Storm Forecast
Valid: Mon 09 Jun 2014 06:00 to Tue 10 Jun 2014 06:00 UTC
Issued: Sun 08 Jun 2014 22:31
Forecaster: PUCIK
A level 3 was issued for NW France and BENELUX for very large hail, damaging wind gusts, tornadoes and excessive precipitation.
SYNOPSIS
In between of the deep low over the Atlantic and the ridge over Central Europe, strong southerly to southwesterly flow will advect hot airmass characterised by steep mid-level lapse rates from N Africa towards France, Germany and then around the ridge towards Poland. Potentially dangerous situation will evolve over France, BENELUX and NW Germany just ahead of the diffuse, wavy frontal boundary that will remain quasistationary close to French coastline during the most of the day. Another low will slowly dig SE-wards across NW Russia. Moderate to strong NW-ly flow is simulated at its southwestern flank. With prevailing low geopotentials over much of Eastern Europe, so scattered DMC is expected also there, albeit severe threat will be smaller than in case of France / BENELUX.
DISCUSSION
... France towards BENELUX and NW Germany ...
Very dangerous setup will develop over the region by the late afternoon hours. With pronounced overlap of low-level moisture and steep mid-tropospheric lapse rates, models agree on the development of high to extreme CAPE values, with Central France towards BENELUX and NW Germany having the highest odds of seeing 3000 J/kg of MLCAPE by the late evening. As 500 hPa winds between 15 to 25 m/s overlap with backed low-level flow thanks to the presence of the surface trough, strong DLS (20-25 m/s) is forecast. By the late evening, with the enhancement of the low-level wind field with deepening trough, SREH values will increase especially over NW France / BENELUX (with values over 300 m2/s2 possible). Such setup will be very conducive for intense supercells / bow-echoes, capable of very large hail and damaging wind gusts. Towards the evening (beyond 18 UTC), as LLS strengthens, tornadoes will become a threat as well, especially if isolated supercells manage to persist into this time frame.
However, models do not simulate any pronounced QG forcing to rapidly reduce CIN. This will, on one hand, allow for CAPE to build-up steadily towards the late afternoon. On the other hand, it is highly questionable how many storms will initiate and where exactly. There is considerable disagreement by individual models. Overnight / morning convection, along with the outflow boundaries laid by these may be crucial in this setup. Current thinking is, that the foci for late afternoon initiation will be NW France, along the surface convergence zone, with storms spreading into BENELUX. It is likely that these storms will be isolated supercells at first, with subsequent clustering resulting in a fast forward propagating bow-echo. Towards the night, Southern to Central France may see convective initiation, with another possiblity of MCS travelling north towards N France.
Level 3 was introduced for the region, where the highest probability of high storm coverage is forecast and where high density of extremely severe events is most likely. With that in mind, any spot in the Level 2 may see extremely severe storms in these highly favourable conditions, provided storms can initiate.
Valid: Mon 09 Jun 2014 06:00 to Tue 10 Jun 2014 06:00 UTC
Issued: Sun 08 Jun 2014 22:31
Forecaster: PUCIK
A level 3 was issued for NW France and BENELUX for very large hail, damaging wind gusts, tornadoes and excessive precipitation.
SYNOPSIS
In between of the deep low over the Atlantic and the ridge over Central Europe, strong southerly to southwesterly flow will advect hot airmass characterised by steep mid-level lapse rates from N Africa towards France, Germany and then around the ridge towards Poland. Potentially dangerous situation will evolve over France, BENELUX and NW Germany just ahead of the diffuse, wavy frontal boundary that will remain quasistationary close to French coastline during the most of the day. Another low will slowly dig SE-wards across NW Russia. Moderate to strong NW-ly flow is simulated at its southwestern flank. With prevailing low geopotentials over much of Eastern Europe, so scattered DMC is expected also there, albeit severe threat will be smaller than in case of France / BENELUX.
DISCUSSION
... France towards BENELUX and NW Germany ...
Very dangerous setup will develop over the region by the late afternoon hours. With pronounced overlap of low-level moisture and steep mid-tropospheric lapse rates, models agree on the development of high to extreme CAPE values, with Central France towards BENELUX and NW Germany having the highest odds of seeing 3000 J/kg of MLCAPE by the late evening. As 500 hPa winds between 15 to 25 m/s overlap with backed low-level flow thanks to the presence of the surface trough, strong DLS (20-25 m/s) is forecast. By the late evening, with the enhancement of the low-level wind field with deepening trough, SREH values will increase especially over NW France / BENELUX (with values over 300 m2/s2 possible). Such setup will be very conducive for intense supercells / bow-echoes, capable of very large hail and damaging wind gusts. Towards the evening (beyond 18 UTC), as LLS strengthens, tornadoes will become a threat as well, especially if isolated supercells manage to persist into this time frame.
However, models do not simulate any pronounced QG forcing to rapidly reduce CIN. This will, on one hand, allow for CAPE to build-up steadily towards the late afternoon. On the other hand, it is highly questionable how many storms will initiate and where exactly. There is considerable disagreement by individual models. Overnight / morning convection, along with the outflow boundaries laid by these may be crucial in this setup. Current thinking is, that the foci for late afternoon initiation will be NW France, along the surface convergence zone, with storms spreading into BENELUX. It is likely that these storms will be isolated supercells at first, with subsequent clustering resulting in a fast forward propagating bow-echo. Towards the night, Southern to Central France may see convective initiation, with another possiblity of MCS travelling north towards N France.
Level 3 was introduced for the region, where the highest probability of high storm coverage is forecast and where high density of extremely severe events is most likely. With that in mind, any spot in the Level 2 may see extremely severe storms in these highly favourable conditions, provided storms can initiate.
