Storm Forecast
Valid: Wed 16 Jul 2025 06:00 to Thu 17 Jul 2025 06:00 UTC
Issued: Tue 15 Jul 2025 23:51
Forecaster: PISTOTNIK

A level 2 and level 1 are issued for S Norway, S Sweden and N Poland for excessive convective precipitation.

A level 2 and level 1 are issued for the Baltic States, parts of Belarus and parts of Russia mainly for excessive convective precipitation and to a lesser degree for large hail and severe convective wind gusts.

A level 2 and level 1 are issued for parts of Germany, the Czech Republic and Austria mainly for severe convective wind gusts and to a lesser degree for tornadoes and excessive convective precipitation.

A level 1 is issued for NE Italy for large hail.

A level 1 is issued for parts of the Ukraine, parts of Romania and Moldova for large hail, severe convective wind gusts and excessivew convective precipitation.

A level 2 and level 1 are issued for parts of Turkiye for large hail, severe convective wind gusts and excessivew convective precipitation.

A level 1 is issued for parts of Georgia for large hail, severe convective wind gusts and excessivew convective precipitation.

SYNOPSIS

South of a blocking anticyclone over the Norwegian Sea, a potent mid-level low slips SE-ward from the southern North Sea (Wed 06 UTC) to Slovakia (Thu 06 UTC). A strong mid-level jet streak with maxima up to 35 m/s at 500 hPa stretches from Ireland to the Alpine region before it fans out further east.
Closer to the surface, an initial diffuse frontal zone consolidates into a frontal wave that moves from Germany to Poland while it quickly matures. Its cold front crosses the greater Alpine region until evening and invades the Balkans overnight, bringing in a cool maritime airmass.
Meanwhile, the extreme heatwave continues under a subtropic mid-level ridge over Iberia, while it is slightly eased by Mistral and Meltemi winds in the Mediterranean Basin, and over Turkiye by a weak mid-level trough that increases thunderstorm activity. Unseasonably warm conditions also continue over central Scandinavia in the range of the blocking high.

DISCUSSION

... S Scandinavia, N and E Poland, Baltic States, Belarus into W Russia ...

Plentiful low-level moisture and converging winds create CAPE on the order of a few hundred J/kg near the center of the mid-level low in Denmark and Poland, and up to 1000 J/kg and locally beyond at its forward flank in S Norway, S Sweden, the Baltic States and adjacent Russia. Deep-layer shear is mostly below 10 m/s. Scattered to widespread, largely daytime-driven thunderstorms will again initiate at numerous sources of meso- to small-scale lift: the remnants of the stationary frontal boundary from S Norway to Belarus separating cooler maritime air to the SW from warmer continental air to the NE, outflow boundaries, sea breeze fronts in coastal areas, and some travelling mid-level vorticity maxima (albeit less than on Tuesday). Thanks to weak vertical wind shear, slow storm motion and a regionally high storm coverage, excessive rain is the main hazard. Stronger pulse storms can also produce isolated large hail and severe downbursts, mainly in the warmer air towards the NE, though modest mid-level lapse rates and weak vertical wind shear keep these hazards on the lower side.
Similar to Tueday, a broad level 1 encompasses the region where at least isolated severe weather (namely excessive rain) may occur. However, model agreement and confidence are higher to upgrade a few confined areas to a level 2:
(+) S Sweden: persistent upgliding of warm and moist air from the NE with CAPE around or above 1000 J/kg onto the stationary frontal boundary can create multiple rounds of thunderstorms. High-resolution models show precipitation peaks around or above 50 mm.
(+) N Poland: despite limited CAPE, persistent convergence near the surface cyclone's center and a "lake effect" situation can also boost precipitation totals into the 50-100 mm range on a local scale.
(+) Estonia and Latvia: While convergence signals are weaker, the mere CAPE magnitude in excess of 1000 J/kg raises the probabilities for stronger pulse storms.

A few non-mesocyclonic, weak and short-lived tornadoes could spin up at pronounced convergence zones, also including land breeze fronts propagating offshore in the night and morning.

... Germany, SW Poland, Czech Republic, Austria ...

On the third day in a row, a pronounced short-wave trough crosses this area in the W-erly to NW-erly flow. Both dynamics and kinematics are even more impressive than on Tuesday, when already a swath of severe to extreme wind events (including a few possible tornadoes) stretched from far-southeast Germany into Austria.
Despite limited CAPE that does not exceed 500 J/kg, intense vertical wind shear (20-25 m/s across the 0-6 km layer, 10-20 m/s across the lowest kilometer) and strong forced ascent will likely create another round of low-topped but well-organized storms southwest of a line Hannover - Prague. Current thinking is that initially stratiform rain shields or bands will increasingly break up into thundery showers in the afternoon, when daytime heating and strong lift act hand in hand. Both a solid or broken convective line or some (semi-)discrete multi- or supercells appear possible. At least scattered severe wind gusts are likely, and a few concentrated swaths of severe to extreme gusts are not ruled out. In addition, any discrete storm propagating off the hodograph could produce a tornado that might even become strong, considering the conjunction of extraordinary low-level shear and storm-relative helicity and low cloud bases.
The highest severe weather hazard is anticipated for the 14 to 20 UTC time frame in Lower Bavaria (DE), Plzensky kraj and Jihocesky kraj (CZ) and Upper Austria (AT). Afterwards, boundary layer stabilization and the more flow-parallel orientation of the convective bands in the wake of the departing trough lower the wind-related hazards, but could create locally excessive rain into the first half of the night.
Northeast of the narrow jet streak, i.e., in E Germany and SW Poland, vertical wind shear is much weaker and severe weather is unlikely, though the lift in the jet's left exit region will also create thundery showers.

... NE Italy, Slovenia, N Croatia, Hungary ...

Strong lift of the mentioned short-wave trough will also cross the Alps in the evening and overnight. Stretching and mid-level cold air advection across the Alpine range will create mostly marginal CAPE, overlapping with steadily increasing vertical wind shear. Forecast models show only embedded (and possibly elevated) storms overnight, hence no hazard level is issued despite a kinematic background that would be sufficient for organized storms.
The only exception is NE Italy, where sea breezes and Alpine pumping raise CAPE to values around 1000 J/kg. A few afternoon or evening storms could originate at a dryline near the Alpine rim and produce a few large hail events while descending into the coastal plains. However, also in this region, the arrival of the mid-level trough is not ideally timed to allow more widespread severe storms.

... Romania, Moldova, Ukraine, Turkiye, Georgia ...

Travelling vorticity maxima will facilitate convective initiation in an environment of moderate CAPE and moderate vertical wind shear, primarily over orographic features, but some storms could also propagate into lowlands / coastal areas later on. Scattered large hail, severe wind and excessive rain events warrant a level 1. A confined area in SW Turkey is upgraded to a level 2, where most abundant CAPE in the sea breeze / upvalley flow regime, steep lapse rates aloft and augmented vertical wind shear could allow some at least transient supercells with particularly enhanced severe weather probabilities, including a possibility of very large hail.