Yarnell Hill Wildfire And NWS Forecast Support

Today is the fourth anniversary of the Yarnell Hill wildfire tragedy. I want to review a bit of the meteorology here and also consider special products issued by NWS Flagstaff.

Above is the 03:00 pm MST regional radar product from NCAR, the radar depicts a well-organized line of thunderstorms from east to north of the wildfire (which is producing the blue, smoke echo southeast of the line. The mesoscale outflow from this line of storms moved across the wildfire from about 04:18 to 04:30 pm causing a dramatic change in the fire's behavior, as would be expected.

Visible satellite images that show the storms and the fire location at 01:00 pm (top) and 03:30 pm bottom (red circle indicates fire location). By the time of the image below clouds from the thunderstorms had spread over the fire location - photos in the Accident Investigation clearly show the dark clouds associated with the storms - second below.

The NWS Flagstaff office handled weather support for this fire, which was at the southern edge of its County Warning Area (CWA). The spot forecasts were general, large-scale forecasts, similar to, but more fire-weather oriented, the general public forecasts issued by the NWS. However, when the line of thunderstorms developed, the Flagstaff Office issued two very specific warnings about the mesoscale outflow that was likely to impact directly the wildfire.

At 1402, FBAN receives a call with a weather update from the NWS office in Flagstaff. The NWS informs him of thunderstorms east of the fire that may produce wind gusts of 35 to 45 mph out of the northeast. FBAN relays the update to OPS1 and OPS2 via radio on state tactical frequency 1 (Tac 1).

At 1526, NWS-Flagstaff calls FBAN with a second weather update 

about expected thunderstorm outflow winds from the north-northeast 

with speeds between 40 and 50 mph. This update does not meet the 

NWS criteria for a Red Flag Warning for this area. FBAN radios this 

second update to OPS1 and OPS2 on Tac 1.

The acronyms can be confusing, but FBAN refers to the on-site Fire Behavior Analyst - the other acroynms can be found at: http://www.iawfonline.org/Yarnell_Hill_Fire_report.pdf

These two "warnings" phoned directly to the FBAN indicate that the outflow from the storms was likely to produce significant wind shifts and speed increases, which would dramatically impact the fire's behavior.

The "Red Flag" statement above seems, to me, to be a red herring, intended to deflect attention from the fire managers' actions after receiving the warning.

After several readings of the report, I can find no evidence that the onsite, fire managers changed their strategy to react better to the approaching outflow boundary. Possibly, a let's wait and see what happens was the approach used. Which is very sad, given the very accurate warnings issued by the Flagstaff NWS Office.