NOAA/CIMSS ProbSevere for an isolated storm in Nebraska

July 9th, 2014
NOAA/CIMSS ProbSevere product, and National Weather Service Warning Polygons, 2302-2334 UTC 9 July 2014 (click to enlarge)

NOAA/CIMSS ProbSevere product, and National Weather Service Warning Polygons, 2302-2334 UTC 9 July 2014 (click to enlarge)

The storm in the animation above produced baseball-sized hail in Nebraska (Visible animation is here, courtesy Dan Lindsey from NOAA at CIRA) although MRMS Mesh Hail sizes were “only” in the 1-inch range (that is, nickel to quarter size). How did the ProbSevere product, which product includes MRMS Mesh size as a predictor, perform?

The visible and infrared satellite animation, below, shows quick development in the absence of cirrus obscuration, and the ProbSevere Satellite components from 2230 UTC are both characterized as ‘Strong’. The model components of ProbSevere (MUCAPE around 2000 J/kg, shear exceeding 30 knots) are also strong. Probabilities increased from 40% to >80% before the warnings for the cell were issued.

MRMS values in this case were not extreme; indeed, when the first warning was issued, MESH was still less than 1″ (but ProbSevere was >80%). Satellite growth rates and environmental information in this case compensated for the modest MRMS Mesh values.

GOES-13 Visible (0.63 µm, top) and Infrared (10.7 µm, bottom) from 2200 UTC 9 July through 0200 UTC 10 July (click to animate)

GOES-13 Visible (0.63 µm, top) and Infrared (10.7 µm, bottom) from 2200 UTC 9 July through 0200 UTC 10 July (click to animate)

Mesoscale Convective Systems over the Upper Midwest, and a Mesoscale Convective Vortex over Wisconsin

June 18th, 2014
Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with cloud-to-ground lightning strikes

Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band images, with cloud-to-ground lightning strikes

A comparison of AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel and 0.7 µm Day/Night Band data (above) showed very large areas of cold cloud-top IR brightness temperatures associated with Mesoscale Convective Systems (MCSs) over the Upper Midwest region of the US at 08:00 UTC (3:00 AM Central time) on 18 June 2014. The coldest IR brightness temperature was -88º C over far southern  Minnesota.  Numerous bright white “streaks” were seen on the Day/Night Band (DNB) image, which indicated portions of the cloud that were illuminated by intense lightning activity. Cloud-to-ground lightning strikes are also plotted on the DNB image, showing how electrically-active these storms were at the time. The western MCS initially formed over eastern South Dakota during the previous evening, producing a few tornadoes there (SPC storm reports). The eastern MCS began to form later along the Wisconsin/Illinois border region — one aircraft flying near the northern edge of a rapidly-developing thunderstorm encountered severe turbulence.

Shortly after the time of the Suomi NPP satellite overpass, a 08:21 UTC overpass of the NOAA-19 POES satellite provided AVHRR-derived CLAVR-x Cloud Top Temperature (CTT), Cloud Top Height (CTH), and Cloud Type products (below). The minimum CTT value was -84º C, and the maximum CTH value was 14 km; much of the MCS cloud shield was classified as the Overshooting Top type (magenta color).

POES AVHRR Cloud Top Temperature, Cloud Top Height, and Cloud Type products

POES AVHRR Cloud Top Temperature, Cloud Top Height, and Cloud Type products

After sunrise, McIDAS  images of GOES-13 0.63 µm visible channel data (below; click image to play animation; also available as an MP4 movie file) showed that the eroding MCS cirrus shield aloft exposed a middle-tropospheric Mesoscale Convective Vortex (MCV) which continued moving eastward across Wisconsin during the day.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

Consecutive overpasses of the Terra and Aqua satellites provided MODIS 0.65 µm visible channel images of the region (below). The convective outflow boundary from the earlier MCS activity had acted to push the warm frontal boundary (which had been acting as a focus for convective development) south of the Wisconsin/Illinois border, leaving a relatively stable boundary layer with a weak capping inversion aloft over Wisconsin — as a result, the MCV circulation did not play a role in initiating any new convective development.

MODIS 0.65 µm visible channel images, with surface reports and surface fronts

MODIS 0.65 µm visible channel images, with surface reports and surface fronts

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.

NUCAPS Soundings available in AWIPS II

June 10th, 2014
Suomi/NPP 11.45 µm IR channel and NUCAPS sounding points (click to enlarge)

Suomi/NPP 11.45 µm IR channel and NUCAPS sounding points (click to enlarge)

NOAA Unique Cross-track Infrared Sounder (CrIS)/Advanced Technology Microwave Sounder (ATMS) Processing System (NUCAPS) Soundings have started flowing into AWIPS-2 at NWS WFOs across the country. These soundings offer high spectral (and high spatial) resolution soundings derived from the CrIS and ATMS instruments that fly on the Suomi/NPP satellite. The toggle above shows the footprint of the soundings in comparison to an 11.45 µm VIIRS instrument (also on the Suomi/NPP satellite) IR image from approximately 1800 UTC on 10 June 2014. The NUCAPS soundings cover a larger area because they are processed by NOAA/NESIS (vs. being downloaded on the X-Band Direct Broadcast antenna at CIMSS in Madison WI, whose antenna is the source of the VIIRS 11.45 µm IR image shown).

The sounding data, if available, are under the ‘Satellite’ menu tab of AWIPS-2, and then NPP Products can be selected to view NUCAPS Sounding Availability, as shown in this screenshot. Once the sounding locations are loaded, the mouse can be used to select a point, and a left click produces a sounding in an NSharpEditor environment; that is, you can edit it (if, for example, you think the surface dewpoint in the sounding is too dry).

The mid-continent overpass at around 1800 UTC can provide valuable information on the possibility of convective development. For example, consider the visible imagery below from 1915 UTC on May 29 2014. Will convection develop out of that broken cumulus field as forecast by the GFS (not shown)?

GOES-13 0.63 µm Visible Imagery, 1915 UTC 29 May 2014 (click to enlarge)

GOES-13 0.63 µm Visible Imagery, 1915 UTC 29 May 2014 (click to enlarge)

The animation below steps through the Suomi/NPP overpass just after 1800 UTC that was used to created NUCAPS soundings on that day, followed by a close-up over Omaha, then a screen-capture of the created sounding. The sounding (which includes surface values close to those reported by the METAR) has only modest values of Convective Available Potential Energy (CAPE), suggesting that convection is unlikely. And, indeed, visible imagery near sunset shows dissipating cumulus clouds.

NUCAPS Sounding over North America, over Omaha and surroundings, and the individual NUCAPS sounding indicated (Courtesy of Dan Nietfeld, SOO at Omaha/Valley WFO, click to enlarge)

NUCAPS Sounding over North America, over Omaha and surroundings, and the individual NUCAPS sounding indicated (Courtesy of Dan Nietfeld, SOO at Omaha/Valley WFO, click to enlarge)

A second case, below, also from Dan Nietfeld, shows NUCAPS soundings before the devastating hailstorm on June 3 in a High Risk region. In this case, the NUCAPS soundings underestimated the temperature/dewpoint at the surface, but the editable sounding software makes quick work of adjusting the lowest part of the sounding, and the CAPE in the adjusted sounding increased from 1800 to more than 3000. (The location of the sounding is shown here; it is the southern of the two circled green dots.) NUCAPS data underscores the potential of any convection.

NUCAPS soundings, original and adjusted, 1849 UTC on 3 June (click to enlarge)

NUCAPS soundings, original and adjusted, 1849 UTC on 3 June (click to enlarge)

(Click here for further information on ATMS; Click here for further information on CrIS). Many thanks to Dan Nietfeld, SOO at Omaha, for imagery above. Hyperspectral Soundings are described in a COMET module that can be viewed here. A paper (pdf format) describing validation of NUCAPS soundings is available here. Suomi/NPP support is provided in part by the NOAA/NESDIS Joint Polar Satellite System (JPSS) program.