Transcript Hydrometeorological Aspects of the Kansas Turnpike Flash


Hydrometeorological Aspects
of the Kansas Turnpike Flash Flood
of August 30-31 2003
Authors: Jeffrey D. Vitale
James T. Moore
Charles E. Graves,
Matt Kelsch
Presented by: Brittanny Snyder
Chris Iraggi
Key Points:

From 2230 UTC to 0130 UTC on August 30-31, 2003 an area 12
miles from the Kansas Turnpike was hit with 6-8 inches of rain
due to a low-echo centroid (LEC) in roughly 3 hours

Results: Extreme Flash Flooding – 6 Casualties - $250,000
worth of property damage

Main Focus will be on the synoptic and mesoscale parameters
that favor the development of LEC storms

Also focus on hydrological considerations that contribute to
extreme flash flooding
What are the characteristics of a severe
thunderstorm?

“Cold-Topped” (IR values)

Equilibrium Level is close to the tropopause

Strong updrafts due to stronger buoyancy in the storm

Reflectivity values > 50 DBZ due to the presence of hail

Generate rain by the Bergeron Process (involves ice
crystals)

Peak rain rates are not very intense
What is a low-echo centroid (LEC)?

“Warm topped storm” (IR values)

Equilibrium Level is below the tropopause resulting in a shallow
storm height and a warmer IR temperature

Weaker updrafts: do not produce hail

Maximum reflectivity values are lower than 50 DBZ

Occur is moist, low-shear environments favoring warm-rain
processes

More efficient at producing precipitation than cold-rain processes

Rain rates: 200 mm / hr

When LEC storms form at the intersection of a strong low-level flow
and a boundary, enhanced LL precipitation growth leads to intense
rainfall
Efficient Ways of Forecasting Storms
 Z-R relationship:
•
LEC storms have warm rain characteristics and are
often formed in maritime tropical air masses and
have many relatively small rain drops
•
Z=250R1.2
Efficient Ways of Forecasting Storms
 Fig 1a. shows the regular Z-R
relationship
 This relationship suggested
that 2-3 inches of rain would
have fell within those 3 hours
Efficient Ways of Forecasting Storms

Fig 1b. Shows the tropical
Z-R relationship

This relationship
suggested that 4-6 inches
of rain was expected
during those 3 hours

We can see that this
relationship was more
accurate for this type of
storm.
Efficient Ways of Forecasting Storms
 Moisture Flux Convergence (MFC)
•
Used to forecast local thunderstorm formation
•
Q is specific humidity
V is the total wind
Term 1=convergence term
Term 2= advection term
•
•
•
Flash Flooding

A flash flood is a storm-scale event that occurs when the
precipitation rate is too great for the basin to
accommodate

Flash flooding is tied to the characteristics of the basin in
which the rainfall occurs

Severe flash floods occur in basins with < 30 square
miles of the drainage area

LEC storms are slow-moving and have a larger wet
footprint than severe thunderstorms making LEC storms
prone to flash flooding
Actual Storm Characteristics

LEC formed 12 miles west of Emporia Kansas at 2242 UTC

Peak Intensity was reached at 0035 UTC with maximum
reflectivity values around 55 DBZ

Maximum reflectivity was extended to a height of only 6 km

Storm moved NE at 4.6 m/s (EXTREMELY slow)

Stratiform precipitation surrounded storm during its entire
lifetime

Dissipated at 0130 UTC only 42 km from original storm site

GOES-IR imagery showed warm cloud-tops between -30°C and 40°C during peak intensity
Actual Storm Characteristics
•
Three major factors: Forcing Analysis, Moisture
Analysis, and Stability/Wind Shear Analysis
Actual Storm Characteristics

Forcing Analysis: large scale lift
•
Positive vorticity advection: max value of 19 x 10-5 /s
-Occurred over eastern Kansas, implyong UVM was favored
down stream from the 500 hpa vorticity maxima
•
Low level WAA: area of frontogenesis maximized near the
storm initiation site due to a frontal zone near 850 hpa
•
Strong convergence: max value of -3.4 x 10 -5 /s
-Positive convergence maximum developed and persisted
over the area of LEC storm development
Actual Storm Characteristics

Moisture Analysis:
•
MFC values: Deep layer (950-850 hpa) 1.6 g/kgh
Surface layer 1.5 g/kgh
-Due to the convergence associated with strong easterly
850 hpa winds
•
MFC values spiked at the time of maximum storm
intensity indicating convergence feedback
•
MFC values indicate that the area over which the LEC
formed was constantly being supplied with moisture
Actual Storm Characteristics

Stability and Wind Shear Analysis:
•
Upwind (South from the Storm):
CAPE= 163 J/kg
EL=350 hpa
Tropopase= 150 hpa
NCAPE= 0.021 m/s2 indicating a profile that is tall and skinny
*Cape divided by the depth of the layer where cape is present.
Distinguishes between tall and skinny, and short and fat cape profiles.
Wind speeds= veering (WAA) 15 to 25 kts with weak speed shear with
height
Actual Storm Characteristics

Location of the storm:
CAPE = Decreased to 30 J/kg
NCAPE = 0.007 m/s2
EL = 480 hpa
Tropopause = 150 hpa
Wind speed = 14 kts
-A low EL height provided an upper level lid on convection during
the time of the storm. Weak wind speeds and flow in this
layer was the cause of slow storm movement
Hydrological Issues
 Interstate Highway 35, the Kansas Turnpike, lies on
top of a raised roadbed as it cuts across the Jacob
Creek drainage basin
Hydrological Issues
 24 hours before the LEC hit, this area was hit with 1.75 inches of
rain, increasing surface runoff
 At 0130 UTC the volume of water in the creek was too great under
the highway, so water ponded upstream of the highway
Hydrological Issues
 At 0200 UTC water backed up onto the highway and
was held back by concrete barriers
Hydrological Issues
 Shortly after, water reached the top of the barriers and the
highway became impassable
 6 people died by not abandoning their cars as the water surge
carried 7 vehicles downstream
Hydrological Issues
 Overall, there is a great sensitivity of drainage basin
to repeated bursts of intense rainfall.
 The combination of saturated soil, heavy rain, and
unnatural structures in the floodplain can be
disastrous when an LEC hits.
Compare 2 LEC Storms

Fort Collins, Colorado:
-Flash Flood July 28,1997
-LEC Storm produced over 10 in of rain in less than 6 hrs
-5 casualties

LEC Characteristics:
-IR imagery showed warm cloud tops
-No hail
-Weak mid-tropospheric winds
-Warm rain process---Mechanism for precipitation growth
Compare 2 LEC Storms
 Comparing Ft. Collins event with Kansas Turnpike event:
Fort Collins
Kansas Turnpike
CAPE
868 J/kg
316 J/kg
Freezing Level
3.6 km AGL
4.2 km AGL
LI
-2.8 deg. C
-2.0 deg. C
LCL
764 hpa (700 m AGL)
911 hpa (365 m AGL)
PW
3.4 cm (179% of
normal)
4.8 cm (120% of
normal)
 We can see that they similar characteristics
Compare 2 LEC Storms
 There are many differences:
-Fort Collins: Region was under the influence of weak S
to SW flow aloft in association with a negative tilted
500 hpa ridge
-Kansas Turnpike: Associated with a cut off low to the
west of the area
 Overall, both cases the flood event was not
associated with a surface frontal boundary
Compare 2 LEC Storms

Major hydrological response differences:
•
Fort Collins:
-Topography, there was heavy precipitation run off flowing down from the mountains
the day before LEC hit
-Water flowed into Spring Creek and overflowed several retention areas upstream
-The storm followed the route of the main drainage area of Spring Creek
•
Kansas Turnpike:
-The culvert under the highway was unable to accommodate the amount of water
flowing through the basin
-This resulted in the powerful flow of water over the interstate
Factors that promote LEC development:
 Overall:
•
Highest reflectivity's are in warm portion of the
cloud
•
Very high influx of moisture into the storm allowing
heavy rainfall characteristics to develop
•
Weak instability, weak cloud layer flow, a deeply
saturated sounding
•
The natural flow of water is altered
Summary
 These LEC storms can become difficult to recognize
in a real time event.
 These factors can be useful to operational
meteorologists in better anticipating LEC storms
because of their subtly heavy rain signatures
 Not all LEC storms are the same. Many
meteorological and hydrological characteristics can
be different but overall will have the same results;
devastating flash floods, property damage, and
deaths.