Transcript The Use of the Hydro-Nowcaster for Mesoscale Convective

The Hydro-Nowcaster:
Recent Improvements
and Future Plans
Robert J. Kuligowski
Roderick A. Scofield
NOAA/NESDIS Office of Research and Applications
Camp Springs, MD USA
Clay Davenport
I.M. Systems Group
WWRP Symposium on Nowcasting and Very Short Range Forecasting
8 September 2005
The Hydro-Nowcaster:
Introduction
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The Hydro-Nowcaster (HN) is an
algorithm for producing 0-3 h nowcasts of
precipitation based on extrapolated
satellite estimates of rainfall rate.
Both advection and growth/decay are
considered.
The Hydro-Estimator (HE):
Basis for the Nowcaster
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The HE is NESDIS’ operational infrared satellite
rainfall algorithm
Rainfall areas are discriminated according to the
value of pixel T relative to nearby values:
– Colder than average:
active rain area
– Warmer than
average: inactive
cold cloud
HE continued: Rain Rates
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Rainfall rates are
based on pixel T, its
value relative to
surroundings, and
moisture availability
(precipitable water)
Corrections are
made for subcloud
RH, orography, and
convective EL
(warm clouds)
How the Nowcaster Works—
Extrapolation
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Identifies clusters (regions bounded by fixed
brightness temperature values) on two
consecutive IR images
Determines cluster motions based on the shift
of the coldest 25% of pixels within a 100x100pixel area that produces the best correlation
between the two images
Cloud motions are extrapolated out to 3 h at 15min intervals based on the resulting motion
vectors
How the Nowcaster Works—
Growth/Decay
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Each cluster on the current image is matched
with one on the previous image according to the
computed motion vector
Three factors to determine growth/decay:
– Change in size of the cluster
– Change in temperature of the coldest pixel
– Change in mean temperature of the cluster
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The growth/decay factor linearly decays to zero
over the 3-h forecast period to avoid unrealistic
results
Example: Hurricane Katrina
on 29 August 2005
1 h nowcast:
1200–1300
UTC
3-h nowcast:
1200–1500
UTC
Ongoing Work

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Recalibration of the HE to improve
performance, particularly underestimation
of rainfall associated with warm clouds
Rain/no rain discrimination is largely
complete; recalibration of rain rate
relationships is ongoing
Example: Mid-Atlantic Cold
Front on 4-5 September 2003
1 h nowcast:
2100–2300
UTC (4)
3-h nowcast:
2100 UTC –
0000 UTC (5)
Where to Get the Data
Nowcasts for 1, 2, and 3 h are updated every 15 minutes for
the entire CONUS on the NESDIS Flash Flood Web page:
http://www.orbit.nesdis.noaa.gov/smcd/emb/ff/
Future Work
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Complete recalibration of the HE, since
the Nowcaster performance is highly
dependent on its accuracy
Improve the scheme for depicting cloud
growth and decay—currently empirical
Develop an advection scheme for circular
storms—motion vectors for multiple lags?
Account for the effects of orography on
nowcasts of rainfall
Additional Plans
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Beginning collaboration between City
College of New York, NOAA/National
Weather Service, and NESDIS to evaluate
and test multiple nowcasting frameworks
(HN, TITAN, RDT) over the New York City
metropolitan area.
Focus is on NYC, but results will be
considered in operational nowcasting
development in the US.
Questions?