Low clouds and fog in the N. Gulf and Texas regions caused MVFR/IFR/LIFR conditions over a large area. The VIIRS Nighttime Microphysics RGB shows aqua to gray coloring to represent these features. In the RGB the scene is fairly complex with high and middle clouds (reds, blues, purples, tans …..). The RGB composite uses the traditional 11-3.9um difference (seen below) and combines other channels to better illustrate the low cloud features between the middle/high clouds. The RGB also improves the characterization of the thick, cold cloud tops associated with the cutoff low producing precipitation along the coast and southern states when compared to the simple 11-3.9um. Other “microphysical” RGBs are possible during the day or in a form that can be applied both day and night (i.e. 24hr product).
Archive for the ‘GOES-R Proving Ground’ Category
So, with the moon now passing into the waning crescent phase, the Day-Night Band imagery is less operationally useful, at least for the detection of fog and other lower level cloud types. That is, at least until the moon is back into the waxing gibbous phase. Nevertheless, when cirrus clouds aren’t present, the Nighttime Microphysics RGB has proven to be a very valuable tool for the detection of fog and other low-level clouds. Just this morning a forecaster at the Huntsville, AL WFO was able to use the imagery not only for the detection of fog, but also to aid in the issuance of a special weather statement about the fog. The image below valid at ~724 UTC (0224 am CDT) 17 Oct shows the fog (whitish-aqua colors) lying across the valley areas of NE Alabama and adjacent areas of southern Tennessee and NW Georgia.
Around the time of this image, the visibility in the foggy locations had decreased to ~1/4 – 1/2 SM or less. Notice the fog in the DeKalb Valley is fainter than the fog in areas to the north and west. Not only is the DeKalb Valley more narrow, but the fog was likely more shallow. This feature of the imagery can also help to guide forecasters in assessing the longevity of the fog once sunrise breaks. Over time, forecasters can develop a sense of pattern recognition with the varying degrees of color shading and tailor forecasts to better match the time of dissipation. In this case, the fog in the DeKalb Valley began to dissipate significantly by about 1430 UTC, while the deeper and more expansive fog to the north and west lasted about an hour longer.
On the evening of Monday, October 6th, several severe thunderstorms producing large hail moved across the Tennessee Valley region. I, along with another colleague, was on the radar desk for severe weather operations at the Huntsville, AL Weather Forecast Office. Some thunderstorms in the region had already produced large hail up to the size of golf balls to our north. As a vigorous short wave moved through the region, leading to increased lapse rates and deep layer shear, the threat for large hail was expected to continue into the early evening hours. As usual here at the Huntsville WFO, total lightning data from the North Alabama Lightning Mapping Array (NALMA) were incorporated into our warning decision process.
At 548 pm CDT, my colleague issued an initial severe thunderstorm warning for a storm cell located over northwestern portions of Jackson County, AL, primarily for the expectations of large hail. Reflectivity from the KHTX radar and the initial polygon can be seen below in image 1.
I had taken over warning responsibility for this severe thunderstorm by 6 pm and was having to decide whether or not to continue the warning when it expired at 615 pm CDT. This storm was tracking very close to the KHTX radar (noted by the black circle) and it was difficult to make out some of its higher level features and characteristics (although the Advanced Radar for Meteorological and Operational Research (ARMOR) was also being utilized at this point). The storm had wavered in intensity since the warning issuance and was only expected to be at the low-end of severe criteria. Another factor complicating the warning decision was that this storm was tracking over an area with very low population density. So, severe weather reports providing ground-truth were difficult to come by, and in fact, we had not received any yet allowing for verification of the warning.
Nevertheless, this is where the NALMA data came into play. Just shortly after the severe thunderstorm issuance, source densities within the storm surged, with values reaching well over 400 sources (image 2) between 550 and 552 pm CDT.
Over the next series of updates from the NALMA, source densities maintained relatively high values. As late as 2302 UTC, when I was beginning to consider the continuance of the warning, source values were still around 400 or higher. Afterward, values did gradually decrease. However, with the understanding that hail production will take some time following the strengthening updraft and that severe weather may not manifest up to about 30 minutes (or longer in some cases) after sustained surges in total lightning, I decided to continue the warning (Image 3). As the storm continued eastward, we finally received our first reports of one inch diameter hail in the town of Stevenson. Interestingly, the hail accumulated to the depth of a few inches according to one report.
So, yet again, this was another case in which total lightning provided value-added data and significant help for an operational warning decision.
From September 20 through September 23, 2014, the Ocean Prediction Center (OPC) was monitoring the development of the season’s first hurricane-force extratropical storm in the East Pacific. Models were suggesting a marginal hurricane-force wind event would unfold well west of the Pacific Northwest, near 140W longitude, north of 40N latitude. OPC is routinely using satellite data to monitor and forecast these strong ocean storms. On this particular event, OPC forecaster James Kells collaborated with Michael Rowland and David Kosier on if and when to pull the trigger on the hurricane-force warning.
The above animation shows the evolution of the hurricane-force low, with an eye-like feature evident near the end of the loop. By 1200 UTC on the 23rd, it was forecast to develop hurricane force winds (64 knots or greater) just west of Oregon near 140W. During the production of the 1200 UTC OPC Surface Analysis, there was question of whether or not the winds had reached hurricane force intensity. The ASCAT pass from ~0600 UTC showed a large area of 50-55 knot winds in the strong cold advection south of the low center, and the GFS model indicated that the system was still developing. The GFS 0-30m boundary layer winds also indicated a very small area with hurricane force intensity.
The 1130 UTC MODIS RGB Air Mass product was timelier, and it showed an area of downward momentum south of the low with the deep purple shading. The corresponding water vapor image was less clear with upper level moisture obscuring the downward motion just beneath it. In addition, there were no surface reports south of the low center as there were no buoys moored nor drifting in that vicinity. Furthermore, most ships were aware of the danger and navigated away from the region neglecting the possibility of a surface report in the area of question.
A cross-section of the 1200 UTC 09/23/14 GFS model potential temperature and dew point temperature was taken through the low center in order to analyze the depth of the stratospheric intrusion, and also to gauge the magnitude of the downward momentum. It showed a deep stratospheric intrusion to roughly 500 hPa, and it corroborated the strong downward momentum indicated by the imagery. The RGB Air Mass image showed the intensity of the downward momentum through the red/purple coloring and gave a good indication of the stronger winds aloft mixing down toward the surface. The imagery increased confidence with classifying the system as a hurricane force low.
~ Guest blogger, James Kells (OPC)
We have a long history of usage of total lightning data via the North Alabama Lightning Mapping Array (LMA) data here at the National Weather Service office in Huntsville, AL. LMA data began flowing here way back in the spring of 2003. There have been minor interruptions of data at times, mainly during and shortly after the implementation of AWIPS II, but total lightning data have been an integral, consistent part of operations here for over 10 years. These data have been used most often for detecting the initiation of electrical activity in developing convection. This is important because studies show that intra-cloud lightning often precedes cloud-to-ground lightning by about 5 to 10 minutes. Thus, total lightning data can serve as an early warning signal of the more dangerous cloud-to-ground component. We’ve also used the data to help identify thunderstorms that may experience rapid intensification, since total lightning activity is directly related to strengthening updrafts. I’ve even posted about an event in March 2012 where I used the LMA data as supplemental evidence that helped prompt a severe thunderstorm warning. This past Sunday evening (August 10th) I had the opportunity to use the data in a unique way (at least for me)…to help with a flash flood warning decision.
The first image below is a loop of KHTX WSR-88D 0.5 Reflectivity from this afternoon. Notice the cell that developed and persisted over northwestern portions of Morgan County. This cell developed directly along the Tennessee River and over the city of Decatur, AL.
The cell was producing heavy rainfall, and the other operational forecaster and I were watching it closely. One-hour rainfall amounts shortly after 2100 UTC were approaching 2 inches according to KHTX and nearby ground stations, which was near flash flood guidance for basins in this area. Of course, we were also dealing with data latency from these various sources, which is generally anywhere from about 5 to 20 minutes or more depending on the source. In a flash flooding situation, just as any other warning situation, things can evolve quickly and data updates as fast as possible are desired.
Perhaps most concerning however, was the fact that this cell was back-building and showing signs of little movement during the period, while some of this rain was falling over the city of Decatur. True, Decatur is a relatively small city, but still has sufficient urban land cover, and is bordered to the north and east by terrain that slopes gently toward the Tennessee River. So, drainage of water can be slow in the city, especially once adjacent backwaters and wetlands associated with the Tennessee River fill with water. While considering a flash flood warning, I still wanted some idea of the potential longevity of the cell over the Decatur area. The area could have handled this much rainfall if the cell dissipated and/or moved off as most others were prone to do in the low shear environment that day. However, looking at the LMA data really helped with my decision. Beginning at approximately 2104 UTC, source (image 2) and flash data (not shown) from the LMA showed the beginning of an enormous increase in total lightning activity with this cell. Also, the increase was taking place directly over the city of Decatur.
This trend in total lightning continued over the next several minutes. With the knowledge that this cell was likely undergoing intensification and moisture-laden updrafts were strengthening directly over the city of Decatur, I decided to issue the flash flood warning, which was officially disseminated at 2115 UTC. We received the first reports of flash flooding at 2145 UTC. The next image below shows the location of the warning issuance.
The total lightning data in this case served as a very valuable severe weather application tool. By providing the warning forecaster with knowledge of the location and likelihood of future deep convection, a flash flood warning was issued in a more timely and effective manner than would have been possible without these data. When used in conjunction with other information and applied properly, these types of data can help to save lives and property.
In late April, NASA SPoRT and the Albuquerque NWS met with scientists at New Mexico Tech to coordinate the integration of the Langmuir Lab lightning mapping array data into our operations. According to Bill Rison, Paul Krehbiel, and Ron Thomas, New Mexico Tech’s Lightning Mapping Array (LMA) is a 3-dimensional total lightning location system. The system is patterned after the LDAR (Lightning Detection and Ranging) system developed at NASA’s Kennedy Space Center by Carl Lennon, Launa Maier and colleagues. The LMA measures the time of arrival of 60 MHz RF radiation from a lightning discharge at multiple stations, and locates the sources of the radiation to produce a three-dimensional map of total lightning activity. The time-of-arrival technique for studying lightning was pioneered by Dave Proctor in South Africa. The NASA SPoRT core project site details that operationally, total lightning data provide several advantages to forecasters. First, total lightning data often give a 3-5 minute lead time ahead of the first cloud-to-ground lightning strike. This improves lightning safety for the National Weather Service’s Terminal Aerodrome Forecasts (TAFs) and Airport Weather Warnings (AWWs). This safety feature also can be used for incident support of special events. In addition, the total lightning data provides information about the spatial extent of lightning that is not available in the traditional cloud-to-ground data (http://weather.msfc.nasa.gov/sport/lma/). This data may also be used to evaluate the degree of lightning activity within active wildfire smoke plumes. The image below is an example of an LMA station at Briggsdale, Colorado taken by New Mexico Tech. These stations are solar-powered and communications are operated via cell technology.
After the first collaboration between NWS Albuquerque and NM Tech, forecaster Jennifer Palucki met with Harald Edens in June to install the xLMA and Live LMA software onto our office outreach laptop. The LMA data that forecasters are evaluating at Albuquerque consists of source densities. The imagery is available as a contour shaded product and describes the overall extent of sources from a particular thunderstorm or complex of thunderstorms. The Live LMA software provides the actual point source information that make up the densities available in AWIPS. The forecaster can actually see the structure of the point sources making up a flash on a 1-minute temporal resolution. Figure 2 below shows the composite radar reflectivity valid at 0200 UTC July 23, 2014 for a complex of thunderstorms developing southward into the Albuquerque Metro Area. The associated LMA source density product at 0202 UTC in Figure 3 illustrates the structure of the shaded point sources for the lightning flash. The graphic shown in Figure 4 details the point sources available with the Live LMA software. The source densities making up the flash during this 1-minute period stretched as far as 30-km from north to south and 20-km from east to west. The altitude of the main source region was near 10-km. The data available in AWIPS also allows the forecaster to slice and dice the data by elevation angle. Forecasters at the Albuquerque NWS will continue evaluating the LMA products through summer 2014 to offer feedback to NASA SPoRT and NM Tech on its operational application.
It is said that a picture says a thousand words…well in this case let’s just say 434 words, as are contained in this post. Anyway, I’d like to point out six features in this morning’s Nighttime Microphysics RGB. The image below (MODIS Nighttime Microphysics RGB) showed several features of varying degrees of operational relevance.
A myriad of cloud features can be observed, including fog in the valleys of central Appalachia, deep convective clouds along the Florida coast, patches of thin and thick cirrus over north-central Alabama, and low stratus clouds in Missouri…to name just a few. Sure, this isn’t an exhaustive list of the potential cloud features to observe, but showcases the ability to contrast effectively between different cloud types. Of perhaps significant interest is the ability to see the contrasting airmasses displayed across the Southeast region. Notice the pinkish colors north and west of the yellow curved line that stretches from central Louisiana to southern Virginia. This represents a lower relative contribution of blue color, or lesser longwave radiation at the 10.8 µm wavelength, which is indicative of cooler temperatures. To the south and east of this line, much more blue is apparent, which is thus indicative of warmer temperatures. Surface observations valid at about the same time have been overlaid with the RGB image to provide temperature data context. Air and dew point temperatures are around 10 degrees F cooler behind the line/front, but notice that the northerly wind shift is still on the south/east side of the line at such locations as Montgomery, AL and Columbus, GA. At those locations, dew point temperatures were still 70 and 71 F, respectively, with air temperatures at 72 F. So, the gradient in temperatures still lingered behind the surface front and is well depicted in the RGB imagery. This type of information can be valuable to forecasters, as temperature, moisture, and wind characteristics are often complex in the vicinity of surface fronts. Thus, while wind shifts may be observed initially, as in this case, the imagery shows the location of the temperature gradient much better.
The importance of this type of imagery is that it offers a much more effective assessment of meteorological phenomena than existing GOES imagery. The only problem currently is the limitation of available imagery to forecasters, since these are from polar-orbiting platforms (Terra, Aqua, Suomi NPP), and thus provide just a few snapshots per night over a given location. Nevertheless, the imagery form the VIIRS and MODIS instruments offer added value to existing GOES imagery and serve as valuable teaching and preparatory aids for future GOES-R and JPSS missions.