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GOES East Convective Initiation Nowcast Products

Detailed Product Information

Who is developing and distributing this product?

The Cooperative Institute for Meteorological Satellite Studies (CIMSS) in Madison, Wisconsin is developing and distributing this product.

Who is receiving this product, and how?

The product is being delivered via a McIDAS-X ADDE server (ADDE group: UWCI, machine name: FLASH.SSEC.WISC.EDU) to Dr. Robert Rabin at NSSL. Dr. Rabin is ingesting these files and distributing them internally in a format suitable for display in N-AWIPS and WDSS-II.

Three products are being provided to NSSL/SPC: 1) An instantaneous CI nowcast using the most recent GOES East images, 2) A 60-min time accumulated CI nowcast which incorporates all CI nowcast information over the last 60 mins to improve the spatial coherency of the output, and 3) A 60-min time accumulated 10.7 micron IR window channel cloud-top cooling rate field. Two versions of these files are being provided: a set of three that are left in the native satellite viewing projection for overlay atop GOES East imagery and another three that are parallax corrected for overlay atop WSR-88D radar reflectivity to aid in product validation. Thus, six total files are being ingested by NSSL/SPC for each GOES scan.

What is the product size?

The examples below show the domain covered by these products. Each one of the six files mentioned above are ~1 Mb in size. The products are processed for all 85 operational 15-30 minute resolution GOES East scans that observe CONUS. Thus, approximately 510 Mb are being transferred to SPC and NSSL per day. The algorithm will automatically process rapid-scan imagery which would increase the number of images processed per day and the data volume.

Purpose of this product

This product objectively identifies rapidly developing cumulus clouds in a pre-convective initiation state during both day and night. Convective initiation is defined here as the transition of the maximum composite reflectivity from below to above 35 dBZ for a given storm cell. Previous research by Roberts and Rutledge (WAF, 2003) show that rapid IR window channel cloud-top cooling rates coupled with a transition to sub-freezing temperatures provide a 30-45 min lead time for nowcasting convective initiation. When a cloud top is cooling rapidly, this indicates that the capping inversion has eroded and the cloud will likely evolve into a mature thunderstorm in the near future. Cloud-top cooling rates are objectively computed using a box-average methodology for pixels with a cloud microphysical type of liquid water, super-cooled water, mixed phase, and ice. When a cloud top transitions to the thick ice phase, the cloud has likely begun to precipitate significantly and convective initiation has already occurred.

This CI nowcast product suite can be used by a forecaster to objectively determine where convection is (and is not) currently developing. Atmospheric wind shear and stability parameters can be analyzed for the surrounding environment of these newly developing storms to estimate their future severity. This can help to increase lead time in the watch and warning process.

How is this product created now?

GOES East imagery is acquired from the University of Wisconsin-Madison Space Science and Engineering Center Data Center, processed through the CI nowcast algorithm framework, and the product output is written to the set of McIDAS AREA files described above.

Product Examples and Interpretation: Daily Quicklooks and UWCI/SPC Validation

a) b) c) d)

e) f) g) h)

Images a) and b) show GOES visible and 10.7 micron IR window channel images at 1915 UTC on 23 March 2009 over the domain being processed and provided to NSSL and SPC. Convection has just begun developing over the Central Plains. Image c) shows the GOES East cloud typing for this scene that is used as input within the CI nowcast algorithm. Image d) shows the composite radar reflectivity at the same time as the previous 3 images. Weak radar rechoes were present across central Kansas, Oklahoma, and Nebraska. Image e) shows the 60-min accumulated cloud top cooling rate which is detecting developing convection over this region. Image f) shows the instantaneous CI nowcast produced at 1915 UTC. The product indicates that CI is likely to occur is Nebraska and Texas and CI is currently occurring in Kansas. Image g) shows that the vast majority of the CI nowcasts were produced within the 0 to 15 min time interval before this image. Image h) shows that the weak radar echoes had intensified within the following hour that the nowcasts were made. Although the clouds in Texas showed some vertical development in IR satellite imagery, this radar image indicates that these clouds did not develop into mature storms within the following hour.

Strengths and Weaknesses

Strengths

1) Diagnoses/nowcasts developing convective clouds in clear to partly cloudy scenes

2) Algorithm is day/night independent because it only uses infrared channels

3) Small time latency, product is available via the UW-CIMSS ADDE server approximately 2 minutes after initial code execution

4) The code is flexible and operates on both rapid (7.5 min) and operational (15 to 30 min) scanning patterns

5) Large spatial coverage eastern 2/3 of CONUS (Rockies to Atlantic Coast; Canadian border to Mexican border/Gulf of Mexico)

6) Product offers as much as 60 minute lead-time before significant radar echoes/cloud to ground lightning is present

7) Validation of algorithm shows low false alarm rate within SPC risk areas (26%). Forecasters can trust 3 of 4 UWCI nowcasts result in a CG producing storm.

Weaknesses

1) Algorithm does not operate in areas dominated by ice clouds (including thin cirrus debris cloud)

2) Fast moving clouds can occasionally induce false alarms, especially along leading cloud edges

3) False alarms may increase with GOES 30 min resolution full-disk scans

4) Due to current satellite temporal resolution, in cases with very rapidly developing thunderstorms, the UWCI product can lack radar/lightning lead-time; in these cases the UWCI product acts more as a diagnostic than nowcast (Note: this should be improved in the GOES-R era when higher temporal and spatial resolution imagery are available)