Part 1b - Do our Wildland Fire (WF) Instructors foster "complete" lessons learned in the WF culture?
Authors - S130 / S190 / L180 Lead Instructor Fred J. Schoeffler and Co-Instructor / SME ( YH Fire ) Joy A. Collura
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Continuing from "Part 1a - Do our Wildland Fire (WF) Instructors foster "complete" lessons learned in the WF culture?"...due to this message when trying to put blog on said I had to break part one into several posts:
Figure 7. The descent of a subsidence inversion may be followed on successive soundings, as shown by dashed lines. As the more humid surface air flows outward, the drier air aloft is allowed to sink and warm adiabatically. Source: Fire Weather Handbook
The inversion will be wiped out only in local areas where surface heating is intense enough to do the job. If the heating is not sufficient to eliminate the inversion, the warm, dry air cannot reach the surface by convection. Convective currents in the layer beneath the inversion may be effective in eating away the base of the inversion and mixing some of the dry air above with the more humid air below. This process will warm and dry the surface layer somewhat, but humidities cannot reach the extremely low values characteristic of a true subsidence situation.
Another method by which dry, subsiding air may reach the surface is by following a sloping downward path rather than a strictly vertical path. A vertical sounding may show that the subsiding air is much too warm to reach the surface by sinking vertically, because the layer beneath it is cooler and denser. However, if surface air temperatures are warmer downstream, the subsiding air can sink dry-adiabatically to lower levels as it moves down stream and may eventually reach the surface. This process is most likely to occur around the eastern and southern sides of a high-pressure area where temperatures increase along the air trajectory. By the time the sinking air reaches the surface, it is likely to be on the south, southwest, or even west side of the High.
Subsiding air may reach the surface in a dynamic process through the formation of mountain waves when strong winds blow at right angles to mountain ranges. Waves of quite large amplitude can be established over and on the leeward side of ranges. Mountain waves can bring air from great heights down to the surface on the lee side with very little external modification. These waves may also be a part of the foehn-wind patterns, which we will touch off only briefly here since they will be treated in depth in chapter 6. In the mountain areas of the West, foehn winds, whether they are the chinook of the eastern slopes of the Rockies, the Santa Ana of southern California, or the Mono and northeast wind of central and northern California, are all associated with a high-pressure area in the Great Basin. A foehn is a wind flowing down the leeward side of mountain ranges where air is forced across the ranges by the prevailing pressure gradient. Subsidence occurs above the High where the air is warm and dry. The mountain ranges act as barriers to the flow of the lower layer of air so that the air crossing the ranges comes from the dryer layer aloft. If the pressure gradient is favorable for removing the surface air on the leeward side of the mountain, the dry air from aloft is allowed to flow down the lee slopes to low elevations. The dryness and warmth of this air combined with the strong wind flow produce the most critical fire-weather situations known anywhere.
Mountain waves, most common and strongest in the West, are also characteristic of flow over eastern and other mountain ranges. When they occur with foehn winds, they create a very spotty pattern. The strongest winds and driest air are found where the mountain waves dip down to the surface on the leeward side of the mountains.
An example of a severe subsidence condition associated with chinook winds, and in which mountain waves probably played an important part, is the Denver, Colo., situation of December 1957. On December 9, chinook winds were reported all along the east slope of the Rocky Mountains in Wyoming and Colorado. Surface relative humidity at Denver remained at 3 percent or below from noon until midnight that day. The Denver observation at 1900 hours showed: Temperature: 60 (°F.), Dew Point: -29 (°F.), Relative humidity: an incredible 1%, Wind direction and speed: West at 22 mph.
The extremely low dew point indicates that the air must have originated in the high troposphere.
Cases of severe subsidence are much more frequent in the western half of the country than in the eastern regions. Moat of the Pacific coast area is affected in summer by the deep semi-permanent Pacific High. This provides a huge reservoir of dry, subsiding air which penetrates the continent in recurring surges to produce long periods of clear skies and dry weather. Fortunately, marine air persists much of the time in the lower layer along the immediate coast and partially modifies the subsiding air before it reaches the surface.
In the fall and winter months, the Great Basin High is a frequent source of subsiding air associated with the foehn winds, discussed above. It is the level of origin of this air that gives these winds their characteristic dryness.
Subsiding air reaching the surface is perhaps less common in eastern regions, but does occur from time to time. Usually the subsiding air is well modified by convection. But subsidence is often a factor in the severe fire weather found around the periphery of Highs moving into the region [east] of the Rockies from the Hudson Bay area or Northwest Canada mostly in spring and fall. It also occurs during summer and early fall periods of drought, when the Bermuda High extends well westward into the country.
Consider now a few wildland fire weather research papers examining the crucial role of Subsidence on wildland fire behavior, revealed as Dry Intrusions and Dry Slots, utilizing WVI, with a look into the Skew-T soundings from those Soaring buffs that depend (life or death) on accurately depicted up and downdrafts.
WEATHER AND FIRE BEHAVIOR INFLUENCING THE 11-12 JUNE 2013 BLACK FOREST COLORADO (USA) WILDFIRE ( https://ams.confex.com/ams/42Broadcast/webprogram/Manuscript/Paper245722/AMS%2042nd%20June%202013%20Black%20Forest%20Fire%202.pdf )
THE INFLUENCE OF DRY SLOTS ON WILDLAND FIRE GROWTH DURING THE 2011 ARIZONA FIRE SEASON ( https://ams.confex.com/ams/10Fire/webprogram/Handout/Paper225272/AMS%202011%20AZ%20wildfires%20influenced%20by%20Dry%20Slots%20In%20The%20U.S.%202.pdf )
Kaplan, M.L., et al (2008) The development of extremely dry surface air due to vertical exchanges under the exit region of a jet streak. Meteorol Atmos Phys ( http://www.mesolab.us/publications%20%28web%29/2008_Kaplan_etal%28MAP_Jet_Streak_and_Fire%29.pdf )
Figure 8. Vertical cross section of simulated Relative Humidity on the June 2, 2002, 1700 UTC (1300 EDT) Double Trouble State Park (DTSP) wildfire. The bright red low RH region would be a dry slot visible in the WVI. Source: Charney et al (2003) The role of a stratospheric intrusion in the evolution of the DTSP wildfire, Figure 6.
Figures 9a. & b. GOES 8 Water Vapor Imagery (WVI) snippet of June 2, 2002, 1445 UTC (10:45 AM - top) and 1745 UTC (1:45 PM - bottom) indicating dry intrusions and dry slots (subsidence) advecting across the DTSP wildfire region. Gold and yellow colors indicate very dry air Source: NOAA Global ISCCP B1 Browse System (GIBBS)
Figures 10. a-c. (a) KALB (Albany County, NY), (b) KCHH (Chatham, MA), (c) KOKX (Upton, NY) June 2, 2002, 12Z (8:00 AM ) Skew-T Soundings all indicating Subsidence Inversions in the 550 to 600 mb range (roughly 15,000' & 20,000') Source: Plymouth State Weather Center
KALB and KCHH generally match at 400 to 600 mb with single digit Relative Humidity values, with like KOKX site values up into the Jet Stream levels at 200 to 300 mb.
Martin, J. (UP) (2015) Skew T’s – How to Read Them. Finger Lakes Soaring Club, Dansville, NY. ( http://flsc.org/portals/12/PDF/Read_Skew_T.pdf )
3. Entrapment Avoidance
Use training and reference materials to study, understand, and adopt the risk management process as identified in the Incident Response Pocket Guide (IRPG), PMS 461, as appropriate to participants, (i.e., LCES, Standard Firefighting Orders, and the Watch Out Situations). Entrapment avoidance and deployment protocols are identified in the IRPG, which also contains the “Last Resort Survival Checklist.”
Another good source for specific case studies - with a caveat - is the Wildland Fire Lessons Learned Center (LLC), Incident Reviews Database.
( https://www.wildfirelessons.net/home ) Search by Fire Name, Match Terms, Incident Year, Incident Type (i.e. "entrapment"), fire name, and Incident Location. And the caveat is, of course, the indisputable fact that any and all Serious Accident Investigation Reports and / or Reviews are considerably more fiction-based. That has become - and is - such a regular business practice, and such a minor detail, in their eyes, that those alleged 'Investigators' first decide on a "conclusion" and then find those specious "facts" to support their predetermined conclusion.
Or as one of the former (acting) SW Region Fire Directors stated at a Fire Mgmt. meeting - "There is a grain of truth in everything I say ..." - when he was attempting to evasively avoid telling us what really happened on the fatal April 22, 1993, Santa Fe NF Buchanan RX Burn Fatality where Jemez Pueblo WF Frankie Toldeo was killed due to overly aggressive Aerial Ignition Induced Fire Behavior. The fire behavior was so intense it burned the boots off his feet. Where 16 WFs were entrapped and deployed fire shelters and five WFs suffered minor burn injuries.
When WFs returned from that assignment, they were visibly scared because the cowardly and nefarious "they" were looking for Scapegoats.
Figure 11. WLF LLC Incident Reviews Database, search terms, match terms, incident year, incident type, incident location drop-downs Snippet. Source: WLFLLC
Premortem exercises are very powerful tools that begin by looking at an incident that will take place in the near future. All participants are instructed to assume that something went spectacularly wrong and are then asked to determine the cause of this tragic ending, and identify ways of preventing this failure from happening.
Can be done on a scheduled prescribed fire or in an incident action plan (IAP).
Let all participants introduce their idea of what went wrong. Supervisors invite subordinates to tell them how this incident or plan can fail. Look for blind spots.
Determine ways to prevent this failure.
NWCG 6-Minutes for Safety - Escape Routes 1 (Take 5@2)
Figure 12. NWCG Leadership categories Source: NWCG