Night Microphysics RGB changes as convection develops over the Texas panhandle

June 1st, 2022 |
GOES-16 Night Microphysics RGB, 0701-0911 UTC on 1 June 2022

The mp4 animation above (produced using CSPP Geosphere‘s latest beta version) shows strong convection over Oklahoma and the eastern Texas panhandle, with lower clouds (in a bluish hue) over the northwestern Texas panhandle. With time, the Night Microphysics RGB acquires a reddish hue (as cloud tops cool), and then convection develops. A nowcaster can use changes in the colors of this RGB to anticipate initiation. (A similar recent example is shown here).

The AWIPS imagery from 0701 UTC below shows the RGB with Level 2 Products: Cloud Top Phase — showing liquid water clouds over Texas where the RGB suggests low clouds, and Cloud Top Temperature — where values of 7-8oC are common. The default color table Cloud Top Temperature has been changed. Recall also that the Level 2 Cloud Top Temperature product is not produced for the CONUS sector, so Full-Disk values are shown. Surface winds suggest low-level convergence: winds are northeasterly over the NW Texas panhandle, and southeasterly to easterly over the southern portions of the Texas panhandle. GOES-16 Cloud Top Heights (not shown) show cloud heights around 12000 feet over the NW Texas panhandle.

GOES-16 Night Microphysics RGB (along with surface observations) (upper left); GOES-16 Cloud Top Phase (Upper right); GOES-16 Cloud-Top Temperature (lower left); GOES-16 Night Fog Brightness Temperature Difference (Lower right). All at 0701 UTC on 1 June 2022 (click to enlarge)

Fifty minutes later, at 0751, the band of low clouds over the northeastern Texas panhandle has reddened somewhat (click here for a toggle between 0701 and 0751). Cloud top temperatures in that cloud band have dropped to between 1o and 4oC, and cloud top heights have increased to 14000 feet. Cloud-top phase is still liquid however (except over northern New Mexico, as might be inferred by the yellower tinge to those low clouds in the RGB). There is also a red tint to the RGB just north of the obvious east-west band of clouds near the Hereford TX airport (where the temperature and dewpoint are 65 and 60, respectively, and no wind is reported). Convective initiation is likely occurring in these regions.

GOES-16 Night Microphysics RGB (along with surface observations) (upper left); GOES-16 Cloud Top Phase (Upper right); GOES-16 Cloud-Top Temperature (lower left); GOES-16 Night Fog Brightness Temperature Difference (Lower right). All at 0751 UTC on 1 June 2022 (click to enlarge)

From 0801 to 0816 UTC, shown below, supercooled clouds are noted, as the Night Microphysics RGB continues to redden. By 0816 UTC, mixed phase clouds are noted in the line developing near Hereford. Cloud-top heights increase from 15000 to 21000 feet between 0811 and 0816 UTC.

GOES-16 Night Microphysics RGB (along with surface observations) (upper left); GOES-16 Cloud Top Phase (Upper right); GOES-16 Cloud-Top Temperature (lower left); GOES-16 Night Fog Brightness Temperature Difference (Lower right). 0801-0816 on 1 June 2022 (click to enlarge)

By 0826 UTC, Cloud Tops are shown to include ice over the line developing over the east-central part of the Texas panhandle.

GOES-16 Night Microphysics RGB (along with surface observations) (upper left); GOES-16 Cloud Top Phase (Upper right); GOES-16 Cloud-Top Temperature (lower left); GOES-16 Night Fog Brightness Temperature Difference (Lower right). All at 0826 UTC on 1 June 2022 (click to enlarge)

A rocking animation of the 4-panels above, from 0801 to 0901 (and back) is here. If convection is expected overnight, and low clouds are present, use the Night Time Microphysics RGB to monitor when convection might initiate. Color changes in the low clouds give important information.

Using NUCAPS and GOES-16 Level 2 Stability products and LightningCast to anticipate lightning

February 25th, 2022 |
LightningCast Probability over Atlantic Ocean, 1731 – 1816 UTC on 25 February 2022, along with ABI imagery and GLM observations (Click to enlarge)

LightningCast (available here) is a CIMSS-developed product (created at the request of OPC and WPC) designed to relate current ABI fields (Band 2 (0.64 µm), 5 (1.61 µm), 13 (10.3 µm) and 15 (12.3 µm)) to the likelihood of future lightning. (A short training video on this product is available here) In the animation above, probability contours are shown (blue: 10%; cyan: 25%; green: 50%; magenta: 75%) for the 45 minutes between 1731 and 1816 UTC, overlain on a sandwich-type RGB that includes visible imagery and enhanced Band 13 imagery for cold cloud tops. Of particular interest for this blog post is the region that develops east of Delmarva (as indicated in this image at 1751 UTC); probabilities increase there starting at 1741 and the first lightning is observed by GLM at 1756 UTC and it becomes more constant by 1806 UTC.

The GOES-16 Band 13 imagery at 1701 UTC — 45 minutes before the onset of the LightningCast — and derived Lifted Index shows convection approaching a ribbon of lower stability (show in yellow) to the east of North Carolina. That stability product is suggesting: this is where convection is most likely to strengthen because stability is lower here. Then 45 minutes later, the LightningCast probability increases and lightning is observed!

GOES-16 Band 13 (10.3 µm) imagery, with derived Stability Indices (in clear air skies) at 1701 UTC on 25 February 2022 (Click to enlarge)

As noted in this blog post, some Level 2 products from GOES-R are clear sky only. The timing of this event was such that NUCAPS profiles could be used to fill in information where clouds obscure what is occurring (GOES level 2 stability product-wise). A challenge is that NUCAPS and GOES Stability products don’t match well (that is, it’s not easy to create a NUCAPS Lifted Index). The Total Totals Index derived from NUCAPS is shown below. (This figure shows the Retrieval Status of the profiles used). A corridor of instability is present where lightning-produced convection subsequently developed.

Gridded NUCAPS fields of Total Totals index at 1716 UTC on 25 February 2022 (click to enlarge)

Use GOES-R Stability indices and NUCAPS stability indices to identify regions where LightningCast might be needed in the future to highlight where lightning might occur. The synthesis of the different products is very helpful to creating the best forecast. AWIPS imagery in this blog post was created using the NOAA/NESDIS TOWR-S AWIPS Cloud Instance. Thank you!

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.