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.

Verifying yesterdays forecast and comparing to NSSL-WRF lightning threat

1800 UTC 24 August - 1200 UTC 25 August 2011 dry thunderstorm probability forecast with NLDN lightning detections from 0030 (top left), 0450 (top right) and 1150 UTC (bottom) on 25 August 2011.
At the beginning of the experiment today we 'verified' our previous day's forecast for dry thunder over much of the NW US. We had probabilities of dry thunderstorms reaching 40% over much of the area (see images above). When compared to the NLDN observed lightning activity, we see that our higher threat areas (30-40%) matched up fairly well with what occurred. Most of the storms over OR were classified as dry thunder, most likely due to their rapid storm motions. We could have extended our area a little further east to cover central ID (see last image above), which was suggested by the NSSL-WRF total lightning threat. When examining the GOES fire / hotspot detection product to our forecast, we did see a few new starts in the area, with at least one large fire confirmed by observers.

When we compare the observed lightning to that which was forecast by the NSSL-WRF total lightning product, we see that overall the NSSL-WRF tended to slightly downplay some of the lightning activity, but the spatial locations and timing were fairly well forecast (see yesterday's post). This product was developed and validated over the SE US, so the values in the west have yet to be compared directly. Part of this experiment is to get a general idea of how well this product could work over the western US, with the potential for use in operational fire weather forecasts.

Dry thunder over southern Oregon

7-day observed surface dryness (top) and dryness anomaly (bottom) from the GOES-West satellite from 23 August 2011.
Today has the potential to be a fairly significant day for fire weather threat over much of the NW US. GOES-West observed surface dryness and dryness anomaly over the past 7 days (images above) indicates significant drying of potential fuels over much of the western US, with a relative maximum over much of eastern OR and into ID, CA and NV. This agrees well with the observed Predictive Service Area dryness product.

A relatively strong vorticity max for the area is expected to move through this afternoon and bring with it some moderate instability with low PW and surface RH. Storms are expected to track fairly quick, so even if there was a chance of wetting occurring at the surface, the duration would be limited, so the potential for dry thunder is fairly high. Given the good amount of instability, the amount of lightning strikes will be relatively high, which increases the potential for new fire starts. The NSSL-WRF experimental lightning threat output shows this to some degree during the 2300-0200 UTC time periods of the 24th and the 25th of August (see images below).

NSSL-WRF experimental lightning threat for 24-25 August 2011 at 2300 (top left), 0000 (top right), 0100 (bottom left), and 0200 UTC (bottom right).

Fire Weather Experiment... Day 2

HWT Fire Weather Experiment participants during domain selection map discussion.
Today we started our second day of the Fire Weather Experiment, building off of what we did yesterday by first examining the forecast we made against base reflectivity, NLDN lightning strikes and the GOES fire rating product (FRP) from UW-CIMSS. We did see the occurrence of multiple lightning strikes and relatively low base reflectivity over the area we forecast a possibility of dry thunderstorms, suggesting that there might have been some. While examining the FRP, we did see a few new start-ups over the area where lightning occurred (see figure below). However, as some participants noted, the fire rating product seemed to have only two colors for rating the fires, pale yellow or red. They were expecting to see a wider variety of fire 'ratings', so after the experiment was finished we made a few modifications to the color tables to help distinguish the ratings better.

Experimental probabilistic forecast for dry thunderstorms from 22 August 2011 with FRP detections overlaid.

NDVI and satellite-based dryness observations versus operational data

PSADryness product for 22 August 2011. This product is routinely available within SPC operations. Areas of yellow and red indicate significantly dry surface measurements
SPC forecasters routinely use a product originally developed by the NWS Salt Lake City and the Eastern Great Basin Predictive Service Office called the Predictive Service Area Dryness (psadryness) product (see above) to help make their day 1-8 fire weather outlooks. This product provides the forecasters with an idea of the dryness of burnable fuels near the surface. In addition, the forecasters use a high-resolution 'land-use' product that attempts to simulate the NDVI product, but is rarely, if ever, updated. One of the goals we wanted to accomplish from this experiment is to see how the higher resolution datasets of observed NDVI and NDVI change (below), as well as the GOES surface dryness and dryness anomaly products (also below), compare to products currently in operations, such as the psadryness product (above).

14-day composite NDVI (top) and 28-day NDVI change (bottom) from 15 August 2011. Areas of green indicate regions where increased 'greenness' is observed.
During our first day, 5 SPC fire weather forecasters participated and examined these products to make an experimental "update" for their day-1 fire weather outlook, or out to 12 UTC the next day. In particular, forecasters were asked to make a forecast graphic depicting the areas of high threat for burnable fuels. When comparing the psadryness product and the satellite-based products, we noticed that there was a noticeable discrepancy over some areas, specifically over central ID (see above). While the psadryness product said that the area was extremely dry, the NDVI and NDVI change depicted areas of increasing 'greenness'. In addition, the GOES surface dryness and dryness anomaly products indicated no significant drying over the area.

GOES 14-day composite surface dryness (top) and 5-year average dryness anomaly (bottom) for 22 August 2011. Areas of yellow and red indicate increased surface dryness.
So what gives? Well we explained to the forecasters that the satellite-based products are limited to sensing the canopy of the location they are observing. this means that if there is any forest in the area, we cannot see the undergrowth, which could be dry and only measurable from surface instruments or observers. Unfortunately, this is a limitation we have to deal with, particularly from geostationary satellite-based instruments. However, the forecasters were impressed by the spatial resolution and relative rapid updates of the products, which is not provided to them from the psadryness or land-use products. It may be useful to combine these datasets to get a more detailed picture of what may actually be going on at the surface when it comes to burnable fuels.

Fire Weather Experiment Begins Today

Example HWT display, showing satellite-based surface dryness anomaly on the left and the online survey worksheet on the right.

Today marks the beginning of the first ever fire weather experiment at the HWT. This year will be a very informal year with only a few local participants. Our goal is to establish a strategy and framework for which future fire weather experiments can occur at the HWT. We plan on examining some satellite based vegetation and surface measurements such as NDVI, NDVI change, surface dryness, and dryness anomaly. We will also be examining some experimental model data including the simulated satellite imagery and lightning threat from the NSSL-WRF.

We hope that we can get some valuable feedback on these products, as well as how to best demonstrate them in future experiments. I will be posting regularly about our progress.

Dual Jet Captured in Upper Level Simulated ABI Water Vapor Imagery

A forecast of SSEC-CIMSS Simulated ABI Band 08 Water Vapor imagery valid at 12z Wed (above) showed two strongly sheared areas, indicative of two upper level jets moving across the upper Midwest. The southern strong water vapor gradient over southern Minnesota is properly positioned when compared to the 12Z TUE GFS 300-200mb wind speed forecast valid at 12Z Wed (below). There is another strong water vapor gradient apparent at the base of the upper level trough, which is also well-placed when comparing it to model data. The simulated water vapor imagery serves as a proxy for identifying and tracking the evolution of upper level jets without having to rely solely on model data.

Submitted by Marcia Cronce (NWS) and Dan Hartung (CIMSS).