Severe weather outlook – forecast across Europe. This forecast features areas of organized severe weather with risk levels and severe weather threats across the European continent.

SEVERE WEATHER OUTLOOK – DAY 1

 
Valid: 05/08/2020 06 UTC – 06/08/2020 06 UTC
Issued by: Severe Weather Europe
Forecaster: Marko Korošec
 

SUMMARY

 
Scattered to widespread severe storms including supercells with a threat for severe winds, tornadoes, large hail, and torrential rainfall with flash floods are expected from the Ionian Sea into Greece and the rest of southern Balkans on Wednesday.
 

Overview of the risk areas across Europe

 
weather forecast

Explanations for abbreviations (TSTM, SLGT, ENH, etc.)
 

SYNOPTIC OVERVIEW

 
An upper low over the central Mediterranean is gradually weakening while drifting southeast towards south Italy. A very large and deep trough is establishing across the North Atlantic, centered near Iceland. In between these features, upper-level ridging is strengthening across the southwestern, central, and eastern Europe. At the surface, a frontal system associated with the upper low pushes into southern Balkans.

FORECAST DISCUSSION

 

+++ Italy, Serbia, Albania, Romania, Bulgaria, North Macedonia, Greece +++

 

weather forecast
 

MDT risk has been issued for extreme south Italy, the western half of Greece, south-central Albania, and western North Macedonia with a threat for robust severe storms, capable of producing severe winds, tornadoes, large hail, and torrential/excessive rainfall with flash floods.

ENH/SLGT risks have been issued for areas surrounding the MDT risk area including south-central Italy, Bosnia and Herzegovina, Serbia, and Romania Hungary with a threat for severe winds, large hail, and torrential rainfall.

Scattered to widespread organized severe storms are expected to continue along with the southeastward drifting frontal system from south-central Italy into the southern Balkans. 

A strongly unstable air mass is spread across the Ionian Sea and western Greece, with more than 2500 J/kg of MLCAPE locally, decaying inland into central Balkans. A moderate deep-layer shear of around 35-40 knots is overlapped with the instability. 

Supercell storms are again likely to develop with the main threats as torrential rainfall with flash floods, large hail, and severe winds. Flash floods threat will be most pronounced especially along with the higher topography of western Greece. Training cells are possible as well, introducing high amounts of rainfall in short periof of time locally.

Again, a rather strong southeasterly low-level flow across the Ionian Sea should enhance the tornadic threat, given the quite strong helicity and low-level shear along the coast of western Greece and towards southwestern Albania.

Scattered organized storms are also expected further north across south-central Balkans but should be less severe due to lower instability and shear. More storms are also expected across southern Italy closer to the upper low. Waterspouts are likely to develop over the southern Adriatic sea.

Storms will also merge into clusters during the afternoon and evening hours across the southern Balkan peninsula, moving southeast with the main front.

+++ other areas +++

 

TSTM risk areas have been placed across Lapland, east Turkey into Georgia and across southern Ireland where some storms are likely to occur but should remain sub-severe.

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Understanding Severe Weather Outlook

 

Severe Weather Outlook features areas of organized severe weather with risk levels and severe weather threats. Risk levels are divided into seven categories:

TSTM – Thunderstorms
MRGL – Marginal risk
SLGT – Slight risk
ENH – Enhanced risk
MDT – Moderate risk
HIGH – High risk
SIG – Significant risk
WNTR – Winter risk

Risk categories stand for the coverage and intensity of organized severe weather. Those could include supercells, squall lines, mesoscale convective systems, wind storms, flooding, snowstorms, or ice storms.

Severe weather threats include:
  • large hail (of at least 2 cm in diameter)
  • Tornadoes (including waterspouts)
  • Wind gusts (convective or non-convective) above 25 m/s (or above 90 km/h)
  • Torrential convective precipitation / Flash floods
  • Excessive rainfall (100 mm within 12 hours) / snowfall (50 cm within 12 hours)
Extremely severe weather threats include:
  • Large hail (of at least 5 cm in diameter)
  • Tornadoes of F2 intensity or stronger
  • Wind gusts (convective or non-convective) above 33 m/s (or above 119 km/h) or 12 Bft
  • Torrential convective precipitation / Flash floods
  • Excessive rainfall (150 mm within 12 hours or above ) / snowfall (above 100 cm within 24 hours)

Categories in the forecast represent the chance of severe weather occurring within a 40 km radius from a location. The used level is based on the conversion table of probabilistic risk into the outlook categories. A threat level is upgraded into a higher category if probabilities meet the threshold criteria for the specific threat (e.g. tornado, wind, hail, or rainfall threat).

Each individual threat area includes a detailed forecast map and discussion on the potential of severe weather threats.

Read more: Explanations for abbreviations (TSTM, SLGT, ENH, etc.)