Modeling and Forecasting Modeling and Forecasting Lee Side Spillover Lee Side Spillover

Precipitation Resulting in Precipitation Resulting in Major Flooding in an Urban Major Flooding in an Urban

Valley LocationValley Location Michael L. Kaplan, Phillip J. Marzette, Michael L. Kaplan, Phillip J. Marzette, Christopher S. Adaniya and K.C. KingChristopher S. Adaniya and K.C. King

Division of Atmospheric SciencesDivision of Atmospheric SciencesDesert Research InstituteDesert Research Institute

Reno, NevadaReno, Nevada

S. Jeffrey UnderwoodS. Jeffrey UnderwoodDepartment of GeographyDepartment of GeographyUniversity of Nevada RenoUniversity of Nevada Reno

Reno, NevadaReno, Nevada

Presentation OverviewPresentation Overview

1. Formation of meso-Γ scale vortices in blocked flow1. Formation of meso-Γ scale vortices in blocked flow

2. Meso-Β/Γ scale observations (Reno) during the 2. Meso-Β/Γ scale observations (Reno) during the 2005 flood2005 flood

3. Simulated counter-rotating vortices during the flood3. Simulated counter-rotating vortices during the flood

4. Sensitivity to model initial conditions during the flood4. Sensitivity to model initial conditions during the flood

5. Summary and key conclusions5. Summary and key conclusions

Counter-Rotating Meso-γ Scale Lee Side Counter-Rotating Meso-γ Scale Lee Side

Vortices (~10-20 km/3-6 hours or less)Vortices (~10-20 km/3-6 hours or less) Lee side blocking of upstream unsaturated flow function of

dry Froude Number (linear theory)

u=2000 m MSL average (valley-crest) cross-mountain top wind velocity

N=2000 m MSL average (valley-crest) Brunt-Vaisalla frequency

H = Average upstream mountain height (~1000 m for Carson Range between valley (1500 m) and crest (2500 m) MSL)

NH

uFr

z

gN

Counter-Rotating VorticesCounter-Rotating Vortices

Key Observations Near Reno For The Key Observations Near Reno For The

2005 Flood Event2005 Flood Event

Multi-sensor analysis of the precipitation field (inches) for 30–31 December 2005.

NARR: 250-hPa Height/Isotachs/Wind Barbs

0600 UTC 1500 UTC

NARR MSLP and Surface Wind Barbs

0600 UTC 1500 UTC

Reno Meteogram – 12/31/05Reno Meteogram – 12/31/05

Upper Air Data: Observed and SimulationUpper Air Data: Observed and Simulation

Observed Reno radiosonde

FFrr = 0.482 = 0.482

NCAR/NCEP Simulation

Fr = 0.406Fr = 0.406

AVN Simulation

Fr = 0.521Fr = 0.521

Simulated PMSL/Surface Winds/Terrain Simulated PMSL/Surface Winds/Terrain at 1500 UTC 12/31/05at 1500 UTC 12/31/05

NCEP SimulationNCEP Simulation AVN SimulationAVN Simulation

Simulated 800 mb Vertical Velocity (w) at Simulated 800 mb Vertical Velocity (w) at 1500 UTC 12/31/20051500 UTC 12/31/2005

NCEP SimulationNCEP Simulation AVN SimulationAVN Simulation

Summary and ConclusionsSummary and Conclusions

Urban scale prediction in complex terrain is Urban scale prediction in complex terrain is difficult reflecting larger scale Froude difficult reflecting larger scale Froude number and simulated blocking errorsnumber and simulated blocking errors

Blocking may be key to organizing lee side Blocking may be key to organizing lee side vortices and convergence zones on the vortices and convergence zones on the urban scale, which control precipitationurban scale, which control precipitation

Better initial data, resolution and Better initial data, resolution and microphysics are likely key to improving microphysics are likely key to improving flooding prediction for spillover precipitationflooding prediction for spillover precipitation in a lee side urban valley regionin a lee side urban valley region