Summary of the Marshall Fire and High WInd Event on December 30, 2021
On December 30, 2021 the devastating Marshall Fire roared through Superior and portions of Louisville, Colorado. The fire started south of Boulder Colorado, and was fanned by intense winds along the Front Range Foothills. Wind gusts from 70 to 100 mph occurred right at the base of the foothills, including Boulder and along Highway 93 south toward Golden. The strong winds fanned a destructive grass fire which originated near Marshall, and then quickly spread east to Superior and Louisville. At last count, 1,084 homes and seven commercial structures were destroyed, and 149 homes and another 30 commercial structures were damaged by the Marshall Fire.
The very strong winds developed in the mid morning hours on Thursday, the result of a mountain wave that developed as very strong westerly winds raced over the Front Range Mountains and Foothills. The mountain wave remained nearly unchanged through the rest of the day, resulting in very persistent and extremely high winds that focused very close to the base of the foothills, along Highway 93 and points east to around Superior and at times, Lousville. It takes just the right combination of meteorological parameters, including stability, wind shear, and wind magnitude to create a powerful and damaging windstorm like this one. To further visualize what a mountain wave would look like, see the image below.
This schematic represents the strong westerly winds moving down the mountain slope (in this case the Front Range Mountains and Foothills) and accelerating all the way to the base of the foothills. From there, they spread east into the Superior and Louisville area, before suddenly weakening to the east (call the jump region). It was interesting to note in this case, that easterly winds were observed at times immediately to the east of the "jump" area around Broomfield and Lafayette. This can also be referred to as a rotor, where winds an actual wind reversal occurs.
The second recipe ingredient for this disaster was the lack of precipitation during the latter half of the year. The Front Range experienced a very wet first half of the year, with much above normal precipitation, lush and tall grass growth. However, starting around July, a persistently dry weather pattern set up and held firm through the entire fall and early winter. Grasses, while typically dry this time of year, were exceptionally dry as very little snow had fallen through the entire fall season. Below, are the July 1 through December 29 temperature and precipitation ranks, showing Denver being the 2nd warmest, and by far the driest in recorded history (since 1872). Boulder was ranked 2nd warmest for precipitation, while 13th dries in recorded history.
Another way to look at the combination of temperatures and dryness can be visualized here, comparing this July - December period with past years.
The images below show the progression of winds and fire during the late morning and afternoon hours of December 30. The eventual fire perimeter is outlined by light purple (upper center of the plot images), while the city of Boulder is located in the northwest corner of these images.
Here is the 11 am surface plot showing wind gusts in red. Winds were gusting to 81 mph in south Boulder, while as high as 99 mph near the intersection of Highway 93 and Highway 72 (Coal Creek Canyon).
The fire started approximately 11:41 am, but raced quickly eastward due to the very strong winds and extremely dry grasses. Here's a video taken from NWS Boulder at approximately 11:55 am, showing just how fast the Marshall Fire was spreading to the east.
By 12 pm, some of the strongest winds from this wind event were occurring, with a peak gust of 115 mph reported at the base of the foothills, just east of the intersection of Highway 93 and Highway 72. Here's the 12 pm surface plot - note the 85 mph gust in south Boulder, and 100 mph gust along Highway 93 (very bottom of the image below) near the top of the hour.
This video below was taken shortly after noon (credit to Twiiter user @Boldmethod for research and event write-up purposes only), was taken from Boulder, looking southeast at the fire. Here, you can visualize the flow in the mountain wave, with the downslope winds racing east toward the Davidson Mesa and Superior, before then flowing upward in the "jump" area seen in the schematic above. This view gives us a mirror-like image to the mountain wave, since we're now looking south toward the wave rather than north as in the schematic.
Between 12 noon and 2 pm, the stronger winds were shifting slightly east, through all of Superior and most of Louisville. At 2 pm (plot below), a wind gust to 68 mph was recorded near Coal Creek Golf Course in Louisville, a community that would see devastation with hundreds of homes burned. The fire had already moved through much of Superior, and was spreading quickly through the Louisville area.
The mountain wave was fully established through this time, and cleary visible in the smoke and cloud structure. This time lapse imagery taken from the southwest side of the Denver metro area was shared by Mike Nelson and Mario Gori, showing the fluidity of the mountain wave. Note the reflection shown in the strongest first wave, and then the subsequent second and even third wave on the far right of the imagery. Smoke is clearly visible as gray, while clouds are also shown on the crest of the wave..
Below is a closer view (credit to Twiiter user @Boldmethod for research and event write-up only) from the other side, this one taken from Boulder looking southeast at the Marshall Fire around 2:50 pm. US36 is in the center of this imagery. The downslope winds are crashing to the ground along Highway 93 and then racing east to Superior and Louisville, before lifting and weakening rather quickly to the east. The fire and smoke (gray and dark gray) show this wind pattern clearly, while the line of clouds shows the "jump" area with enough lift (even on this very dry day) to produce a line of clouds.
The loop below, shows the radar returns from the fire (smoke and ash), being lofted far into the atmosphere and thrown east across DIA and the eastern Colorado Plains.
Winds eventually calmed down through the late afternoon and evening hours, but unfortunately much of the destruction had been done. A view of the fire around 6:00 pm from the NWS Office in Boulder, to the west/northwest of the fire.
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And then a view of the fire from nearly the same time from the east side of the fire. This picture was taken from Broomfield.
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Finally, here's a look from space (22,200 miles up), with satellite showing the intense heat being released by the Marshall Fire. This was taken around 8 pm.
...HIGHEST WIND REPORTS... Location Speed Time/Date Lat/Lon ...Colorado... ...Adams County... 0.7 Mi S Of Northwest Pkwy 56 MPH 1235 PM 12/30 39.97N/104.99W ...Boulder County... 3 SSW Boulder 108 MPH 0225 PM 12/30 39.99N/105.27W 1 NE Crisman 102 MPH 1120 AM 12/30 40.05N/105.35W 3 NW Marshall 90 MPH 0125 PM 12/30 39.98N/105.28W Boulder 75 MPH 0215 PM 12/30 40.03N/105.23W 036e03750rws1rp1 At Baseline 73 MPH 1123 AM 12/30 40.00N/105.26W Wondervu 72 MPH 0956 AM 12/30 39.91N/105.38W Atoc - Univ. Colorado Campus 71 MPH 1050 AM 12/30 40.01N/105.27W Lyons 3W 70 MPH 1042 AM 12/30 40.22N/105.33W Lafayette 70 MPH 1001 AM 12/30 40.06N/105.12W Louisville 68 MPH 0200 PM 12/30 39.96N/105.15W Longmont 68 MPH 1147 AM 12/30 40.13N/105.23W Nederland 66 MPH 0900 AM 12/30 39.99N/105.45W Nederland 65 MPH 0938 AM 12/30 39.99N/105.45W Boulder 64 MPH 0325 PM 12/30 40.06N/105.29W Boulder 64 MPH 1117 AM 12/30 40.04N/105.26W Boulder 63 MPH 1116 AM 12/30 40.02N/105.29W Boulder 62 MPH 0223 PM 12/30 40.06N/105.21W Boulder 61 MPH 1042 AM 12/30 40.00N/105.20W Ward 60 MPH 0833 AM 12/30 40.10N/105.50W Boulder 57 MPH 0808 AM 12/30 40.03N/105.28W ...Broomfield County... 025s229 Sh7 57 MPH 1153 AM 12/30 40.00N/104.98W ...Clear Creek County... Corral Creek 67 MPH 1158 AM 12/30 39.64N/105.46W I-70 Georgetown Lake 61 MPH 1235 PM 12/30 39.73N/105.69W I-70 Floyd Hill 60 MPH 1204 PM 12/30 39.72N/105.41W ...Douglas County... Cheesman 67 MPH 1223 PM 12/30 39.18N/105.27W Carpenter Peak 56 MPH 0357 PM 12/30 39.42N/105.08W Franktown 56 MPH 0320 PM 12/30 39.39N/104.75W Surrey Ridge 55 MPH 1224 PM 12/30 39.49N/104.87W ...Elbert County... Elizabeth 60 MPH 0250 PM 12/30 39.35N/104.53W ...Gilpin County... Black Hawk 58 MPH 1253 PM 12/30 39.84N/105.47W Dakota Hill 58 MPH 0955 AM 12/30 39.87N/105.55W Aspen Springs 57 MPH 1250 PM 12/30 39.83N/105.48W Golden 56 MPH 1131 AM 12/30 39.90N/105.40W ...Grand County... Winter Park Eagle Wind 73 MPH 0345 AM 12/30 39.85N/105.78W Berthoud Pass 63 MPH 0935 AM 12/30 39.80N/105.77W Keyser Ridge 55 MPH 0427 AM 12/30 39.89N/106.04W ...Jefferson County... Arvada 115 MPH 1206 PM 12/30 39.86N/105.22W Rocky Flats Hwy 93 and 72 110 MPH 1123 AM 12/30 39.87N/105.24W 2.8 NE White Ranch Open Spac 103 MPH 0126 PM 12/30 39.85N/105.25W 2 NW Rocky Flats 98 MPH 1155 AM 12/30 39.91N/105.23W 470w014 Wadsworth 81 MPH 0348 PM 12/30 39.55N/105.08W 1.7 NE Rocky Flats (CDPHE) 78 MPH 1215 PM 12/30 39.91N/105.19W I-70 at C470 73 MPH 1224 PM 12/30 39.71N/105.19W Genesee 71 MPH 1212 PM 12/30 39.71N/105.29W Coal Creek Canyon 69 MPH 1016 AM 12/30 39.88N/105.39W Lakewood 67 MPH 0346 PM 12/30 39.70N/105.15W Golden 66 MPH 0901 AM 12/30 39.79N/105.28W Arvada 62 MPH 0146 PM 12/30 39.84N/105.17W Arvada 62 MPH 0139 PM 12/30 39.85N/105.16W Littleton 56 MPH 0316 PM 12/30 39.59N/105.13W 4 SSE Rocky Flats 55 MPH 0230 PM 12/30 39.83N/105.19W ...Larimer County... Glen Haven 89 MPH 0827 AM 12/30 40.47N/105.45W Livermore 79 MPH 0846 AM 12/30 40.71N/105.41W Lyons 62 MPH 1156 AM 12/30 40.28N/105.31W Virginia Dale 62 MPH 1134 AM 12/30 40.95N/105.35W Buckeye 60 MPH 0235 PM 12/30 40.81N/105.04W Red Feather RAWS 58 MPH 1224 PM 12/30 40.80N/105.57W Livermore 57 MPH 0933 AM 12/30 40.87N/105.36W 3 WNW Loveland 56 MPH 0217 PM 12/30 40.43N/105.12W ...Summit County... Red Cliff Pass 55 MPH 0515 AM 12/30 39.48N/106.15W ...Weld County... Erie Muni 59 MPH 0915 AM 12/30 40.02N/105.05W Observations are collected from a variety of sources with varying equipment and exposures. We thank all volunteer weather observers for their dedication. Not all data listed are considered official. $$
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