14 April 2012 - Simulated Band Difference

Part of the NSSL-WRF simulated satellite imagery that we get from CIRA includes a band difference unique to GOES-R that we began looking at during last year's Spring Experiment. One of the advantages of simulating satellite data from a model is that we have the opportunity to produce channels that we don't have currently, and we take full advantage of this by producing all 9 of the non-solar GOES-R IR bands. The 10.35 micron channel is a very clean window, and thus is very sensitive to surface temperature. The 12.3 micron channel however is sensitive to low- and mid-level water vapor. As moisture moves into a clear pixel area, the 12.3 micron brightness temperature will decrease, whereas the 10.35 micron temperature should stay the same. When this occurs, the 10.35-12.3 micron channel difference will become strongly positive and indicates areas of moisture convergence or pooling, which can lead to destabilization and subsequent convective initiation.
Unfortunately, because the imagery is generated by a numerical model, it is a) not an observation and b) only available on an hourly timescale. However, we can use the imagery generated from the model as a experimental tool to demonstrate some of the unique things we can do once we have the increased spectral resolution of the GOES-R Advanced Baseline Imager (ABI). In this example from the 14 April 2012 outbreak the 10.35-12.3 micron channel difference is useful in identifying the evolution of the dryline across western KS, OK and TX from 1900 UTC on the 14th to 0100 on the 15th (see images below). As moisture converges at the surface, the difference becomes more positive. These positive values show up as yellow, orange and red on the images below. The edge of the dryline is easy to detect and follow using this simple band difference within the NSSL-WRF. It will be very interesting to see observations of this band difference, and other imagery techniques such as RGBs, every 5 minutes over the continental US once we have the GOES-R ABI available to us.

14 April 2012 - Sounder Airmass RGB

Well, it's not quite the Spring Experiment yet, but we did have a significant severe weather event over the plains this past weekend that I figured would be a good opportunity to capture some of the GOES-R Proving Ground products that we receive at the Storm Prediction Center and Hazardous Weather Testbed. We will start with the GOES Sounder Airmass RGB that is provided to us by CIRA and NASA SPoRT. RGB simply stands for Red-Green-Blue, which is a composite image created by combining three separate channels or channel differences into one image. This technique helps us identify specific features in the atmosphere without the use of complex derived products. The airmass RGB is a combination of thermal infrared, water vapor and ozone channels that help us identify regions of warm and moist versus cold and dry airmasses, spin in the atmosphere and jet streaks. The airmass RGB has been used extensively over Europe using the Meteosat Second Generation satellite, which has similar spectral channels to what will be available on the GOES-R Advanced Baseline Imager (ABI). Current GOES imagers do not contain the spectral bands necessary to generate this product, but we are able to simulate the RGB using the GOES sounder, which does have some similar channels to the ABI. Unfortunately this data only arrives once hourly from the sounder, but when GOES-R is launched, we will be able to create this product every 5 minutes over the continental US.
Below is a time-series of the SPC's outlooks from day 7 up until the event on Saturday 14 April 2012 from the SPC Facebook page. You can see clearly that the SPC had a good handle on the threat a week in advance and that the threat area depicted on day 1 well outlined the events that occurred in NE, KS, OK and IA. Preliminary storm reports from the SPC website indicate 135 tornado reports (likely will end up being about 75 individual tornadoes following official surveys) occurred during this event, with what appears to be several long tracks across OK and KS.

If we take a look at the sounder airmass RGB product at 12 UTC on 14 April 2012 (top image below), we can see a strong center of circulation over CA/AZ/UT/NV with indications of a significantly lowered tropopause, associated jet streaks and high PV (red hues) within the circulation and extending along the Pacific coast up into Canada. This can be confirmed by overlaying the tropopause pressure from the RUC analysis (middle image below) or the the 500 mb heights and vorticity (bottom image below).

If we move forward to 15 UTC (image below), just prior to initiation in KS, we can begin to see evidence of a moisture boundary (blue-to-green hue gradient) setting up along a line extending from NW KS near the KS/NE border down into the OK panhandle and down into west TX. Initiation in southern KS and down through the OK panhandle into TX would occur along a dryline located in this area, which is likely what the airmass RGB is picking up at this time.

Moving forward to 02 (top image below), 03 (middle image below) and 04 UTC (bottom image below) on 15 April 2012, the moisture gradient feature really begins to tighten up and better define itself as the dryline continued to evolve and the Pacific cold front approached, initiating a line of storms extending into central TX.

GOES R Proving Ground MVFR/IFR Assessment

There was an excellent area of mixed MVFR/IFR clouds across eastern OH, western PA and all of WV that was used to assesses the performance of the GOES R MVFR/IFR satellite product. The GOES R product did an excellent job with the depiction of the area covered by the clouds, but some perceived weakness in the accuracy of showing the appropriate percentage of MVFR and IFR. The series of images below show how the cloud area did not change over about 1 1/2 hours (see 4 vis images), yet the MVFR satellite analysis showed the percentages increasing with time. The obs at this time showed the deck was solid mvfr with a few sites sitting in ifr conditions. This was pretty stable. We were speculating whether this had to do with the increasing visible reflectance with increasing sun angle, or some other underlying element within the algorithm.

















A suggestion would be to reassess the enhancement curve applied to the MVFR/IFR products. Due to the sharp color shift at a specific percentage, it causes your attention to focus (probably too much) on specific areas that aren't significantly different. For example, the "yellow" 74% is not statistically different from the "red" 76%. Yet, the product suggests this is a big jump. We discussed using a curve with more of a gradient, in this case a grey scale from the vis enhancement. This introduced a more natural looking product. It is understood that colors are a very personal thing and this is open to lots of opinions! :)





Steve Davis NWS Milwaukee/Sullivan
Justin Sieglaff CIMSS

Notes from 9/27/11 CIMSS/NWS Testbed Session

We discussed many different ideas and made notes about improvements that each of us can make to help in forecast operations.

One question to ask yourself when working on the short term shift is, "Will there be some clearing in the clouds tonight?" A stationary upper low pressure system has been sitting over southern Lake Michigan and northern Illinois for the past 4 days at least. Timing the clearing skies vs. the cloudy skies has been a big challenge, to say the least. It makes a big difference when forecasting minimum temperatures. There are some products provided by the CIMSS group that are available in AWIPS that can help us with our sky cover forecast for tonight.

The first image is actual, current infrared (IR) satellite imagery of the midwest at 1930Z Tue Sep 27 (230 pm). The second image is the GOES-R ABI simulated IR imagery Band 11 (8.5 um) for 0400Z Wed Sep 28 (11 pm Tue Sep 27). The simulated imagery shows clearing in the lower/mid levels over central WI tonight. This actually verifies with several other model output, including NAM and GFS sky cover grids available in the Gridded Forecast Editor. We can infer that this Band 11 imagery is showing clearing in the low levels because we also looked at Bands 8, 9 and 10 which show more of the water vapor-type imagery, and there were no high clouds depicted in that area either.

There are many satellite-derived products from CIMSS that are available in AWIPS, including cloudy type, MVFR/IFR probability, fog depth and a cloud mask. The cloud mask is shown below, valid at 1445Z (945 am) Tue, Sep 27, and is compared to the actual IR satellite 11-3.9 um difference field at 1431Z. The cloud mask is most useful in operations at night where it may be unclear if we're seeing clouds or snow on IR imagery, or where the actual edge of the clouds are. The ABI channels are combined, or made into a consensus, to develop the cloud mask product.

These derived products and simulated ABI products spawned numerous ideas for future products that may be produced by CIMSS. First, it would be great to see the simulated ABI products from its run time all the way out to 36 hours (or the length of the run). Right now, we only see the 12-36 hour forecast products. It would also be useful if the fog product could be simulated into the future (using the ABI simulated bands). This could help with seeing where fog over the lake (if it is picked up by the model) may advect during the day and if it will spread inland. It also could help to forecast fog development 6-12 hours in advance if we're in a situation with high pressure and great diurnal cooling, or another fog-conducive environment.

The cloud type product (see below) has the ability to detect cirrus that is overlaid on top of low clouds. It works best if there is a semi-thin cirrus shield with much warmer clouds below it. This situation is famous for producing "sneaky" snow events with the seeder-feeder process.

There is a new product available online now (not yet in AWIPS) that is ABI simulated visible satellite imagery (see below). The link is http://cimss.ssec.wisc.edu/goes_r/proving-ground/nssl_abi/nssl_abi_rt.html . We compared this simulation to visible satellite imagery (see below) at 20Z (3 pm) this afternoon and it verified quite well.

Submitted by Marcia Cronce, NWS

Andrew Heidinger, NOAA at CIMSS/SSEC

Wayne Feltz, CIMSS/SSEC

Notes From 9/6/11 Training Session

This image is from the simulated water vapor ABI imagery, band 8, forecast at 1800z on 9/6/11. This simulated water vapor image shows quite a bit of high clouds/moisture across the high plains and western Texas. This band usually shows moisture in the upper levels of the atmosphere, thus the cirrus clouds. It also shows a fair amount of dry air wrapping into the circulation of the remnants of Lee over the Ohio River Valley. Compare this to the image below:

This is a simulated water vapor ABI image, band 10, forecast at 1800z on 9/6/11. This simulated water vapor image shows moisture in the low to mid levels of the atmosphere. Thus, it shows a lot of dry air in the southern high plains and western Texas. It also shows this dry air wrapping around the circulation with the remnants of Lee over the Ohio River Valley. From these images, it can be concluded that just some high clouds were moving into the southern high plains and western Texas, with the dry conditions in the lower to mid levels continuing. One could also say that the dry air wrapping into the remnants of Lee may reduce the clouds and precipitation associated with it.

Example 2:

In this GOES-R probability of MVFR ceilings product, from 1115z on Tuesday, September 6, 2011, several areas of higher probabilities were noted. These areas included parts of northwest Wisconsin, southeast Wisconsin, north central Illinois and far northeast Minnesota. There was also a large area of higher probabilities over Minnesota back into the northern Plains. Let's compare with an operational GOES East image below:

This visible GOES East image was taken at 1125z on 9/6/11, 10 minutes later than the MVFR probability image earlier. The MVFR probability product did identify the clouds that were present across the area. This product showed probabilities of MVFR ceilings of generally 50 to 80 percent. However, the observations showed all of the ceilings were VFR (generally 3500 to 5000 feet above ground level). These values are on the lower end of the VFR ceiling spectrum, so even though the ceilings were not MVFR, they were close. This would give the forecaster more confidence that lower end VFR ceilings were occurring.

J. J. Wood
Meteorologist
National Weather Service
Milwaukee/Sullivan, WI

Examining the 30 August 2011 Oklahoma City fire with the GOES Fire Rating Product

NESDIS operational 24 hour fire hotspots and smoke detections from 30 August 2011.
A relatively large and dangerous fire occurred over NE OKC yesterday which burned homes and injured multiple firefighters throughout the evening and into the night. The origin of the fire is yet to be determined, but I thought it would be interesting to go back and examine what the GOES Fire Rating Product (FRP) observed from this event. The FRP uses GOES observed hotspots and attempted to rate their intensity based on the relative saturation of the pixel in the 3.9 micron band.


The OKC fire began sometime around 11-11:30am local time (or about 17 UTC). The fire was initially detected by the FRP at 1845 UTC with very weak 'rating' (gray color) of the hotspot, but it was several pixels wide (see image above).


At 2015 UTC the FRP detected the max intensity of the fire, as seen by the bright yellow pixels (see image above).


At 2130 UTC two additional fires were also detected by the FRP SW and NE of the OKC fire (see image above). These are also shown by the 24hr composite (topmost image). By 0015 UTC the OKC fire was no longer detected by FRP, but firefighters continued to put out small hotspots to avoid another start-up today. It should be noted that the FRP did shown a trend for each fire of starting with a low intensity, ramping up, reaching a peak intensity and then finally decreasing the intensity gradually until they disappeared, giving us confidence that the FRP is operating correctly.

Relying on GOES observed dryness

GOES surface dryness product from 30 August 2011 with the PSA dryness grids overlaid from 31 August 2011. Areas in red and yellow indicate significant surface dryness, with areas in green indicating relative moist surface areas. We see that the PSA dryness grids drop off sharply at the OK/KS/CO border, which is not reflected in the GOES surface dryness product.
Today during our fire weather forecast we attempted to analyze the burnable fuel threat and the relative dryness over our forecast area covering much of TX, OK and KS. Apparently there has been a data problem with the operational PSA dryness grids over KS today which forced us to rely on the GOES observed surface dryness and NDVI products, which gave us a unique 'data denial' experiment to determine the availability of dry fuels (see image above). We see that GOES observed surface dryness is very high (reds) over much of KS, so we had to include this area within our burnable fuels threat today.


7-day NDVI composite (left) and 28-day NDVI change (right) from 29 August 2011. Areas of green indicate regions of increased (or increasing) vegetation, while areas of brown indicate regions of decreased (or decreasing) vegetation.
We also examined the NDVI and NDVI change composites in our analysis to determine the amount of vegetation available over these extremely dry areas. If we look at the NDVI composite, much of this area is shown as not containing a lot of green vegetation (leftmost image above). However, examining the experimental NDVI change product, we do see that most of this area is showing signs of 'greening' (rightmost image above). From this we determined that the amount of vegetation is slightly increasing, but still relatively dry and burnable (from our observations using the GOES dryness and NDVI composite products).

MVFR-IFR Cloud Assessment - 3 Areas

The accuracy of the GOES-R probability of MVFR and the probability of IFR products were assessed in three areas across the U.S. and Ontario, Canada. This type of product will have clear utility in aviation forecasting, especially in areas where distance between surface observations is large, or if/when we lack observations due to communication failures.

Nebraska

The first area of concern was across Nebraska. This was an area of low clouds that formed in the wake of a departing convective complex early in the morning of August 30, 2011. Initially, much of the cloudiness was IFR (ceilings below 10kft,) lifting to a widespread MVFR deck after sunrise. The image below is around 1630Z, August 30, 2011. Upper left - MVFR Probabilities. Upper right - IFR probability. Lower left - Visible imgery. Lower right - Vis imagery with GFS 1000-850mb RH analyzed.



This product did a pretty job of placing high probability of MVFR across eastern Nebraska, but largely underplayed the existing widespread MVFR cigs over the central areas, especially around North Platte and points southwest where the deck was very solid. I suspect the holes forming in the overcast between the central and eastern areas were responsible for the more optimistic probabilities. But, subjectively, I don't believe these holes are near big enough to bring scattered conditions, or better than MVFR conditions. All of the surface obs across the area are bkn-ovc between 10kft-22kft.

South Carolina

The next low cloud area existed over the eastern/southeast half of South Carolina on the same day. The area of high probability (greater than 80%, red color) did a very good job capturing the existing MVFR deck. But, the MVFR deck stretched up into southeast North Carolina and the product appeared to become much too optimistic with the probabilities from northeast SC into southeast NC. Similar to the Nebraska stratus, this lower probability area had some holes in the stratus that appeared to be given too much influence. The surface observations throughout this lower probability were bkn-ovc from 21kft-26kft.





Ontario, Canada

This did a pretty good job depicting the existing MVFR deck south of Hudson Bay/James Bay on August 30, 2011. There was one, maybe two, observations in this entire area and these were limited to the far eastern portion. I suspect, though no way to prove it, that the clouds streaming in off of Hudson Bay were IFR, but then lifted into an MVFR deck farther inland. Similar to conditions that occur near the Great Lakes. A couple of curious areas were noted in this example. One, is the "weakness" in IFR probabilities (upper right panel) roughly in the center of northwest to southeast oriented stratus deck. We couldn't really find any discontinuities in other supporting satellite products. Admittedly, this is a very minor point. The other feature in question was the disparity in the very sharp southern edge to the MVFR deck as seen on the visible imagery and the large (stretched out) gradient in probabilities along this same edge. It appears the GFS 1000-850mb rh prog (cyan analysis in the bottom right panel) may have had a lot of influence on that.



In looking at all three of these examples, it appears to me that not enough influence is given to the current observations. This is a great product and has lots of potential for the operational environment.