Storm Forecast
Valid: Mon 02 Nov 2015 06:00 to Tue 03 Nov 2015 06:00 UTC
Issued: Mon 02 Nov 2015 00:48
Forecaster: VAN DER VELDE

A level 2 was issued for eastern Spain and southern France mainly for significant chances of excessive convective precipitation, severe convective wind gusts and tornadoes.

SYNOPSIS

While a large high pressure area keeps central and western Europe stable and free of clouds, a vigorous low affects the Iberian Peninsula, shifting towards France. In the early morning, a trough moves out of the Alboran Sea, focusing strong advection of moist unstable air (SBCAPE over 1500 J/kg, MLCAPE over 500 J/kg) and low-level convergence over the coastline of southeastern Spain, triggering convective bands impinging perpendicularly onto the coastline and 50-100 km downstream zone inland. The upper level lifitng is very strong with the PV intrusion and left exit region of the 60 m/s 300 hPa jetstream tracking from southeastern to notheastern Spain (15Z). Low level easterly winds will be strong to the north of the surface trough with non-convective gusts over 20-25 m/s present in some WRF models, and force saturated air over higher terrain, adding to large precipitation sums.

DISCUSSION

From 06Z-12Z a large area of eastern Spain will be affected by convective and stratiform rainfall. The high precipitation intensity (precipitable water 38 kg/m2) and convective cloud train formation will easily produce 50-200 mm of rainfall and associated flash flooding and small river floods. The speed of northeastward shift of the main convergence zone will be fast, which reduces to some extent the rainfall amounts.
0-6 km shear (15-30 m/s) and SREH are supportive of embedded supercellular structures with severe wind gusts and potential for weak and significant tornadoes (0-1 km shear 10-20 m/s). During the afternoon GFS and ECMWF-based WRF CAPE seem to decrease or converted into storms and some will also advect through the Ebro Valley towards the Pyrenees, where the left exit region moves in late afternoon and evening, and rain sums may well be partially convective. The main threat should remain along the coastline of Catalonia, particularly 23Z-03Z with long-lasting moist air lifting over the slopes of the eastern Pyrenees, continuing into southern France and into the next morning.