Using GOES-R Level 2 stability products to help nowcast the cessation of convective initiation

July 4th, 2020 |

GOES-16 Visible Imagery (0.64 µm), left, and Derived Stability estimates of Lifted Index (right), from 1001 to 1656 UTC on 4 July 2020 (click to animate)

The animation above shows GOES-16 visible imagery (Band 2, 0.64 µm) and stability indices. Initially an obvious gradient in stability is present where isolated convection is developing over southwestern Wisconsin. As the gradient relaxes, the convection dissipates even though instability is, in general increasing. A radar animation (clipped from RealEarth) is shown below.  The showers have largely dissipated over southwestern Wisconsin by 1700 UTC.

The absence of gradients in the derived stability product can often mean that convection will not initiate.  In this case, the relaxation of the gradient went hand-in-hand with the dissipation of convection.

MRMS Base Reflectivity, 1000 – 1700 UTC on 4 July 2020 (Click to enlarge)

Shower initiation over Wisconsin

June 12th, 2020 |

GOES-16 ABI Band 2 (0.64 ) visible imagery (left) and Midwest Composite Radar (right), 1736 – 2100 UTC on 13 June 2020 (Click to animate)

Showers developed over southern Wisconsin late in the day on 12 June 2020. What satellite products could be used to anticipate where the showers would develop? The animation of visible and radar, above, shows that the storms initiated near a boundary (mostly stationary) that separated Lake Michigan-influenced air with less stable air (based on cumuliform cloud development) to the south and west. Showers develop near the lake breeze front starting around 2000 UTC; a parallax shift is obvious between the radar and satellite (2100 UTC example) A parallax correction on the satellite imagery would shift the cloud locations towards the sub-satellite point (0, 75.2 W for GOES-East).

NUCAPS (NOAA-Unique Combined Atmospheric Processing System) soundings combine infrared and microwave information from the high spectral resolution CrIS (Cross-track Infrared Sounder) and ATMS (Advanced Technology Microwave Sounder) instruments on NOAA-20 to yield estimates of the thermodynamic structure of the atmosphere. NOAA-20 overflew the western Great Lakes shortly after 1800 UTC on 12 June, and clear skies at the time means the infrared information was complete. (In cloudy skies, NUCAPS soundings are more typically driven by ATMS data, which has coarser spectral and horizontal resolution).

The Total Totals index shown below was derived from the NUCAPS thermodynamic information. A gradient in stability exists between the most unstable air in western Wisconsin and the more stable lake-influenced air over eastern Wisconsin.

Total Totals index derived from NOAA-20 NUCAPS data, 1840 UTC on 12 June 2020 (Click to enlarge)

The low-level lapse rate, below, (from 900-700 mb), also shows a gradient in stability in the region where shower development occurred. It is not unusual for shower initiation to occur in gradients of stability (Example 1, Example 2,…), so that is a region on which to focus when waiting for convection to start.

900-700 mb Lapse Rates derived from NOAA-20 NUCAPS data, 1840 UTC on 12 June 2020 (Click to enlarge)

Once the shower development occurs, when will lightning occur?  As noted in this blog post, the Day Cloud Phase Distinction Red-Green-Blue imagery that includes the 1.61 µm band (at which wavelength reflectance is greatly affected by the presence of ice) gives a visual clue to when glaciation occurs, and cloud-top glaciation commonly precedes lightning development.  The animation below shows the Day Cloud Phase Distinction on the left, and the Day Cloud Phase Distinction overlain with Geostationary Lightning Mapper (GLM) Flash Extent Density.

There are only two detected lightning flashes in this animation — and in both cases, the Day Cloud Phase Distinction has become more orange/yellow and less green/blue before the lightning strike. This color change occurs as the 1.61 µm imagery becomes darker: ice in the cloud top increases the absorption (and reduces the reflectance) of 1.61 µm solar energy. Compare the 2111, 2116 and 2121 imagery for the lightning strike near Madison in Dane County; Similarly, compare the 2051, 2056, 2101 and 2106 imagery for the 2101 UTC lightning strike in Waukesha county). There are subtle color changes (on other days the changes are more obvious!) in the Day Cloud Phase Distinction RGB that preceded lightning events.

GOES-16 Day Cloud Phase Distinction (left), and Day Cloud Phase Distinction overlain with Geostationary Lightning Mapper (GLM) data (Click to animate)


GOES-16 Level 2 Products include Derived Stability Products (these can be found online here as well), and the mostly clear skies on 12 June meant a good signal.  The Baseline Lifted Index, shown below from 1701 through 2256 UTC,  shows convection developing along the eastern edge of less stable air.

GOES-16 Derived Stability Index (Lifted Index) in clear regions, GOES-16 ABI Band 13 (10.3 µm) infrared imagery in cloud regions, 1701-2256 UTC on 12 June 2020 (Click to animate)

Is there an easily identifiable trigger that spawned these storms? Water Vapor imagery often shows impulses in clear skies. The two RGB products below combine different water vapor channels.  There is a subtle increase in the amount of orange in the Differential Water Vapor before the convection starts.  This increase in the red component is an increase in the brightness temperature difference between upper and lower water vapor channels, a difference that can be associated with upper-tropospheric forcing.  The simple water vapor RGB (that includes the upper and lower water vapor channels, but not the difference between them) on the right shows no obvious signal.

GOES-16 Differential Water Vapor RGB (left) and SImple Water Vapor RGB (right) from 0916 to 2116 UTC on 12 June 2020 (Click to animate).

The Air Mass RGB (described here) also has the split water vapor difference as its red component. The animation below (from this site), shows a subtle change in air mass (cooler, dryer air moving southward from Canada) that could have provided an additional triggering mechanism for the convection.

GOES-16 Air Mass RGB, 1541 to 2141 UTC on 12 June 2020 (Click to enlarge)


Webcams in Madison, WI, that capture the evolution of these storms, and also show the GOES-16 imagery (derived from this site), are available at this tweet from @GOESGuy.

Severe Weather over the Upper Midwest

June 2nd, 2020 |

GOES-16 ABI Band 13 (10.3 µm) imagery and clear-sky estimates of Convective Available Potential Energy (CAPE), 1921-2146 UTC (Click to enlarge)

Severe weather occurred over Minnesota and Wisconsin on 2 June 2020, and the storms developed in clear skies. This allowed GOES-16 Derived Stability Indices (a clear-sky product) to provide information on the near-storm environment. The animation above combines GOES-16 Clean Window infrared (10.3 µm) imagery (where clouds exist) with Convective Available Potential Energy (CAPE) estimated from GOES-16 Advanced Baseline Imager channel information (that adjusts an initial field created using GFS data); this Baseline product (and others including all-sky products) can be found online here).  Strong convection over Minnesota at this time was supported in part by instability diagnosed to its south.

Note how, south of the main convection, a second line of convection initiated over southern Minnesota at around 2030 UTC, along the northern edge of the diagnosed CAPE maximum.  When do you think lightning initiated with this second line of convection? What imagery/products will help in that assessment?

The 4-panel animation, below, shows the initiation of convection in the southern line, from 2031 to 2101 UTC.  The developing convection is fairly bright in the Snow/Ice channel initially, consistent with the presence of clouds made up of water droplets.  The Cloud Phase product shows water (or supercooled water) at these times, and the Day Cloud Phase Distinction color of the clouds is mostly greenish.

As glaciation occurs, the clouds in the Snow/Ice channel become darker:  ice absorbs (rather than reflects) energy at 1.61 µm so less is detected by the satellite.  The change in the 1.61 µm channel reduces the amount of blue in the Day Cloud Phase Distinction RGB (so pixels acquire a yellow or red hue), and the Cloud Phase product also detects mixed phase and ice clouds.  Once the glaciation has occurred, lightning production is more likely, and at 2101 UTC, the GLM detects lightning activity.  (Here is the 2101 UTC Day Cloud Phase Distinction image without GLM overlain; here are toggles between 2056 and 2101 UTC without and with GLM overlain;  a toggle between the 2056 and 2101 UTC Cloud Phase product is here; ice is present at 2056 UTC (and actually at 2051 UTC!) but more widespread at 2101 UTC). Of course, a 1-minute mesoscale sector could give even better temporal resolution of cloud phase changes than CONUS scans’ 5-minute time steps.

GOES-16 ABI Band 2 Visible (0.64 µm, upper left), the Band 5 “Snow/Ice” channel (1.61 µm, upper right), the derived level 2 Cloud Phase  Product (lower left), and the Day Cloud Phase Distinction Red/Green/Blue Composite (with GLM observations of Flash Extent Density, lower right) from 2031 to 2101 UTC

NOAA-20 overflew this region shortly after noon on 2 June, and the thermodynamic information from the infrared and microwave sounder instruments on board can be used to diagnose instability. The toggle below compares the total totals index computed from gridded NUCAPS data with the GOES-16 clear-sky estimates of CAPE.

Both measures of instability agree that the region of instability is narrow, and that its axis extends from central Wisconsin west-southwestward to southwest Minnesota and southeast South Dakota.

GOES-16 Derived Convective Available Potential Energy and Gridded NUCAPS field of total totals index, ca. 1830 UTC on 2 June 2020 (Click to enlarge)

Gridded NUCAPS fields are created from soundings that may or may not have converged (that is, from points displayed in AWIPS as green — infrared and microwave retrievals converged), yellow (infrared retrieval failed, microwave retrieval converged) or red (infrared and microwave retrievals failed)).  The image below shows surface observations with the G16 Clean Window (10.3 µm) overlain with NUCAPS Sounding Points (This figure shows the total totals index overlain with the NUCAPS sounding points).  As expected because of the clear skies, most of the NUCAPS Soundings south of the convection show both infrared and microwave retrieval convergence: dots are green.

GOES-16 Clean Window (Band 13, 10.3 µm) infrared imagery, surface observations, and NUCAPS Sounding observation points, 1831 UTC on 2 June 2020 (Click to enlarge)

NUCAPS data that is gridded can include effects that are related to how well (or how poorly) a NUCAPS sounding observes and estimates the boundary layer. The sounding below is from a ‘green’ point in extreme south-central Minnesota (to the northeast of the observation plotted at Spencer Iowa). Surface dewpoints are observed in the mid-60s; however, the original NUCAPS sounding, shown below, shows a dewpoint near 60. When the lower-tropospheric dewpoints values are increased towards more representative values, estimated MLCAPE and MUCAPE as reported in the NSharp readout in AWIPS increase as well, from 2466 to 3404, and from 2635 to 3630, respectively. When using gridded NUCAPS estimates of thermodynamic variables that include surface or near-surface variables, consider just how well the NUCAPS soundings can observe that part of the troposphere.

NUCAPS Sounding, original and modified, at 43.78 N, 94.73 W at ~1800 UTC on 2 June 2020 (Click to enlarge)

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with SPC Storm Reports plotted in red [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-16 “Red” Visible (0.64 µm) images with time-matched plots of SPC Storm Reports (above) showed the development of these storms during the 1700-0112 UTC period.

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below) revealed pulsing overshooting tops which exhibited cloud-top infrared brightness temperatures in the -70 to -79ºC range (darker black to brighter shades of white). Evidence of Above-Anvil Cirrus Plumes (reference | VISIT training) was seen in the Visible and Infrared imagery.

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC storm reports plotted in cyan [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with SPC storm reports plotted in cyan [click to play animation | MP4]

NUCAPS Soundings surrounding an isolated Thundershower

August 14th, 2019 |

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 (Click to enlarge)

The GOES-16 Visible (0.64 µm) image above shows a weak thunderstorm over southeastern Oklahoma surrounding an decaying outflow boundary.  (Click here to see an animation of the visible imagery). The convection did not look particularly robust, but it did produce lightning that was detected by the Geostationary Lightning Mapper (GLM), as shown below.

GOES-16 ABI Band 2 (0.64 µm) and GLM observations of Flash Extent Density at 1946 UTC on 14 August 2019

Lightning requires charge separation in a cloud; typically lightning occurs after the cloud top glaciates. During daytime, glaciation can be detected with ABI Band 5, at 1.61 µm, the so-called Snow/Ice band. The toggle below shows the visible, snow/ice band, and the Baseline Cloud Phase product. Glaciation is indicated.

GOES-16 ABI Band 2 (0.64 µm), Band 5 (1.61 µm) and Baseline Cloud Phase at 1946 UTC on 14 August 2019

This case is interesting because NOAA-20 overflew the convection, and soundings were produced around the convection, as shown below.

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 along with NUCAPS Sounding Points at 1945 UTC

The animation below steps north-south through seven profiles that surround the weak convection. Note that a profile near the convection has thermodynamic parameters more favorable for convection than at the other profiles.  For example, NUCAPS profiles show the convection at the northern edge of a precipitable water gradient, and also in a local minimum of inhibition.    Although the convection has initiated here, the fields do suggest that NUCAPS can be used to monitor thermodynamics at small scales before initiation.

NUCAPS Soundings at various points north, south and within convection at 1946 UTC on 14 August 2019 (Click to enlarge) Thermodynamic variables from the sounding are noted.

Horizontal gridded information derived from NUCAPS data will be in AWIPS shortly.  See this post from Emily Berndt at SPoRT!