A ridge of high pressure moved into the desert southwest in the wake of a strong winter storm system that impacted the region last weekend. Strong low level inversions beneath the ridge and melting snow cover increased the potential for an extended period of low clouds and freezing fog. The MODIS Nighttime Micropyhsics product valid at 0501 UTC November 29, 2013 showed low clouds and possible areas of freezing fog along the I-70 corridor over and west of Grand Junction. Observations at Grand Junction verified IFR low clouds at 900′ with visibilities above 6 miles. The following VIIRS Nighttime Microphysics product at 0904 UTC November 29, 2013 showed low clouds and freezing fog expanding eastward into the Colorado, Gunnison, and Uncompahgre River Basins and the Grande Valley south of Grand Junction. Visibilities have been significantly reduced to 1/4 mile at Montrose and farther south at Cortez. The ceiling at Montrose is 200′ with visibility at 3/4 mile. The nighttime microphysics product shows exceptional detail within the narrow valleys along Roan Creek to the northeast of Grand Junction. Notice the fog and low cloud deck is very close to Rifle at 0904 UTC but the observation still suggests clear skies. 31 minutes later at 0935 UTC the observation at Rifle dropped to LIFR at 400′ however visibilities remained at or above 6 miles.
Archive for the ‘GOES-R Proving Ground’ Category
The event in this blog post was provided by Amanda Terborg, satellite champion at the Aviation Weather Center.
SPoRT has been coordinating with the Aviation Weather Center (AWC) for a little over a year to incorporate the pseudo-geostationary lightning mapper (PGLM) mosaic demonstration product in operations, derived from ground-based lightning mapping arrays and part of the GOES-R Proving Ground. This work culminated with the transition from demonstration mode to the AWC’s operations floor in September, thanks to Amanda’s coordination. Shortly thereafter we received this particular event from October 7th.
On this day, one of the major items of interest was a line of storms moving through Washington D.C. and northern/western Virginia (Fig. 1). The storms were not creating major disruptions as flights were able to remain ahead of the line or work their way behind the line of storms. Figure 2 shows the aircraft tracks from 1402 UTC, which corresponds to the radar image in Fig. 1. Due to the different projection types in N-AWIPs, the primary point of interest is circled in each image. The major item of note is that there are no National Lightning Detection Network (NLDN) cloud-to-ground strike observations in the entire image. However, the circled region shows a cluster of 3-4 flashes observed by the PGLM product. As there are no corresponding NLDN strikes, these are solely intra-cloud flashes. By observing the flight tracks, the aircraft were flying behind the main line of highest reflectivities. Although the aircraft were behind the main line, Fig. 2 shows that approximately five aircraft flew into the region where the PGLM flashes were observed. At around 1400 UTC one of those flights was struck by lightning. The best news was that, while struck, the aircraft suffered no damage and continued safely on to its destination.
This example shows one of the major benefits of the future GOES-R Geostationary Lightning Mapper (GLM), as a space-borne instrument capable of observing total lightning (both intra-cloud and cloud-to-ground). Radar is an excellent tool for helping develop safe flight tracks. The ability of total lightning to observe intra-cloud flashes, as well as the spatial extent of these flashes, gives aviation planners additional information as to how to route aircraft, particularly in storms that have no cloud-to-ground observations. This will be very important in data sparse regions were radar and total lightning are currently not available.
As the Satellite Proving Ground for Marine, Precipitation, and Hazardous Weather Applications at the NOAA Center for Weather and Climate Prediction (NCWCP) prepares for the winter 2013-2014 demonstrations, it’s always nice when Mother Nature provides some examples, albeit we prefer non-life threatening. The Ocean Prediction Center (OPC), Weather Prediction Center (WPC), NESDIS Satellite Analysis Branch (SAB), and the NHC Tropical Analysis and Forecast Branch (TAFB) will be evaluating the RGB Air Mass product once again and the storm that affected northern Europe this morning is a great case of product utility!
The animation above shows the evolution of a Shapiro-Keyser (1990) type storm that affected the UK, France, Belgium, the Netherlands, Germany, and Denmark with strong winds early this morning. The highest observed wind gust was 99 mph on the Isle of Wight in the English Channel. Wind gusts ranged from 50-90 mph on average with multiple trees down. some structural damage, and at least 3 deaths. So, what in this storm caused the strong winds? The Air Mass product may have a clue.
At this first time step (0700 UTC on 10/28/13), the white circle on the Air Mass product (first image) shows an intruding area of reddish/pink coloring mixing into the blues and greens to the east. The reddish/pink coloring indicates dry, stratospheric air intruding into the deepening cyclone’s core. The water vapor image (2nd image) shows the drying (blue) and along with the Air Mass product, suggests a strong stratospheric intrusion that would help to transport high moment air (winds aloft) to the surface with deep mixing. This is the approximate time that high wind gusts were affecting southern England and northern France. It is tough to gauge the depth of the stratospheric intrusion in these images.
Five hours later, the intrusion appears to intensify (based on imagery) with a stronger/deeper reddish/pink coloring developing near and over Denmark on the Air Mass product, while the water vapor image really accents the drying with deep blues and even a bit of brown coloring along the western Denmark coastline. Now, this suggests that the stratospheric drying increased over this time, possibly helping to further mix down high moment air from the mid-troposphere, especially where there is clearing allowing the sun’s heat to aid in deep mixing of the atmosphere.
I’m sure this is not going to be the last example as we are just starting our winter storm season. I will be sure to include more updates in the next few months.
I leave you with this great photo of waves crashing around a lighthouse in South Wales. Thanks for reading!
The nighttime microphysics (NTmicro) RGB comparison below provides some insight into the traditionally difficult challenge of differentiating low clouds from fog. The RGB product enhances the regularly employed 10.8-3.9 channel difference (Green) to include an additional 12.0-10.8 channel difference (Red) and repeat use of the 10.8 thermal channel (Blue). The NTmicro RGB valid at 311am MDT on October 17, 2013 showed an area of cloud cover developing in the Pecos River Valley from Carlsbad north to Artesia and just east of Roswell (aqua shades). Observations within this cloud cover indicated a low cloud deck developing toward the north with ceilings in the 1,500-2,000′ level. The hybrid 11-3.9 imagery indicated the low clouds continuing to expand north toward Roswell through 11Z (yellow areas). The aviation forecaster anticipated that low clouds would move into Roswell and thus amended the TAF to include IFR ceilings for several hours. Fog was not added to the TAF however a brief period was observed. The NTmicro RGB valid the following day at 251am MDT on October 18, 2013 showed a significantly more widespread area of cloud cover impacting much of southeast NM and the Permian Basin of west TX (purple shades). Observations within this cloud cover indicated a very low cloud deck of 100-200′ and numerous reports of fog. The hybrid 11-3.9 imagery indicated the low clouds were expanding north toward Roswell however remaining to the east of the site through 12Z (yellow areas). The aviation forecaster did not expect fog and/or low clouds to impact Roswell based on this imagery and the clear sky forecast was maintained. Without the support of observations across the region on the 18th the forecaster may have been able to distinguish shallow/thin fog from the low clouds on the 17th. The green contribution has been reduced because the 3.9micron channel is seeing some emission from not only the shallow/thin fog but the surface as well. The 3.9 channel is thus warmer and the difference from the 10.8 channel is less, resulting in less green color. Greater amounts of red and blue lead to the strong purple shades.
The VIIRS Night-time Microphysics RGB shows the early season snow storm over the northern Front Range and the variety of clouds with the system. Low clouds in aqua to the east, and mid-level clouds to the west are differentiated by less blue coloring (i.e. colder) in the mid-level clouds while still retaining green coloring indicating water-based particles making up the clouds. Other microphysical information is also seen as the inflow of moisture to the storm system changes from yellows to oranges over southwestern CO as the cloud particles change from water to ice phase. Then, vast areas of oranges and reds characterize the main storm clouds indicating thick, ice clouds, and in some cases a speckled appearance. The speckling results when very cold clouds cause the 3.9um channel to rapidly decrease in brightness temperature, therefore contributing maximum green to the pixel. This combined with a maximum red (thickness) results in bright orange. Darker reds are seen to the east representing thin, high cirrus clouds associated with the jet streak in the area rapidly spreading the ice particles in this area. The evolving changes in cloud temperature, thickness, and particle phase will be depicted rapidly with this type of product in the GOES-R era. For now, several passes of MODIS and VIIRS instruments per night provide users a learning opportunity.
The Nighttime Microphysics RGB helped again to delineate small areas of locally dense fog on the late evening of the 21st and the early morning hours of the 22nd. The Terra MODIS image below (image 1) valid at 0347 UTC shows fog (white-aqua colors) already beginning to develop in the narrow valleys cutting through the far southern end of the Cumberland Plateau in northeastern Alabama, as high clouds in association with a front boundary cleared the region (red-colored clouds). Fog shows up especially well in the Paint Rock River Valley in NE Alabama…a valley which is prone to fog formation during about any month of the year, particularly following rain events. Notice the extent of the fog though in the valleys of eastern Kentucky, which is much larger in extent. This first image was disseminated to collaborative offices before midnight local time, and would have been available for midnight shift forecasters, allowing them to easily see locations of developing fog. Due to the resolution of the imagery and the effiiciency it provides for fog detection, it could be helpful for limiting the extent of areas under advisory, and allowing for more descriptive impacts in advisory products (i.e., fog mainly in valley locations, fog across portions of Hwy 72 north of Scottsboro, etc).
The fog became locally dense in some, if not most, of these locations. Observations from Fort Payne during the morning indicated visibility at or below 1/4 statue miles from 0500 UTC through 1300 UTC. Interestingly, as the loop of available VIIRS and MODIS images shows that morning (image 2), the fog did not become widespread, but was confined mainly to the narrow river valleys of the region. Also, the subdued nature of the colors in the DeKalb Valley (Ft Payne) suggests the fog was probably quite shallow.
Notice the the fog could also be observed in the VIIRS Day/Night Band imagery valid at 0658 UTC in most of the valley locations, but becomes difficult to discern in the DeKalb Valley near Ft. Payne due to the presence of the city lights.
With the RGB Imagery for Aviation and Cloudy Analysis evaluation underway, we’re already getting some good feedback from our end-users. From WFO Morristown – “I looked at the Nighttime Microphysics product in hindsight to see how fog around TRI was depicted this morning. The (RGB) product did an outstanding job of clearly showing areas of fog vs. clouds, even though there were some thin midlevel clouds over the fog areas.” Below is a loop of the available MODIS (Aqua and Terra) and Suomi NPP VIIRS images from the southern Appalachain region early from late last evening through early this morning (click the image to see the loop).
The image shows the early production of fog (ligher, aqua colors) in the Cumberland and Allegheny Plateau region of eastern Kentucky and SW Virginia by the time of the first MODIS pass at 0359 UTC. Notice how the fog spreads to include other valley locations in East Tennessee by the time of the last images at 0736 UTC and 0810 UTC.
Meanwhile, the fog is clearly not as apparent using the standard 11-3.9 µm imagery (and standard color curve) even with the 1km Aqua MODIS image inserted (image 2, ~0810 – 0815 UTC).
…and is even less noticable in the 4km GOES-East image alone a little later at 0832 UTC (image 3).
Fog in the narrow valleys in the region shows up quite well in the VIIRS Day/Night Band Radiance RGB, developed by SPoRT (image 4). The forecaster noted that, “the DNB Radiance RGB showed fog clearly as well, but maybe not quite as well as the Nighttime Microphysics product.” I would agree, however I was encouraged by the detail and the relative ease with which fog was discernible in the image.
The typical issues with the timeliness of the polar-orbiting imagery, for opertional considerations, appears to be the largest concern for forecasters at this point in the survey process. Of course, this won’t be an issue in the GOES-R era, and acquanting forecaters with these types of imagery before the next generation of GOES satellites is launched is an important step in the learning process.
As a part of ongoing GOES-R and JPSS Proving Ground activities, NASA SPoRT is conducting an evaluation of various RGB imagery with some of our collaborative NWS offices. Day/Night Band RGBs, produced by SPoRT and available from the VIIRS instrument onboard Suomi NPP, include both the Radiance RGB and Reflectance RGB products. Nighttime Microphysics RGBs from the VIIRS and MODIS (Aqua and Terra satellites) instruments will also be evaluated. The offices participating in the evaluation span a broad area, from Huntsville, Morristown, Nashville and Raleigh in the Southeast, to Albuquerque in the Southwest, and Great Falls at the Front Range of the Northern Rockies. Through late September and into October, forecasters will be evaluating the utility of these types of imagery from an operational perspective. The imagery have been made available to WFOs for viewing within their AWIPS I systems, so that they may overlay with other data and/or imagery. However, imagery are also available online or through ftp download (kmz format). A plug-in is still required for viewing in AWIPS II, so WFO Huntsville will be utilizing the online option for now.
A forecaster at WFO Huntsville remarked that “the Nighttime Microphysics imagery…did show the low clouds really well (bright aqua) over north GA this morning and confirmed in greater detail what we were seeing with the 11-3.9 um channel GOES output.” Other surveys have already been received by staff at the Albuquerque and Raleigh WFOs, so the evaluation is well underway!
Showers and thunderstorms developed over the northern half of PR Sat Sep 14 and produced localized areas of 2 to 4 inches of rain that resulted in urban flooding and a new daily rainfall record at the San Juan (SJU) LMM Int’l Airport. A total of 2.88 inches fell at the SJU airport on Sat Sep 14 with 2.52 inches falling in less than 2 hours between 1145 AM and 130 PM. These showers and thunderstorms developed as a result of upper level diffluence ahead of an upper level low over the central Caribbean Sea aided by surface convergence due to sea breeze interaction and abundant moisture. Figure 1 below shows a four panel display of various water vapor channels from the GOES-Sounder and GOES imager overlaid with ECMWF model height fields and 15/00Z RAOB data. Figure 2 below shows the 12Z Sat Sep 14 Skew-T for SJU. Note the 20-35-kt south southwest flow at 300 and 200 mb on both the four panel display and the 12Z Skew-T respectively.
Animation of GOES-IR imagery (Fig. 3 below) with increased temporal resolution due to Rapid Scan Operations (RSO) in effect shows the development of showers and thunderstorms first over the San Juan area around 1445 UTC and then over north central and northwest PR through 2015 UTC. The imagery shows cold cloud tops ranging from -50C to -70C that were displaced to the north due to 20-35 kt south southwest flow aloft seen on the 12Z SJU RAOB data.
As part of GOES-R Proving Ground activities, WFO SJU continues to evaluate the NESDIS QPE product which uses mainly GOES-IR channel to estimate rainfall rates. Satellite based rainfall estimates for the 24-hr period ending 12 UTC Sun Sep 15 (Fig 4 below) showed up to an inch of rain fell just offshore of San Juan due to the coldest cloud tops being displaced to the north due to 20-35 kt south southwest flow seen on the 12Z upper air data.
Gauge data (Fig. 5 below) and Dual-Pol radar estimates (Fig. 6 below) indicate that in general between 1 to a little over 3 inches fell over parts of northern PR. This clearly indicates the need to continue to improve the GOES-R QPE algorithm to estimate rainfall and also to account for shear and cloud storm motions.
A wide VIIRS swath covering parts of the Southeast U.S. provides a Night-time Microphysics RGB image showing wide fog in the valleys of Tennessee, Georgia, and North Carolina (see yellow outline in upper center of image). Also of note is the difference in coloring between the areas above and below the white line stretching east-west from Mississippi to South Carolina. The brighter purple coloring indicates drier air compared to the darker shades south of the line where the dewpoints were relatively high (in the +70F range). In this case the red component of the RGB (12-11 micron difference), which is related to optical thickness, contributes less color in the areas of higher moisture; this results in a darker color of purple compared to the relatively drier air to the north. The red decreases in the southern area because the difference in the 12-11 micron channels decreases from the values in the drier air. Looking at the individual channels, this change is fairly small, on the order of 1-2 K; but the range of the channel difference for the red component is limited to 6 K total. Hence a noticeable change in the red occurs and it brings out the change in air density.