The NOAA/CIMSS ProbSevere LightningCast model uses GOES-R ABI reflectances and brightness temperatures along with artificial intelligence methods to predict next-hour lightning anywhere in the GOES-R field of view. It is particularly adept at nowcasting lightning initiation.

A long, potent cold front spawned a number of storms from Iowa to Texas today (many of which were severe). The GOES-16 mesoscale sectors were providing rapid-scan service to forecasters in the middle of country, providing 1-minute updates of satellite imagery.

In Texas, the cold front is clearly delineated between clear sky to its west and low clouds to its east, in the warm/moist sector. The probabilities of lighting from LightningCast increased rather quickly from <10% to >75% in many regions, prior to the first detection of GLM flashes (Figure 1). Elevated probabilities of lightning were observed from 15 to 35 minutes prior to lightning initiation for most of these storm cells.

Further north, along the Kansas / Missouri border, LightningCast accurately highlighted the line of lightning initiation forced by the cold front (Figure 2). Along this part of the front, there is good evidence that the model’s contours of probability are leading the convective regions, anticipating the prevailing motion. While LightningCast currently only uses a single time of data to make predictions, it seems to have learned (to some extent) the motion of storms from patterns in single images of reflectance and brightness temperature data.

LightningCast will be evaluated by forecasters at the 2023 Hazardous Weather Testbed. Forecaster feedback is important to help direct research-and-development and potential transition-to-operations efforts.

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The animation above, created at the CSPP Geosphere site (direct link to the animation), shows showers dissipating over and south of the Samoan island chain shortly after sunset, and then redeveloping to the north of the island chain. The redevelopment in the RGB imagery followed the usual color change associated with developing convection: faint pink/red colors that became deeper and deeper red as clouds grew. Note that the RGB also has characteristic color — blue — that suggests clear skies. This means that clear-sky Level 2 products from GOES-18 such as Total Precipitable Water (TPW) and Derived Stability Indices might give useful information to help a forecaster anticipate the redevelopment of convection. The animations below show those TPW and Lifted Index overlain on top of GOES-18 “Clean Window” Band 13 infrared (10.3) imagery, from 0600 – 1000 UTC; the animations end before the developing convection generated clouds to mask the view. Note also that the Default AWIPS enhancements for TPW and Lifted Index have been altered, as noted in the caption.

The convection at the beginning of the animation was aligned along the southern edge of abundant total precipitable water, and it dissipated as it moved to slightly more stable air, that is, air with slightly less negative Lifted Indices (brighter yellow in the animation). There is greater instability to the north — and that’s where convection subsequently developed as noted in the Night MIcrophysics RGB animation.

Make sure you look at Level 2 Products such as TPW and Lifted Index (or CAPE, or K Index, or Total Totals Index) when skies are clear to get a better idea of gradients in regions that are void of data other than satellite information.

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Much of the mid-Mississippi River valley was placed under a Moderate Risk of severe weather by the Storm Prediction Center on 31 March 2023. Day Night Band imagery from NOAA-20 (mislabeled as Suomi NPP), above, shows two bore-like features with very different orientations (there is also a notable lightning feature over eastern South Dakota!). The feature over Iowa is oriented southeast to northwest, the one over Minnesota — at a lower level (note the shadow cast by the higher clouds over Iowa on the lower clouds over Minnesota) — is oriented southwest to northeast. Winds are typically perpendicular to such cloud bands, so this one still image suggests very strong shear (consistent with the SPC forecast). The 0000 UTC SkewT from Minneapolis/Chanhassen, below, from the Wyoming Sounding site (here’s the AWIPS NSharp image), shows very strong low-level shear and veering winds. Winds below 850 are nearly perpendicular to the cloud bands in southern Minnesota; winds above 850 are nearly perpendicular to the cloud bands in north-central Iowa.

Surface observations overlain on top of the Day Night Band imagery, below, show a 180-degree windshift across the cloud band feature in Minnesota. The influence of the Iowa Bore does not appear to extend to the surface, perhaps because of the strong inversion present.

Shear Analysis (Surface to 3 km) from the Storm Prediction Center, below, for 0800 UTC, does show a change in shear from the environment near the northern bore feature over southern Minnesota to the environment surrounding the southern bore feature over northern Iowa.

The Day Night band image above is also available (for 5 days) at the CIMSS Direct Broadcast ftp site (here) and at the CIMSS VIIRS Image Viewer (here).

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Himawari-9 imagery for the hour surrounding an RCM-1 pass over the center of Severe Tropical Cyclone Herman, below, shows strong convection (with widespread brightness temperatures colder than -85^oC — light purple in this enhancement — with isolated pixel values cooler than -90^oC — in purple). Peak Synthetic Aperture Radar (SAR) winds from the Radarsat Constellation Mission-1 satellite exceeded 80 m/s! Click here to view the storm track, and text describing the storm, both from this Australian Bureau of Meteorology website. (Here’s the 1-hour animation without the SAR winds).

A zoomed-in picture of the SAR wind analysis is shown below. The data can also be viewed at this SAR Tropical Cyclone site specific to Herman (Direct link to image). Strong winds encircle the entire eye.

The image below, from the Australian Bureau of Meteorology ‘MetEye‘ website, shows Herman’s track relative to Australia.

Herman is moving through an atmosphere of low shear, as shown below (image from this site), and is over waters with sea-surface temperatures of 27-28^oC (not shown).

The MIMIC-TC animation below (from this site) shows the closing off of the eyewall that accompanied Herman’s rapid intensification

More information on Herman is available at the Joint Typhoon Warning Center. Also, note that the Target Sector from JMA Is over Herman (link).

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JMA Himawari-9 Infrared Window (10.4 µm) images, from 0902 UTC on 30 March to 0132 UTC on 31 March (credit: Scott Bachmeier, CIMSS) [click to play animated GIF | MP4]

2.5-minute Target Sector Himawari-9 Infrared Window (10.4 µm) images (above) showed Herman as it rapidly intensified to a Category 3 storm, eventually displaying a pinhole eye. Note that the eye exhibited some trochoidal motion (wobble) as the storm moved south-southeastward — a behavior often seen with intense tropical cyclones.

===== 31 March Update =====

JMA Himawari-9 Infrared Window (10.4 µm) images, from 0602 UTC on 31 March to 1707 UTC on 31 March (credit: Scott Bachmeier, CIMSS) [click to play animated GIF | MP4]

Herman continued its remarkable rapid intensification on 31 March, with 2.5-minute Target Sector Himawari-9 Infrared images showing an intermittent open eye persisting past 15 UTC (above).

A Himawari-9 Infrared – Water Vapor Difference product from the CIMSS Tropical Cyclones site (below) displayed large values (shades of red to violet) — indicating that cloud tops within the eyewall were overshooting the tropopause (reference).

Himawari-9 Infrared – Water Vapor Difference product

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