Cutoff low over northern Alaska

June 12th, 2020 |

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red [click to play animation | MP4]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red [click to play animation | MP4]

GOES-17 (GOES-West) Mid-level Water Vapor (6.9 µm) images (above) showed the circulation of an anomalous middle-tropospheric cutoff low over the northwestern portion of Alaska on 12 June 2020. A Potential Vorticity (PV) anomaly associated with this low was causing the dynamic tropopause — represented by the pressure of the PV1.5 surface — to descend as low as the 500 hPa pressure level.

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red and available NUCAPS sounding profiles denoted by green/yellow points [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) images, with contours of PV1.5 Pressure plotted in red and available NUCAPS sounding profiles denoted by green/yellow points [click to enlarge]

Just after 21 UTC, an overpass of the Suomi NPP satellite provided NUCAPS soundings (above) within much of the core of the cutoff low — the green NUCAPS sounding profile about 40 miles east/southeast of the 500 hPa PV1.5 pressure contour (below) displayed an apparent tropopause near the 400 hPa pressure level.

NUCAPS sounding profile [click to enlarge]

NUCAPS sounding profile [click to enlarge]

GOES-17 “Red” Visible (0.64 µm) images (below) revealed the development of numerous showers and thunderstorms across the Brooks Range and North Slope of Alaska, aided by instability beneath the cutoff low.

GOES-17 "Red" Visible (0.64 µm) images, with hourly surface reports plotted in red [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) images, with hourly surface reports plotted in red [click to play animation | MP4]

A higher spatial resolution view of these showers and thunderstorms was provided by a sequence of VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP, as viewed using RealEarth (below). A few of these thunderstorms moved toward the Arctic Coast, with one fairly impressive storm just southwest of Katovik which exhibited cloud-top infrared brightness temperatures near -60ºC (red enhancement) around 23 UTC.

VIIRS True Color (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [click to enlarge]

VIIRS True Color (RGB) and Infrared Window (11.45 µm) images from NOAA-20 and Suomi NPP [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.

Mount St. Helens: June 1980

June 12th, 2020 |

SMS-2

Vis and IR

Visible and Infrared NASA SMS-2 animation on June 13, 1980 between 02:30 and 07:00 UTC. The red square denotes the  approximate location of Mount St. Helens, and the arrows highlight the plumes of the two separate eruptions.  [Click to play mp4]

The main Mount St. Helens eruption was May 18, 1980 — yet there were also later paroxysmal eruptions. Imagery from NASA’s SMS-2 (Synchronous Meteorological Satellite) monitored two more Mount St. Helens eruptions on June 12th (local time), 1980, as shown above. Note that in “UTC-time”, the eruption took place on June 13th. A similar side-by-side SMS-2 visible and infrared animation (without the arrows) is available here (in addition to one without the red location box).

SMS-2 Visible image

NASA SMS-2 visible animation from June 13th (02:00 to 04:00 UTC), 1980. The red square denotes the  approximate location of Mount St. Helens. [Click to play mp4]

A visible band animation without the red square at the location of Mount St. Helens is shown above. The second plume coated Portland (OR) with ash. For more on this case, see Wikipedia and the USGS. Here’s the same loop and image, but without the red location box.

The volcanic ash plume was also evident in the infrared window band, below, but the imagery has fairly coarse spatial (and temporal) resolution compared to today’s GOES-R series ABI (which allows much improved volcanic cloud monitoring). This longer IR loop shows the 2nd plume as well.

IR image

NASA SMS-2 infrared animation from June 13th (02:45 to 04:00 UTC), 1980. The red square denotes the  approximate location of Mount St. Helens. [Click to play mp4]

Swipe between SMS-2 Visible and Infrared bands. Red square notes Mount St. Helens location.

Fade between a SMS-2 Visible and Infrared band.

Note that there is a geolocation offset between the two spectral bands. The satellite times listed are the image scan start times.

GOES-3

The experimental SMS series followed the ATS series, and was a precursor to the operational GOES.

GOES -3 also observed both volcanic ash plumes.

GOES-3 IR

GOES-3 Infrared animation from June 13, 1980. [Click to play mp4]

A slightly longer GOES-3 infrared animation is available here. NASA SMS-2 and NOAA GOES-3 data are via the University of Wisconsin-Madison SSEC Satellite Data Services.