Santa Ana Winds and Dust Identification

It is that time of year again, to observe Santa Ana Wind events for Southern California. On 15 October 2018, an upper-level trough advected into the southwestern United States (i.e. see GOES-16, Upper Level Water Vapor imagery below), produced cold air advection aloft, and brought strong subsidence (i.e. sinking motion) to the surface. The strong subsidence, brought cold, dry, and fast, downsloping winds along the Sierras, towards the coastline. The downsloping winds produced compressional warming, a process that warms the surface air tens of degrees fahrenheit over a short period of time. The following satellite imagery and surface observations of the event are taken between 9-20Z, 15 October 2018.

GOES-16 -> Upper Level Water Vapor (6.2um) : 12-20Z, 15 October 2018


Surface Wind Observations: 10-20Z, 15 October 2018

Note the strong, northeasterly winds in Southern California, with wind gusts over 40 mph. Additionally, notice rapid warming of air temperatures along with a significant decrease in dewpoint temperatures, especially along the coast.


GOES-16 -> Low Level Water Vapor (7.3um): 17-20Z, 15 October 2018 

A rapid warming of Brightness Temperatures (BT), represented by pink and yellow colors, advects from northeast-to-southwest bringing warm, dry air to the Los Angeles Metropolitan area. Note, the wave-like patterns produced off of the Sierras create turbulence in the boundary layer, and are hazards for the aviation industry.


Microwave Sensors -> CIRA Advected Layered Precipitable Water (CIRA-ALPW): 9-18Z, 15 October 2018 

Another way to see how dry the surface air is, one can use the CIRA-ALPW product, comprised of microwave data. CIRA-ALPW estimates the precipitable water (i.e. moisture content) within a vertical column of the atmosphere. Unlike other precipitable water products, CIRA-ALPW produces precipitable water values within four layers of the atmosphere (i.e. surface-850mb, 850-700, 700-500 and 500-300mb) and utilizes GFS model winds in the algorithm. In the following CIRA-ALPW, surface-to-850mb video, see the moisture gradient, and dry air (i.e. low TPW values) shift southwestward, towards the coastline.


GOES-16 -> Split-Window Difference (10.3um-12.3um): 17-20Z, 15 October 2018  

The Split-Window Difference product shows areas of dust, produced by the high winds, seen within the black ellipses. Regions of low-level dust are denoted as negative values, and represented by dark brown signatures. The Split Window Difference product identifies these areas as dust, due to the 10.3um Brightness Temperature (BT) is colder than the 12.3um BT; where silicates in dust are absorbed in 10.3um.


GOES-16 -> GeoColor: 17-20Z, 15 October 2018  

In complement to the Split Window Difference product, one can use the GeoColor product to identify dust within the black ellipses. Play the following video. Notice dust over land may not be as discernible to dust advecting over bodies of water. If one is still having trouble identifying dust, focus on the following cities: Long Beach, Mission Viejo, Oceanside, Temecula, the Salton Sea, Ocotillo, and Barstow.

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Hurricane Michael

Hurricane Michael has made landfall today, along the Florida Panhandle, between Tyndall Air Force Base, FL and Mexico Beach, Florida. Radar and satellite products observed Michael, as it approached the Florida Panhandle (seen below). Over the last 12 hours, Michael increased in maximum wind speed to 155-mph and had a pressure level of 919-mb.

Radar – Base Reflectivity (Tilt – 0.5 degrees) between 15-17Z, 10 October 2018 (via College of Dupage). Notice the heavy rain bands in the inner and outer core of Hurricane Michael, producing heavy precipitation, and very high wind speeds. 


Blended Total Precipitable Water (TPW) at 1456Z, 10 October 2018. A microwave product that estimates TPW throughout the entire column of the atmosphere. Purple and white colors express high moisture content (i.e. high TPW values, ~2.5-3 inches) that Hurricane Michael encapsulates, which can lead to heavy precipitation and flooding. 

Advected Layered Precipitable Water (ALPW) from 18Z, 9 October 2018 to 15Z, 10 October 2018. Different from the Blended TPW, ALPW estimates precipitable water values in 4 different layers (i.e. refer to 4-panel below: surface-850mb (top-left), 850-700mb (top-right), 700-500mb (bottom-left), and 500-300mb (bottom-right)), where the majority of moisture content is located in the lower layers of the atmosphere (i.e. within 3-km above the surface). GFS model winds are incorporated into the algorithm. Black pixels in the imagery represent precipitating regions, denoted as ‘missing data’. Although microwave retrievals can be made in cloudy regions, they cannot be made in precipitating regions. 


GOES-16, infrared band 13 (10.3 um) at 1634Z, 10 October 2018. Imagery shows Hurricane Michael, on the cusp of landfall, showing a well defined eyewall and cold brightness temperatures (i.e. red to dark-red colors) within the inner and outer core of the hurricane. 

NHC Forecast (below) for the next few days, as of 1 PM CDT update. Hurricane Michael will interact with an upper level trough, and move to the northeast, producing heavy precipitation in Florida, Georgia and the Carolinas. The system will be downgraded to a Tropical Storm by Thursday and will eventually move out to sea, by the weekend.

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The Arizona Hurricane Rosa Heavy Rainfall Event for Late September to Early October 2018

This blog entry is by Sheldon Kusselson and in the format of a PDF document:

Hurricane Rosa Event_LateSept_EarlyOct2018

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Hail damage swaths from severe storms over the High Plains as viewed from satellites during July 2018

By Louie Grasso, Dan Bikos, Jorel Torres and Ed Szoke

During the summer of 2018 over the High Plains, several significant severe storms occurred.  Several hailstorms moved southward over the Central High Plains and produced noticeable hail swaths and damage scars on the ground that were captured by GOES-16 ABI.  The purpose of this blog is to compare and contrast GOES-16 imagery before and after each event.  In addition, SNPP and NOAA-20 imagery will be shown that also contains damage scars. Supplemental observations of the tracks of the severe storms is provided the MRMS Mid-level rotation tracks along with SPC storm reports.

To begin with, a brief discussion of imagery before and after the hail swaths and damage scars is given below.  Before the events (left side image  in the figure below) this is how the GOES-16 ABI imagery appeared on 10 July 2018.  For those not familiar with the region displayed in the imagery, the dominant brownish color is typical due to the semi-arid climate of the western High Plains.  During the three weeks following 10 July a persistent northwesterly flow pattern existed that supported multiple severe weather episodes.  As a result, several surface features, indicated by black line segments are evident at the end of the period (right side image in the figure below).

Our first case study occurred on 26 July 2018.  Thunderstorms began developing during the afternoon of the 26th, a few of which are seen in the figure below.  Of particular interest are the two white ovals, one located along the Colorado/Wyoming border, the second located in western Kansas. At that time no hail swaths were evident in either oval.  A comparison of the figures above and below can be used to orient the reader about the 2 regions just discussed.


At 0230 UTC 27 July two hail producing storms were evident in imagery in the GOES-16 ABI 3.9 micron band and is displayed below.  Within the white ovals, darker line segments were evident in the wake of the storm paths as they moved towards the southeast.  In the color table used below, the dark line segments correspond to cooler brightness temperatures compared to the light gray region around each swath.  The colder and dark line segments represent hail swaths due to the hail be colder than surrounding ground.

On the next day, imagery near noon is used to indicate the hail scar due to the previous day’s storms.  Unluckily the swath along the Colorado/Wyoming was obscured by persistent clouds.  On the other hand the swath in western Kansas is evident within the oval: compare the figure below with the previous two figures.

An independent observing system that captured the storms is the MRMS mid-level rotation tracks.  As is seen in the figure below, the pairs of black arrows correspond to the location of rotating storms.  A comparison of the figure below with the previous three figures above provide additional evidence of convective activity where the hail swaths occurred.

Our second case study occurred on 28 July 2018.  Unlike the first case above, no thunderstorms have developed in the image below since it is late morning.  Of particular interest are the three white ovals, one located just south of the Colorado/Wyoming border, the second located in extreme northeast Colorado, while the third is located over east central Colorado. At that time no hail swaths were evident in either oval.  A comparison of the first figure (see beginning of blog) and the figure below can be used to orient the reader about the 3 regions just discussed.

At 0615 UTC 29 July the hail producing storm was evident over extreme northeast Colorado as seen in the GOES-16 ABI 3.9 micron band imagery as displayed below on the left.  Within the white oval in extreme northeast Colorado, two darker line segments were evident in the wake of the storm path as it moved towards the southeast over extreme southwest Nebraska.  Later on that day, severe storms developed and also produced a hail swath; the northern portion of the hail swath is seen in the northern portion of the white oval near the Colorado/Wyoming border.  The thunderstorm producing the hail swath covers the rest of the oval as is seen in the figure below on the right.

On 30 July 2018 at 1415 UTC imagery in the early morning is used to indicate the hail scars due to the previous two convective events (see figure below).  The hail damage scars from the first case are denoted by two black line segments.  Within each oval, hail damage scars are evident. A comparison of the figure below with the first figure of the blog can be used to help the reader identify hail damage scars.

As in the other case, the MRMS mid-level rotation tracks are used an additional source of information.  As is seen in the figures below, the pairs of black arrows correspond to the location of rotating storms.  A comparison of the figures below with the previous figures for this case provide additional evidence of convective activity where the hail swaths occurred.

All of the hail damage scars were also imaged by SNPP-VIIRS as seen in the image below on 31 July 2018 at 1917 UTC.  Black arrows point to scarring locations while the white arrow points to Cheyenne, WY.

We leave it to the interested reader to identify hail damage swaths in the NOAA-VIIRS Day Night Band image displayed below.  Also of interest a number of cities appear in the imagery.

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