Abstract
The deadly shift of the Yarnell Hill, Arizona wildfire was associated with an environment exhibiting gusty wind patterns in response to organized convectively driven circulations. The observed synoptic (>2500 km) through meso-β (approximately 100 km) scale precursor environment that organized a mid-upper tropospheric cross-mountain mesoscale jet streak circulation and upslope thermally direct flow was examined. Numerical simulations and observations indicated that both circulations played a key role in focusing the upper-level divergence, ascent, downdraft potential, vertical wind shear favoring mobile convective gust fronts, and a microburst. This sequence was initiated at the synoptic scale by a cyclonic Rossby Wave Break (RWB) 72 h prior, followed by an anticyclonic RWB. These RWBs combined to produce a mid-continent baroclinic trough with two short waves ushering in cooler air with the amplifying polar jet. Cool air advection with the second trough and surface heating across the Intermountain West (IW) combined to increase the mesoscale pressure gradient, forcing a mid-upper tropospheric subsynoptic jet around the periphery of the upstream ridge over Southern Utah and Northern New Mexico. Convection was triggered by an unbalanced secondary jetlet circulation within the subsynoptic jet in association with a low-level upslope flow accompanying a mountain plains solenoidal circulation above the Mogollon Rim (MR) and downstream mountains.
Highlights
The Yarnell Hill Fire was a wildfire near Yarnell in Yavapai County, Arizona
The following observational datasets were employed in the subsequent analyses: (1) Plymouth State Weather Center hourly surface meteograms [24], (2) European Centre for Medium Range Weather Forecasts ERA-Interim and ERA5 6-hourly and hourly upper-air analyses of dependent variables [25,26], (3) high-frequency radar control message datasets from the Plymouth State Weather Center archive [24], as well as high-resolution Doppler radar datasets and dual polarimetric radar datasets from the NOAA NIDS archive for the TPHX Doppler [27] and the Flagstaff, Arizona NWS Forecast Office [28], (4) soundings plotted from data downloaded from the NCEP NCEI integrated global radiosonde archive [29], and (5) remote automatic weather station (RAWS) [30] surface data
Consistent with a cyclonic Rossby Wave Break (RWB) within the upper tropospheric polar jet stream, a negatively tilted trough developed over the Great Lakes, as the first lobe of potential vorticity (PV), propagates southeast during the 00/27–00/29 period
Summary
The Yarnell Hill Fire was a wildfire near Yarnell in Yavapai County, Arizona We will refer to this tragedy as the Yarnell Hill Fire Tragedy (YHFT) It was one of the deadliest wildfires in U.S history [1] and the deadliest for firefighters since the 1933 Griffith Park fire in Los Angeles [2]. These observations, as well as others across the entire western and northern regions of the state, represented extreme drought conditions favorable for substantial diurnal surface sensible heating. This extreme heating is exemplified at Stanton, AZ, with an observation of 38 °C at 10:01 MST in response to a surface sensible heat flux of approx of 29 imately 756 Wm−2 [4]
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