Mesoscale Discussion
Valid: Wed 30 Jun 2021 20:00 to Thu 01 Jul 2021 00:00 UTC
Issued: Wed 30 Jun 2021 19:42
Forecaster: TUSCHY

MESOSCALE DISCUSSION:

Update to the second round of excessive rain for tonight.

Cross-track spread decreased for the shallow warm core low, with GFS representing the western fringe of the track plume towards NE Germany, whereas the rest converged to a track right into the Pomeranian Bay during the night. But even those models still show a timing issue with ICON being more progressive compared to IFS.

Current lull in convective activity should be only temporal with another round of embedded convective elements forecast in the broad straiform rain shield during the following hours. The passing vortex tightens a zonally aligned convergence zone with enhanced LL lift, so release of 300-600 J/kg MUCAPE into thundery convection is possible. Forecast soundings support very efficient rainfall rates with deep moisture, skinny CAPE profiles, enhanced/unstable inflow from the NE and ongoing ventilation into an upper jet to the S/SW.

NWP guidance indicates concurring QPF maxima over N-Brandenburg with 12h rainfall amounts of 50-100 l/qm. EPS data indicates more than 70 l/qm in 12h with 70-80% probabilities in this region, so this area could see flooding issues during the night despite the dry conditions during the previous weeks. Convective elements could support extreme rainfall amounts with one report of 51 l/qm in 30 min already received. Therefore local swaths of even higher amounts are well possible, although this risk could be a bit lowered due to the ever so slowly but still slightly progressive nature of this line to the S.

To the W (towards Hamburg and further N), the cell motion is a bit more progressive with less CAPE and a somewhat weaker inflow. Slow moving convection still poses a risk of very heavy rainfall amounts on the local scale, which could also approach 60-80 l/qm in a few spots.

A gradual weakening trend is forecast until 06Z, so the main time-frame of activity should be from 20-06Z.

Please note: The duration of this MD does not reflect the duration of the severe event, which continues well into the evening hours. This MD is just a nowcast update.