Orographic Precipitation in Potentially Unstable Alpine Storms: MAP IOPs 2b, 3, and 5

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 IOP2b33-hour Mean Radial velocity

S-Pol radar

NNW

MAP IOP2b33-hour Mean Reflectivity

S-Pol radar

NNW

MAP IOP2bFrequency 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 dropletsgraupel growingby riming

rain growingby coalescence

Slightly unstable

air

Medina and Houze 2003

MAP Conceptual Model for precipitation enhancement inPotentially 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 IOP324-hour Mean Reflectivity

S-Pol radar

NNW

MAP IOP54-hour Mean Reflectivity

S-Pol radar

NNE

S-Pol radar

MAP IOP324-hour Mean Radial velocity

NNW

S-Pol radar

MAP IOP54-hour Mean Radial velocity

NNE

S-Pol radar

MAP IOP3Frequency 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 IOP5Frequency 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 IOP14Mean wind shear from Lonate profiler

Mean and SD over 16 hours

MAP IOP1434-hour Mean Reflectivity

S-Pol radar

NNW

MAP IOP1434-hour Mean radial velocity

S-Pol radar

NNW

MAP IOP14Polarimetric 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 IOP14Reflectivity from vertically pointing S-band radar

at Locarno Monti

Time UTC

Hei

ght

(km

)

OPRA radar