Storm Forecast
Valid: Wed 16 Jun 2021 06:00 to Thu 17 Jun 2021 06:00 UTC
Issued: Tue 15 Jun 2021 20:59
Forecaster: PUCIK
A level 1 was issued across NW Spain mainly for excessive rainfall and to the lesser degree for large hail.
A level 1 was issued across N - Central Spain mainly for large hail and severe wind gusts.
A level 1 was issued across S France mainly for large to very large hail and severe wind gusts.
A level 1 was issued across NW and Central France mainly for large hail, severe wind gusts and to the lesser degree for heavy rainfall.
A level 1 was issued for extreme SE UK mainly for heavy rainfall.
A level 1 was issued for Morocco and SE Spain mainly for large hail and severe wind gusts.
A level 1 was issued across S Ukraine, Moldova, E Bulgaria and E Romania mainly for heavy rainfall and to the lesser extent for severe wind gusts.
A level 2 was issued across S Russia mainly for large to very large hail, damaging wind gusts, tornadoes and heavy rainfall.
A level 1 was issued across Central Russia mainly for large hail, severe wind gusts and heavy rainfall.
SYNOPSIS
Main synoptic-scale feature over the forecast domain will be an extensive ridge stretching from Algeria through the Mediterranean into S Sweden. The ridge is forecast to shift slowly eastwards during the day with a trough over the Atlantic moving towards the UK, France and Iberia. A short-wave trough will move from the Atlantic over Morocco. Towards the E, a deep cyclone will reside over the Black Sea and its short-wave will rapidly eject from Turkey towards S Russia. Towards the north, a short-wave embedded in a strong zonal flow will move across central - N Russia.
Closer to the surface, a wavy frontal boundary will stretch from S Scandinavia across the Northern Sea into the UK, extreme W France and W Iberia. Ahead of it, very warm airmass will be advected across BENELUX and Germany. Towards the E, a surface cyclogenesis is forecast across S Russia in the evening to overnight hours and a cold front will cross central Russia.
DISCUSSION
...N Spain to S UK...
As of Wednesday morning, scattered to widespread storms may be ongoing over NW Spain with primary threat of excessive rainfall given the moist profiles and weak mean wind. Towards the central Spain, further initiation is forecast in the late morning to early afternoon hours along the weak frontal boundary or tied to the local orography. Here, 0-6 km bulk shear will allow for well-organised multicells or transient supercells with risks of large hail and severe wind gusts.
By late afternoon / evening hours, initiation is forecast also across S / SW France. Early on, the storms will be surface-based and given the bulk shear around 15 m/s and MLCAPE between 1 and 2 kJ/kg, they will pose a threat of large or very large hail and severe wind gusts. Lack of synoptic-scale lift across the area and also uncertainty concerning the degree of low-level moisture and CIN values prevents issuance of Lvl 2 for the risk of MCS bearing more widespread risk of severe wind gusts. That said, this is a scenario that has been depicted by some of the more aggresive high-res models. Storms will likely spread towards N and NE during the ovenight / early morning hours (possibly in elevated form), but their easternmost extent is also uncertain at the moment.
Initiation is more certain along a warm wave in the frontal boundary developing over NW France, where storms will likely form by 15/18 UTC, congeal into an MCS and trek across the Channel towards SE UK. Across France, the early storms will bear the risk of large hail and severe wind gusts. The severe wind gust risk will be lower over the UK, where the MCS will likely be in a purely elevated form.
... Morocco towards SE Spain ...
Isolated supercells with threat of large hail or severe wind gusts will be possible across SE Spain during the afternoon hours given the strong vertical wind shear with lift provided by local orography. As the short-wave approaches in the evening hours, scattered to widespread storms will form across Morocco and spread towards SE Spain. These storms will likely be elevated, bearing mostly heavy rainfall and large hail risk, though a severe wind gust or two can not be ruled out.
... S Ukraine, Moldova, E Romania, E Bulgaria ...
Widespread storms are forecast to form in a moist environment with low LCLs, suggesting potential for heavy rainfall. Heavy rainfall threat may be reduced to some degree by fast storm motion over Romania or Bulgaria, where mean wind reaches 10 - 15 m/s. With 850 hPa flow between 15 to 20 m/s locally, isolated severe wind gusts may occur with stronger downdrafts.
... S Russia ...
Two rounds of storms are forecast across this area. In the afternoon hours, isolated initiation is expected over the area in the environment of moderate CAPE and 0-6 km bulk shear exceeding 20 m/s. Curved hodographs with SRH exceeding 200 m2/s2 in 0-3 km layer are forecast, so supercells are likely in this environment with threats of large to very large hail and damaging wind gusts or even tornadoes. The second round of storms in the evening / during the night will be tied to the development of easterly low-level jet thanks to the cyclogenesis across the area. A large MCS is forecast by all models that will spread NW. Despite the fact that it will be likely rooted mostly in the elevated layer, it may bear considerable severe wind gust risk given the impressive kinematics (0-3 km bulk shear > 20 m/s and SRH0-3 > 400 m2/s2) and non-zero MLCAPE simulated at its eastern flank. Besides the wind gusts, very heavy rainfall is very likely with this system.
... Central Russia ...
A cold front along with a short-wave trough will initiate scattered storms across the area. Near the cold front, strong shear will allow for better convective organisation and storms may be capable of large hail and severe wind gusts. Towards the south, shear will be weaker and storms will mostly bear the risk of excessive rainfall.
