Using NUCAPS soundings to nowcast convective evolution

August 15th, 2019 |

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1721 – 1946 UTC on 15 August 2019. NUCAPS Sounding Points — from 1926 UTC — are present over the image at 1946 UTC (Click to animate)

GOES-16 Visible Imagery, above (Click to animate), shows shower/thundershower development over eastern Oklahoma moving into Arkansas. At the end of the animation, 1946 UTC, NUCAPS Sounding profiles from 1926 UTC are shown, and they’re shown below too.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1946 UTC on 15 August 2019. (Click to enlarge)

The time 1946 UTC is about the earliest you could hope to have NUCAPS profiles in an AWIPS system — and only if you had access to a Direct Broadcast antenna. The more conventional method of data delivery, the SBN, means NUCAPS will be available about an hour after they are taken, so by 2036 UTC. The visible imagery at 2036 UTC is shown below.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1946 UTC on 15 August 2019. (Click to enlarge)

At 2036 UTC, which time is about when in the forecast office the NUCAPS soundings would become available, would you expect the convection in western Arkansas to move southward, or eastward, based solely on Satellite imagery? How could you use NUCAPS profiles to gain confidence in this prediction? Visible imagery alone suggests a moisture boundary; the southern quarter of Arkansas shows markedly less cumulus cloudiness. The animation shows motion mostly to the east, with higher clouds moving more west-northwesterly. The GOES-16 Baseline Total Precipitable Water product, below, shows a maximum in TPW over central Arkansas, with values around 1.5″;  values are around 1.3″ in southern Arkansas, and around 1.2-1.3″ in northwest Arkansas.  A corridor of moisture is indicated.

GOES-16 Baseline Level 2 Total Precipitable Water at 1946 UTC; Visible imagery is shown in cloudy regions. (Click to enlarge)

Baseline Total Precipitable Water, above, part of a suite of products that emerge from Legacy Profiles, is heavily constrained by model fields, however;  the image above could simply show the GFS solution.  In contrast, NUCAPS observations are almost wholly independent of models.  What do NUCAPS profiles show? The animation below steps through vertical profiles east and south of the developing convection.

NUCAPS profiles from the ~1900 UTC overpass at points plotted over the 1946 UTC GOES-16 Band 2 Visible (0.64 µm) image (Click to enlarge)

AWIPS will soon (planned for shortly after Labor Day at the time of this post) include horizontal fields of information derived from NUCAPS vertical profiles. The images below show values computed within the NSharp AWIPS software for a variety of fields: Total Precipitable Water, MU Lifted Index, MU CAPE, MU CINH. All fields suggest that convection more likely to build eastward than to expand southward.

NUCAPS Sounding Points and derived quantities, as indicated, at 1926 UTC 15 August 2019; NUCAPS data are plotted over the 1946 UTC GOES-16 ABI Band 2 Visible 0.64 µm image. (Click to enlarge)

Convection did not move southward; motion and development was to the east. The timing of NUCAPS profiles means that they give a good estimate of atmospheric thermodynamics in mid-afternoon, a key time for assessing convective development.

GOES-16 Visible (Band 2, 0.64 µm) Imagery, 1721 UTC on 15 August 2019 to 0001 UTC on 16 August 2019 (Click to animate).

NUCAPS Soundings surrounding an isolated Thundershower

August 14th, 2019 |

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 (Click to enlarge)

The GOES-16 Visible (0.64 µm) image above shows a weak thunderstorm over southeastern Oklahoma surrounding an decaying outflow boundary.  (Click here to see an animation of the visible imagery). The convection did not look particularly robust, but it did produce lightning that was detected by the Geostationary Lightning Mapper (GLM), as shown below.

GOES-16 ABI Band 2 (0.64 µm) and GLM observations of Flash Extent Density at 1946 UTC on 14 August 2019

Lightning requires charge separation in a cloud; typically lightning occurs after the cloud top glaciates. During daytime, glaciation can be detected with ABI Band 5, at 1.61 µm, the so-called Snow/Ice band. The toggle below shows the visible, snow/ice band, and the Baseline Cloud Phase product. Glaciation is indicated.

GOES-16 ABI Band 2 (0.64 µm), Band 5 (1.61 µm) and Baseline Cloud Phase at 1946 UTC on 14 August 2019

This case is interesting because NOAA-20 overflew the convection, and soundings were produced around the convection, as shown below.

GOES-16 ABI Band 2 (0.64 µm) at 1946 UTC on 14 August 2019 along with NUCAPS Sounding Points at 1945 UTC

The animation below steps north-south through seven profiles that surround the weak convection. Note that a profile near the convection has thermodynamic parameters more favorable for convection than at the other profiles.  For example, NUCAPS profiles show the convection at the northern edge of a precipitable water gradient, and also in a local minimum of inhibition.    Although the convection has initiated here, the fields do suggest that NUCAPS can be used to monitor thermodynamics at small scales before initiation.

NUCAPS Soundings at various points north, south and within convection at 1946 UTC on 14 August 2019 (Click to enlarge) Thermodynamic variables from the sounding are noted.

Horizontal gridded information derived from NUCAPS data will be in AWIPS shortly.  See this post from Emily Berndt at SPoRT!

NUCAPS Soundings and GOES-16 Derived Stability Index Lifted Index Comparison

March 6th, 2019 |

GOES-16 ABI Band 2 (0.64 µm) and Clear-Sky Lifted Index at 1730 UTC on 6 March 2019 (Click to enlarge)

The toggle above compares a CONUS Sector visible image (0.64 µm) over the Caribbean (at 1732 UTC) with a 1730 UTC Full Disk Legacy Atmospheric Profile (LAP) Derived Stability Lifted Index field.  (A “Veggie” Band 03 0.86 µm image, here, means that coastlines need not be drawn in because of the outstanding land/sea contrast at the wavelength).  The LAP Derived Stability Lifted Index shows modestly stable air southwest of the island of Jamaica;  the blue enhancement suggests positive lifted indices (stable air) vs. the yellow regions north and south where values range from -1 to -2.  Visible imagery over the stable region does show fewer clouds than to the north and south.  Does that help you believe the small variations in stability?

GOES-16 Legacy Atmospheric Profile Derived Lifted Index at 1730 UTC along with NUCAPS Sounding Locations, ~1730 UTC on 6 March 2019 (Click to enlarge)

Suomi NPP Overflew the region shortly before 1800 UTC, and NUCAPS soundings that are produced using data from the CrIS (Cross-Track Infared Sounder) and ATMS (Advanced Technology Microwave Sounder) on Suomi NPP are available at the points shown above. Points indicated in green show where both the Infrared and Microwave retrievals successfully completed, and the animation below shows NUCAPS Soundings (at 18.66ºN, 18.20ºN, 17.74ºN, 17.28ºN, 16.82ºN and 16.36ºN) that bisect the region diagnosed as stable by the LAP Lifted Index.  Note that the NUCAPS sounding with the smallest MU Parcel CAPE, at 17.28ºN, is in the middle of the GOES-16-diagnosed stable region.

NUCAPS Soundings over the Caribbean, location as indicated by the large Purple dot. Most Unstable Parcel CAPE is noted (and also available in the nSharp readout)

Using NUCAPS Soundings near Tropical Cyclones

February 25th, 2019 |

Himawari-8 Advanced Himawari Imagery (AHI) “Clean Window” Band 13 (10.41 µm) at 0330 UTC on 25 February 2019 (Click to enlarge)

Tropical systems over the western Pacific are in a region where surface observations are few and far between.  Imagers on geostationary satellites, such as the Advanced Himawari Imagery (AHI) on Himawari-8, shown above, capably track such systems, but sounders do a much better job diagnosing the atmosphere through and towards which storms are moving.  Data from the Cross-track Infrared Sounder (CrIS) on Suomi NPP (and NOAA-20) is combined with microwave sounder from ATMS (the Advanced Technology Microwave Sounder) also on Suomi NPP (and NOAA-20) to produce NUCAPS (NOAA-Unique Combined Atmospheric Profiling System) Soundings.  These vertical profiles (independent of numerical model simulations) can provide information that is difficult to find elsewhere.  The AHI Clean Window image above is overlain with a swath of NUCAPS Sounding points, and seven (noted on the image as 1-7) are shown below. In the image, NUCAPS profile points coded green denote successful infrared and microwave retrievals; yellow denotes an infrared retrieval that failed, but a microwave retrieval was successful; red denotes failure in both infrared and microwave retrievals — typically meaning that they both failed to converge. Infrared retrievals are most likely to fail in regions of thick clouds, microwave retrievals are most likely to fail in regions of heavy precipitation.

MIMIC Total Precipitable Water, 1500 UTC 24 February – 1400 UTC 25 February 2019 (Click to enlage)

Microwave data alone can also be used to diagnose precipitable water, and an estimate from the MIMIC Total Precipitable Water website for the 24 hours ending at 1400 UTC on 25 February 2019 is shown above.  There is considerable dry air in advance of Wutip, and dry air is also wrapping around the south and east of the storm.

Profile 2 for example, was taken over Guam at 0329 UTC on 25 February 2019 and is shown below. Total Precipitable Water at this time was 1.32″, fairly low for a tropical region. The animation of the Guam radiosondes from 0000 UTC on 24 February to 1200 UTC on 25 February is shown beneath the NUCAPS profile.  Total Precipitable Water values over Guam as determined by the radiosonde exceeded 2.3″ on 24 February before dropping to 1.86″ at 00 UTC on the 25th, and 1.37″ on 1200 UTC on 25 February.  The NUCAPS plot over Guam gives an extra observation point — at 0330 UTC, in between ‘normal’ synoptic times — to confirm the arrival of dry air.

NSharp readout of NUCAPS profile over Guam (point 2) at 0329 UTC on 25 February 2019 (Click to enlarge)

PGUM Rawinsondes, 0000 and 1200 UTC on 24 and 25 February 2019 (Click to enlarge)

NUCAPS suggests that the dry air south of Wutip is exceptionally dry indeed. The NUCAPS plot from Point 7, above, shown below, shows a total Precipitable water in the deep tropics of only 0.5″!

NSharp readout of NUCAPS profile at 5.7 N, 140.1 E (point 7) at 0329 UTC on 25 February 2019 (Click to enlarge)

You can also view other NUCAPS profiles by clicking on the number: 1, 3, 4, 5, 6. Point 4, to the north of Wutip, shows more moisture than the other points. Equilibrium Levels for each of the points north of Wutip are near the tropopause.

Horizontal fields derived from NUCAPS values (for example, Dewpoint temperature at 700 mb) will be available in AWIPS later this year. Himawari imagery in this post courtesy of the Japan Meteorological Agency (JMA).