Using NUCAPS to nowcast convective development

August 27th, 2019 |

GOES-16 Visible Imagery (0.64 µm) at 1721 UTC on 27 August 2019. A swath of NOAA-20 NUCAPS soundings from 1718 UTC is also shown, and individual profiles from the Upper Peninsula of Michigan southeastward to southwest Lower Michigan are plotted. (Click to enlarge)

The animation above shows the 1721 UTC GOES-16 Visible (0.64 µm) image along with NUCAPS profile locations from a NOAA-20 overpass. Convection is approaching from the west, from central Wisconsin. NUCAPS soundings can give a good estimate for how far south that convective line might develop, and a north-south series of profiles is shown in the imagery above.  Note in particular how soundings show increasing mid-level stability;  a strong inversion between becomes apparent between the NUCAPS Sounding just south of Door County on the western short of Lake Michigan and over eastern Lake Michigan on the Michigan shoreline.  This thermodynamic snapshot would argue that convection should not develop much farther south than central Lake Michigan!  the 1926 UTC Visible image, below, toggled with radar, confirms this forecast.

GOES-16 Visible Imagery (0.64 µm) at 1926 UTC on 27 August 2019 — toggled with Base Reflectivity at 1924 UTC (Click to enlarge)

 


NUCAPS from one satellite will periodically, north of about 40 N, supply profiles on two consecutive passes.  That happened on 27 August over Lake Michigan as might be expected given that the 1718 UTC pass had its westernmost swath over Lake Michigan.  The animation below shows the swath from 1901 UTC.  The strengthening inversion as you move south over Lake Michigan is apparent at 1901 UTC as well.

GOES-16 Visible Imagery (0.64 µm) at 1906 UTC on 27 August 2019. A swath of NOAA-20 NUCAPS soundings from 1901 UTC is also shown, and individual profiles over Lake Michigan Michigan are plotted. (Click to enlarge)

VIIRS imagery and NUCAPS profiles near the North Pole

August 22nd, 2019 |

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

A sequence of 4 consecutive Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.4 µm) images (above) showed a small swirl of clouds associated with a weak area of low pressure near the North Pole — north of Greenland (surface analyses) — on 22 August 2019.

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) images, with plots of NUCAPS availability [click to enlarge]

There were Suomi NPP NUCAPS soundings available in the vicinity of the surface low (above) — profiles from the 4 squared green dot locations (green dots indicate successful sounding retrievals from both the CrIS and ATMS instruments) which were closest to both the surface low and the North Pole (below) revealed characteristically-low arctic tropopause heights of around 7-8 km, and surface temperatures dropping to below freezing at the 2 most northerly points of 88.28º and 88.57º N latitude. Note: the Suomi NPP (SNPP) CrIS anomaly that began on 24 March 2019 was resolved via a switch to the redundant Side-2 electronics on 24 June — so CrIS data once again became available for incorporation into SNPP NUCAPS soundings beginning on 01 August. Training material for NUCAPS in AWIPS is available here.

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

NUCAPS temperature (red) and dew point (green) profiles [click to enlarge]

According to GCOM-W1 AMSR2 data (source), this weak surface low was over a portion of the Arctic Ocean where sea ice concentration was still high (below).

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]

GCOM-W1 AMSR2 sea ice concentration [click to enlarge]

Split Window Difference fields over the Ocean

August 20th, 2019 |

GOES-17 ABI Split Window Difference (10.3 – 12.3) at 0100 UTC on 20 August 2019 (Click to enlarge)

The Split Window Difference field (10.3 µm – 12.3 µm), shown above in the south Pacific around Samoa and American Samoa (Leone is on the island of Tutuila just west of 170º W Longitude; Fitiuta is on the island of Ta’u just east of 170º W Longitude), can be used to estimate the horizontal distribution of water vapor. The Split Window Difference can give a good estimate of moisture distribution in the atmosphere over the ocean where conventional moisture measurements are limited. The image above shows greater values (3.5 – 4 K, in yellow and orange) over the northern part of the image and smaller values (2-3 K, in yellow and blue) over the southern part of the image, divided by a band of cloudiness that passes through 20º S, 170º W.

NOAA-20 overflew this region at 0056 UTC, and NUCAPS profiles were available, as shown below.

GOES-17 ABI Split Window Difference (10.3 – 12.3) at 0100 UTC on 20 August 2019 along with NUCAPS Sounding locations (Click to enlarge)

The animation below steps through soundings at different locations. Total precipitable water as determined from the sounding is indicated. In the region where the Split Window Difference field was around 4 K, precipitable water values were in the 1.5-1.7″ range; in regions where the Split Window Difference was closer to 2 K, precipitable water values were closer to 0.5-0.75″.

NUCAPS Vertical Profiles at different locations, as noted. (Click to animate)

Microwave-only data, shown below from the MIMIC website, shows a sharp gradient at 20º S, 170º W.

MIMIC Total Precipitable Water, 0000 UTC on 20 August 2019 (Click to enlarge)

At ~1200 UTC, when NUCAPS again passed over this region, profiles could again be used to discern gradients in total precipitable water.  At that time, however, the Split Window Difference field was not computed because warming of the Advanced Baseline Imager (ABI) associated with the sub-optimal performance of the Loop Heat Pipe meant that Band 15 data were not available.  (Baseline Level 2 Products, such as total precipitable water, are also unavailable from GOES-17 because of the Loop Heat Pipe issue) The Split Window Difference field could be computed from Himawari-8 data however.

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).