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A quick-moving upper-level trough and associated cold front moved across the TN and lower OH valleys this morning, producing snow showers around the region.  The Nighttime Microphysics RGB image below from the VIIRS instrument (Image 1), from around 0805 UTC, shows low/mid clouds associated with the trough. Notice most of the clouds appear light green/yellow and or green/red, indicating predominantly low/mid cloud types.  A synthesis of radar and sounding data indicates these clouds were dominated by snow/ice crystals and perhaps some super-cooled liquid droplets.  Reports of only light snow have been received at surface stations in the region this morning.

Suomi NPP VIIRS Nighttime Microphysics RGB ~0805 UTC 18 Feb 2015

Image 1.  Suomi NPP VIIRS Nighttime Microphysics RGB ~0805 UTC 18 Feb 2015

Notice the narrow swath of darker green colors stretching from NE Mississippi northeastward into northern middle Tennessee.  Although it may not be apparent, the green color contribution (green represents the 10.8-3.9 µm channel difference in the RGB recipe) in this swath was actually lower than in adjacent clouds. In addition to lower contributions of green, red and blue color contributions were also lower in this narrow swath.  The resulting interpretation is that this area was composed of lower, warmer clouds.  Due to the variations in green color contribution across the cloud deck, it was immediately unclear whether there was a mix of super-cooled liquid water and ice/snow crystals.  Radar imagery from the Nashville, TN and Columbus, MS radars from about the same time indicate mostly uniformity in falling hydrometeors.  The image below (Image 2) shows Correlation Coefficient values from the KOHX and KGWX radars at ~0806 UTC.

Image 2.  VIIRS Nighttime Microphysics RGB overlaid with Correlation Coefficient (CC) values from KOHX and KGWX radars

Image 2. VIIRS Nighttime Microphysics RGB overlaid with Correlation Coefficient (CC) values from KOHX and KGWX radars

A small area of slightly lower CC values can be seen to the northwest of Nashville and an inspection of ZDR values (not shown) indicated slight/moderate wet snowflakes.  Although, standard reflectivity imagery from the same time shows little in the way of precipitation in that area (Image 3).  It should be noted that precipitation echoes were somewhat absent from the darker green swath.  However, since these clouds and any resulting precipitation (if present) was relatively low, echoes were below the lowest scans of the regional radars.

Image 3.  VIIRS Nighttime Microphysics RGB overlaid with 0.5 Reflectivity from KOHX and KGWX radars

Image 3. VIIRS Nighttime Microphysics RGB overlaid with 0.5 Reflectivity from KOHX and KGWX radars

Incidentally, the KHTX radar was down for a needed repair and thus not available during this time.  One advantage of this type of satellite imagery is that it is safer to make inferences about the presence of precipitation, and in some cases, perhaps even precipitation intensity and type, given similar RGB cloud characteristics.  During an event such as this where standard radar data may not be available at a given location, the value of the imagery becomes even more apparent.

The prospect for additional snow and mixed precipitation events over the upcoming week or so will offer more interesting observations of the Nighttime Microphysics RGB.  More posts to follow soon!

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It is the time of the year when deep plumes of tropical moisture known as atmospheric rivers tend to bring heavy precipitation to the west coast.  A particularly strong atmospheric river impacted the west coast this weekend (6-8 February) bringing over 10 inches of rainfall to parts of northern California and nearly 20 inches of snowfall across portions of the Sierra Nevada.  The CIRA total layered precipitable water product clearly shows the large amount of moisture streaming into California from the tropics.

Image 1.  SPoRT-CIRA total layered precipitable water valid on 7 February 2015 at 12 UTC.

Image 1. CIRA total layered precipitable water valid on 7 February 2015 at 12 UTC.

However, there is another component to this atmospheric river event that does not get much attention but they can significantly impact precipitation from these storms.  They are dust aerosols originating from the deserts in Asia, the Middle East, and Africa, and pollution aerosols from the megacities of eastern Asia.  These aerosols are transported across the Pacific most frequently during the late winter and early spring when the wind pattern is ideal.  In fact, a currently ongoing NOAA-led field investigation (i.e. CalWater 2) is focused on investigating the interaction between aerosols and atmospheric rivers to better understand how they modify precipitation.  SPoRT is supporting this effort by disseminating a near-real time product that combines aerosol optical depth (AOD) retrievals from geostationary and polar-orbiting satellites to monitor and track the long-range transport of aerosols.  Extensive cloud cover over the Pacific can often make it difficult to track the aerosols via satellites, therefore, the SPoRT product takes advantage of MODIS, VIIRS, MTSAT, and GOES AOD retrievals in order to provide a more comprehensive look at aerosol activity across the Pacific.  SPoRT is disseminating 6-hourly and daily AOD composites throughout the extent of CalWater 2 field campaign set to end mid-March with the overall goal of supporting their aerosol forecasting and flight planning activities.  Shortly before the atmospheric river made landfall on 7 February, the SPoRT daily AOD composite shows unusually high AOD of 0.3 to 0.5 (Image 2) in the vicinity of the atmospheric river in Image 1.  Higher values of AOD indicate an increasing amount or loading of aerosols in the atmosphere.  AOD is typically minimal (< 0.2) over the eastern Pacific when long-range transported aerosols are not present.

Image 1. NASA SPoRT daily AOD composite valid on 7 February 2015 at 00 UTC.

Image 2. NASA SPoRT daily AOD composite valid on 7 February 2015 at 00 UTC.

The CalWater 2 field investigators flew an aircraft equipped with advanced instruments directly through this atmospheric river on 7 February, which sampled an abundance of long-range transported dust according to CalWater investigator Dr. Jessie Creamean.  Further investigation is warranted to determine the source region of the dust.  With weeks to go still in the CalWater 2 campaign, field investigators are hoping for more opportunities to fly through aerosol laden atmospheric rivers.  If the trend from the past week continues, the CalWater 2 team should be able to gather a wealth of unique measurements that will ultimately lead to improved forecasting of these atmospheric river events.

Aerosol activity over the Pacific was relatively calm during January, but February kicked off with a bang.  The SPoRT daily AOD composite on 3 February shows a very thick, extensive aerosol plume propagating from eastern Asia to the western Pacific (Image 3).  Closer analysis suggested this plume was a mixture of dust and pollution aerosols.

Image 3.  NASA SPoRT daily AOD composite valid on 3 February 2015 at 00 UTC.

Image 3. NASA SPoRT daily AOD composite valid on 3 February 2015 at 00 UTC.

SPoRT AOD composites can be found at http://weather.msfc.nasa.gov/sport/aod/aodCalendarView.html

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We’re near full-moon phase now so I thought I’d take a moment to show some recent VIIRS Day-Night Band (DNB) observations from the Suomi-NPP satellite. This first DNB image from the early morning of Feb 2nd, shows a broad swath of snow on the ground across portions of the Midwest, in addition to a variety of clouds across the Tennessee and Ohio Valleys and further east.  The snow field in the DNB image (Image 1) is fairly easily distinguishable from the clouds due to presence of the river valleys cutting across the snow field in the image.  Notice the edge of the snowpack extends about as far south as Kansas City, but is mainly on the northern half of the metro area.  In this case, having the city lights as a reference can be operationally beneficial…for help in determining surface snow impacts.

VIIRS Day-Night Band Radiance RGB

Image 1.  VIIRS Day-Night Band Radiance RGB ~0806 UTC 2 Feb 2015.  The

This VIIRS Nighttime Microphysics RGB can further help to distinguish snow from clouds (Image 2).  Notice that the snow doesn’t really show up well in this RGB (although it encompasses the slightly more orange hues against the surface pink colors).  Toggling these two images in AWIPS II would allow a forecast to more readily distinguish snow from clouds .

Image 2.  Suomi-NPP VIIRS Nighttime Microphysics RGB 0806 UTC 2 Feb 2015

Image 2. Suomi-NPP VIIRS Nighttime Microphysics RGB ~0806 UTC 2 Feb 2015

Following are a couple of DNB images from the past couple of mornings.  Notice that the snowpack remains but has been shrinking slightly at its edges over the past couple of days.

Image 3.  Suomi-NPP VIIRS DNB Radiance RGB 0728 UTC 4 Feb 2015

Image 3. Suomi-NPP VIIRS DNB Radiance RGB ~0747 UTC 3 Feb 2015

Image 4.  Suomi-NPP VIIRS DNB Radiance RGB ~0728 UTC 4 Feb 2015

Image 4. Suomi-NPP VIIRS DNB Radiance RGB ~0728 UTC 4 Feb 2015

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SPoRT and NESDIS are currently collaborating on an assessment of a snowfall rate (SFR) product that includes data from the Suomi-NPP Advanced Technology Microwave Sounder (ATMS) instrument.  ATMS provides more channels, better resolution, and a wider swath than previous operational microwave sounders, like the Advanced Microwave Sounding Unit (AMSU) and Microwave Humidity Sounder (MHS).  The SFR product uses information in microwave channels to estimate liquid-equivalent snowfall rates that forecasters can use for pinpointing the locations of the heaviest snowfall during winter weather events.  These observations are being provided in near-real-time (less than 30 minutes latency) through access to data from direct broadcast provided by the University of Wisconsin/CIMSS.

The northeast is currently experiencing a historic blizzard with areas of New England recording more than a foot of snow with more snow to come later today.  Below is an example of the output from the ATMS SFR product depicting heavy snow over most of New England.  This image indicates that the heaviest snowfall at this time was centered over southeastern Connecticut with rates anywhere from 1-1.5 inches of solid snow per hour.

ATMS SFR depicting the 2015 Blizzard at 0650 UTC (around 2:00 A.M. local time) on 27 January 2015.

ATMS SFR depicting the 2015 Blizzard at 0650 UTC (around 2:00 A.M. local time) on 27 January 2015.

Coupled with other microwave sensors on board other NOAA and European satellites, up to 10 swaths of observations are available to provide observations of where the heaviest snowfall is falling and allows forecasters to track these features when used in conjunction with GOES imagery and radar.

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A strong cold front is ushering in markedly colder air for much of the central and eastern U.S. over the next several days.  The cold front today is highlighted by extreme temperature contrasts over the Southern Plains, with high winds and blowing dust along and behind the front as it surges southward through Colorado and Kansas.  Figures 1 and 2 show the VIIRS dust RGB images over the Plains at 1906 to 2049 UTC, respectively.  One can easily identify the increase in dust coverage (given by the darker pink colors) by 2049 UTC over southeastern Colorado as the front propagates southward.  A corroborating surface analysis valid at 2043 UTC in Figure 3 depicts visibility reductions at Lamar, CO (LAA; 2 miles), La Junta, CO (LHX; 1 mile), and Pueblo, CO (PUB; 3 miles) in southeastern Colorado.  Notice temperatures in the 80s across the Oklahoma and Texas Panhandles, while temperatures are in the 20s and 30s across northeastern Colorado and northwestern Kansas.  Quite the contrast!

Figure 1.  VIIRS dust RGB image valid at 1906 UTC 10 November 2014.

Figure 1. VIIRS dust RGB image valid at 1906 UTC 10 November 2014.

Figure 2.  Same as Figure 1, except valid at 2109 UTC 10 November 2014.

Figure 2. Same as Figure 1, except valid at 2049 UTC 10 November 2014.

Figure 3.  Surface analysis valid 2043 UTC 10 November 2014.

Figure 3. Surface analysis valid 2043 UTC 10 November 2014.

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SPoRT has been investigating options to obtain near-real time NUCAPS (NOAA Unique CrIS and ATMS Processing System) data to expand the ozone products to Suomi NPP retrievals.  The AIRS ozone products cover a Northwestern Hemisphere domain (Link to SPoRT AIRS products) and were specifically created for the National Centers (WPC and OPC) to aid interpretation of the Air Mass RGB for identifying and forecasting stratospheric intrusions that can lead to rapid cyclogenesis and hurricane-force wind events in the North Atlantic and North Pacific Oceans. The AIRS data are obtained from NASA Land Atmosphere Near-Real Time Capability for EOS (LANCE), rather than Direct Broadcast, so that the products can be created in hourly swaths that cover the OPC domain. Since the ozone products are created from polar-orbiting retrievals, forecasters are eager for better temporal and spatial resolution.  Use of retrievals from newer instruments such as Suomi-NPP CrIS/ATMS can provide additional overpasses to improve spatial and temporal resolution when paired with AIRS.

Suomi NPP data are available on the NOAA Comprehensive Large Array-Data Stewardship System (CLASS).  Typically data are obtained from CLASS by choosing options such as data type, domain, and time on the website and placing an order. Depending on the size of the order, it can take about an hour to 24 hours for your request to be processed and ready for download via ftp.  Manually placing an order is not an optimal approach for near-real time data processing and product development.

Recently SPoRT investigated the CLASS subscription service and has had success in obtaining NUCAPS data with a 2-3 hour latency. The CLASS subscription service is a valuable tool, comparable to NASA LANCE, for obtaining near-real time NUCAPS data. Others in the community who are interested in obtaining NUCAPS data with reduced latency and need a larger domain than what is available from Direct Broadcast should investigate the CLASS subscription service. Below is a outline of steps to set up a CLASS subscription for NUCAPS data.

First go to CLASS, create a user account and sign in. Click on “Subscriptions” in the left side menu. Choose your data product from the dropdown menu and click “Add New” to begin setting up the subscription details.  For NUCAPS choose S-NPP Data Exploitation Granule Data (NDE_L2)

Step1

Next, set up the search criteria for your subscription by choosing the domain either by making a box on the map or entering latitude and longitude values beside the map.  Click on the box next to “NUCAPS Environmental Data Records” and click on  “S-NPP”.  Click on “Delivery Options” to continue.

Step2

Last set up the delivery options.  Choose “yes” for a recurring schedule and set the start and end dates.  The start and end dates do not include the year, therefore you’ll need to modify the start and end date as the end of the year approaches.  Choose whether or not you want email notifications. I would initially choose “yes” so you can start to gauge how quickly your subscription is being processed from the time your data arrives in CLASS.  Note that you will get an email for every granule and sometimes the email notifications are delayed quite a bit after your data is ready.  The notifications are initially helpful as you first set-up your subscription. As a side note I did enjoy spamming myself with approximately 20-30 CLASS email notifications per hour when I first set up my subscription so I could see how it was working and could gauge the data latency.  Most important, choose how often you want to receive data in the dropdown list beside “Include delivery manifest”. I’ve chosen “Every 1 hour”, but depending on the product and your needs, you can choose any interval from 1-24 hours. Features such as the digital signature and checksum aren’t always necessary but you can decide if you need them by reading about them on the class help pages.  Now click “Save” to finish.

Step3

Once your subscription is set up, you can log in at any time to view, modify, or disable your subscription.  Just click on “Subscriptions” on the left side menu after you have logged in.

Once your data arrives in CLASS your order will be processed. Therefore the subscription service can provide automatic distribution of near-real time products as long as the data is arriving in CLASS near-real time. If the data is not pushed to CLASS near-real time by the product developer or NDE than the subscription service can’t be used for near-real time purposes (unless you don’t mind a 6-24 hour or longer latency).  Not all Suomi NPP products are pushed to CLASS in a real-real time capability. Thankfully NUCAPS is pushed to CLASS relatively quickly after it is processed and can be obtained via CLASS near-real time.  Your subscription will have a unique ID and your order will be available on the ftp site in a directory named with your username and subscription ID.  The data will also be available via a unique http site named with your username and subscription ID. Now your data is in one place and can be accessed via scripting and ftp without manually submitting an order on CLASS.

Latency of products getting to CLASS and figuring out how to order data without manually submitting an order on the website have been the largest deterrents for SPoRT using CLASS data for real-time product development.  Not all Suomi NPP data is immediately pushed to CLASS near-real time, however contacts at NESDIS have indicated that in the next 6-months or so, more Suomi NPP data will be pushed to CLASS in near-real time mode. Utilizing the CLASS subscription service opens up a new opportunity for SPoRT and the community to use NUCAPS data (and in the near future, other Suomi NPP data sets) from CLASS for product development.

More information on CLASS subscriptions can be found within the CLASS help pages.

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One night after a widespread dense fog event, we have been monitoring more fog formation very closely.  Unlike the previous night, the visibility has not fallen quite so far, so fast at most of the airports across the Tennessee Valley; just a few sites in typically fog-prone valleys are reporting visibility of less than 1 mile.  However, coverage is the question, and the default 11-3.9 micron satellite imagery was not particularly helpful in diagnosing that.  There are hints of fog in the valleys of northeastern Alabama, but it’s tough to be sure how widespread the fog might be.

11-3.9 Micron GOES Imagery - 0800 UTC 27 October 2014

11-3.9 Micron GOES Imagery – 0800 UTC 27 October 2014

The Nighttime Microphysics RGB imagery was much, much more useful–and confirmed what the surface observations were telling us.  The 0802 UTC pass indicated that much of the fog is confined to the river valleys in and around the Huntsville CWFA, especially in the northeast Alabama valleys and the Elk River around the Tennessee-Alabama border (near where the mouse pointer is located).  Furthermore, the fainter gray-cyan colors surrounding the Tennessee River (bisecting the CWA) supported some of the less-dense fog reports coming from airports such as Muscle Shoals (KMSL) and Huntsville (KHSV).

Nighttime Microphysics RGB - 0802 UTC 27 October 2014

Nighttime Microphysics RGB – 0802 UTC 27 October 2014

This imagery helped confirm the surface observations, and helped with the decision to avoid a widespread dense fog advisory–at least temporarily.

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