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Hole punch clouds over the Upper Midwest

On the morning of Sunday, November 7th, numerous elongated hole punch clouds were visible over the Upper Midwest, including parts of Wisconsin, Illinois, Iowa, and Minnesota. Also called fall streak clouds, these are a relatively rare phenomenon that form because of the unusual properties of cloud droplets.While most people know... Read More

On the morning of Sunday, November 7th, numerous elongated hole punch clouds were visible over the Upper Midwest, including parts of Wisconsin, Illinois, Iowa, and Minnesota. Also called fall streak clouds, these are a relatively rare phenomenon that form because of the unusual properties of cloud droplets.

Photo of a hole punch cloud and the associated fall streaks, taken on the east side of Madison, WI, at 11:20 AM CST on Sunday, November 7th. Photo by the author.

While most people know the freezing temperature of water is 0 °C (32 °F), that’s only true when dealing with a flat surface.  A curved droplet has more energy in it due to surface tension squeezing the droplet together, and so the air temperature has to be colder in order to make the droplet cold enough to freeze.  As a result, clouds of liquid water below freezing are relatively common, especially in the spring and fall when temperatures at cloud level are just below freezing.  These are called supercooled clouds.

Another commonly-known fact about water is if the relative humidity of the air is less than 100%, liquid water will evaporate.  Again, that’s not necessarily true for cloud droplets. What is especially interesting is that the relative humidity required to support growth is bigger for a cloud droplet than it is for an ice crystal.  Given an environment with both cloud droplets and ice crystals, the droplets will evaporate and the ice crystals will grow.  This is known as the Bergeron-Findeisen process and is a key part of forming precipitation from cold clouds. 

Both cloud droplets and ice crystals require a nucleus to form. Dust, pollen, and other aerosols are common nuclei.  While water can condense on many different aerosols, ice crystals are much more selective. Due to the rigid crystal shape of ice, it can only form on aerosols that have a similar structure. This is, in part, why supercooled clouds are relatively common: there’s just not enough ice nuclei around for ice crystals to form.  

That brings us to Sunday morning: a rather large altostratus deck was present across the upper midwest. Even though the surface temperature was approaching 16 °C (60 °F), the clouds were high enough above the surface that their temperature was below freezing.  The morning sounding from Davenport, IA, showed that the freezing level was around 3300 m (11,000 ft) above sea level, but airport observations around the region showed that cloud bases were around 5100 m (17,000 ft). Without a sufficient amount of ice nuclei present, they stayed in the liquid phase and were thus supercooled clouds.

1200 UTC (6 AM CST) sounding from Davenport, IA, showing the freezing level was approximately 3300 m (11,000 ft) above sea level. Image from the University of Wyoming sounding archive.

However, numerous aircraft were flying through those clouds as they ascended from or descended into airports across the region.  The moisture-rich exhaust from the planes was deposited into the low-pressure wake behind the airplane, where it cooled very quickly and formed ice.  Normally, this would form the classic contrails seen behind many aircraft in the sky.  However, in this case the contrail served as a nucleation site within the supercooled cloud.  The droplets near the ice rapidly evaporated and the ice crystals generated by the airplanes grew even larger. In some cases, the crystals grew so large that they could no longer be supported aloft, and they started falling to the ground as snow.  They didn’t reach the ground because the air was warm and dry beneath the cloud, and so the ice crystals either melted and evaporated, or they sublimated (going directly from solid to vapor).  

The Terra polar-orbiting satellite happened to be passing overhead at the right time to capture this phenomenon while it was happening around 10:30 AM CST.  Almost-clear holes are seen in northeastern Iowa and southeastern Minnesota, while in northern Illinois they appear as elongated ice clouds surrounded by a clear region embedded within a larger cloud.  

MODIS True-color image from the 10:30 AM CST overpass showing hole punch clouds, circled in white.

The loop from Band 2 (0.64 micron) from GOES-16 also shows these clouds propagating through the region. This view, over Dane County (Madison) Wisconsin, shows one hour of visible-wavelength satellite imagery. The embedded ice clouds are clearly visible as structures that propagate from the west to the east. While the airplanes that created these structures have long since departed to other locations, their impact remained for some time.

Animation of GOES-16 Band 2 reflectance over south central Wisconsin. Dane County, home of Madison, is outlined.

Other blog posts showing examples of hole punch clouds can be found here.

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Radiation fog across the Lower Mississippi Valley and Gulf Coast

The suite of nighttime GOES-16 (GOES-East) Fog / Low Stratus products — Marginal Visual Flight Rules (MVFR) Probability, Instrument Flight Rules (IFR) Probability, Low Instrument Flight Rules (LIFR) Probability, and Cloud Thickness — along with the subsequent daytime “Red” Visible (0.64 µm) images (above) showed the increasing areal coverage of vertically shallow (Cloud Thickness... Read More

GOES-16 MVFR Probability, IFR Probability, Low IFR Probability, Cloud Thickness products, along with “Red” Visible (0.64 µm) images [click to play animated GIF | MP4]

The suite of nighttime GOES-16 (GOES-East) Fog / Low Stratus products — Marginal Visual Flight Rules (MVFR) Probability, Instrument Flight Rules (IFR) Probability, Low Instrument Flight Rules (LIFR) Probability, and Cloud Thickness — along with the subsequent daytime “Red” Visible (0.64 µm) images (above) showed the increasing areal coverage of vertically shallow (Cloud Thickness values less than 1000 feet) radiation fog across parts of Texas, Louisiana, Arkansas and Mississippi on 07 November 2021. The surface visibility was reduced to zero at a few sites, with cloud ceilings as low as 100 feet being reported. Visible images showed that this shallow fog layer then quickly dissipated within a few hours after sunrise.

This fog was forming due to optimal radiational cooling conditions — light winds, along with a general lack of cloud cover — beneath a ridge of high pressure over that region (below). Surface air temperatures dropped into the 30s and 40s F across much of the area where this fog formed.

GOES-16 IFR Probability product at 0901 and 1201 UTC, with overlays of mean seal level pressure at those times [click to enlarge]

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Early November with little snow

A MODIS-based true-color cloud-free image, above, from SSEC’s Real Earth (link) shows a distinct lack of snow cover — for early November!!! — over the USA and Canada. These BRDF (Bidirectional Reflectance Distribution Function) fields account for sun angle, viewing angle and surface type; data over the past 16 days are used in... Read More

BRDF Imagery from MODIS, 7 November 2021 (Click to enlarge)

A MODIS-based true-color cloud-free image, above, from SSEC’s Real Earth (link) shows a distinct lack of snow cover — for early November!!! — over the USA and Canada. These BRDF (Bidirectional Reflectance Distribution Function) fields account for sun angle, viewing angle and surface type; data over the past 16 days are used in this computation. Monitor these fields at the RealEarth link in the coming weeks to see the inevitable (albeit delayed!) increase in snow cover over North America!

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Karymsky eruption on Kamchatka

Imagery from the NOAA/CIMSS Volcanic Monitoring website (link) shows derived Ash loading (above) from the 3 November eruption of Karymsky on the Kamchatka peninsula. The website identified an eruption beginning around 0720 UTC, with an obvious eruptive plume by 0740 UTC. In addition to Ash Loading, shown above, Ash Height... Read More

Himawari-8 derived Ash Loading, 0440 – 1230 UTC on 3 November 2021

Imagery from the NOAA/CIMSS Volcanic Monitoring website (link) shows derived Ash loading (above) from the 3 November eruption of Karymsky on the Kamchatka peninsula. The website identified an eruption beginning around 0720 UTC, with an obvious eruptive plume by 0740 UTC. In addition to Ash Loading, shown above, Ash Height (click here for an 8-h mp4 animation) was also derived; a still image from 1110 UTC, below, shows two separate plumes, one around 6 km (indicated by the white arrow), one closer to 10-12 km (indicated by the magenta arrow).

Retrieved Volcanic Ash height, 1110 UTC on 3 November 2021 (Click to enlarge)

In addition to quantitative estimates of ash, Himawari-8 (and GOES-R and GK2A) channels can be combined in RGBs to highlight qualitatitely regions where ash is likely. The animation below (from Scott Bachmeier) shows the Ash RGB. (Click here for a Quick Guide on this RGB)

Himawari-8 Ash RGB Imagery showing the Karymsky Ash Cloud, 0710-1250 UTC 3 November 2021 (click to enlarge)

A tip of the (winter) Hat to Nathan Eckstein, NWS AAWU in Anchorage, for alerting us to this event.


Update: Nate Eckstein sent along the following Himawari imagery time-matched with VIIRS SO2 Index imagery provided by Carl Dierking at GINA. The 1300 UTC RGB imagery suggests that the north (and east, given the projection) side of the plume is rich in ash whereas the southern (and western) part of the plume contains more SO2. The Suomi NPP VIIRS SO2 Index product (more information on that product is here) tells a similar story: most of the SO2 from this eruption is confined to the southwestern portion of the plume.

Himawari-8 RGB products from 1300 UTC on 3 November 2021: Ash RGB (upper left) and SO2 RGB (lower left); a VIIRS SO2 Index image from 1400 UTC on 3 November 2021. (click to enlarge)

Imagery from later (0050 UTC on 4 November), below, tells a similar story. The SO2 aspect of the plume can be detected in the False Color Imagery below in the upper left — the region of bright yellow to the south of the arcing red feature that is the ash cloud. Ash/Dust Cloud Height (below, bottom left) keys in on that arced feature, and the SO2-rich feature is mostly ignored in the figure. In contrast, the SO2 index product, below on the right, from NOAA-20 VIIRS data at 0050 UTC, shows a strong signal of SO2 — but the arcing ash cloud is barely apparent!

Himawari-8 False Color Imagery, upper left, at 0050 UTC on 4 November 2021; Himawari-8 Derived Ash/Dust Height Product, lower left, also at 0500 UTC on 4 November 2021 (both images from https://volcano.ssec.wisc.edu); NOAA-20 VIIRS SO2 Index, 0500 UTC on 4 November 2021 (Click to enlarge)

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