Subtropical storm Melissa

By Sheldon Kusselson and Dan Bikos

Subtropical storm Melissa exists off the Eastern coastline of the U.S. on 10-11 October 2019, as GOES-16 visible imagery on 11 October shows:

note the lack of deep convection over the center of the circulation, however convection does exist north and northeast of the center at this time.

Another perspective on this storm can be seen on the Advected Layer Precipitable Water (ALPW) product:

The ALPW product depicts precipitable water in 4 layers.

Upper left (Surface to 850 mb), Upper right (850 to 700 mb), Lower left (700 to 500 mb), Lower right (500 to 300 mb).

Note the advection of subtropical moisture from two distinct areas in the Atlantic at the two lowest layers and at least one of the two highest layers. Dry areas are probably the blocks to the low off the East Coast.

The storm has brought rainfall from coastal New Jersey to Massachusetts, the moisture associated with this rainfall can also be viewed in a Total Precipitable Water (TPW) product. Here we show the experimental merged TPW product which makes use of observations from both microwave instruments on multiple polar orbiting satellites and the GOES-16 ABI:


Posted in Heavy Rain and Flooding Issues, Tropical Cyclones | Comments Off on Subtropical storm Melissa

JPSS/GOES Fire Detection Capabilities – Swan Lake Fire, AK

The Swan Lake Fire, located in the Kenai National Wildlife Refuge, south of Anchorage, AK initiated in June 2019 due to lightning. Over the past few months, the fire has steadily grown, and as of 20 August 2019, more than 130,000 acres have burned.

To get a close look at the fire refer to the following comparison (see imagery below) at 2248Z, 19 August 2019. Imagery compares SNPP VIIRS 3.7μm to the GOES-17 3.9μm infrared imagery. GOES 3.9μm is at 2-km while the VIIRS 3.7μm is at 375-m spatial resolution. Notice the fine details of the fire areal extent seen by VIIRS, exhibiting warm brightness temperatures (i.e. fire hotspots seen in black). In contrast, the GOES imagery does not capture the intricate fire perimeter, due to its coarser resolution and that it is affected by parallax. Parallax consists of the satellite displacement of features in the imagery, where geostationary observations over northern latitudes are far away from the GOES satellite subpoint (i.e. nadir). The geostationary imagery results in elongated pixels over the fire producing ambiguity in the fire location and perimeter.

Although GOES-17 has a coarser temporal resolution, the animation below highlights the fire at a finer temporal resolution (i.e. 1-minute data) from 2230-2330Z, on 19 August 2019. The visible (0.64μm) and infrared (3.9μm) imagery shows the evolution of the fire location, fire hotspots, and corresponding smoke. Surface observations are overlaid onto the imagery to highlight the air temperature/dewpoint, wind direction and speed, along with smoke and haze identifiers.

[Click animation link]

To get an idea of the atmospheric environment aloft and near the surface, users can refer to satellite derived NUCAPS soundings that provide temperature and moisture profiles. Remote areas that lack RAOB observations can take advantage of NUCAPS soundings in the operational forecasting environment. The closest NUCAPS profile in proximity to the fire is chosen below (i.e. green dot encompassed by the white circle) at ~23Z, 19 August 2019.

The 23Z NUCAPS and 00Z, 20 August 2019 RAOB sounding from Anchorage, AK are compared below. The NUCAPS and RAOB soundings are ~45 miles apart from each other, where NUCAPS soundings provide a volumetric measurement of the atmosphere and ‘smoothes’ (i.e. averages) the temperature/dewpoint measurements within the profile. In contrast, RAOBs produce measurements along a ‘point’ throughout the atmosphere, producing a finer vertical resolution. Note the RAOB observation provides wind data (surface and aloft), while NUCAPS does not provide wind measurements.

The RAOB sounding observes a weak inversion containing a dry boundary layer and light surface winds, keeping smoke in the lower atmosphere. Precipitable water values are also low in both NUCAPS (0.41 inches) and RAOB (0.53 inches) observations, indicating a relatively dry atmosphere. The NUCAPS profile provides a general idea of what the atmosphere is like, and is sampled closest to the fire in comparison to RAOB (i.e. sounding further away from the fire). However, NUCAPS misses the low-level inversion along with the higher moisture content observed in the mid-levels, noticed by RAOB measurements.

Lastly, one cannot forget the VIIRS Near-Constant Contrast (NCC) product that provides a nighttime visible capability in support of active fires. From the SNPP VIIRS overnight pass at 1235Z, 20 August 2019, the NCC observes the emitted lights produced from the fire, along with the emitted city lights. But how can users decipher between the two features? The images below compare NCC to VIIRS 3.7um to address the question.  Note the emitted lights from the fires correspond with the fire hotspots (high brightness temperatures seen in black), where the emitted city lights do not exhibit this correlation. Fire is observed in between Sterling and Cooper Landing, Alaska. Emitted city lights can be seen from Nikiski to Soldtona, AK and up north, near Anchorage, AK.

Posted in Fire Weather, GOES, POES, Satellites | Comments Off on JPSS/GOES Fire Detection Capabilities – Swan Lake Fire, AK

VIIRS flood observations along the Arkansas River

Heavy rain fell in Kansas, Oklahoma and Arkansas the past few weeks, causing major flooding along portions of the Arkansas River. In the RealEarth image below (i.e. 1930Z on 27 May 2019), major flooding is indicated in orange and red colors and extends from Fort Gibson in northeast Oklahoma to New Blaine in northwest Arkansas.

In the example above, satellite observations are employed to identify the inundated areas, where the Visible Infrared Imaging Radiometer Suite (VIIRS) Flood Areal Extent is utilized. Product is at 375-m spatial resolution and is available for forecasters via Local Data Manager (LDM).

A VIIRS Flood Areal Extent animation is also provided (see below) from 23-28 May 2019, highlighting the flooding along the Arkansas River. The VIIRS Flood Areal Extent discriminates between different scene types (i.e. MS = missing data (black), LD = land (brown), SI = supra-snow ice (mixed ice and water, or water over ice denoted in purple), SN = snow (white), IC = ice (aqua), Cl = clouds (grey), CS = cloud shadows (dark grey), WA = open water (blue)). The product also calculates the floodwater fraction percentage of a pixel (e.g. the product determines if a pixel is 20%, 40%, 100% flooded). The floodwater fraction percentage is from 0-100% and ranges from green-to-red colors. Notice in the animation, the evolution of the flooding along the Arkansas River and the increased flooding near Fort Smith, AR.

For additional perspective on how much rain accumulated over the area, Advanced Hydrologic Prediction Service (AHPS) 7-day and 14-day observed and normal (i.e. average) precipitation images are shown below at 12Z on 30 May 2019. Observed precipitation is expressed as gridded data with a spatial resolution of 4 kilometers, where precipitation is represented in inches. Notice the high precipitation amounts scattered throughout northeastern Oklahoma and northwest Arkansas over the 7-day and 14-day periods, and how observed precipitation values are significantly higher than their respective 7-day and 14-day normal precipitation values. Maximum 7-day and 14-day observed precipitation reached ~5-6 inches and 10+ inches respectively. The 30-day observed and normal precipitation values (not pictured here) also inferred that soils were saturated, suggesting a conducive environment for flooding as well.

7-Day Observed (left) and Normal (right) Precipitation Values

14-Day Observed (left) and Normal (right) Precipitation Values

More flooding along the Arkansas River is expected throughout the next week, where the latest flooding updates can be accessed via the following National Weather Service (NWS) link.

Posted in Heavy Rain and Flooding Issues, Hydrology, POES, Satellites | Comments Off on VIIRS flood observations along the Arkansas River

VIIRS observations of Katabatic Winds from the Transcontinental Mountain Range Adjacent to the Ross Ice Shelf in Antarctica

By Lewis Grasso and Jorel Torres

One of the goals of the JPSS program set forth by NOAA is enhanced monitoring of the Earth’s environment. One specific type of event of the Earth’s environment that was captured by VIIRS on-board not only the operational NOAA-20 satellite platform, but also the demonstration S-NPP satellite platform was katabatic winds. Katabatic winds that flow through the glacial canyons of the Transcontinental Mountain Range represent a wind regime that transports some of the coldest surface air off the Antarctic ice sheet to the Ross Ice Shelf.

In the figure below a few key features are annotated. The glacial canyons where the katabatic winds flow along the Ross Ice Shelf are denoted. Furthermore, McMurdo research facility is also annotated. As a side note, McMurdo is one of the locations where VIIRS data is downloaded; Svalbard, Norway is the second location. Annotations in the figure are superimposed on top of Imagery Band (I-5, 11.45um), which has a 375-m sub-satellite footprint.

VIIRS offers high-resolution imagery as a means to monitor local-environments, however still images may limit interpretation of the imagery. The following sets of animations provide a GOES-16/17 ABI-like loops from combination of both S-NPP and NOAA-20 VIIRS instruments.

Animation 1: 29 April 2019  (click following link)

Animation 2: 2 May 2019  (click following link)

Animation 3: 3 May 2019  (click following link)


For the interested reader here are some references.

The entire February 2003 MWR Volume One article is the following: Antarctic Satellite Meteorology: Applications for Weather Forecasting.<0371:ASMAFW>2.0.CO;2

Besides the February 2003 MWR Volume, we offer the following articles.

A Strong Wind Event on the Ross Ice Shelf, Antarctica: A Case Study of Scale Interactions

Circumpolar Mapping of Antarctic Coastal Polynyas and Landfast Sea Ice: Relationship and Variability

Insight into the Thermodynamic Structure of Blowing-Snow Layers in Antarctica from Dropsonde and CALIPSO Measurements

Numerical Prediction of an Antarctic Severe Wind Event with the Weather Research and Forecasting (WRF) Model 

Posted in Miscellaneous | Comments Off on VIIRS observations of Katabatic Winds from the Transcontinental Mountain Range Adjacent to the Ross Ice Shelf in Antarctica

Dryline Bulges Identified in GOES-16 Split Window Difference on 30 April 2019

By Dan Bikos and Lewis Grasso

During the afternoon of 30 April 2019, a dryline mixed eastward from New Mexico into the Texas panhandle, as seen in this GOES-16 visible loop with METARs overlaid:

Thunderstorms initiate along various segments of the dryline during the animation.

The moisture gradient is substantial across the dryline so we may expect to see this in the GOES Split Window Difference (SWD) (10.3 minus 12.3 micron) product as well:

Upper left: CIRA SLIDER default enhancement applied to the SWD product

Upper right: AWIPS default enhancement (dust_and_moisture_split_window) applied to SWD product

Lower left: Linear enhancement with a modified range of 0 to 8 degrees Celsius applied to the SWD product

Lower right: Linear enhancement with a modified range of 0 to 5 degrees Celsius applied to the SWD product

Water vapor in the boundary layer is an absorbing gas to energy at 10.3 and 12.3 microns that is emitted from the earth’s surface.  Water vapor absorbs more energy at 12.3 compared to 10.3 microns; therefore, when the temperature decreases with height the brightness temperature at 12.3 microns is less than the brightness temperature at 10.3 microns, hence the difference is positive.  The magnitude of the SWD is greater on the moist side of the dryline compared to the dry side.

The above animation shows why it’s important to experiment with different color tables and range when looking at imagery.  Certain features of interest may stand out more than others.  For example, since there is a temperature dependence in the SWD, there is a diurnal variation in the animation as we approach sunset in the later half.  The diurnal variation may mask the moisture variation of interest, this is particularly true of the color tables in the top two panels, whereas the diurnal variation is not as obvious in the bottom two panels.

One feature that the SWD product really highlights more than visible imagery is the fact that there are smaller scale bulges along the dryline.  These are important as they may be indications of localized moisture convergence which may trigger convective initiation.  The smaller scale bulges are annotated with white arrows on the image below:

In the loop, notice that these smaller scale dryline bulges appear earlier in the bottom two panels compared to the top two.

The visible imagery shown earlier does show indications of some cumulus along segments of the dryline, so are these regions actually more moist or being obscured by clouds as seen in the GOES imagery?  To help answer that question we introduce surface observations from the west Texas Mesonet. Below is a zoomed in SWD image using the linear color table and range of 0 to 8 degrees Celsius at 22:06 UTC.  At that time, there are two dryline bulges evident in the SWD product:

The SWD product suggests that Denver City, TX is still on the moist side of the dryline while Morton, TX is on the dry side.  The meteogram below is from the observations at those locations, red arrows for the timeline in the Morton meteogram indicate the time of the above image (near 2200 UTC):

Meteograms courtesy of the West Texas Mesonet.

The dewpoint (shown in the solid green curve) clearly drops at Morton, TX BEFORE it does so in Denver City, TX.  This is confirmation that the features identified in the GOES-16 SWD product are indeed associated with smaller scale dryline bulges.  In fact, note the winds at Morton, TX increase in speed and veer in direction before it does so in Denver City, TX.

We conclude with a comparison of the GOES-16 SWD product with other familiar bands (0.64 micron visible, 10.3 micron IR, and 7.3 micron water vapor):

How well do the dryline bulges discussed above show up in other bands?

Which bands can you see outflow from the southernmost storm in?

Posted in Convection, GOES R, Severe Weather | Comments Off on Dryline Bulges Identified in GOES-16 Split Window Difference on 30 April 2019