Storm Forecast
Valid: Sun 21 Apr 2019 06:00 to Mon 22 Apr 2019 06:00 UTC
Issued: Sat 20 Apr 2019 16:02
Forecaster: TUSCHY
A level 1 was issued across parts of NW Algeria mainly for excessive rain.
A level 1 was issued across parts of Iraq mainly for isolated large hail and severe wind gusts.
A level 1 was issued for E-CNTRL Spain for excessive rain.
SYNOPSIS
Ongoing blocking pattern assists in a relatively quiet convective weather day over Europe. The main change is a weakening trend of the strong ridge over NW Europe while geopotential heights increase over S-CNTRL and CNTRL Europe. Broad upper lows affect SW and E/SE Europe. Embedded cyclonic vortices will be the main foci for today's CI. Otherwise a dry low-tropospheric layer or warm mid-levels with ongoing synoptic-scale subsidence suppress deep moist convection.
DISCUSSION
... Belarus to Romania ...
Overlap of cold mid-levels (augmented mid-level lapse rates), marginal BL moisture and temporal diabatic heating create a belt with low-end CAPE and weak shear. Scattered diurnal driven thunderstorms with graupel and gusty winds peak during the afternoon/evening before weakening after sunset. No severe risk is anticipated although a dry/well mixed layer in the lowest 100-200 hPa could enhance the gust risk somewhat.
... W-CNTRL France ...
Residual BL moisture beneath cold mid-levels results in another day with enhanced thunderstorm probabilities. Meager CAPE and shear preclude organized convection with the dominant risk being graupel and gusty winds. This acticity weakens after sunset.
... NW Algeria and E Spain ...
A tilted vortex over far NW Algeria lifts gradually N during the day. Downstream WAA results in a northward fanning EML plume, which affects most of N-CNTRL and NE Algeria. Its source region is the desert, so expect bone-dry and well mixed profiles with good EML signatures. A stout cap precludes CI. The focus for initiation resides along the western fringe of the EML, where cap weakens and synoptic-scale forcing increases. Not much onshore advection of a marine air mass is forecast, so 400-800 J/kg MUCAPE are expected (with most models indicating some sort of capping - either at lower levels or further west at around 700 hPa). 0-6 km shear in excess of 20 m/s is forecast but there are doubts that this is an effective shear magnitude due to the capped layers. Hence the current idea is that scattered elevated thunderstorms evolve in the highlighted area and move north. Moderate shear assists in an isolated large hail and heavy rainfall risk. The latter risk was the main reason for upgrading because of the arid climate and the complex orography. Isolated flash flooding is possible.
During the night the risk of elevated thunderstorms translates north which is in line with the northward progression of the LL vortex. Also a few elevated thunderstorms are possible as far east as Sicily during the night with the approach of mid-level forcing, which interacts with the extensive MUCAPE plume. Nothing severe is forecast with this activity.
During the night a heavy rainfall event could evolve along the W fringe of the LL vortex impacting E-CNTRL Spain. The vortex' path remains a bit uncertain in model data although ICON/IFS now show quite similar tracks. Wrap-around moisture with some MUCAPE and strong LL convergence may result in heavy rain. Embedded thunderstorms locally increase rainfall amounts and a confined level 1 area was added.
... Syria, S Turkey, Lebanon and parts of Iraq ...
An eastward rotating upper vortex interacts with moderate BL moisture. This air mass is weakly capped, so scattered and early CI is forecast. 300-600 J/kg SBCAPE and weak shear suppress organized convection.
Somewhat better conditions for severe thunderstorms exist over N Iraq, where steeper mid-level lapse rates result in enhanced CAPE (roughly 800 - 1000 J/kg) with well mixed lower levels. Hence a few severe downburst events and isolated large hail events are possible and a small level 1 was added. This activity weakens from W to E during the night.
