Valid: Mon 15 Jan 2018 06:00 to Tue 16 Jan 2018 06:00 UTC
Issued: Sun 14 Jan 2018 22:15
A positive NAO pattern evolves as an intense and spacious cyclonic vortex with anomalous low mid-level heights over Iceland faces a 1040 hPa high pressure area near the Azores. In between both vortices, a powerful zonal flow pattern becomes established with 300 hPa winds in excess of 90 m/s and 500 hPa winds of more than 70 m/s. This jet dives east/southeast during the forecast and approaches CNTRL-Europe during the end of the day. Substantial height falls accompany that jet, as it carves out a negatively tilted trough, which extends from the Faroe Islands towards Germany.
No substantial changes occur further east with an ongoing but gradually weakening high-over-low blocking pattern over E-Europe. A positive tilted trough runs from the CNTRL-Mediterranean towards Morocco and further to the SW.
Numerous aging synoptic-scale fronts are analyzed over SW-/ and SE-Europe with limited input to this thunderstorm outlook. This is also valid for an occlusion over NW-Europe, which shifts towards CNTRL-Europe until 06 UTC.
Despite the dynamics with the aforementioned powerful jet, a smooth flow pattern at mid and upper levels keeps CI probabilities for enhanced and organized convection (due to favorable kinematics) rather low. The main forcing arrives with the passage of the occlusion. However, a disjoined LL moisture tongue from steeper mid-level lapse rates results in meager CAPE during the forecast. During the night, as the upper trough still amplifies to the SE, an overlap of steeper mid-level lapse rates exists with an already weakening LL moisture tongue and hence neutral to slightly unstable profiles are forecast over a broad area (including the S-North Sea, Benelux and Germany). With 850 hPa winds of 15-20 m/s downdrafts may bring strong to isolated severe gusts to the surface, but the missing focus for better forcing precludes the issuance of a fine tuned level 1 area. Ingredients in general also look too marginal for a broad level 1 area. As mid-levels cool down, graupel or small hail may accompany strongest postfrontal activity. This applies to Ireland, UK, Benelux, far NE-France and Germany.
Augmented LL shear (speed and directional) and low LCLs overlap, but meager LL lapse rates and (once again) missing foci for enhanced (mesoscale) forcing keep the tornado risk on the very low side.
Isolated and non-severe thunderstorms occur over parts of the Mediterranean.