Orographic Precipitation in Potentially Unstable Alpine Storms: MAP IOPs 2b, 3, and 5 Socorro Medina and Robert A. Houze

Lago Maggiore region

IOP2b

Equivalent Potential Temperature IOP2b Milan sounding 12Z 20 Sep 99

MAP IOP2b 33-hour Mean Radial velocity S-Pol radar NNW

MAP IOP2b 33-hour Mean Reflectivity S-Pol radar NNW

MAP IOP2b Frequency of occurrence of particle types accumulated over 33 Hours S-Pol radar NNW graupel (2% contour) melting snow (30% contours) weak echo snow (50% contour)

ALPS snow rain 0ºC cloud droplets graupel growing by riming rain growing by coalescence Slightly unstable air Medina and Houze 2003 MAP Conceptual Model for precipitation enhancement in Potentially Unstable Upstream Conditions

Other potentially unstable upstream flow cases: MAP IOPs 3 and 5

IOP3

IOP5

Equivalent Potential Temperature IOP3 Milan sounding 00Z 26 Sep 99

Equivalent Potential Temperature Milan sounding IOP3 00Z 26 Sep 99 IOP5 12Z 03 Oct 99

MAP IOP3 24-hour Mean Reflectivity S-Pol radar NNW

MAP IOP5 4-hour Mean Reflectivity S-Pol radar NNE

S-Pol radar MAP IOP3 24-hour Mean Radial velocity NNW

S-Pol radar MAP IOP5 4-hour Mean Radial velocity NNE

S-Pol radar MAP IOP3 Frequency of occurrence of particle types accumulated over 24 Hours NNW graupel (2% contour) melting snow ( 3% contours) weak echo snow (10% contour)

S-Pol radar MAP IOP5 Frequency of occurrence of particle types accumulated over 4 Hours NNE graupel (5% contour) melting snow (10% contours) weak echo snow (50% contour)

CONCLUSION Despite differences in the upper-level flow direction, the lower slope precipitation processes were similar in 3 IOPs. The observations were consistent with the conceptual model for potentially unstable upstream flow. Convective cells formed intermittently on the first major peak of terrain as a radial velocity jet rose over it. Both riming and coalescence were key microphysical processes in the cells.

Mixed case: MAP IOP 14

Equivalent Potential Temperature IOP14 Milan sounding 00Z 4 Nov 99

MAP IOP14 Mean wind shear from Lonate profiler Mean and SD over 16 hours

MAP IOP14 34-hour Mean Reflectivity S-Pol radar NNW

MAP IOP14 34-hour Mean radial velocity S-Pol radar NNW

MAP IOP14 Polarimetric Particle Identification over 34 Hours weak echo snow (low dBZ, low ZDR) large aggregates and/or graupel (high dBZ, low ZDR) melting aggregates (high dBZ, high ZDR) S-Pol radar NNW

MAP IOP14 Reflectivity from vertically pointing S-band radar at Locarno Monti Time UTC Height (km) OPRA radar