Transcript Nowcasting in NYC area

Satellite-Based Nowcasting over the New York City Metropolitan Area
Bernard.Mhando & Nasim Nourozi, of Graduate Center of City University of New York
Dr. Shayesteh Mahani and Dr. Reza Khanbilvardi, Department of Civil Engineering, City College of New York at CUNY
ABSTRACT
Selected existing nowcasting models are:
 Hydro-Nowcaster (HN) from NOAA-NESDIS,
 the Rapidly Developing Thunderstorm (RDT) models from France,
 the NSSL WDSSII Multiscale Storm Identification and Forecast
algorithm,
 the Thunderstorm Identification, Tracking, Analysis, and Nowcasting
(TITAN) module of the NCAR Autonowcast (ANC) system
GOES IR, at 17:02 UTC
METHODOLOGY
Two of the selected nowcasting algorithms: Hydro-Nowcaster (HN) and
Rapid Developing Thunderstorm (RDT) have already been installed to
be tested for nowcasting over the NYCMA.
Modifying an existing nowcasting algorithm for NYCMA to nowcast rainfall
at every 15 minutes up to 6 hours duration using satellite-based cloud
information.
STUDY AREA
The study area is located in Eastern United States, between latitudes 36º
N to 47º N, and longitudes 67º W to 82º W.
GOES IR, at 17:15 UTC
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Latitude (Degrees, North)
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36
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Rainfall Nowcastes, at 18:15 UTC (after 1-hour)
Rainfall
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Rainfall
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INCH
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INCH
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0
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Longitude (Degrees, West)
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Longitude (Degrees, West)
 Visualization of HN Results. The GOES image have been reproduced into rainfall
images showing increasing intensity (color changes) and spatial scatering of the storm.
This is compared to Stage III radar data for validation.
1. Motions of rain cells by identifying cloud clusters bounded by isotherms
of brightness temperature (BT) and dignosing their motions in a 100 x
100-pixel regions
2. Growth or Decay of the rain cells is based changes of characteristics of
cloud cluster of one image to the next. The chnges considered are cloud
cluster size, temperature of coldest pixel and average temperature of the
cluster.
The RDT Model: The RDT model can be split into 3 stages;
1. Detecton of Cloud System using an adaptative temperature threshold of
infrared image (GOES’ IR 10.8)
2. Tracking of cloud system using an algorithm based on the geographical
overlaping of the cells.
3. Discrimination of the convective systems among the tracked clouds by
identifying trajectories of the cloud systems using either lighting data or
the IR characteristics of the cloud systems.
The output is the RDT product coded in BUFR format and stored in binary
files and can be visualized as in the figure below.
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Rainfall Nowcastes, at 19:15 UTC (after 2-hours)
Latitude (Degrees, North)
1. Infrared (IR) cloud-top brightness temperature (BT) from GOES 10
satellite (Channel 4 [10.8m] wavelength), was used as input for the
both models. Information about other cloud properties such as relative
humidity, temperature, and precipitable water were also used for rainfall
estimation in conjunction with IR cloud information.
2. NEXRAD stage III and IV rainfall product and rain gauge observations
are used for evaluating the nowcasts.
Latitude (Degrees, North)
DATA USED
The HN Model: The HN algorithm focuses on two primary components of
nowcasting. These are:
OBJECTIVES
HN was implemented for the storm developed on June 12th 2006
at 17:15 UTC. The GOES IR cloud information for this and
previous time at 17:02 UTC in addition to relative humidity (RH),
precipitable water (PW) and temperature (T), were used as input
of the HN model to nowcast the progression, growth/decay, and
intensity of the storm for the next 3 hours. The GOES IR images
used and the HN output are presented below.
Latitude (Degrees, North)
Accurate forecasting of convective precipitation for time periods of
less than a few hours (Nowcasting) has always been a big challenge to
scientists and engineers. Nowcasting, up to 6 hours, in New York City
Metropolitan area (NYCMA) is a new challenge because the NYCMA is
the largest in the Nation and accurate reliable nowcasts of heavy
precipitation would have enormous economic and social value.
Over the years the performance of the quantitative precipitation
forecasts (QPF) using numerical weather prediction (NWP) models,
weather radar data, lightning detectors and satellite imagery as their
primary tool for detection of convective storms, have significantly
improved, despite some shortcomings on each system. NWP model QPF
continues to lag in skill during the first several hours after model
initialization, due largely to the “spin-up” problem of having to produce
dynamically consistent vertical motion fields. Satellites data have the
ability to overcome many of the limitations of NWP model and radar data.
Geostationary satellites are capable of providing information about cloud
properties at very high temporal resolution (15 minutes) on continuous
basis and therefore addressing many of the previous systems’
shortcomings.
Efforts in this study will be directed in trying several existing
nowcasting algorithms from NOAA-NESDIS, EUMETSAT, NSSL, and
NCAR for the NYCMA and modifying the suitable one for using satellitebased cloud information.
PRELIMINARY RESULTS:
NOWCASTING ALGORITHMS
Yellow contour =
newly detected system
Yellow line = the
trajectory
of
the
convective system.
Red contour = the
system is growing
Violet contour = the
system is mature.
Blue contour = the
system is decreasing.
Green contour = the
convective system in
the previous satellite
image.
Black arrow = the
expected move of the
convective system
 Visualization of the RDT Product superimposed on its IR.10.8 image
FUTURE WORK
New York City Metropolitan Area (NYCMA)
Left: METEOSAT infrared image of the 15/08/97 at 1800 UTC; Right: Detected “cells” with colors
indicating the temperature threshold used to detect the corresponding cluster.Source: SAF-NWCIOP-MFT-SCI-SUM-11_v1.0.doc
National Oceanic and Atmospheric Administration (NOAA/ NESDIS) Cooperative Research Program (CoRP)
3rd Annual Science Symposium, Fort Colins, Colorado, 15 – 16 August 2006
Vigorous testing of HN and RDT will be carried out for NYCMA
Improvement to the models will be carried out to suite the
NYCMA. This might include various parameters as realized from
the results analysis.
The use of 700mb wind fields as a steering current for
convective storms will be studied.
Automation of nowcasting will be developed with products made
available to the public domain through internet