NUCAPS fields across an upper tropospheric front

January 20th, 2021 |

GOES-16 ABI Airmass RGB, Band 10 and Band 8 (7.34 µm and 6.19 µm, respectively), and GOES-16 Airmass RGB overlain with NUCAPS sounding availability plots, 0801 UTC oni 20 January 2021 (click to enlarge)

The AirMass RGB from GOES-16 at 0800 UTC on 20 January 2021 showed a distinct color change across central Missouri, from red to green.  The enhanced red coloring suggests a large difference in water vapor brightness temperatures.  The toggle above (including an image with NUCAPS* sounding points), shows structures in the water vapor imagery consistent with an upper tropospheric front.

Water Vapor and Airmass RGB imagery fields are useful because they be compared to model fields of the tropopause, and similarities in model fields and satellite imagery lend credence to the idea that the model initialization is accurate.  Compare the Airmass RGB and the Rapid Refresh mapping of the pressure on the 1.5 PVU surface below.  There is good spatial correlation between model and satellite fields.

GOES-16 Airmass RGB and Rapid Refresh model field of Pressure on the 1.5 PVU surface, 0800 UTC 20 January 2021 (Click to enlarge)

How do vertical profiles from NUCAPS vary across the tropopause fold?  The animation below shows six different profile in Missouri and Arkansas, spanning the reddish region of the airmass RGB.

GOES-16 Airmass RGB image with selected NUCAPS profiles, as indicated. (Click to enlarge)

A more efficient way to view information from NUCAPS is to view gridded fields.  Polar2Grid is used to transform the vertical profile to horizontal fields at the individual NUCAPS pressure levels (and then vertical interpolation moves those fields to standard levels).  The animations below show gridded values that are all in agreement with the presence of a tropopause fold where the Airmass RGB and model fields suggest.  Gridded temperature and moisture can be combined in many ways.  Gridded Ozone is also available in AWIPS (some of these fields were created using the Product Browser).

Ozone from NUCAPS, below, does show an enhancement, as expected, in the region where the tropopause fold is suggested by the airmass RGB.

NUCAPS-derived ozone anomalies, ca. 0800 UTC on 20 January 2021 (Click to enlarge)

The gridded NUCAPS tropopause level, shown below, can also be inferred from the individual profiles shown above.

Gridded NUCAPS Tropopause level, ca. 0800 UTC on 20 January 2021 (click to enlarge)

Note how the lapse rates show relatively less stable air (in the mid-troposphere) in the region of the tropopause fold.

Gridded 500-700 mb Lapse rates, ca. 0800 UTC on 20 January 2021 (click to enlarge)

Mixing ratio shows dry mid- and upper-tropospheric air, in the region of the tropopause fold, as might be expected from the GOES-16 water vapor imagery.

Gridded NUCAPS esimates of 300-700 mb mixing ratio, ca. 0800 UTC on 20 January 2021 (Click to enlarge)

In general, NUCAPS data can be used to augment other satellite and model data to better understand the thermodynamic structure of the atmosphere.  For more information on NUCAPS profiles, refer to this training video.

*The careful reader will note that the timestamp of the NUCAPS Sounding Availability plot, 0753 UTC, is different from the GOES-16 imagery.  Why?  The NUCAPS Sounding Availability plot is timestamped (approximately) when NOAA-20 initially overflies North American airspace.  NOAA-20 was flying over Missouri shortly after 0800 UTC, as shown in this plot (from this website).  Gridded NUCAPS fields are timestamped when NOAA-20 is overhead.

Severe Weather in southeast Texas

January 6th, 2021 |

GOES-16 Day Cloud Phase Distinction RGB, 1646-2136 UTC on 6 January 2021, along with surface METARs (Click to animate)

The Storm Prediction Center in Norman issued a Slight Risk (click for map, from here) of severe weather over portions of southeast TX on 6 January 2021. The Day Cloud Phase Distinction RGB, shown above (click the image to animate) shows a developing line of convection stretching through the SLGT RSK area (The tallest convective cloud tops acquire a yellowish tint as they glaciate; lower clouds are blue/green/cyan).  The Day Cloud Phase Distinction RGB also allows for easy visualization of vertical wind shear:  the high cirriform clouds (orange and red) move in a distinctly different direction than the low cumuliform clouds (blue and green).  A Severe Thunderstorm Watch (Watch #2 on the year) was issued at 1900 UTC (Click here for Radar image that accompanied the watch issuance).  How could various satellite-based (or satellite-influenced) products be used to anticipate and to quantify the likelihood of severe weather during the day?

Polar Hyperspectral Sounding (PHS) data (from CrIS on Suomi NPP/NOAA-20 or from IASI on MetOp, for example) can augment Advanced Baseline Imager (ABI) data from GOES-16 (or GOES-17) to allow for better initialization of moisture fields in models. PHS data are linked to ABI information at the time of the polar orbiting overpass, and that relationship is carried forward in time. This data fusion process (PHSnABI) combines the excellent spectral resolution of the PHS with the superior spatial and temporal resolution of the ABI. When those data are used to initialize a model, it is frequently the case that the better moisture distribution within the PHSnABI fields leads to a more refined forecast of convection. (See this website for more information and for current model fields) Was that true on this day?

The toggles below show data from models runs initialized at 1400 and 1500 UTC, with model fields at 1800, 2000 and 2200 UTC. Lifted Index fields are shown with data from a Rapid Refresh-type simulation (that is, with no incorporation of fused PHSnABI data) identified as ‘RAP’ in the label; with data from a Single Data Assimilation (‘SDA’) system; and with data from a Continuous Data Assimilation (‘CDA’) system.

The CDA model system does appear best at simulating the timing of the convection that moves through southeast Texas (if one can use simulated Lifted Index as a proxy for the leading edge of convection).

Lifted Index at 1800 UTC from Models (RAP, SDA, and CDA) initialized at 1400 UTC (Click to enlarge)

Lifted Index at 1800 UTC from RAP, SDA and CDA models initialized at 1500 UTC (Click to enlarge)

Lifted Index at 2000 UTC from RAP, SDA and CDA models initialized at 1400 UTC (Click to enlarge)

Lifted Index at 2000 UTC from RAP, SDA and CDA models initialized at 1500 UTC (Click to enlarge)

Lifted Index at 2200 UTC from RAP, SDA and CDA models initialized at 1400 UTC (Click to enlarge)

Lifted Index at 2200 UTC from RAP, SDA and CDA models initialized at 1500 UTC (Click to enlarge)

NOAA-20 VIIRS imagery at 1823 UTC: 1.61 µm, True Color and False Color (Click to enlarge)

NOAA-20 overflew the convection at 1823 UTC, and the imagery above was processed at the Direct Broadcast site at CIMSS. (It is available for AWIPS via an LDM feed, and also as imagery for one week at this website; data for other days is here). VIIRS I3 (1.61 µm), True-Color and False-Color imagery from VIIRS all show a well-developed convective system at 1823 UTC.

As the convective event is unfolding, NUCAPS profiles derived from NOAA-20 can be used to diagnose the thermodynamic state of the atmosphere.  The toggle below shows 5 different profiles over southeastern Texas (along a line to the west of Galveston Bay) at ca. 1830 UTC.  The green points are NUCAPS profiles for which the infrared retrieval has converged to a solution.  A general decrease in stability (and increase in moisture) is apparent for profiles closer to the convection.  The red point (a profile for which the infrared and microwave retrieval both failed) is included as well.

NUCAPS profiles at select points as indicated over southeast Texas, 1830 UTC on 6 January 2021 (Click to enlarge)

A simpler, faster way to view the thermodynamic fields within NUCAPS profiles is to use gridded fields.  NUCAPS data are gridded onto constant pressure surfaces (using Polar2Grid software). The Total Totals Index field, below, shows a corridor of instability inland over southeast Texas with values exceeding 50.

Total Totals index from gridded NOAA-20 NUCAPS values, ca. 1830 UTC (Click to enlarge)

During the actual convective outbreak, NOAA/CIMSS ProbSevere (available online here) offers a data-driven way to highlight the radar echoes most likely to be producing severe weather in the next 60 minutes. The animation below shows values at 15-minute timesteps (for simplicity); ProbSevere values can change every 2 minutes, however. Use ProbSevere in combination with radar scanning to increase confidence in warning issuance.

NOAA/CIMSS ProbSevere, every 15 minutes, 1715 – 2300 UTC on 6 January 2021 (Click to enlarge)

Severe Weather reports(source) for 6 January are shown below.

SPC Storm Reports from 6 January 2021 (Click to enlarge)

Signatures of the Alaska Range on Water Vapor imagery

December 5th, 2020 |

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with topography [click to play animation | MP4]

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with topography [click to play animation | MP4]

GOES-17 (GOES-West) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) revealed cold thermal signatures (brighter shades of white) associated with the highest-elevation portions of the Alaska Range on 05 December 2020. Note the slight northward shift (16-20 km, or 10-12 miles) in the apparent location of Denali in the GOES-17 images, due to parallax.

Plots of GOES-17 Water Vapor (ABI spectral band 8, 9 and 10) weighting functions calculated using 00 UTC rawinsonde data from Fairbanks (north of the Alaska Range) and from Anchorage (south of the Alaska Range) are shown below. Even with very large satellite viewing angles (or zenith angles) greater than 70 degrees — which would tend to shift the Water Vapor weighting function plots to higher altitudes —  the presence of very dry air within much of the middle to upper troposphere had the effect of bringing the weighting function peaks downward to pressure levels corresponding to those of the higher elevations of the Alaska Range.

GOES-17 Water Vapor weighting functions, calculated using 00 UTC rawinsonde data from Fairbanks [click to enlarge]

GOES-17 Water Vapor weighting functions, calculated using 00 UTC rawinsonde data from Fairbanks [click to enlarge]

GOES-17 Water Vapor weighting functions, calculated using 00 UTC rawinsonde data from Anchorage [click to enlarge]

GOES-17 Water Vapor weighting functions, calculated using 00 UTC rawinsonde data from Anchorage [click to enlarge]

The Total Precipitable Water (TPW) values seen on the 00 UTC Fairbanks and Anchorage soundings were 0.07 inch. However, a NOAA-20 NUCAPS sounding profile just 20-30 miles southwest of Denali around 12 UTC (below) yielded TPW values of only 0.01 inch. The green color of that sounding point indicated successful retrievals from both the Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) instruments.

GOES-17 Water Vapor (6.9 µm) image with plots of available 12 UTC NOAA-20 NUCAPS sounding points [click to enlarge]

GOES-17 Water Vapor (6.9 µm) image, with plots of available 12 UTC NOAA-20 NUCAPS sounding points [click to enlarge]

NOAA-20 NUCAPS profile just southwest of Denali around 12 UTC [click to enlarge]

NOAA-20 NUCAPS profile just southwest of Denali around 12 UTC [click to enlarge]

Another NOAA-20 NUCAPS green sounding profile just southwest of Denali around 22 UTC (below) also yielded a TPW value of only 0.01 inch.

GOES-17 Water Vapor (6.9 µm) image with plots of available 22 UTC NOAA-20 NUCAPS sounding points [click to enlarge]

GOES-17 Water Vapor (6.9 µm) image, with plots of available 22 UTC NOAA-20 NUCAPS sounding points [click to enlarge]

NOAA-20 NUCAPS profile just southwest of Denali around 22 UTC [click to enlarge]

NOAA-20 NUCAPS profile just southwest of Denali around 22 UTC [click to enlarge]

Comparing NUCAPS temperature values to forecast fields

November 29th, 2020 |

Gridded NUCAPS estimates of 850-mb Temperature, 1851 UTC on 30 November 2020 (Click to enlarge)

Late November is a time when cold outbreaks can pass over relatively warm Great Lakes waters (click here for recent observations) and produce lake-effect snow. Gridded NUCAPS observations derived from NOAA-20 CrIS and ATMS data, above, shows a large area with temperatures colder than -12ºC over northwest Ontario and northern Minnesota, just upwind of the Great Lakes;  Lake Superior’s surface temperature at the time was around 5ºC —  a temperature difference that support lake-effect precipitation.  How well do the NUCAPS observations compare to model predictions of the environment?

Forecasts from the 1200 UTC run of the NAM, below, valid at 1800 UTC, and from the 1500 UTC run of the Rapid Refresh, valid at 1900 UTC, show -12ºC in bright magenta.  (Model analyses taken from this website)  NUCAPS analyses suggest the cold air is moving south faster than anticipated by the model.

 

6-h forecast of 850-mb Temperature, valid 1800 UTC on 29 November 2020 (Click to enlarge)

4-hour forecast of 850-mb temperature from the Rapid Refresh, valid 1900 UTC on 29 November 2020 (Click to enlarge)

This site can be used to view gridded NUCAPS fields outside of AWIPS.  The 850-mb analysis from the pass is shown below.  It’s important to recall that Gridded NUCAPS fields include data from all retrieved profiles — including profiles for which the infrared retrieval failed (usually in locations with thick clouds, and those from which the infrared and microwave retrievals both failed (usually in locations with rain). This mapping for the temperature gridding below shows where infrared retrievals failed (yellow) and where infrared and microwave retrievals both failed (red).

850-mb Temperature fields, 1849 UTC on 29 November 2020 (Click to enlarge)

The ‘yellow’ points north and west of the Great Lakes were associated with clouds that are apparent in this VIIRS True Color image, taken from the UW-Madison Direct Broadcast ftp site (Link). The clouds were associated with a departing low pressure system (link).

NOAA-20 VIIRS True-Color imagery, 1850 UTC on 29 November 2020 (Click to enlarge)