Severe Weather in Nebraska

June 16th, 2014

Unusual twin tornadoes (click here for a summary of photos/videos from the Capitol Weather Gang) formed in northeastern Nebraska (Storm Reports from SPC) late in the afternoon of the 16th of June 2014. How did satellite data anticipate the development and progression of the severe convection? GOES-13 Sounder data painted a picture of ongoing destabilization in the area. For example, the CIMSS NearCast Product, which  arises from a two-layer Lagrangian Transport Model of Equivalent Potential Temperature, shows increasing stability in a forecast for 2100 UTC on 16 June in forecasts from 1800, 1900 and 2000 UTC, below.

CIMSS NearCast forecasts of Theta-e Differences between two layers, all at 2100 UTC, with initial times at 1800, 1900 and 2000 UTC (click to animate)

CIMSS NearCast forecasts of Theta-e Differences between two layers, all at 2100 UTC, with initial times at 1800, 1900 and 2000 UTC (click to animate)

The NearCast output, derived from GOES Sounder data, can predict in advance where axes of instability (and more importantly, where gradients in instability; see also comments on NearCast here and here) will occur. GOES Sounder data can also be used to diagnose the present state of the atmosphere. On this particular day, GOES Sounder estimates of Lifted Index (1400, 2000 and 0000 UTC) and CAPE (1400, 2000 and 0000 UTC) all showed ongoing destabilization over the Plains.

GOES-13 Sounder DPI Analyses of Lifted Index and Convective Available Potential Energy at 1400 and 2000 UTC on 16 June and at 0000 UTC on 17 June

GOES-13 Sounder DPI Analyses of Lifted Index and Convective Available Potential Energy at 1400 and 2000 UTC on 16 June and at 0000 UTC on 17 June

The products above outline the general area where convection might develop. Once the convection has developed, the NOAA/CIMSS ProbSevere product can be used to diagnose/monitor the likelihood of severe weather (large hail, strong winds, or tornadoes) developing — specifically, the likelihood of when severe weather might first occur. The animation below shows the evolution of the tornadic cell as it moved northeastward through Nebraska. Satellite predictors (Normalized Vertical Growth Rate and Maximum Glaciation Rate) for this cell were strong; both were observed at 1925 UTC, nearly an hour before the observed severe weather. ProbSevere first exceeded 50% at 1950 UTC, 13 minutes before the warning at 2003 UTC. 1-inch diameter hail was reported at 2016 UTC. The first tornado report occurred at 2040 UTC.

NOAA/CIMSS ProbSevere model

NOAA/CIMSS ProbSevere model

MUCAPE in the ProbSevere product above is around 4000-5000 J/kg. A special sounding at OAX (1900 UTC) shows similar CAPE values.

The Suomi NPP satellite had a timely overpass over the Great Plains at around 2000 UTC on 16 June 2014. NUCAPS Soundings from Suomi NPP are available, as plotted below, and can be used to estimate instability.

Suomi NPP VIIRS 11.45 µm imagery with NUCAPS sounding positions (Green Dots) Superimposed (Click to enlarge)

Suomi NPP VIIRS 11.45 µm imagery with NUCAPS sounding positions (Green Dots) Superimposed (Click to enlarge)

A sounding at ~42º N, ~97.8º W, below, shows CAPE values around 1000. However, note that the boundary layer temperature and dewpoint are too cool (surface temperature = 21º C) and too dry (surface dewpoint = 12º C). A benefit of the Sounding Software in AWIPS II, however, is that soundings can be easily modified. If the boundary layer is altered such that dewpoints are closer to observed METAR values (20º C), then CAPE values increase to 3000; if the temperatures are modified to be closer to observed values, CAPE increases to more than 4800.

NUCAPS Sounding at 42.07 N, 97.78 W, ~2000 UTC on 16 June 2014 (Click to enlarge)

NUCAPS Sounding at 42.07 N, 97.78 W, ~2000 UTC on 16 June 2014 (Click to enlarge)

Suomi NPP VIIRS data at different wavelengths (0.64 µm visible, 1.61 µm near-IR and 11.45 µm longwave IR), below, give a view of the storm just before severe hail was observed. The 1.61 µm imagery suggests a fully-glaciated anvil, and the 11.45 µm imagery shows evidence of several isolated overshooting tops.

Suomi NPP VIIRS data (0.64 µm, 1.61 µm and 11.45 µm) at 2004 UTC on 16 June 2014 (Click to animate)

Suomi NPP VIIRS data (0.64 µm, 1.61 µm and 11.45 µm) at 2004 UTC on 16 June 2014 (Click to animate)

Click here for a visible image animation from GOES-13; here is an infrared image animation. The famous twin tornadoes in Elkhart, IN, during the Palm Sunday outbreak in 1965 can be seen here.

GOES-14 SRSOR: Thunderstorm development over Kentucky

May 22nd, 2014
GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-13 DPI Convective Available Potential Energy (CAPE) on May 22, times as indicated (click to play animation)

GOES-14 operations in SRSOR mode deliver the ability to monitor convective development at very short time-scales. A good example of this occurred over the lower Ohio Valley/western Kentucky on May 22nd. The animation of GOES-13 Sounder Derived Product Imagery of CAPE (above) and of Lifted Index (1300 and 1700 UTC) showed considerable instability waiting to be released.

GOES-14 SRSOR animations can be used to monitor the evolving cumulus field in the search for the tower that will break the cap (Nashville, TN/Lincoln IL Soundings from 1200 UTC). The animation below shows visible imagery from 1800 UTC through 2011 UTC, at which time the convection has developed. Initial convection dissipates, but eventually develops along the Ohio River in western Kentucky (cumulus clouds continue to grow/dissipate over the Mississippi River valley throughout the animation).

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

GOES-14 Visible Imagery (0.62 µm) on May 22, times as indicated (click to play animation)

By 1900 UTC, convective development over the lower Ohio Valley is vigorous enough that Cloud-Top Cooling algorithm from CIMSS (below) has flagged growing clouds, with values exceeding 20º C/15 minutes.

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

Instanteous Cloud-Top Cooling computed from GOES-13 at 1900 UTC 22 May 2014 (click to enlarge)

How does the NOAA/CIMSS ProbSevere model  then change with time as the convection intensifies? The 1904 and 1906 UTC ProbSevere products, toggled below, shows values increasing from 49% to 54% as Satellite Growth rates at 1900 UTC are incorporated at 1906 UTC. ProbSevere values then dropped (1912 UTC, 1922 UTC) as MRMS MESH decreased.

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1904 and 1906 UTC on 22 May 2014 (click to enlarge)

By 1936 UTC, ProbSevere has again increased above 50%, in two regions where MRMS has MESH sizes over 0.50″. MESH values are equivalent in the two regions, as are environmental values, but higher satellite predictors associated with the smaller eastern radar object drive higher ProbSevere values there.

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

NOAA/CIMSS ProbSevere from 1936 UTC on 22 May 2014 (click to enlarge)

The animation below shows the evolution of NOAA/CIMSS ProbSevere from 1948 UTC through 2000 UTC, with focus on a second cell that was warned. NOAA/CIMSS ProbSevere is designed to give an estimate of when severe weather might initially occur. Severe weather was not reported in Kentucky with these storms (link); however, observations of severe weather did occur as the storms moved near Nashville.

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

NOAA/CIMSS ProbSevere from 1948-2000 UTC on 22 May 2014 (click to animate)

Related Hazardous Weather Testbed blog posts on this event can be found here, here, and here.

Severe Storms over Wisconsin

May 7th, 2014

Convection developed along the edge of warm air moving northward into Wisconsin early in the morning on May 7th. The Day 1 Outlook from the Storm Prediction Center showed the region to be in a Slight Risk.

The NOAA/CIMSS ProbSevere model, which fuses together information from GOES-derived cloud products, Multi-Radar Multi-Sensor (MRMS) data, and Rapid Refresh (RAP) NWP data, picked up on these convective storms on the north side of a baroclinic zone. The environment was characterized by 1000-2000 J kg-1 of MUCAPE and adequate effective bulk shear (~30-40 kts). The instability was elevated, as the surface airmass reflected a cool easterly flow. (Click here to see the DVN and GRB soundings from 1200 UTC 7 May)

Very early Wednesday morning (1000-1100 UTC), a storm developed in west-central Wisconsin moving eastward. ProbSevere pegged the storm at 25% probability of producing severe weather, given the environment, strong normalized vertical growth rate (inferred from IR-derived data), and moderate maximum expected size of hail (MESH). As the MESH increased over 1.0”, ProbSevere increased to about 70%. By 1026 UTC, the probability was 74%, and 1 minute later the National Weather Service (NWS) issued a severe thunderstorm warning. The warning was issued 5 minutes after ProbSevere’s first probability > 50%. This storm later weakened and decreased in probability, but then picked up again and produced 1.0” hail in Clark county at 1218 UTC, all the while maintaining a warning.

westcentral_WI_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

Other storms developed near Richland County in Wisconsin around 1400 UTC. A strong satellite vertical growth signal could not be computed for these storms because of thick cirrus overhead from decaying convection to the north. ProbSevere nevertheless had high probabilities (due to a favorable environment and large MESH) prior to these storms being warned. The eastern of the two storms showed a ProbSevere value exceeding 50% thirteen minutes before the first NWS warning; ProbSevere for the western storm exceeded 50% 26 minutes before the first NWS warning. Both storms dropped severe hail in Richland county (Storm Report) — 1.25″ diameter hail at 1443 UTC for the eastern storm (4 minutes after the NWS warning), 2.0″ diameter hail at 1442 UTC with the western storm (coincident with its first warning). A storm southeast of these two in Sauk county had a high probability of severe (> 70%) by 1442 UTC, also because of large MESH, good MUCAPE and effective shear, but it was never warned and never produced any severe reports (until it coalesced later with the other storms into a convective line)

southwest_WI_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

Lastly, a storm west of Milkwaukee quickly developed and was monitored by ProbSevere. By 1454 UTC, the storm’s probability of severe jumped from 7% to 24% (at the start of the animation) because its normalized vertical growth rate became very strong (see the visible and IR loops).

Milwaukee_20140507

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

AWIPS 10.7 µm imagery,below, shows the evolution of the storms as viewed from GOES-East. The first storm, over central WI at 1030 UTC, shows considerable electrical activity but overshooting tops are not detected. The storms over Richland/Sauk Counties around 1400 UTC, and near Milwaukee around 1500 UTC do show overshooting tops.

Reg_IR_Sat_20140507loop

MRMS Radar returns and NOAA/CIMSS ProbSevere objects and NWS-issued Severe Thunderstorm Warning, times as indicated (Click to enlarge)

VIIRS and AVHRR both overflew these systems around 0730 UTC. The toggle of imagery below shows the great detail in the cloud-top that is available with 1-km resolution as from VIIRS and AVHRR. In addition, the Day/Night band can be used at night (especially when the lunar illumination is low, as was the case on 7 May) to detect lightning, characterized as streaks of white in the Day/Night band imagery. One such streak is visible near Manitowoc, WI.

POES_VIIRS_GOES_20140507_0745

POES AVHRR 10.7 µm imagery at 0736 UTC, Suomi/NPP VIIRS imagery (11.0 µm and Day/Night Band) at 0746 UTC, and GOES-East 10.7 µm imagery at 0745 UTC (Click to enlarge)

The NOAA/CIMSS ProbSevere product is being evaluated at the Hazardous Weather Testbed. Additional examples can be found at the HWT Blog.

von Kármán vortex street downwind of Madeira Island

May 1st, 2014
Meteosat-10 0.75 µm visible channel image (click to play animation)

Meteosat-10 0.75 µm visible channel image (click to play animation)

McIDAS images of EUMETSAT Meteosat-10 0.75 µm visible channel data (above; click image to play animation) showed a beautiful example of a von Kármán vortex street downwind of Madeira Island on 01 May 2014. Northeasterly winds in the marine boundary layer were perturbed by the topography of the island, whose highest point rises to an elevation of 1,862 m (6,109 ft) above sea level. Note how some of the downwind vortices rotate in a clockwise direction, while other rotate counterclockwise.