Using NUCAPS to help nowcast Midwest convection

May 23rd, 2020 |

GOES-16 ABI Band 2 (0.64 µm) visible imagery at 1821 UTC 23 May 2020 (Click to enlarge)

The NOAA Storm Prediction Center’s Convective Outlook (graphic) from 1630 UTC 23 May 2020 shows an enhanced risk of Severe Thunderstorms in northern Illinois with a sharp cutoff in probabilities to the north in southern Wisconsin. The imagery above shows the GOES-16 ABI Band 2 (0.64 µm) visible imagery (click here for Band 13 (10.3 µm) Infrared Imagery), and it shows convection over northern Illinois/southern Wisconsin ahead of an obvious vorticity center in Iowa. How far north will the convection build?

This question can be answered by considering lower-tropospheric (900-700) and mid-tropospheric (850-500) lapse rates diagnosed from the NUCAPS Profiles produced from the NOAA-20 pass over the Upper Midwest at ~1818 UTC (NOAA-20 orbit for this day shown here); these data were available within AWIPS by 1915 UTC! 

The toggle below shows ABI Bands 2 and 13 (0.64 µm and 10.3 µm, respectively) as well as the lapse rates. The Lower Tropospheric lapse rates show a north-south gradient in stability, with air that is more stable over Wisconsin; convection over Illinois should weaken as it moves north. Mid-tropospheric lapse rates show a similar gradient in stability albeit less pronounced. (Click here to view the lower-tropospheric lapse rates overlain with NUCAPS sounding availability points from AWIPS, color-coded to show whether or not Infrared and/or microwave retrievals converged. Over southwest Wisconsin/northwest Illinois, perhaps you can argue that the gradient is influenced by soundings that did not converge; that argument would be harder to make over northcentral/northeast Illinois and southcentral/southeast Wisconsin).

GOES-16 ABI Bands 2 (0.64) and 13 (10.3) at 1821 UTC and Lower- and Mid-Tropospheric Layer Lapse Rates (900-700 and 850-500 mb, respectively) at nominal times of 1818 UTC over the upper Midwest (Click to enlarge)

This post is to remind you that satellite-derived retrieval data (independent of model data) is available in AWIPS in a timely manner to help you diagnose the thermodynamic state of the atmosphere. (Added: Storm reports for this event are here. Severe weather did cross into Wisconsin but was very close to the Illinois border).

Where will convective initiation occur? NUCAPS can help.

May 7th, 2020 |

GOES-16 Band 2 (0.64 µm) visible imagery, 1900-2030 UTC rocking animation from 7 May 2020 (Click to animate)

Consider the rocking animation (if you click on it) of 1-minute visible imagery, above, showing the high plains of West Texas from 1900-2030 UTC on 7 May 2020. A dryline is present; can you predict from this imagery where convection will initiate? (Will it? Spoiler alert: Yes, and Yes!)

The Split Window Difference field shows the difference in brightness temperatures sensed at 10.3 µm and 12.3 µm. In clear skies, a distinct signal can be apparent along a dryline because of more water vapor absorption at 12.3 µm than at 10.3 µm. (A classic example is shown here, and discussed in this journal article) On 7 May 2020, however, abundant thin cirrus (which cirrus also has a very strong signal in the split window difference) masked much of the surface-based dryline signal.

GOES-16 Split Window Difference (10.3 µm – 12.3 µm) field, 1801-2056 Rocking animation, 7 May 2020 (click to animate)

On 7 May 2020, NOAA-20 overflew the high plains shortly at around 2000 UTC (map, from this site). Data from individual NUCAPS profiles (shown as green, yellow or red dots on the image below) can be interpolated to horizontal grids that allow for an easy presentation of thermodynamic features. Total precipitable water, below, derived from those individual vertical profiles, shows a gradient over west Texas, as expected when a dryline is present.  Any kind of impulse moving eastward from New Mexico will encounter an increasingly moist airmass as it traverses the Texas panhandle.

Gridded NUCAPS estimate of Total Precipitable Water, ca. 2000 UTC on 7 May 2020 (Click to enlarge)

How does NUCAPS gauge the instability of this airmass? Convective Available Potential Energy (CAPE) from the NUCAPS profiles is shown below.  A maximum in CAPE occurs just southwest of Childress, TX.  Perhaps this region of maximum instability is where the strong convection will initiate?

NUCAPS-derived Convective Available Potential Energy, ca. 2000 UTC on 7 May 2020 (Click to enlarge)

Note the NUCAPS sounding profile point that sits within the maximum in CAPE in the image above.  It is green — a color that denotes an infrared retrieval that converged to a solution.  That CAPE-filled vertical profile is show below.

NUCAPS Profile, ca. 2000 UTC on 7 May 2020 at 34.1 N, 100.4 W (Click to enlarge)

Animated visible imagery, below (at a 5-minute time step) — click here to see the animation at every minute) — shows initiation just after 2130 UTC near where the western gradient of the CAPE maximum sits at 2000 UTC.

GOES-16 Band 2 (0.64 µm) visible imagery, 1800-2156 UTC on 7 May 2020 (Click to animate)

The 2356 UTC 7 May 2020 Clean Window image, below, (toggled with the 2056 UTC image) shows the result of rapid development!

GOES-16 Band 13 (10.3 µm) infrared imagery, 2056 and 2356 on 7 May 2020 (Click to enlarge)

NUCAPS and dry air in the Upper Midwest

May 1st, 2020 |

GOES-16 ABI Band 2 (0.64 µm, visible) and Band 13 (10.3 µm, infrared) along with gridded NUCAPS fields of 925-700mb Relative Humidity, Midwest Base Reflectivity and NUCAPS Sounding availability points (Click to enlarge)

A cloud band passing through the upper midwest on 1 May 2020, shown above in the GOES-16 ABI Visible and Infrared imagery (toggled with NUCAPS products and radar), was accompanied by radar echoes. Would you expect that radar-indicated precipitation to reach the ground?  Gridded NUCAPS fields (shown here with NUCAPS Sounding availability points) show very dry air in the lower troposphere over eastern Wisconsin.  Individual NUCAPS soundings, one over Lake Michigan just east of Racine, and one over Green Bay, toggled below, similarly show very dry air.

NUCAPS Profiles over Lake Michigan and Green Bay (Click to enlarge)

Gridded NUCAPS fields around nocturnal convection over the southern Plains

April 22nd, 2020 |

GOES-16 Clean Window (10.3 µm) infrared imagery, 0346 – 1021 UTC, 22 April 2020 (click to animate)

GOES-16 Clean Window (10.3 µm) infrared imagery, above (click to animate) shows two regions of convection over the southern Plains, one moving through central/southern Oklahoma, one developing over the Texas Panhandle and moving east). A similar (but slightly later) animation of GOES-16 Low-Level water vapor infrared imagery (7.34 µm) is below.

GOES-16 Low-Level water vapor (7.3 µm) infrared imagery, 0456 – 1441 UTC, 22 April 2020 (click to animate)

At 0821 UTC, two distinct mesoscale convective complexes are apparent, with a clear region between. This time approximated an overpass by NOAA-20; data from the Cross-track Infrared Sounder (CrIS) and the Advanced Technology Microwave Sounder (ATMS) are combined to create NUCAPS soundings.

GOES-16 Low-Level water vapor (7.3 µm) infrared imagery, 0826 UTC, 22 April 2020, along with NUCAPS sounding points (click to enlarge)

During this time, there were three soundings launched at Amarillo — at 0000, 0600 and 1200 UTC.  They are shown below and all three suggest steep mid-level lapse rates.

Radiosonde from Amarillo TX at 0000, 0600 and 1200 UTC on 22 April 2020 (Click to enlarge)

The NUCAPS profile south of Amarillo (in the water vapor image above, the ‘green’ point just south of the ‘red’ point just south of the convective system over Amarillo) is shown below.  It also shows fairly steep mid-level lapse rates.  Click here to see a toggle between the NUCAPS profile below and the 0600 UTC Amarillo Radiosonde.

NUCAPS Profile at 35 N, 101 W, 0821 UTC on 22 April 2020 (Click to enlarge)

Gridded NUCAPS fields allow a forecaster to view thermodynamic information from the entire pass more easily than can be achieved by examination of individual soundings, or by viewing soundings via the pop-up SkewT.  The animation below shows the Total Totals index, the 850-500-mb lapse rate, and the lapse rate from 700-300 mb.  Strong instability (Total Totals values around 50) is indicated downstream of the system over the Texas panhandle; also, lapse rates are steeper between 700 and 300 mb (about 7.5º C/km) compared to those between 850 and 500 mb (about 6.8º C/km).

Gridded NUCAPS data gives timely satellite-derived (and model-independent) estimates of the thermodynamic state of the atmosphere.

Gridded NOAA-20 NUCAPS estimates of Total Totals index, 850-500 mb Lapse Rate and 700-300 mb Lapse Rate (Click to enlarge)