1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the development of severe thunderstorms over southern/central Arizona from 1600-1900 UTC on 23 September 2019. The far western storm exhibited a well-defined Above-Anvil Cirrus Plume (AACP) that extended northeastward from the cold overshooting top (whose coldest infrared brightness temperature was -74ºC); note that the AACP feature appeared colder (shades of yellow to orange) on the Infrared images (for example, at 1817 UTC).

As the western storm began to weaken somewhat, a new storm just to the east (located about 20-30 miles north-northeast of the Phoenix metro area) began to intensify, prompting the issuance of a Tornado Warning at 1914 UTC (the last tornado warning issued by NWS Phoenix was 21 January 2010) — a brief EF0 tornado was documented (NWS Phoenix summary).

Tornado Warning including Cave Creek AZ, Carefree AZ, Camp Creek AZ until 12:45 PM MST pic.twitter.com/M5BDw2fuIE

— NWS Phoenix (@NWSPhoenix) September 23, 2019

Much of the moisture helping to fuel the development of this severe convection was from the remnants of Tropical Storm Lorena in the East Pacific Ocean — the northward transport of this moisture could be seen using the hourly MIMIC Total Precipitable Water product (below).

---

 

 

Stability parameters from GOES-16 showed that the reigon of thunderstorm development was just east of a strong gradient in Convective Available Potential Energy.  The animation above shows the GOES-17 Clean Window;  in regions of clear sky, the baseline Derived Stability Index CAPE is shown.  CAPE values are zero over much of California (except for the southeasternmost corner) but they increase rapidly over Arizona to values approaching 1000 J/kg.

On 23 September, skies were clear enough that an instability signal was obvious in the clear-sky baseline CAPE. An ‘All-Sky’ product has been developed that can be used on days with more widespread cloudiness; it is available at this link. Values of All-Sky CAPE at 1156 and 1556 UTC on 23 September are shown below, and they also show a sharp gradient in the instability, and the link down to moisture from Lorena’s remants.

NOAA/CIMSS ProbSevere is a product designed to indicate the likelihood that a given object will produce severe weather within the next 60 minutes. An animation of the product at 5-minute intervals, below, shows that the right-moving radar cell (also associated, as noted above, with an AACP) that developed over far southwestern Arizona (becoming a warned storm at 1647 UTC) was very likely to produce severe weather.

Parameters that are used to determine the probability can be revealed at the ProbSevere site by mousing over the colored object contours.  The values for the warned storm over SW Arizona are shown below at 1650 UTC, 3 minutes after the warning was issued.  This image shows the 1710 UTC readout with the highest ProbWind value (76%); this image shows the 1725 UTC readout with the highest ‘ProbHail’ value (99%); ProbTor values on this day were not exceptionally large — for the later tornado-warned storm farther east, they were 28% at 1915 UTC and 30% at 1920 UTC.

CIMSS is developing a machine-learning tool that combines ABI and GLM imagery (that is, only satellite data) to identify regions where supercellular thunderstorms capable of producing severe weather might be occurring. An mp4 animation for this event (courtesy John Cintineo, CIMSS) is shown below.  (This experimental product was also shown in this blog post)

View only this post Read Less

GOES-7 Infrared Window (11.25 µm) images (above) showed Hurricane Hugo as it made landfall as a Category 4 storm around 04 UTC on 22 September 1989. This GOES-7 data was accessed from the SSEC Satellite Data Services archive.

A GOES-7 Visible animation from 21 September and a longer Infrared animation spanning the period 13-22 September are shown below (courtesy of Tim Schmit, NOAA/NESDIS).

More information on Hugo is available from NWS Charleston and NWS Wilmington.

View only this post Read Less

GOES-16 (GOES-East) Split Window images (above) showed a large plume of the Saharan Air Layer (SAL) that moved westward off the coast of Africa then westward and northwestward across the eastern and central Atlantic Ocean during the 15-20 September 2019 period.

On 20 September, the hazy SAL plume could be easily seen in Full Disk GOES-16 True Color Red-Green-Blue (RGB) images from the AOS site (below).

The SAL plume was also apparent in True Color RGB images from Suomi NPP and NOAA-20 as viewed using RealEarth (below).

A comparison of GOES-16 CIMSS Natural Color RGB, Aerosol Optical Depth and Dust Detection product images from 1500-1900 UTC on 20 September (below) revealed AOD values as high as 0.5 within the hazy dust-laden SAL plume; the Dust Detection product indicated large areas of Low- to Medium-Confidence dust (with isolated pockets of High Confidence).

Yes, that’s quite a plume. Here’s the #SNPP #OMPS aerosol index from yesterday that shows how big it is. pic.twitter.com/WrQjRMZwRK

— Colin Seftor (@colin_seftor) September 21, 2019

On a side note, the Full Disk True Color shown above images revealed 3 different types of solar backscatter: a small spot of very bright sun glint off the water of the Amazon River and its tributaries, which moved from east to west — similar to this example from October 2018  (below)

along with 2 separate (and larger) areas of more diffuse solar backscatter, which propagated from west to east: the first (possibly a 180º-42º=138º or “rainbow” backscatter) appeared about midway between the Equator and the southern tip of South America — and the second  (a 180º backscatter) appeared farther north, closer to the Equator, slightly later in time (this type of solar backscatter was previously discussed here). These 3 solar backscatter features can also be seen in a rocking animation below.

Thanks to Fred Wu (NOAA/NESDIS) and Steve Miller (CIRA) for providing further insight regarding the nature of the 2 larger types of solar backscatter.

View only this post Read Less

GOES-17 (GOES-West) “Red” Visible (0.64 µm), Near-Infrared “Snow/Ice” (1.61 µm), Day Snow-Fog Red-Green-Blue (RGB) and and Day Cloud Phase Distinction RGB images (above) showed portions of the Brooks Range and eastern North Slope of Alaska that had significant snow cover on 18 September 2019. Some areas received 4-6 inches of snowfall during the previous day (a Winter Storm Warning had been issued, forecasting accumulations in the 4-8 inch range).

Snow cover appeared brighter white in the Visible images, and darker shades of gray in the Snow/Ice images; in the RGB images, snow was darker shades of red in the Day Snow-Fog, vs brighter shades of green in the Day Cloud Phase Distinction. Note that the Day Cloud Phase Distinction RGB provided sharper images than the Day Snow-Fog RGB (below), since the former makes use of higher spatial resolution 0.64 µm data for its Green component.

Although much of the Bettles (PABT) area was masked by cloudiness on 18 September, that site received moderate to heavy snow for a few hours on 17 September (below), and reported a snow depth of 4 inches at 17 UTC (9 am local time).

Here are a few snow totals from the Brooks Range area. Did you get snow where you are? Comment below how much you received and where and we will add it to the list! pic.twitter.com/2Z5VN8mt6g

— NWS Fairbanks (@NWSFairbanks) September 18, 2019

View only this post Read Less