The Storm Prediction Center placed portions of the upper Midwest United States in a marginal risk of severe weather on 8 February 2024 and issued two mesoscale discussion on the thunderstorm development, one at 2053 UTC, one at 2345 UTC. The graphic from the 2053 UTC MD is shown below. The animation above shows clean window infrared imagery overlain by the Level 2 product Lifted Index (LI) that gauges the stability in the atmosphere. The AWIPS scaling for LI has been changed from the default to -5 to 10. Thunderstorms develop at the leading edge of the unstable air as it pushed into Wisconsin, and the first recorded February tornado in Wisconsin history was reported!

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GOES-16 Mid-level Water Vapor infrared imagery, below, shows the evolution of the atmosphere over the upper-midwest as the convection developed. As in the Window Channel imagery above, the swirl of the large upper-level cyclone moving through central Minnesota is obvious. A more subtle feature moving northeastward from northwest Missouri through southern Iowa and into northwest Illinois at the end of the animation might also be affecting the developing convection

The animation below shows LightningCast probabilities contoured over visible imagery, and the probability product gave lead time in most cases during this unusual lightning event.

The LightningCast website (here) includes time series plots (‘Aviation Lightning Dashboards’) of Probabilities along with GLM observations. Data from Rock County (KJVL) and Dane County (KMSN) airports, below, show an increase in probabilities about an hour before the GLM observations occurred.

The most unusual aspect of this convective line in southern Wisconsin was the tornado it produced (link), as shown below. The 2337 UTC time of the tornado is after the animations shown above. Did ProbSevere give information for this tornado?

ProbSevere version 3 is available at this website and the screen-capture, below, shows the view at 2336 UTC, just before the tornado observation, when ProbSevere was at 70%. The time-series plot of the values within the ProbSevere object (#253605) is shown at bottom.

It’s difficult to isolate a signal in ProbSevere that unilaterally says a tornado is present. Storm-relative helicity (the purple line in the Kinematics plot) and Environmental Bulk Shear (the cyan line in the Kinematics plot) are suggestive, but no field shows a peak near 2337 UTC. Use products such a ProbSevere as a tool, along with others (satellite, radar, etc), to judge whether or not a warning is warranted. Note that a warning was issued for this cell at 2304 UTC on 8 February 2024.

GOES-16 Mesoscale Sector 2 observed the Midwest at 1-minute intervals on 8 February. Band 13 imagery, below (rescaled so that the coldest cloud brightness temperatures are -80^o C vs. the default -109^o C), shows the cold cloud tops associated with the strong convection moving from Lafayette into Green County in Wisconsin.

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A closer look at 1-minute GOES-16 Visible and Infrared images centered over southern Wisconsin (below) included plots of Local Storm Reports — pulses of overshooting tops were evident in the vicinity of most of the reports of severe (or sub-severe) weather. The thunderstorms that produced wind/hail and two tornadoes across southern Wisconsin apparently developed just ahead of an approaching cold front / warm front intersection (WPC surface analysis). Here are a few AWIPS cursor samples of Local Storm Reports associated with the 2 tornadoes: 2333 UTC | 2335 UTC | 2336 UTC | 2341 UTC | 0000 UTC | 0020 UTC | Animation.

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The Sandwich Product is a composite image created by stacking visible light (0.64µm) and infrared (10.3 µm) channels. The resulting multi-dimensional image gives meteorologists and researchers an efficient way to study severe weather in near real-time with an added texture from the sandwich-like layers.

In this animation the preliminary tornado reports from SPC in Henry and Magnolia, Illinois are shown as a red “T” approximately when & where they were reported. The approximate location of the tornado on the north side of Albany, Wisconsin is shown as a red X at the end of the animation. The animation ends at 22:59 UTC, which is well before the tornado in Wisconsin was reported at 23:37 UTC (which was 5:37pm local, CST). The Sandwich Product is only useful during daylight hours.

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A model run that incorporates Polar Hyperspectral Soundings (that has been discussed on this blog, and at the Hazardous Weather Testbed) in the past gave good results with this strongly-forced event. The image below shows a 3-4 h forecast of composite reflectivity and Significant Tornado Parameter. Composite Reflectivity shows supercellular-like features, and also two separate locations of convection, one over southern Wisconsin, one over Illinois. The animations above (especially the Sandwich Product) also show those two main regions of convection. A model run initialized near 2000 UTC would include fine-scale moisture information from the early afternoon Polar overpasses that occurred that day (NOAA-20; NOAA-21), leading to a better definition of subsequent convection.

This event/set-up vaguely reminded the lead blog post author of this late-January 2023 event over Ohio, mostly because of the clear patch that allowed the used of derived stability indices!

The NWS forecast office in Milwaukee/Sullivan WI (WFO MKX) has a write-up on this event here, and a story map describing the event is available here.

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A distinct hot thermal signature (black to yellow to red pixels) of a new Sundhnúkagígar fissure eruption on the Reykjanes Peninsula in southwestern Iceland was apparent in GOES-16 (GOES-East) Shortwave Infrared (3.9 µm) imagery on 08 February 2024 (above). Station identifier BIRK is Reykjavik Airport, and BIKF is Keflavik International Airport.

Since the fissure eruption and subsequent lava flows began during the nighttime hours, the thermal signature also showed up well in GOES-16 Near-Infrared 1.61 µm and 2.24 µm imagery (below).

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.3 µm) images (above) showed thunderstorms that moved across Puerto Rico and the US Virgin Islands on 06 February 2024. These storms produced up to 4-5 inches of rainfall in parts of central Puerto Rico, with wind gusts as high as 41 kts (47 mph).

These thunderstorms were fueled by a plume of tropical moisture that was moving north-northeastward from northern South America, which passed directly over Puerto Rico during the entire day — as depicted by the MIMC TPW product (below).

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As tropical storm Nat moves away from the Samoan Islands and towards Tahiti, another Invest area, 98P, has developed north of the Samoan Islands. The animation above, from the MIMIC Total Precipitable Water site (link), shows a cyclonically-rotating concentration of moisture just north of Samoa, and moving east-southeastward toward Olosega and Ta’u. The Tropical Cyclone Formation Alert (TCFA) graphic (click here for text explanation) from the Joint Typhoon Warning Center (link), below, moves the center of the disturbed weather towards those islands. skirting the larger islands of Samoa. Flood watches and Heavy Surf Warnings are in effect for all of American Samoa.

Imagery from the CIMSS Tropical Weather website, below, helps gauge the threat of the storm. The imagery shows the Invest location at 1200 UTC along with the 1730 UTC infrared imagery, then the Invest Location with the 1730 UTC water vapor imagery along with the 1500 UTC analysis of 850-mb vorticity (notice its motion east-southeastward from the 1200 UTC Invest location, and also the vorticity associated with Tropical Storm Nat at the eastern edge of the domain), then the 1500 UTC analysis of 200-850 mb shear overlain on top of the infrared imagery (note that Nat has moved poleward into stronger shear, but invest 98P to the north of Samoa is within a persistent corridor of low shear that has existed for days), and finally the deep layer mean motion appropriate for a fairly weak system, motion that moves the system towards the eastsoutheast.

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Scatterometry is a useful tool to find circulation centers, but observations over the center must happen! The animation below (from this source) shows MetopB and MetopC observations in the past 2 days. The circulation of Tropical Cyclone Nat is sampled well on the 5th, but the region north of Samoa, where 98P is developing, has not had good coverage.

However, HY-2B and HY-2C satellites from China (available at this website), shown below, had good coverage over the region, as shown below. The 0930 UTC image shows the circulation (with much stronger winds towards the Equator) associated with 98P.

GOES-West imagery (taken from the CSPP Geosphere site) over the South Pacific on 6 February, above, shows 98P north of American Samoa, and Tropical Storm Nat to the east. Nat is showing the effects of increasing shear as the low-level circulation starts to emerge from beneath the deep convection by the end of the animation. One of the GOES-West mesosectors has been positioned over Samoa to monitor the evolution of the system. A 2-hour animation, below, of visible imagery shows the active convection, and low-level flow to the northwest (north of Tutuila).

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Added, 2200 UTC: Advisories on Tropical Depression 11P have started from JTWC and on Tropical Cyclone 08F from the Fiji RSMC. Despite the different numbers, they’re the same system.

The animation below (source), from 2130 UTC 6 February to 0120 UTC 7 February, shows the continued spin-up of the Tropical Depression in American Samoa waters. The GLM does not show lightning near the center of the storm. Meanwhile, Tropical Storm Nat, to the east, continues to exhibit characteristics of a sheared storm, with the low-level circulation separated from convection.

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