QPE Evaluation for the 2013 Colorado Flood
Paul Kucera1, Andrew Newman1, Christian
Klepp2 and Jörg Burdanowitz2 Longmont
1National
Center for Atmospheric Research
2University of Hamburg/Max Planck
Institute for Meteorology
Evacuating Jamestown residents
Photo: Dennis Pierce, AP
Jamestown
Lafayette
Jamestown
Portions of I-25 closed
19 November 2014
Photo: Matthew Gurnsey
Flooding in CU dorms
Photo: Cliff Grassmick, Daily Camera, via AP
Boulder County
Aurora
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Outline
• Lifecycle of the flood event
• Operational QPE estimation results (radar and
satellite)
• Disdrometer and storm structure QPE
estimation results
• QPE Impacts on streamflow prediction
• Summary and future work
IPWG7 November 19, 2014
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Time-line of Flood Event
• The historical flood occurred over 10-16 September 2013
Gochis et. al. (2014)
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Northeastern Colorado Flash Floods
9-13 September 2013
ü Upper level closed Low Pressure system located over
SW United States
ü Funneled SW monsoon moisture over mountains and
NE Colorado
ü Low-level, moist SE flow created upslope flow along
the foothills bringing additional moisture and rainfall to
NE Colorado
Boulder/Denver NWS office
GOES Water Vapor and 500 hPa Heights/Vorticity
Movie Loop: 9-13 September 2013
Boulder
CountyAurora
Courtesy of Eric Nelson, NCAR/RAL
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NCAR’s Marshall Field Site Rain Gauge Measurements
Accumulation (mm)
Courtesy of Roy Rasmussen
~10 inches accumulation
Intensive Period #2
Intensive Period #3
10 Sept
10 Sept 06 UTC
00 UTC
13 Sept
02 UTC
Intensive Period #1
11 Sept
21 UTC
12 Sept
18 UTC
Three main intensive precipitation periods were observed:
- Initial convective period: 00-06 UTC Sep 10
- Second precipitation phase: 21 UTC 11 Sep – 18 UTC Sep 12
- Third precipitation phase: 18 UTC 12 Sep – 02 UTC Sep 13
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Radar Observations (1st Wave)
00-06 UTC 10 September
Marshall
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Radar Observations (2nd Wave)
21 UTC 11 Sep – 18 UTC 12 Sep
Marshall
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Radar Observations (3rd Wave)
18 UTC Sep – 02 UTC 13 Sep
Marshall
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Event Precipitation Totals
• Total Precipitation map for
storm event (9-17 Sep 2013)
From the Colorado Climate
Center
• Max accumulations
- Boulder: 429.3 mm (16.9 in)
- Front range 530 mm (21 in)
• Max precipitation located
along the foothills from S.
Boulder to Fort Collins
Gochis et. al. (2014)
Marshall Field Site
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Operational QPE Evaluation
• A variety of operational QPE were evaluated:
–
–
–
–
–
Default NEXRAD Z-R
“Tropical” Z-R
NSSL Multi-sensor precipitation estimates (MPE)
Polarimetric precipitation estimates
Stage IV
Typical NEXRAD Z – R Relationship
Z = 300
R1.4
Boulder 60 mm
Large underestimate
Tropical Rainfall Z-R relationship
Z = 32.5 R1.65
Boulder 230 mm
Only slightly High
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QPE Comparison
• Comparisons at high
quality precipitation
sites
• 11-13 Sep
accumulation period
• Underestimation of
rainfall
– Default NEXRAD
– Dual-Pol
• Overestimation of
rainfall
– Default Tropical Z-R
Gochis et. al. (2014)
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QPE Bias Comparison
• Default Z-R and
dual-pol QPE
significant
underestimation
bias
• MPE best
estimates
• Stage IV mixed
Gochis et. al. (2014)
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Satellite Precipitation Estimation
• This study evaluated CMORPH (CPC MORPHing technique)
product at the produces global precipitation analyses at 8 km,
30 min resolution for the three main periods and for the total
accumulation over the 3 day period
Ft Collins
Boulder
Marshall
DIA
Denver
Ft Collins
Ft Collins
Boulder
Marshall
Boulder
DIA
Denver
Marshall
DIA
Denver
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Satellite Precipitation Estimation
Ft Collins
Boulder
Marshall
Erie
DIA
Denver
CMORPH underestimation bias is 13 times lower than observations and
precipitation shifted eastward
compared max precipitation area
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Why are there significant
underestimation biases in QPE products?
• The precipitation observed during the second
and third IP’s was not “typical” of high plains
convection
– Efficient warm rain processes
– “Tropical” like drop size distributions
• Large concentration of small drops
• A new storm-based Z-R relationships were
based on drop size distributions observations
from disdrometers located at the Marshall
research field site located south of Boulder
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(#/m3 mm1)
• IP2 and IP3 DSDs differ substantially from the rest of the event
• IP2 shows increase in drop number of 1 to 3 mm diameter
• IP3 shows strong increase in small drops between 1 and 2 mm diameter and
overall larger drop numbers
IP3: large number of
1-2 mm drops
IP2: increased number
of 1-3 mm drops
All 3454 1-min spectra
outside IP2 & IP3 time
periods show small increase
in the 1-3 mm size drops
IP2: 11 SEP 21 UTC to 12 SEP 18 UTC; 1103 minutes (spectra)
IP3: 12 SEP 18 UTC to 13 SEP 02 UTC; 491 minutes (spectra)
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Reflectivity-Rainfall Relationship
1st (Intensive Period)
IP had a continental
Z-R
• Z-R’s for IP2 and IP3
were more typical
tropical Z-R
relationships
•
– Short and Kucera
(1997)
– Z=120R1.43
•
•
The default NEXRAD
Z-R fit the DSD in IP1
The default tropical ZR is not a good fit to
the observed DSD
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IP1 Z-R
• Z-R: Z=305R1.49
• Convection in
IP1 typical,
deeper
continental
convection
• Default
NEXRAD Z-R
worked well in
this initial regime
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QPE Comparison at Marshall
•
•
•
•
•
•
Storm total Rainfall: 285 mm
DSD Z-R performed well: 5
mm overestimation
NEXRAD Z-R: 118 mm
underestimation
Tropical Z-R: 224 mm
overestimation
CMORPH precipitation: 220
mm underestimation
However, CMORPH agreed
well for the initial deep
convection system
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QPE Impacts on Streamflow
Prediction
WRF-Hydro SIMULATED Streamflow from NEXRAD (Tropical Z-R)
Little Thompson
St. Vrain
James/Lefthand
Fourmile Canyon Cr.
Valid: Sep 12 1:15 a.m. LT
Fourmile Cr.
Boulder Cr.
South Boulder Cr.
NCAR Seminar Oct. 4, 2013
Coal Cr.
Streamflow
Courtesy of D. Gochis
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QPE Impacts on Streamflow
Prediction
Validating Streamflow
Simulations: Tropical
Z-R
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Courtesy of D. Gochis
QPE Impacts on Streamflow
Prediction Modeled Streamflow at
St. Vrain at Lyons
Forced by: NEXRAD Z=300R^1.4
Forced by: Tropical Z-R
No Flood
Predicted
with default
Z-R
Courtesy of D. Gochis
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Future Work – Storm Type Z-R QPE
• The DSD based Z-R’s could be further stratified by
rain type and storm structure
• Friedrich et al. (2014) estimated precipitation by
storm type – identified 4 rain regimes
12 Sep
13 Sep
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Friedrich et al. (2014)
Summary
• The Colorado Flood had large societal impacts on the Front Range
• Unique precipitation conditions
– First deep convective system was typical for Eastern plains of Colorado
– Second precipitation transitioned to a more “tropical” environment
– Third intensive period was “tropical like” – large concentration of small
drops, shallow convection, efficient rain processes
• Some operational QPE products underestimated storm totals
• Knowledge of DSD provided a better QPE products
• Significant impact on flood forecast and early warning
– Many people were stranded in the foothills
• Follow on work
– Evaluate the DSD Z-R QPE over the entire domain
– Stratify DSD Z-R further by storm structure
– Develop tools to provide a dynamic Z-R for operational QPE products
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Colorado Flood Photos
Boulder Flooding – Table
Mesa Drive below NCAR
Table Mesa Facilities
- Photos courtesy of R. Cifelli
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