Precipitation in the Olympic Peninsula of Washington State

Robert Houze and Socorro MedinaDepartment of Atmospheric Sciences

University of Washington

Cold-Season Algorithm GV meeting, Fort Collins, 9 Nov 2009

The Olympic Peninsula is a natural “precipitation laboratory”

• Persistent southwesterly flow during the winter provides a reliable source of moisture

• Extremely large precipitation accumulation produced as the moist SWly flow impinges on coastal terrain

• Low 0ºC level rain at low elevations, snow at higher levels

The Olympic Peninsula is a natural “precipitation laboratory”

• Persistent southwesterly flow during the winter provides a reliable source of moisture

NCEP long-term mean sea level pressure (mb) for winter (December to January) and topography

The Olympic Peninsula is a natural “precipitation laboratory”

• Extremely large precipitation accumulation produced as the moist SWly flow impinges on coastal terrain

Annual average precipitation (PRISM)

Maximum

The Olympic Peninsula is a natural “precipitation laboratory”

• Low 0ºC level rain at low elevations, snow at higher ones

Distribution of Nov-Jan 0°C level for flow that is onshore and moist at low levels (KUIL sounding)

Mean 0°C level during storms = 1.5 km

See this full range in individual storms!

Fre

quen

cy o

f oc

curr

ence

0°C level Plot provided by Justin Minder

Resources and experience in the region

• 1965-2000: Cascade Project, CYCLES, COAST

• 2001: IMPROVE field experiment

• 2004-2008: Detailed observing network across a southwestern Olympics ridge

• 2009: NOAA Mobile Atmospheric River Monitoring System in Westport

• 2012: NWS Coastal radar expected to be in place

• Ongoing: Regional Environmental Prediction

Resources and experience in the region

• 2001: IMPROVE field experiment (Stoelinga et al. 2003)

Coastline

• 2004-2008: Detailed observing network across a southwestern Olympics ridge (Minder et al. 2008)

Resources and experience in the region

Detailed gauge network

SNOTELRAWS sitesCOOP siteAnemometersDisdrometers

Resources and experience in the region

• 2009: NOAA Mobile Atmospheric River Monitoring System in Westport

Time

Hei

ght

Hei

ght

Signal-to-noise ratio

Radialvelocity

Data from vertically-pointing S-band radar

Resources and experience in the region

• 2012: NWS Coastal radar expected to be in place

Dark gray areas indicate regions where the 0.5° elevation scans are blocked

Example of Olympic Mountain slopes views from coastal radar

Current radar coverage

Radar coverage with coastal radar

Resources and experience in the region

• Ongoing: Regional Environmental Prediction-- WRF, hydrology, air quality, etc (Mass et al. 2003)

Real-time mesoscale numerical simulations

dx = 4 kmdx = 36 km

Resources and experience in the region

• Ongoing: Regional Environmental Prediction-- WRF, hydrology, air quality, etc (Mass et al. 2003)

Real-time simulations with 1.33 km spatial resolution will be available shortly!

Resources and experience in the region

• Ongoing: Regional Environmental Prediction-- WRF, hydrology, air quality, etc (Mass et al. 2003)

Verified by gauges: Minder et al. 2008

Long period of continuous mesoscale simulations provides model climatologye.g., 5-yr MM5 Nov-Jan precipitation climatology (mm)

Resources and experience in the region

• Ongoing: Regional Environmental Prediction-- WRF, hydrology, air quality, etc (Mass et al. 2003)

Ensemble forecasting probabilistic information e.g., probability that theprecipitation accumulated in a 3 h period > 0.1in

Resources and experience in the region

• Ongoing: Regional Environmental Prediction-- WRF, hydrology, air quality, etc (Mass et al. 2003)

Hydrological prediction:

Mesoscale numerical output drives a distributed hydrological model basin streamflow forecast

Possible field experiment configuration

NPOL would have an unimpeded view of the Quinault valley and the Olympic mountains

Coastal Radar

Conclusions

• The Olympic Peninsula is an ideal natural precipitation laboratory given:– Persistence of moist flow, complex terrain, huge

precipitation amounts, and low 0°C level

• The existing and planned resources and the past experience in this region provide a strong framework for a field campaign

Acknowledgment

This research was supported by NASA grant NNX07AD59G and NSF grant ATM-08205586