Monitoring severe weather as it happens

March 17th, 2021 |

NUCAPS/MADIS Lifted Index, GLM Group Density, GOES-16 Band 13 Infrared Imagery, and ProbSevere polygons, all at ~0939 UTC on 17 March 2021 (Click to enlarge) All imagery from RealEarth

When NOAA’s Storm Prediction Center issues a High Risk of severe weather (below), people sit up and take notice. Are there easily accessible tools to monitor the state of the atmosphere in/around a region of expected severe weather?

The toggle above shows products (early in the morning on 17 March — at 439 AM CDT) in RealEarth that can help. NOAA-Unique Combines Atmospheric Processing System (NUCAPS)/MADIS (Meteorological Assimilation Data Ingest System) Lifted Indices combine tropospheric information from NUCAPS profiles with lower-tropospheric/surface information from MADIS to create Lifted Index fields, twice daily. These fields are generated using HEAP (Hyper-spectral Enterprise Algorithm Package) software (incorporated into CSPP — the Community Software Processing Package) at the UW-CIMSS Direct Broadcast site. A Suomi-NPP (or NOAA-20) overpass will quickly yield stability information. Today’s afternoon Suomi-NPP overpasses occurs around 1730 UTC (east of the High Risk area) and 1915 UTC (Link, from this site.) The toggle above also includes GOES-16 Band 13 infrared (Clean Window, 10.3 µm) information, GLM Group Density, and NOAA/CIMSS ProbSevere (ProbSevere has a stand-alone RealEarth-based site here).  All of these products are useful in monitoring this evolving, dangerous event.   As is often the case, the strongest convection was occurring at 0939 UTC along the edges of the most unstable air, that is, in the instability gradient.

People within the region of elevated risk of Severe Weather on 17 March 2021, especially the region High Risk, should pay especial attention to the weather.

NOAA Storm Prediction Center Risk assessment for 17 March 2021, issued 1300 UTC on 17 March (Click to enlarge)

Added: the Geosphere site (link) gives rapid access to GOES-16 imagery (including mesoscale sectors) and can be used to monitor this evolving situation.

The afternoon image of stability is shown below.

NUCAPS/MADIS Lifted Index, GLM Group Density, and GOES-16 Band 13 Infrared Imagery, all at ~1830 UTC on 17 March 2021 (Click to enlarge) All imagery from RealEarth

Hail Storm in Daytona Beach

March 6th, 2021 |

GOES-16 Convection RGB over Florida, 1431 – 1701 UTC on 6 March 2021 (Click to animate)

Accumulating hail fell in Daytona Beach FL (Link) on 6 March 2021 in association with a front over the Florida peninsula.  Preliminary storm reports from SPC (link) show reports of 1″ to 1.75″ hail. (The region was under a general thunderstorm outlook from SPC: link). The animation above shows the Convection RGB from 1431 through 1701 UTC on 6 March, bracketing the hail event over Daytona Beach near 1600 UTC. A strong white/yellow signal develops in a cell over Volusia County (Dayton Beach is within Volusia County) around 1545 UTC. This is the cell that deposits the hail.

NOAA/CIMSS ProbSevere display, 1535 UTC on 6 March 2021 (click to enlarge)

ProbHail values for this event (from this website) were small, at less than 10%. The value of ProbSevere here could be in identifying the cell responsible for the Hail, and showing values for the radar object that exceed others nearby; that is, providing guidance as to which radar cell to interrogate most often. The image above shows ProbSevere at 1535, just before a Severe Thunderstorm Warning was issued. The image below shows ProbSevere at 1600 UTC, just after the Special Marine Warning was issued (and while the Severe Thunderstorm warning was still in effect).

NOAA/CIMSS ProbSevere readout, 1600 UTC on 6 March 2021 (click to enlarge)

The time series plot for the radar object that produced the hail is shown below. Note that ProbHail (and lightning) increased (marginally) before the hail events (reported between 1535 and 1615 UTC) before collapsing.

ProbSevere values associated with Storm Object 84638, which object produced hail over Daytona Beach, 1500-1800 UTC on 6 March 2021 (click to enlarge)

There are several features in the visible imagery, below, that might be affecting the thunderstorm producing the hail. An east-west boundary is moving down the Atlantic coastline, passing through Daytona Beach around 1551 UTC. A very strong reflective signal becomes apparent after 1541 UTC as well (link): the convective cell has penetrated through the cirrus shield in the region.

GOES-16 Band 2 Visible (0.64 µm) imagery, 1431 – 1701 UTC on 6 March 2021 (click to animate)

This was a challenging forecast in a marginal environment.

NOAA/CIMSS ProbSevere with a tornado in Tallahassee, FL

January 27th, 2021 |

NOAA/CIMSS ProbSevere display, 1545 – 1700 UTC on 27 January 2021 (Click to animate)

A tornado struck the Tallahassee, FL, airport at 1643 UTC on 27 January 2021 (SPC Storm Report).  The animation above shows ProbSevere (version 2) fields (from this site) in the hour leading up to tornadogenesis.  The animation demonstrates how ProbTor values can be used to identify for closer scrutiny a particular radar object:  the radar object that ultimately caused a tornado showed greater ProbTor values (than surrounding identified radar objects) in the hour leading up to tornadogenesis. In addition, ProbTor values ramped up quickly just prior to tornadogenesis as low-level azimuthal shear jumped.

One time series below compares ProbWind, ProbHail and ProbTor for the radar object (#15080) that produced the tornado; for this event, ProbWind and ProbTor values were comparable until a ramp-up in ProbTor values before the tornado occurred. The second time series shows the various components of ProbTor for radar object 15080 (both time series courtesy John Cintineo, SSEC/CIMSS).  Note in particular that this storm was not a lightning-producer.  Much of ProbTor’s variability was determined by changes in low-level azimuthal shear.

NOAA/CIMSS ProbSevere values (ProbWind, ProbHail, ProbTor) for radar object #15080, 1530 – 1658 UTC on 27 January 2021 (Click to enlarge)

NOAA/CIMSS ProbTor and component values for Radar object #15080, 1530 – 1658 UTC on 27 January 2021, associated with the Tallahassee FL tornado (Click to enlarge)

Lead time with ProbTor in this example was not exceptional.  However, its elevated values in the hour leading up to the tornado could have provided better situational awareness, and perhaps enhanced confidence in warning issuance for this well-warned event.



GOES-16 “Red” Visible (0.64 µm, left) and “Clean” Infrared Window (10.35 µm, right) images, with plots of SPC Storm Reports [click to play animation | MP4]

Unfortunately, the default Mesoscale Domain Sectors were positioned too far north to cover the Florida Panhandle — but 5-minute CONUS Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) depicted a west-to-east oriented line of thunderstorms across the northern portion of the Panhandle; a trend of cooling cloud-top infrared brightness temperatures was seen as the convection began to produce the tornado.

There was an overpass of the Terra satellite about 19 minutes before the start of the tornado event, at 1618 UTC — 1-km resolution MODIS Visible (0.64 µm) and Infrared Window (11.0 µm) images are shown below.

Terra MODIS Visible (0.64 µm) and Infrared Window (11.0 µm) images [click to enlarge]

Terra MODIS Visible (0.64 µm) and Infrared Window (11.0 µm) images [click to enlarge]

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)