500m mixing rations 12-14 g/kg) build-up ML CAPE in the warm sector up to 1500-2000 J/kg, which is confirmed in the recent atmospheric sounding from Legionowo. A Legionowo sounding displays also a very good low-level temperature gradient and pockets of dry mid-levels which enhances a potential for downbursts capable of producing damaging winds.

A convergence line is currently shaping in the axis from south-central Poland to north-east Poland. According to most of the NWP models convective initiation is expected in the next 1-3 hours in the southern part of this area. A slowly breaking cap and not prominent synoptic-scale lift should allow a discreet mode at the early stages. Isolated updrafts developing in the environmental wind shear of 16-18 m/s and veering wind profile (~ 150-250 m2/s2 SRH) should evolve into mesocyclones capable of producing locally large and very large hail. Tornadoes cannot be ruled out within these storms (especially towards evening hours when LCLs will drop) but limited wind shear (especially low-level) will decrease conditional probability for their occurrence.

Later, a rapid clustering into multicells is expected. These storms will have a main potential of heavy rain, but along with increasing wind shear towards evening hours, severe wind gusts within linear and bowing segments are likely. Storms will move into NNE direction. A large MCS is expected in the evening hours which later will move to Baltic states.