1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed a mesoscale convective system (MCS) that produced large hail and damaging winds — including gusts to 85 mph around 2120 UTC — across southern Minnesota on 04 June 2019 (SPC storm reports). Numerous well-defined overshooting tops were seen in the imagery, along with cloud-top gravity waves across the western portion of the MCS anvil.

The corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below) revealed overshooting tops with infrared brightness temperatures as cold as -70ºC — which corresponded to an air parcel rising to altitude around 13 km according to 18 UTC rawinsonde data from Chanhassen, Minnesota.

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GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed thunderstorms that developed across Interior Alaska on 02 June 2019. Some of these storms produced small hail, prompting the issuance of a Severe Thunderstorm Warning:

Severe Thunderstorm Warning including Fairbanks AK until 6:30 PM AKDT pic.twitter.com/DguPuFDsbg

— NWS Severe Tstorm (@NWSSevereTstorm) June 3, 2019

Usually the GOES-17 Mesoscale Domain Sector #2 is positioned over Alaska to provide 1-minute imagery — but on this day it was relocated to cover severe thunderstorms across New Mexico and Texas — so imagery over Alaska was only available at the 10-minute Full Disk scan interval.

In addition to the hail, these storms also produced heavy rainfall — especially at Fairbanks, with 0.65 inch falling in only 21 minutes.

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A comparison of a Landsat-8 False Color Red-Green-Blue (RGB) image and the GOES-16 River Flood Areal Extent product near the confluence of the Mississippi and Ohio Rivers as viewed using RealEarth (above) showed areas of river flooding in the Cape Girardeau, Missouri and Cairo, Illinois areas on 01 June 2019.

The River Flood Areal Extent product — derived using GOES-16 data — as depicted in AWIPS is shown below.

Farther to the northwest, a similar comparison of a Landsat-8 False Color RGB image and the GOES-16 River Flood Areal Extent product near the confluence of the Mississippi and Missouri Rivers (below) revealed river flooding near St. Louis, Missouri.

The GOES-16 River Flood Areal Extent product over this area as depicted in AWIPS is shown below.

The Mississippi River has not been as high as it is right now in St. Louis since 1993! At 43.41 ft. the river is now at it's second highest level on record at St. Louis. It's still rising! #stlwx #mowx pic.twitter.com/JkRPkRxPOZ

— NWS St. Louis (@NWSStLouis) June 2, 2019

Maps of 7, 14 and 30-day precipitation (below) depicted heavy rainfall focused across southern Iowa, northern Missouri and northwestern Illinois — it was this heavy rain that exacerbated the ongoing river flooding problems in parts of the central US.

Much of the 30-day precipitation north (upstream) of the flooding areas shown above was 4-8 inches above normal, or 200-300% of normal (below).

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Strong near-surface inversions over the upper-midwest early on 1 June 2019 (as shown by 1200 UTC Skew-Ts at Green Bay, WI, Detroit/WhiteLake, MI and Gaylord, MI) helped support the presence of southward-propagating bore features, as shown in the still image (an animation) of radar imagery above (Courtesy Fred Best, SSEC), and (more subtly) in the water vapor imagery (Courtesy Scott Bachmeier) below.

The pressure sensor at the top of the Atmospheric Oceanic and Space Science Building showed many small time-scale pressure perturbations on this day. (Image courtesy Pete Pokrandt)

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Later in the day, strong convection developed over southwestern Lower Michigan, starting shortly after 2215 UTC.  The visible imagery below shows 1-minute imagery (GOES-16 ABI Band 2, 0.64 µm) from a Mesoscale sector positioned over the convection.  At the start, the parallel lines of low clouds suggest a bore feature is propagating southward towards strong convection over northern Indiana and northern Ohio.  Two things happen when that feature meets the convective outflow: some energy is apparently reflected to the north, but very strong convection rapidly develops near Battle Creek MI, where 2″ hail was observed at 2235 UTC (SPC Storm Reports).

The clean window (GOES 16 ABI Band 13, 10.3 µm) animation during the day, below, show many features suggesting bore/gravity wave propagation over the area. It is challenging to pick out the impulse from this animation that lead to the severe convection that hit Battle Creek.

The Low-Level water vapor animation, shown below, also shows many features that resemble gravity waves or bores, but it also shows a line of parallel features moving towards the site of convective initiation (Consider this short loop from 2126 to 2156 UTC, for example).

For convection to initiate, instability should be present. The graphic below from the Storm Prediction Center mesoanalysis website shows a nose of unstable air (represented by high values of CAPE) encroaching into southwestern Lower Michigan.

GOES-16 Baseline Products can also diagnose instability. On 1 June 2019, however, abundant cloudiness limited the utility of the Baseline clear-sky only products, but AllSky versions have been developed and are available online at this website. The animation below shows the evolution of the AllSky Lifted Index from 1826 through 2356 UTC on 1 June 2019. In agreement with the SPC analysis, the AllSky product shows a nose of instability pushing into southwestern lower Michigan. An southward-propagating impulse (apparent in both visible and low-level water vapor imagery) meeting this gradient in instability did initiate convection on this day.

NOAA/CIMSS ProbSevere (v.2), a tool designed to give confidence that severe weather might occur in the next 60 minutes, shown below, tracked the rapid evolution of the storm. ProbHail increased from 7% at 2220 UTC to 81% at 2230 UTC!

The chart below, from John Cintineo, SSEC/CIMSS, graphically shows the very rapid development of Prob Hail values. Much of the increase in ProbHail was driven by MESH and Total Lightning observations. When an impulse enters a region of instability in a good environment, explosive growth can result.

Many thanks to TJ Turnage, NWS Grand Rapids, for alerting us to this very interesting case.

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