Using NUCAPS to diagnose threats in a region of Enhanced/Moderate risk

October 13th, 2021 |
GOES-16 Low-Level water vapor infrared imagery (Band 10, 7.34 µm) at 1931 UTC on 12 October 2021 (Click to enlarge). NOAA-20 NUCAPS Sounding Availability points are indicated as colored dots. METAR plots are also included.

The Storm Prediction Center in Norman issued a convective outlook on 12 October 2021 that included a large area of Enhanced Risk over western Kansas and Oklahoma, noting the expected development of a strong low-level jet creating favorable shear profiles for supercells. (SPC increased the threat to a Moderate Risk for a small part of southwestern Kansas and parts of the Oklahoma and Texas panhandles at 2000 UTC). The Band 10 low-level water vapor image above, from 1931 UTC. An initial round of convection is moving eastward over central Kansas. Did that convection stabilize the atmosphere? NUCAPS profiles can give information on that, information that is not dependent on numerical model simulations.

The plot below, taken from RealEarth, shows the Lifted Index computed from NUCAPS soundings blended with MADIS surface observations. The greatest instability, shaded in red, lies along the Kansas/Colorado border, and it extends to the southeast along the western Oklahoma/north Texas border. (Click here to see surface-based CAPE at the same time).

NUCAPS/MADIS Surface-based Lifted Index, 1952 UTC on 12 October 2021 (Click to enlarge)

What do individual profiles show? 20 different profiles over southwestern Kansas are in the stepped animation below. Steep mid-level lapse rates (greater than 8 K/km) are indicated in the soundings, and Most Unstable Convective Available Potential Energy (MUCAPE) values persist in the lower troposphere. It also appears that moisture is pooling along the Kansas/Colorado border: precipitable water values from two soundings (at 38.42 N/102.60 N and 38.04 N /101.89 W) and are greater than surrounding values. So: instability is present, and moisture is available. Model-independent information like this can help a forecaster during the wait for initiation.

GOES-16 Day Cloud Phase Distinction image at 1931 UTC, along with NUCAPS Sounding Availability plots. Individual profiles as indicated are shown in the inset; values from those soundings are shown in the grey box in upper left (Click to enlarge)

It can be time-consuming in AWIPS to look through multiple soundings (the Pop-up SkewT functionality can be helpful, but for subtle changes in precipitable water, or in lapse rate, that use is limited). Gridded NUCAPS fields are available in AWIPS, and also online. The 700-500 mb lapse rate, shown below, from this website, diagnoses the steep lapse rates that were present (perhaps to be expected given the suggestion of an elevated mixed layer in the water vapor imagery at the top of this blog post!)

Lapse Rate (700-500 mb) diagnosed from NOAA-20 NUCAPS, 1949 UTC on 12 October 2021 (Click to enlarge)

So what happened with this event? Convection developed along the Colorado/Kansas border, and spawned severe weather over western Kansas, western Oklahoma, and western Texas. GOES-16 clean window infrared imagery (10.3 µm), below, shown on top of the Level 2 stability Lifted index product, shows the instability and the development of the convection (Click here for a Band 13 animation only).

GOES-16 clean window infrared imagery (Band 13, 10.3 µm) and Level 2 Derived Stability Index (Lifted Index, clear sky only) from 2201 UTC on 12 October 2021 through 0646 UTC on 13 October 2021 (Click to enlarge).

Displaying NUCAPS data with Matlab

October 1st, 2021 |
NOAA-20 NUCAPS Temperature values at 853 mb, 1817-1819 UTC on 01 October 2021 (Click to enlarge)

Alexa Ross, a scientist at CIMSS (and CIMSS Blog contributor) has created a Matlab program that reads in NUCAPS EDR data from any Direct Broadcast datastream (here, for example), or from NOAA CLASS, and creates color-coded plots at NUCAPS data levels (that is, at any one of the 100 pressure levels used in the Radiative Transfer Model that drives the retrieval). Output from the program for four separate granules between 1817 and 1819 UTC is shown above. Temperatures are notably warmer over land than over the Atlantic Ocean, a temperature distribution in agreement with GFS model output (GFS model imagery from the College of Dupage website).

This program does not (as yet) indicate whether or not the retrieved profile has converged to a solution. It is up to a user to apply some quality control to the data. The very warm pixel at 1817 UTC over the Atlantic Ocean, for example, looks suspect. Cloud imagery is an important tool for anticipating whether a retrieval will converge — click here to see an 1820 UTC GOES-16 True-Color imagery over the scene, taken from the CSPP Geosphere site.

Gridded NUCAPS (available from this NASA SPoRT website) can also be used to view the horizontal distribution of temperatures across the NUCAPS data swath. The toggle below shows the 850-mb Temperature field and also the Quality Control flags.

850-mb gridded NUCAPS temperatures and Quality Flags from the NOAA-20 overpass at ~1815 UTC on 1 October 2021 (Click to enlarge)

Viewing NUCAPS profiles with Sharppy

September 29th, 2021 |
Available soundings from divers sources between 0000 and 1200 UTC on 29 September over the United States (Click to enlarge)

Scientists at STC and at SPoRT have created a website to view NUCAPS profiles using Sharppy and cloud resources. The animation above shows the user interface for Observed Soundings (i.e., upper-air soundings), for NUCAPS Soundings for different passes, and NAM Nest model profiles. The green points have been chosen for subsequent display. Points near KARB — Aberdeen, South Dakota — were selected; on this day, subsequent NOAA-20 NUCAPS passes produced data 90 minutes apart very near Aberdeen.

Soundings in/around Aberdeen SD: 0000 UTC Radiosonde, 0735 UTC NOAA-20 NUCAPS Sounding, 3-h Forecast soundings from the NAM Nest, valid at 0900 UTC, 0915 UTC NOAA-20 NUCAPS Sounding, 1200 UTC Radiosonde; the final image includes all the soundings at once (Click to enlarge)

The toggle between the 0000 and 1200 UTC radiosondes at Aberdeen shows a general moistening of the atmosphere (especially above 500 mb). NUCAPS soundings in between give a forecaster information on the character of that increase: linear? step-wise? The two NUCAPS soundings, below, separated by 90 minutes, and in between the two radiosondes, show moistening after 0700 UTC.

NOAA-20 NUCAPS Soundings near Aberdeen, SD, 0745 and 0915 UTC on 29 September 2021 (Click to enlarge)

NUCAPS soundings are volumetric, in comparison the radiosonde and model-derived soundings, both of which are valid at one point that is ascending through the atmosphere. NUCAPS soundings from NOAA-20 are a blend of information from up to 9 CrIS (Cross-track Infrared Sounder) fields of regard and one Advanced Technology Microwave Sounder (ATMS) footprint. A comparison between radiosonde or model soundings and NUCAPS soundings should always be tempered with that information.

The beginning of the extratropical transition of Hurricane Larry

September 10th, 2021 |
GOES-16 Airmass RGB, 0000 UTC on 8 September through 1200 UTC on 10 September 2021 (Click to enlarge)

The animation above (created using Geo2Grid) with a 3-h time step shows the approach of a mid-latitute shortwave trough (that produced large hail over Wisconsin on Tuesday 7 September; SPC Storm Reports) to Hurricane Larry over the tropical Atlantic. The Potential Vorticity anomaly associated with the mid-latitude trough (moving from the western Great Lakes on the 8th to the east coast on the 10th) appears as red/orange in the RGB imagery, and by 1200 UTC on the 10th, the anomaly sits over the eastern United States with Larry to its east. The RGB at 1200 UTC on the 10th shows orange/red hues to the south and east of the the hurricane center; in that region, however, the orange colors do not signify upper level potential vorticity anomalies, but rather dry air in the mid-tropopshere.

The correlation between red/orange values in the RGB and large values of potential vorticity in the upper troposphere with the feature in the midwest United States is confirmed by the overlay below that shows a pressure analysis on the 1.5 Potential Vorticity Unit (PVU) surface. The UKMET Office model data shows pressure values below 500 mb.

GOES-16 Airmass RGB (2100 UTC 9 September, 1200 UTC 12 September) and UKMET Model Simulation of 1.5 PVU Pressure values (0000 and 1200 UTC on 10 September), Click to enlarge

NUCAPS (NOAA-Unique Combined Atmospheric Processing System) profiles yield information about the thermal structure of the atmosphere, and also measure ozone concentration. Gridded values from the profiles, shown below (from this url) show a low tropopause and enhanced ozone (both suggestive of a tropopause fold/stratospheric intrusion) over the eastern US at 0647 UTC on 10 September (and also at 1812 UTC on 10 September).

NOAA-20 gridded NUCAPS estimates of Tropopause Height, and of Ozone anomalies, 0647 UTC, 10 September 2021 (Click to enlarge)

For more information on Larry, refer to the webpages of the National Hurricane Center.