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Severe Weather Outlook – Aug 23rd, 2020

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: 23/08/2020 06 UTC – 24/08/2020 06 UTC
Issued by: Severe Weather Europe
Forecaster: Marko Korošec
 

SUMMARY

 
Severe storms with large hail and severe winds are likely to form along the cold front across the Baltic region into Finland, over the Alps and northern Italy on Sunday.
 

Overview of the risk areas across Europe

 
weather forecast
 

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

 

SYNOPTIC OVERVIEW

 
A large upper-level trough is entering northern Europe, while an associated surface cold front continues further east. It is extending from northwestern Russia across eastern Europe into the northern Balkans and Mediterranean. The upper ridge ahead of the trough is gradually weakening, but a new one is shaping up over southwestern Europe.

FORECAST DISCUSSION

 

+++ Switzerland, Italy, Austria and Slovenia +++

 
weather forecast area 1
 

SLGT risk has been issued for southern Switzerland, northern Italy into southern Austria and northwestern Slovenia with a threat for severe storms, capable of producing large hail, severe winds, and torrential rainfall.

Storms are expected to initiate in the moderately sheared and unstable environment over northern Italy and the Alps, gradually spreading towards the east-northeast. Mainly isolated storms are expected. The strongest storms could bring large hail, torrential rainfall, and severe winds.

The activity should gradually decay in the evening hours.

MRGL risk has been issued for areas surrounding the SLGT risk area over the Alpine region, north-central Italy, and across eastern Austria into Slovakia with only isolated severe storms possible. Still, some large hail and severe winds will be possible.

 

+++ Belarus, Lithuania, Latvia, Estonia, Finland into Lapland +++

 
weather forecast area 2
 

SLGT/MRGL risks have been issued for part of eastern Poland, northern Belarus, eastern Lithuania, and Latvia, Estonia into most of Finland and northeastern Sweden into northern Norway with a threat for isolated severe storms, capable of producing severe winds, marginal hail, and heavy rainfall.

Related to the large long-wave trough over northern Europe, isolated to scattered storms are likely to for during the daytime. Moderate shear but limiting instability could support a few strong multicells and also a few supercells. Marginal hail can occur, but mainly severe wind threat and heavy rain is expected with the strongest cells.

+++ other areas +++

 

MRGL risk has been issued for Georgia and surroundings, eastern Spain, and northern Algeria with isolated severe storms possible. Marginally large hail and severe winds will be possible.

TSTM risks have been issued for southern Sweden, Denmark, and the Balkans with a threat for daytime driven storms. Limited shear is present, so the storms 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.)

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