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Working midnight shifts this past weekend, I had the opportunity to take a look at the VIIRS Day-Night Band Imagery for the detection and analysis of fog.  Early Monday morning, the observation at Ft. Payne was indicating fog with 1/2 statute mile visibility.  However, the presence of thin cirrus over parts of the area did not allow for the observation of ground phenomena, including fog, in the region via traditional Shortwave IR imagery (Image 1).  However, low clouds and fog were observed in the VIIRS Day-Night Band imagery since the cirrus were sufficiently translucent in the visible portion of the spectrum (Image 2).

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Image 1. VIIRS 3.9 µm IR image provided by NASA SPoRT, valid 0728 UTC 22 Aug 2016. Fog cannot be observed in the 3.9 um imagery since the cirrus are sufficiently opaque at this wavelength.

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Image 2. VIIRS Day-Night Band Reflectance provided by NASA SPoRT, valid 0728 UTC 22 August 2016. Fog can be seen in the narrow Paint Rock Valley of western Jackson County (in northeastern Alabama). Despite the observation of fog at Ft. Payne (DeKalb County AL, –located to the SE of Jackson County), fog cannot be readily observed in the imagery, suggesting that the fog was very localized and perhaps shallow.

I could show the standard fog product imagery (11-3.9 µm), but the story is essentially the same as that of the 3.9 µm imagery of course.  The ability to see through thin cirrus is one of the primary advantages offered by the VIIRS Day-Night Band imagery and thus is among its most useful applications, operationally speaking.  These imagery are a part of the JPSS Proving Ground and have been available in AWIPS here at the HUN office for several years now, including other SPoRT collaborative partners.

In this particular case, it was operationally advantageous to see that the extent of the fog was not widespread and was just confined to some of the more fog-prone valley locations, especially the Paint Rock Valley, and may have only been highly localized to Ft. Payne, or even just the Ft Payne airport observation location.  Had the fog been observed through a larger area in Jackson and especially in DeKalb Counties, then a dense fog advisory might have been necessary.

 

About a week ago, southern Louisiana began to experience heavy rainfall from a storm system that remained relatively stationary over the Gulf Coast.  The SPoRT-LIS, a real-time, high-resolution implementation of the the NASA Land Information System, captured trends in soil moisture that provide some insight into the evolution of this flooding, including hints at precursor conditions that may have led to the extreme nature of this event.

The 0-200 cm integrated relative soil moisture (RSM) fields have been used in the past to identify flood precursor conditions.  These fields give an indication of the total amount of water in the soil moisture column and provide information about how much additional precipitation can be accepted by the soil before all becomes runoff into nearby streams and rivers.  About 2 weeks ago (August 3 00Z; Fig. 1), Southern Louisiana showed soil moisture values in the 50% range, which are higher than other parts of the country, but likely about normal given the swampy nature of that region.  However, following a couple of precipitation events in that area on August 3, 7, 9, and 10), these integrated RSM fields bump up the 60-65% range (Fig. 2), which has become somewhat of an unofficial threshold for antecedent saturated soils that could lead to areal flooding events.  Based on various reports, it appears that the official start of the flooding event began on August 11.

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Fig. 1: SPoRT-LIS valid at 00Z on 03 August 2016 showing 0-200 cm integrated relative soil moisture values around 50% over Southeastern Louisiana.

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Fig. 2: SPoRT-LIS 0-200 cm integrated relative soil moisture values valid at 00Z on 10 August 2016 showing impact of multiple precipitation events since the 03 August figure above. Soil moisture values are elevated in southeastern Louisiana to values around 60-65%.

 

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Fig. 3: SPoRT-LIS 0-200 cm integrated relative soil moisture values valid at 00Z on 14 August 2016 following the heaviest precipitation. Soil moisture values are above 90% in most areas, indicating major ongoing flooding across much of southern Louisiana.

Starting on 11 August, the 0-200cm integrated RSM begins to exhibit signs of flooding (starting to get into 70-80%; not shown).  By Aug. 12, most of SE LA is above 80% Integrated RSM with pockets above 90% (not shown).  By Aug. 14 (Fig. 3), nearly all of southern Louisiana is covered with soil moisture values above 85-90%, which indicates major ongoing flooding in this area.

These products are provided to select National Weather Service partner offices to aid in these flooding forecast challenges.  For more details on this product and to view additional days or hours, please visit the real-time SPoRT-LIS page.

If you are near the Gulf Coast, you’ve probably gotten a little drenched over the last few days. In fact, there have been reports of floods and flash floods as a result of the days of heavy rain developing off the coast and moving inland. This season, SPoRT is assessing a new suite of precipitation products derived from NASA’s GPM mission: GPM passive microwave swath rain rates and IMERG, a morphed rain rate product that is available every 30 minutes and also in accumulations. For those of you who aren’t readily familiar with passive microwave rain rate products, here is a quick key point. Passive microwave really shines where our WSR-88ds are totally in the dark, namely over the oceans. Here are some screen captures of the new precip products on AWIPS.

The accumulated IMERG products are helpful to determine how much rain has fallen in radar- and gauge-void regions. According the IMERG 24-hr accumulation estimates (lower right panel), greater than 4 inches of rain had fallen in the 24hr period ending in August 9 at 12Z just south of Tallahassee along the coast and another 3+ inches had fallen south of Melbourne. Just off the coast, there were pockets of 8 and even 12 inches of total rain fall in 24 hours, according to IMERG.

IMERGRR09Aug16_1200Z

For Aug. 9 at 12Z, IMERG instantaneous rain rates are shown in the upper left, IR in the upper right, IMERG 3-hr accumulation in the lower left, and IMERG 24-hr accumulation in the lower right.

The instantaneous rain rate product, shown in the upper left in the above image, can be compared to IR or other imagery or observations to help highlight areas with the heaviest rain fall. Passive microwave is especially sensitive to precipitation-sized ice, so it points out the locations of strong convective updrafts within the larger system, whereas IR is sensitive to the cloud tops and can miss some important components of storm development that lead to heavy rain. Note on the animation below that although the rain rates corresponde well the IR imagery, as it should, the locations of heaviest rain are not always the locations with the coldest cloud top temperatures.

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Aug. 9 at 14Z, IMERG rain rates are toggled over IR.  Note that the coldest cloud tops don’t always coincide with the heaviest rain rates estimated by IMERG.

 

 

 

So, recently I’ve had the opportunity to use and evaluate soundings from the NOAA Unique Combined Atmospheric Processing System (NUCAPS).  These soundings, produced by the ATMS and CrIS instruments onboard the Suomi NPP satellite, are available in AWIPS generally twice per day over any given location.

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Image 1.  NUCAPS Sounding data availability example, ~19 UTC 24 July 2016. Colors represent quality control flags — green are considered best available and most representative data.

A couple of advantages of the NUCAPS soundings is they’re available in relatively high spatial resolution (image 1) and also in between radiosonde launches.  So, a forecaster wanting to know more about tropospheric conditions during the midday or early afternoon (usually the most crucial period for severe weather analysis) can utilize NUCAPS sounding data, since radiosonde data won’t be available until later in the evening (unless ~18 UTC launches are being conducted at their location).  On a number of days in recent weeks, a lack of sufficient boundary layer moisture (probably partly due to an ongoing drought in the region) have dampened convective development.  A good understanding of the degree of convective inhibition (CIN) present on a given day can be difficult to obtain and model analyses and forecasts don’t always seem to have a good handle on this.  Even other robust analyses often struggle with a seemingly accurate depiction of CIN on many days.  However, knowledge of CIN, among other factors, can be important when forecasting probabilities for convective development on summer days.

Recently however, I’ve noticed that NUCAPS soundings did indicate the presence of CIN when convective development was perhaps less than expected or forecast.  July 20th was one of these days.  Take a look at the NAM Bufr Sounding for HSV, valid for 19 UTC on 20 July 2016 (image 2).

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Image 2.  NAM Bufr Sounding for KHSV, 19 UTC 20 July 2016

The NAM Bufr model sounding indicated robust CAPE values (generally >2500 J/Kg) and little to no CIN.  Now, let’s take a look at a couple of nearby representative NUCAPS soundings (unfortunately, they don’t include the associated data tables).  Image 3 shows the locations of the NUCAPS soundings with respect to the KHSV observation site and the location in the NAM forecast sounding above (image 2).

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Image 3.  NUCAPS Sounding locations for image 4…also, the KHSV location in northern Alabama

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Image 4.  NUCAPS Soundings at 19 UTC for location A (left, west of KHSV) and location B (right, southwest of KHSV), 20 July 2016

Even though data tables are not shown from the NUCAPS soundings, notice that they indicate much less instability and less steep lapse rates than the NAM Bufr sounding prognostications for the same time (19 UTC).   Also, notice that LCL levels are below the LFC, indicating some amount of CIN at both locations.  If memory serves correctly, NUCAPS soundings indicated CIN values around 25-50 J/Kg at this time.  So, for a forecaster struggling with the likelihood/coverage of convective development and the strength of convective updrafts, the NUCAPS data would have suggested lesser magnitude for both, over the NAM progs.  Image 5 shows the general dearth of convective activity in the area of northern Alabama near 19 UTC that day.  And indeed, convection was generally limited through the afternoon, with mostly isolated, small cells present.

CompRefl_NUCAPSLocations_20July2016_1856Z

Image 5. Composite reflectivity (dBZ) at 1830 UTC 20 July 2016

When viewing the NUCAPS soundings, I’ve generally been looking for CAPE/CIN values while in the convective season.  Of course, having to click on a number of soundings can be a bit laborious.  As part of a JPSS Proving-Ground/Risk Reduction multi-organization project, researchers at CIMSS, CIRA, GINA and NASA SPoRT have developed gridded NUCAPS data, which were utilized in the Hazardous Weather Testbed this past spring.  I’ll be working with members of the SPoRT team to ingest those data in AWIPS II here at the HUN office in the near future for my own testing, evaluation and feedback to the NUCAPS group within the JPSS Proving Ground.  I’m looking forward to the future use and evaluation of these potentially useful operational data sets.

Here at the Huntsville, AL Weather Forecast Office (WFO) we’ve pointed out total lightning data’s operational utility a number of times in this blog.  After all, the data have been a rather integral part of our severe weather operations for at least 13 years.  Anyway…I’m going to do it again.  I think it can be beneficial to reiterate the value of certain data sets from time to time, especially to reemphasize their operational utility to new members of the forecasting and research community and perhaps newcomers to the SPoRT blog.

This afternoon and evening was a somewhat typical summertime convective event for the Tennessee Valley.  Showers and thunderstorms developed in the early afternoon and gradually increased in coverage and intensity during the mid to late afternoon hours.  By the time I arrived on shift at about 3 pm CDT, a few thunderstorms were showing signs of intense updrafts (~50 dBZ at the -10C isotherm level), but were still not to the level of producing severe weather.  Nevertheless, multiple outflow boundaries interacting with the hot, humid and unstable airmass caused decent coverage of shower and thunderstorm activity, especially in northeastern portions of Alabama during the mid afternoon into the early evening.  A few thunderstorms contained strong updrafts, heavy rainfall, frequent lightning and wind gusts up to about 40 mph.  The first of these started showing signs of strengthening in eastern portions of DeKalb County, AL shortly after 3 pm CDT.  The first image below (image 1) shows a snapshot of total lightning data (flash extent density) from the North Alabama Lightning Mapping Array (NALMA) at 2014 UTC.  Values at this time in the developing storm were just around 10 flashes per 2-minutes.  By 2022 UTC however, flashes had increased to nearly 50 flashes per 2-minutes (Image 2).

Total Lightning (per North Alabama Lightning Mapping Array), 23 July 2016 2014 UTC

Image 1. Total Lightning (per North Alabama Lightning Mapping Array), 23 July 2016 2014 UTC

Image 2.

Image 2.  Total lightning (per NALMA), 23 July 2016 2022 UTC

Importantly, increases in total lightning activity are directly related to updraft strength within storm cells so it was no surprise that reflectivity values increased correspondingly.  The next two images show the increases in Multi-radar Multi-sensor (MRMS) isothermal reflectivity (dBZ) at the -20 C level during the same period (Images 3 and 4).

Image 3. Multi-radar Multi-sensor isothermal reflectivity (dBZ) 23 July 2016 2014 UTC

Image 3. Multi-radar Multi-sensor isothermal reflectivity (dBZ) at -20 C over portions of NW Alabama and NW Georgia, 23 July 2016 2014 UTC

 

Image 4.

Image 4.  Multi-radar Multi-sensor isothermal reflectivity (dBZ) at -20 C over portions of NE Alabama and NW Georgia, 23 July 2016 2022 UTC

Data such as the MRMS isothermal reflectivity when used in conjunction with other data such as total lightning (or flash extent density) allow for a good evaluation of updraft development within thunderstorms and their evolution through time.  Environmental parameters on this day suggested that severe weather was not likely.  Nevertheless, the strengthening updrafts were followed by wind gusts around 30 to 40 mph, which were recorded at a few of our surface observation sites.  Special Weather Statements were used to address this marginal thunderstorm threat during the afternoon and evening.  Interestingly, notice that the total lightning data at 2022 UTC (Image 2) indicated that the updraft in the northern cell in DeKalb County was perhaps the strongest at the time (due to higher values on flash extent density), while MRMS reflectivity values were higher at the same time in the southern cell (image 4).  Subsequently, the northern cell strengthened and became the dominant cell over the next 30 minutes.  On days such as this when there are often multiple thunderstorms ongoing at any one time, and this happens often here in the TN Valley in the summertime, total lightning data can be an effective situational awareness tool for evaluating storms that are undergoing strengthening and helping to provide proper focus for operational meteorologists.

NWS Huntsville is providing Impact-Based Decision Support Services (IDSS) to protect life and property at an outdoor sporting competition in the Decatur, Alabama area this week.  A decaying Mesoscale Convective System (MCS) moved across north Alabama this afternoon, forcing a delay in the competition for several hours.  While the North Alabama Lightning Mapping Array (NALMA) helped determine what to tell local emergency managers about the start of the lightning threat, the NALMA really shined in trying to figure out when the lightning threat would end.

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 1949 UTC 14 July 2016

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 1949 UTC 14 July 2016

The example images include NALMA Flash Extent Density data, which are represented by irregular pink and purple shapes displayed over the KGWX radar reflectivity.  Both the 1949 and 2007 UTC indicate scattered very low flash rates extending over a broad area–including the Decatur area–suggesting occasional in-cloud flashes within the trailing stratiform region of the MCS.  This is a known threat with MCSs, but it was not clear at the time how long the lightning threat would persist.  Use of total lightning information from NALMA enabled NWS Huntsville staff to determine that the lightning threat would not subside until rain subsided.

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 2007 UTC 14 July 2016

KGWX Radar Reflectivity and North Alabama Lightning Mapping Array, valid 2007 UTC 14 July 2016

With the launch of GOES-R and the Geostationary Lightning Mapper, these kinds of data will improve lightning-based IDSS across a much wider cross section of the CONUS.

On April 27, 2011, a severe weather outbreak occurred across the southeastern United States, resulting in 199 tornadoes across the region and over 300 fatalities (NWS 2011 Service Assessment).  Alabama was among the states hardest hit, with 68 tornadoes surveyed by the National Weather Service (NWS) Weather Forecast Offices (WFOs) in Huntsville, Birmingham, and Mobile, Alabama, and over 250 reported fatalities in the state. Huntsville, home to NASA’s Marshall Space Flight Center and the Short-term Prediction Research and Transition (SPoRT) Center, lost power along with most of Madison County after tornadoes severed major utility lines.  The power outage lasted well over a week in some areas. Once power was restored, SPoRT team members were able to provide satellite imagery to our partners in the National Weather Service to help clarify some of the high-intensity tornado damage tracks that occurred throughout the state. SPoRT provided pre- and post-event difference imagery at 250 m spatial resolution from the Moderate Resolution Imaging Spectroradiometer (MODIS) and 15 m false color composites from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). These surveys helped our NWS partners confirm their ground surveys, but also helped to correct the characteristics of several tracks (Molthan et al. 2011). Many of these products remain available through the SPoRT web page (link) and also through the USGS Earth Explorer portal (link).

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The MODIS Band 1 difference image above shows some of the scars left behind by the April 27, 2011 tornado outbreak. Radar snapshots were taken from various times to identify the supercell thunderstorms associated with each track.  Reproduced from Molthan et al. 2011.

Follow-on studies examined the capability of various NASA sensors for detecting and measuring the length and width of scars visible when using the Normalized Difference Vegetation Index, or NDVI, a measurement of vegetation greenness and health commonly derived from multiple satellite imaging platforms.  SPoRT examined NDVI products from MODIS (250 m), Landsat-7 Enhanced Thematic Mapper Plus (ETM+, 30m) and ASTER (15 m) collected in May and June 2011. Possible tornado tracks were identified, mapped, and were then measured to compare against the official NWS damage surveys.  In general, many of the major tornadoes (defined here with maximum intensity EF-3 and greater) were at least partially visible at resolutions of 15-250 m, though weaker tornadoes or those that occurred in complex terrain were more difficult to detect using NDVI and a single snapshot in time. As tornadoes initiated and increased in intensity, or dissipated and decreased in intensity, some of their characteristics became more difficult to detect.  However, some weaker tornadoes were also apparent in Landsat-7 imagery (30 m) in well-vegetated areas.  A summary of the study is available as a publication in the National Weather Association’s Journal of Operational Meteorology. In 2013, SPoRT received support from NASA’s Applied Sciences: Disasters program to partner with the NWS and facilitate the delivery of satellite imagery to their Damage Assessment Toolkit (DAT).  The DAT is used by the NWS to obtain storm survey information while in the field. Satellite imagery from NASA, NOAA, and commercial sensors (acquired in collaboration with USGS and the Hazards Data Distribution System) helps to supplement the survey process by providing an additional perspective of suspected damage areas.

Many of the damage scars apparent from the April 27, 2011 outbreak exhibited signs of recovery and change in the years following the outbreak.  Other tornado events also brought additional vegetation damage and scarring to the region. With five years passing since the 27 April 2011 tornado outbreak, annual views of cloud-free imagery have been obtained from the Landsat missions, operated and managed as a collaboration between the USGS and NASA.  In the viewer linked below, SPoRT has collaborated with the USGS Earth Resources Observation Systems (EROS) Data Center to acquire 30 m true color and vegetation index information from Landsat 5, Landsat 7, and Landsat 8 during the late spring and summer months when local vegetation is at its greenest, allowing the greatest contrast between damaged and undamaged areas. Users can take a look at these images in a web viewer that allows toggling between different products and years, view some of the tornado tracks surveyed by the NWS following the April 27, 2011 event, and zoom into areas of interest to examine how some of the affected areas have evolved over time:

Tuscaloosa, AL

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The above animation shows the year before and years after the EF-4 tornado impacted the Tuscaloosa area. The tornado track has seen a significant recovery, but a scar still remains in 2015. In addition to seeing how the landscape as recovered from tornado, development in and around Tuscaloosa is also apparent.  Missing pixels in 2012 are due to an issue with the Landsat-7 imager.

Hackleburg-Phil Campbell

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Similar to the Tuscaloosa animation, this animation shows the recovery of the EF-5 tornado that moved through Hackleburg and Phil Campbell, before tracking northeast across the Tennessee River.  Missing pixels in 2012 are due to an issue with the Landsat-7 imager.

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