True-color imagery from the CSPP Geosphere site, above, shows 4 named storms — Carlotta, Daniel, Emilia and Fabio — over the Pacific basin on 5 August. It is not common for 4 storms to exist simultaneously! The animation below during the day on the 5th shows the motion of the storms. Although Carlotta and Daniel, and Emilia and Fabio, are within close proximity, Fujiwhara interactions (during which the two storms rotate around each other) do not appear to be occurring.

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GOES-16 Band 2 Imagery from Mesoscale Sector 1, from the CSPP Geosphere site, above (click here for an animation with state/country borders), shows convection developing along the northern shore of Lake Erie and moving into Buffalo. One of these convective towers generated a weak tornado (storm report) at 1649 UTC.

The large-scale environment on this day was not expected to generate tornadoes. The (1300 UTC) Convective Outlook from the Storm Prediction Center, below, in a toggle with the tornado probabilities, showed a marginal risk, and very low tornado probabilities.

GOES-16 Day Cloud Phase Distinction RGB imagery, below, shows the glaciation of the developing convection as it moves out of Ontario, across extreme northern Lake Erie and into New York: the color in the RGB changes from green/cyan to yellow/orange. Note also the large-scale surface convergence in the plotted surface observations: west-southwesterly flow to the south of the developing line, west or west-northwest flow to the north of the developing line.

NOAA/CIMSS ProbSevere (v3) is a Machine-Learning tool that estimates the probability of severe weather. How did it perform in this environment? The animation below shows the ProbSevere polygon from 1535 UTC through 1710 UTC. ProbSevere highlights the cell that produced the tornado, and consistently tracks it through Buffalo.

ProbSevere objects can be probed to show how probabilities are changing, and to show the different observed parameters used to diagnose the probability. Values from 1635-1710 UTC are shown below. ProbTor and ProbHail values peaked at 1700 UTC, ProbWind peaked at 1655 UTC. Both times are after the tornado.

Note in the readouts above the clickable icon that references Object ID# 592509. That click yields a time series of various ProbSevere variables and components that are shown below (there are 4 more shown here). ProbSevere for this object increased at around 1615 UTC, but values are not large. GLM values — in the lower right — showed an increase as the tornado was occurring. This was a very difficult tornado to predict based on the ProbSevere values.

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GOES-16 Day Cloud Phase Distinction RGB imagery is overlain with GLM Flash Extent Density in an animation from 1640-1700. Note that the default AWIPS enhancement for FED has been altered considerably: the maximum value was changed from 260 to 20. FED increases to a peak of 15 at 1655 and 1656 UTC, having risen from 7 at 1649 UTC, the time of the tornado, before falling back to 6 by 1700 UTC. This subtle change is apparent because the default AWIPS enhancement for Flash Extent Density was altered.

The 1200 UTC Buffalo upper air soundings is shown above. Low-level shear is favorable. This tornado appears to have emerged out of a Lake-influenced circulation within broad convergence and its very small scale nature makes its affect on satellite imagery a distinct challenge to interpret.

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Added: It’s curious that this event occurred on the same day as the packet of gravity waves that developed over Michigan hours earlier (blog post). I tried very hard to see if there was a direct link between that event and this one. I didn’t find one.

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Strong convection developed over southern Lake Michigan early in the morning on 5 August, as depicted in the animation above. Multiple pilot reports of moderate turbulence occurred in/near the developing convection. Gravity waves developed on the upwind side of the deep convection, shown in the enhancement above as darker blue (that is, warmer brightness temperatures); the circulation with the gravity waves had an observable effect on approaching clouds as well. Note, for example, how the convection initially on the eastern central Lake Michigan shoreline (highlighted by the black arrow in the animation below) dissipates as it moves under the gravity wave structure. Clouds moving in from the northwest also change abruptly as they encounter the gravity wave barrier (and its vertical circulation).

Weighting Functions from the 1200 UTC Detroit Rawinsonde site, below (source), show contributions to the signal in the Band 8 water vapor imagery originating from a layer between 500 and 200 hPa.

The strong convection formed in the exit region of a 100-knot jet at 200 mb as shown in the analysis below. Note the large scale difluence in the region: north-northwest winds (40 knots) at Lincoln, IL; Northwest winds at 55 knots at Detroit MI; West winds at 65 knots in Maniwaki, QB!

The CIMSS Turbulence Product — that predicts via a Machine-learning algorithm the likelihood of Moderate or Greater (MOG) turbulence — increased markedly as the convection developed, as shown below.

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GOES-16 Visible imagery, below (from the CSPP Geosphere site), also shows the gravity waves, and their interaction with/affect on convection.

I am grateful to Greg Mann and TJ Turnage, Science and Operations Officers (SOOs) in Detroit and Grand Rapids, respectively, for their comments on this event (and for letting me know about it!)

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MIMIC Total Precipitable Water fields, above (source), for the 24 hours ending at 1700 UTC 4 August 2024, show the cyclonic spin (and ample moisture) associated with Tropical Storm Debby as the system moves northward from Cuba into the eastern Gulf of Mexico. (A tropical disturbance is also present south of Mexico in the tropical Eastern Pacific.) Abundant moisture is also present off the southeast coast of the USA, and as Debby moves north (landfall as a hurricane is predicted Monday morning in Florida’s Big Bend region; for the latest on Debby, consult the website of the National Hurricane Center), the storm’s circulation will draw that moisture inland. Very heavy rain is anticipated from Florida northeast into the Carolinas.

Scatterometry from OSCAT-3 on India’s OceanSat-3 and from ASCAT on EUMETSAT’s Metop-C, below, (available here) captured the changes in the circulation between 0515 UTC and 1607 UTC on 4 August 2024. At 0515 UTC, the strongest winds were on Debby’s eastern flank. Unfortunately, Metop-C (and Metop-B, not shown) did not sample that part of the storm during the day on 4 August.

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The animation below shows half-hourly imagery from 0406 – 1836 UTC on 4 August, bracketing the times of the Scatterometry overpasses above. Debby shows an increase in organization by the end of the animation, with the development of a central core of convection (albeit small!). Dry mid-level air is suggested to the west of the storm by the yellow enhancement in the water vapor imagery and the general lack of convection over the central Gulf of Mexico, but the dry air does not appear to be affecting the evolution of the system.

A GOES-16 mesosector (#2) has been positioned over the storm. One-minute imagery, below, for the hour ending 1850 UTC on 4 August 2024 (combined with GLM observations of Flash Extent Density) show the slow increase in organization of the storm.

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For the latest information on Debby, refer to the webpages of the National Hurricane Center. The SSEC/CIMSS Tropical Weather website also contains storms information. You can find more information as well at the websites of National Weather Service offices in Tallahassee, Jacksonville, Charleston (SC), Columbia, Atlanta and Wilmington (NC) . NOAA’s Weather Prediction Center is issuing excessive rainfall graphics for the storm as well, with 16-20 inches of rain predicted from Savannah GA to northeast of Charleston SC.

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