Storm Forecast
Valid: Tue 12 Jul 2011 06:00 to Wed 13 Jul 2011 06:00 UTC
Issued: Mon 11 Jul 2011 19:57
Forecaster: KOROSEC

A level 2 was issued for E Iberia into SE France mainly for very large hail, strong wind gusts, intense rainfall and a few tornadoes.

A level 1 was issued for surrounding areas across Iberia and S France mainly for large hail and strong winds.

A level 1 was issued for E Finland and parts of NW Russia mainly for an isolated marginally large hail or strong wind event.

SYNOPSIS

A complex pattern across Europe on Tuesday. A progressive trough enters western-southwestern Europe while another trough affects Scandinavia. Another round of active severe storms is expected over highlighted areas with a few significant events possible locally.

DISCUSSION

... E Iberian peninsula into SE France ...

A progressive mid-level trough will be a focus for quite robust activity across the eastern Iberia towards SE France today. Strong mid-level jet around the base of the trough will provide strongly sheared environment, 25-30m/s of deep layer shear will become available. At surface, an elongated SFC depression results in moistening and deepenening BL with rather strong WAA from the W Mediterranean sea. Models are in good agreement of high LL mixing ratio values beneath a healthy EML aloft, resulting in high instability once the strong diurnal heating takes place. Both ECMWF and GFS are showing MLCAPE up to near 2000 J/kg along the eastern Iberia. Once strong SFC heating overcomes the capping, storms will initiate near the complex terrain of coastal E Spain as well as over the Ebro valley and around Pyrenees. QG forcing and favorable conditions will support rapid storms organization into multicells and supercells. Intense rain, severe winds and large to very large hail can be expected with the most intense cells. Persisting easterly LL flow will maintain moderate/high SREH in excess of 200 m^2/s^2 as well, so intense supercells with threat of a few tornadoes could occur. Given the robust conditions coming together, a couple of significant severe weather events are possible.

Later towards the evening, storms will merge into one or two large systems, moving NE into SE France in the evening hours. However, GFS rather quickly vanishes instability in the evening, while ECMWF maintains moderate CAPE well into the night hours. But with improving LL wind/moisture field at the same time, its likely that activity will continue well into the night hours. Large hail and damaging winds will remain the primary threats, while even a tornado cannot be ruled out with such high shear/SREH in place.

... CNTRL France into W Germany ...

Another focus for rather robust severe storms exists along the slowly N-wards advecting warm front, extending from a SFC low in W-CNTRL France into W Germany. Placed under a strong mid-level jet, rich BL moisture results in moderate instability in the afternoon hours. GFS model is indeed again overestimating BL dewpoints and instability (Tds near 22-23°C / SBCAPE 3000 J/kg or more) while ECMWF seems more reasonable with around 1000 J/kg MLCAPE / 16-18°C SFC dewpoints. Backed flow near the warm front provides sufficient LL shear/SREH to support rotating updrafts. Storms initiation is mostly expected along the frontal convergence in mid/late afternoon hours. Favorable dynamics and kinematics should result in scattered multi and supercellular storms with threat for very large hail and damaging winds. Tornadoes could be possible as well, but this threat seems a bit limited with rather high dewpoint depression and meager wind field. Though, it improves in the evening when LLJ slightly intensifies. Storms should cluster into large MCS towards the evening, trailing NE-wards from NE France into NW Germany. A broken line with bowing segments could bring severe wind gusts and large hail.

However, conditions will be closely monitored for a possible upgrade into level 2 over these areas, especially if moisture field improves significantly on the morning SFC observations.

... E Finland into parts of NW Russia ...

Ahead of a frontal system, warm airmass advects across the level 1 area. However, poor BL moisture results in only weak instability, coupled with deep layer shear near 15-20 m/s. With good forcing in place, storms are expected to form mostly along the E-wards progressing cold front. Threat for an isolated marginal hail/strong wind will exist.

... Alpine region, SE Balkans, CNTRL Italy ...

Diurnal driven convective activity is expected over these areas, where scattered showers and thunderstorms will form along the convergence zones in the hilly/mountainous terrain. Only weak shear and moderate MLCAPE poses a threat for marginal hail and some strong wind gusts, but no organized severe storms are expected.

A level 1 was placed over the western Alpine region and parts of NW Italy where considerable confidence exists for a few isolated intense storms to take place. With quite high instability and moderately sheared environment, those could pose a threat for large hail and severe wind gusts locally.