Strong convective winds over Arkansas

July 23rd, 2014 |
GOES-13 0.63 µm visible channel images (click to play animation)

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

Arkansas and surrounding states experiences strong convectively-forced winds on July 23 2014 (SPC Storm Reports for the day are shown below). The visible imagery, above, shows the merging of two convective systems: one is moving south-southeastward through eastern Kansas and one is building southwestward from the lower Ohio River Valley into northern Arkansas. (Mesoscale Discussions for this event were issued from SPC at 1656 UTC, 1827 UTC and 2001 UTC on the 23rd).

Storm Reports from 23 July 2014

Storm Reports from 23 July 2014

GOES-13 Sounder DPI Lifted Index (click to play animation)

GOES-13 Sounder DPI Lifted Index (click to play animation)

Analyses from the GOES-13 Sounder (above) showed the atmosphere into which the convective features were building to be very unstable. A large area with Lifted Indices around -10 (light red) is present; values exceed -12 (purple) at 1800 UTC. GOES Sounder DPI Analyses of CAPE (Convective Available Potential Energy, below) (from this site) likewise show strong instability at the start of the day. Convection is initially at both ends of the area of most unstable air; by 1900 UTC, the end of the animation, it has overspread the entire region of instability.

GOES Sounder CAPE (click to play animation)

GOES Sounder CAPE (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

The GOES-13 Infrared Imagery, above, likewise shows the convective systems from Kansas and from the lower Ohio Valley merging over Arkansas.

Suomi-NPP VIIRS data were available over Arkansas on two successive passes on 23 July, at 1829 UTC and 2010 UTC, and these high-resolution infrared images show the quick development and vigor of the convection. The high resolution allowed for the detection of very cold cloud tops at 2010 UTC; minimum values were near -88ºC! Coldest GOES-13 10.7 Brightness Temperatures at 2015 UTC (not shown) were -78ºC.

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

Suomi NPP VIIRS 11.35 µm infrared channel images (click to enlarge)

The storms produced considerable lightning as well, as shown in the animation below that overlays hourly lightning strikes on top of the Suomi NPP 11.35 µm imagery: there were 5800 strikes (400 positive) in the hour ending at 1800 UTC, and 12000 strikes (800 positive) in the hour ending at 2000 UTC!

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

Suomi NPP 11.35 µm infrared channel imagery and Detected Lightning (click to play animation)

NOAA/CIMSS ProbSevere showed values from 80-95% at the leading edge of the convection as it moved southward through Arkansas. In this event, satellite data were not available as one of the ProbSevere predictors because of the widespread cirrus shield. MRMS Mesh was generally in the 3/4″ to 1-1/2″ range; that combines with model CAPE values exceeding 4000 and generous shear lead to the high ProbSevere values.

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

NOAA/CIMSS ProbSevere display including MRMS Base Reflectivity, 1922-2128 UTC 23 July 2013 (click to play animation)

Overshooting Tops, such as those apparent in the 11.35 µm imagery from Suomi NPP, above, can be detected automatically in GOES-13 10.7 µm imagery. The animation of auto-detected overshooting tops, below, from this site, shows a peak in convective intensity (as measured by the number of overshoots) between 2000 and 2100 UTC on the 23rd. This image shows the daily sum of detected overshoots. There is good spatial correlation between that image and the storm reports.

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Overshooting Tops Detected from GOES-13, 1545-2300 UTC 23 July 2013 (click to play animation)

Finally, CRiS/ATMS data can be used to generate soundings (NUCAPS Soundings) that are available in AWIPS II. The image below shows the spatial coverage of soundings at 2000 UTC on 23 July. The NUCAPS sounding from the easternmost column, third point south of the Oklahoma/Texas border, bottom, is shown at the bottom of the post. The boundary layer of this sounding is too cool and dry — the surface temperature is around 80º F and the surface dewpoint is in the mid-60s. Consequently, the MUCAPE is far too small (about 120 J per kilogram). If the sounding is edited so that surface values are closer to observations (it was 90º F with a 75º F dewpoint in Texarkana at this time) then MUCAPE values jump to near 5000. The sounding is also too dry; the precipitable water is 1.45″ vs. an actual value closer to 2″ at this time.

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP VIIRS 11.35 µm Imagery at 2010 UTC, with NUCAPS Sounding Locations in Green (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)

Suomi NPP NUCAPS Sounding at 32.7º N, 94.9º W (Click to enlarge)

Tropical Storm Arthur forms east of Florida

July 1st, 2014 |
GOES-13 0.63 µm visible channel images (click to play animation)

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

The first tropical depression (update: Arthur was named as a tropical storm at 1500 UTC 1 July) of the season in the tropical Atlantic has formed just to the east of Florida. The visible imagery animation, above, shows persistent strong thunderstorms with overshooting tops in the area of disturbed weather over the Gulf Stream and the Bahamas. Refer to the National Hurricane Center and the CIMSS Tropical Cyclones sites for particulars on the future track of this system. Note that current forecasts have the system strengthening to a hurricane in the next few days, and close to the North Carolina coast on July 4th.

Metop ASCAT surface scatterometer winds at 1541 UTC, below, indicated that the strongest winds (green barbs, 30-39 knots) were found within the northeastern quadrant of the tropical storm.

GOES-13 visible images with Metop ASCAT surface scatterometer winds (click to play animation)

GOES-13 visible images with Metop ASCAT surface scatterometer winds (click to play animation)

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GOES-13 10.7 µm infrared channel images (click to play animation)

GOES-13 10.7 µm infrared channel images (click to play animation)

The tropical Atlantic has lately been besieged by Saharan Air Layer (SAL) dust (see, for example, this post from last week, or this image from today); that dry air suppresses tropical cyclone formation. The animation of GOES-13 10.7 µm imagery, above, shows that this Tropical Depression formed out of an impulse that sank southward from the Carolinas over the past 6 days, so its gradual development has not been impeded by the SAL.

The VIIRS instrument on board the Suomi NPP satellite provided high-resolution imagery over this tropical system shortly after midnight on the 1st (see below). A large cirrus shield with brightness temperatures cooler than -70º C (Green in the enhancement) with a few overshooting tops that are colder than -85º C are present. An analysis of some NUCAPS Soundings from this overpass is here.

Suomi NPP VIIRS 11.35 µm infrared imagery, Day/Night Band imagery (0.70 µm) and lightning data at ~0715 UTC on 1 July 2014 (click to toggle through images)

Suomi NPP VIIRS 11.35 µm infrared imagery, Day/Night Band imagery (0.70 µm) and lightning data at ~0715 UTC on 1 July 2014 (click to toggle through images)

Arthur’s projected track moves the storm up the East Coast over very warm waters associated with the Gulf Stream. Both MODIS and VIIRS analyses of SSTs show widespread temperatures in excess of 80º F.

A comparison of Suomi NPP VIIRS 11.45 µm IR channel images at 0717 UTC and 1840 UTC, below, showed that the areal coverage of cold cloud tops was increasing during the day on 01 July, but the deep convection remained well to the southeast of Arthur’s low-level center of circulation.

Suomi NPP VIIRS 11.45 µm IR channel images

Suomi NPP VIIRS 11.45 µm IR channel images

At 1840 UTC, a comparison of the Suomi NPP VIIRS 11.45 µm IR channel image with the corresponding 0.64 µm visible channel image with an overlay lightning data, below, revealed a large number of cloud-to-ground strikes within the 1-hour period ending at 1900 UTC.

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image (with lightning data)

Suomi NPP VIIRS 11.45 µm IR channel image and 0.64 µm visible channel image (with lightning data)

===== 02 July Update =====

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

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

Arthur continued to slowly intensify on 02 July, and began to show hints of an organized eye structure on GOES-13 0.63 µm visible channel images (above; also available as an MP4 movie file).

A comparison of AWIPS-2 images of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images (below) showed that the coldest cloud tops were north of the center of Arthur at 1822 UTC. A buoy just southwest of the center reported winds gusting to 52 knots (60 mph).

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Even though an eye was not evident on GOES-13 10.7 µm IR channel imagery around 2045 UTC, a DMSP SSMIS 85 GHz microwave image at 2049 UTC did display a well-organized eye signature (below).

GOES-13 0.63 µm visible channel image and DMSP SSMIS 85 GHz microwave image

GOES-13 0.63 µm visible channel image and DMSP SSMIS 85 GHz microwave image

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 VIIRS 11.45 µm IR channel and NUCAPS sounding points (click to enlarge)

Suomi/NPP VIIRS 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.