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.

NDVI and GOES surface dryness comparisons

GOES observed surface dryness with the PSA dryness product overlaid for 29 August 2011. Areas of low dryness in green with areas of extremem dryness in red.
Today we examined the GOES surface dryness and dryness anomaly fields to help outline our fuel threat area and noticed that there were one significant mismatch between it and the official PSA dryness product provided within SPC operations (see image above). An area extending across much of western and central OR where we saw a good amount of rain over the past week is being described as extremely dry and extremely anomalous within the GOES dryness products, whereas the PSA dryness products have this area outlined as not a threat for dry fuels, which is what we were expecting. We are not sure why the GOES surface dryness products are not picking up on this, so we tended to put more faith on the PSA dryness product today over that area. otherwise, the dryness and dryness anomalies tend to match up fairly well with the PSA dryness values.

14-day NDVI change with PSA dryness product overlaid. Areas of green indicate areas of increased "greenness" in the NDVI change.
We did also compare the 7- and 14-day NDVI composite and NDVI change products with the official PSA dryness product and we were seeing similar features as the PSA dryness product, especially with this area over OR that shows up as increased "greenness" in the NDVI change (see image above). It suggests that a combination of the NDVI and surface dryness measurements might provide a more accurate analysis of the fuels, with a higher resolution to that of some of official dryness products currently provided within operations.